UB EE522 Power Plant Reliability and Safety Issues

Power Plant Reliability Issues that Matters
(Electric Reliabilty)

Table of Contents
As a society we are growing more dependent upon sophisticated electrical and electronic devices in our home and business for our quality of life. Equipment malfunction caused by electric reliability problems can range from inconvenient to catastrophic.

We understand a reliable power supply is more important than ever and we are working hard to improve the reliability of the utility system. Because most reliability problems are the result of incompatibilities between equipment and the electrical environment, solutions require work on both our part and yours.

This paper has been put together to help you understand how the electric utility system works, what kinds of electrical problems can impact your equipment, what actions you can take, and how we can help you to improve your electric reliability.

About the Power System

Utility Grade Power
Electric Utility System Operations
Picture of the Electric Grid
Operations Tour
What we will be Doing to Improve Reliability
Voltage Standards
Outage and Generator Preparation Checklist
Emergency Preparedness for Your Electronic Equipment
Your Electric Equipment
Reliability Requirements
Equipment Sensitivities (pdf)
Electrical Disturbances
Indications of Voltage Disturbances
Reference Chart of Most Common Electrical Disturbances and Their Causes (pdf)
Troubleshooting, First Steps
Troubleshooting Guide (pdf)
Sample Disturbance Log (pdf)
Power Disturbance Monitoring (pdf)
Top 10 Tips for Reducing Reliability Problems
Sample One Line Diagram (pdf)
Reliability Solutions
Electrical Infrastructure
Reliability Enhancement Devices
Summary Chart - Reliability Enhancement Devices (pdf)
Emergency Preparedness for Your Electronic Equipment
Equipment Specifications
Electrical Maintenance
Top 10 Tips for Reducing Reliability Problems
The Bottom Line
Reliability Economics
Managing Reliability
Services we provide
Utility System Information
Phone Consultation
Field Consultation
Electric System Reliability Check-Up
Education and Training
Brochures
Staff Bios
Links to Other Resources
FAQs
Glossaries, Terms and Definitions
Glossary of Electrical Terms
Glossary of System Equipment
Glossary of Utility System Reliability Terms
Contact Us Via Email


Electric Reliability - Frequently Asked Questions

This page has been developed to answer common questions concerning power reliability. What is a power reliability (also known as power quality) problem? Any event resulting in failure or mis-operation of end-use equipment as a result of the power provided.

Getting started
Disturbances
Wiring
Safety
Standards
Protective equipment (Surge suppression, UPS, back-up generators)
End use equipment (motors, variable speed drives, computers)
Other


Getting Started

Why should I be concerned about power reliability?We don't think much about electric power until an outage or other power disruption causes problems for our business. The Electric Power Research Institute estimates that across all business sectors, the US economy is losing up to $175 billion annually due to power outages and other power disturbances. Most of these interruptions can be prevented with some planning and investment.

Where do power disturbances come from?

Extensive research has verified 70 to 80% of all power disturbances originate in your facility. These disturbances are caused by equipment in your facility and are often compounded by wiring and grounding issues. The other 20 to 30% of these problems originate on the utility side. These problems are often caused by weather, foreign object contact (animals, trees, metallic balloons) and equipment failure.

My facility cannot tolerate equipment downtime due to electrical disturbances. What should I do?

You should consider establishing an ongoing power quality monitoring program, along with the addition of the necessary power conditioning equipment. A properly administrated power quality monitoring program will increase the opportunity to detect changes in the electrical environment before they cause equipment operating problems.

What is the benefit of maintaining equipment operating logs?

Accurate and detailed logging of equipment operating problems and unscheduled down time provide essential information on power quality problems. These logs will help in analyzing power quality monitoring measurements and will help correlate equipment problems with the recorded electrical disturbances. Downtime logs should indicate which equipment experiences a problem; the date, time and duration of the problem; what the problem was; and any notations of noticeable changes in electrical or other conditions before or during the failure.

Where should I monitor in my facility?

Depending on the monitoring objective, locations may include the main building power service; specific distribution busses; panelboards; or control power transformers of a sensitive load.
Why should I monitor my electrical service prior to installing new equipment?

Monitoring power quality in the early stages of planning or the installation of sensitive loads will provide information on whether power quality problems exist.

Disturbances

What is the most common type of power disturbance seen by your customers?
Voltage sags (or reductions below normal) constitute the most common type of disturbance seen by customers. On the utility side, these disturbances are most often caused by weather, equipment failure, and animal contact. In your facility, sags are generally caused by start-up of large motors.

What is a "flashover"?

A flashover is a brief (seconds or less) instance of conduction between an energized object and ground (or other energized object). The conduction consists of a momentary flow of electricity between the objects, and is usually accompanied by a show of light and possibly cracking or loud exploding noise.

What are other common disturbances experienced by customers of utilities?

Other types of disturbances include overvoltages (increases above the nominal value), interruptions, harmonic distortion, and Electromagnetic Interference.

What is harmonic distortion?

Commercial and residential electricity is generated, delivered, and used at a frequency of 60 cycles per second (or Hertz, abbreviated Hz) in North America, and 50 Hz in most other parts of the world. In actual use, however, there are components of electricity occurring in even and odd multiples of these frequencies, e.g., 120 Hz, 180 Hz, 240 Hz, etc., or second, third, fourth "harmonics" of the fundamental of 60 Hz.

I have heard that harmonics can be a real problem. How big an issue is this?

Even though this topic gets a lot of press, the number of documented problems caused by harmonics are relatively few even though harmonic producing loads are increasing. Although you need to be aware of potential harmonic issues voltage sags are responsible for the majority of equipment malfunction.

Why are harmonics a problem?

The electric system was designed to operate with power at one frequency, namely 50 or 60 Hz. The electric system and end use equipment can react in unexpected and often undesired ways when other power frequencies are present.

What are the most common indicators of harmonic problems?

Symptoms of harmonic problems include transformers, motors, electrical panels, and building wiring that appear not to be overloaded but are overheating. Harmonics can also cause problems with generator, Uninterruptible Power Supply, and power factor correction capacitor interaction and compatibility. Harmonics may also be responsible for telephone/communication interference. Sometimes, nuisance tripping of circuit breakers and other overcurrent protective devices is also observed.

What causes harmonics?

Harmonics are caused by non-linear loads (equipment). Examples of non-linear loads include solid state power supplies for computers, variable speed drives, and electronic ballasts.
What are linear and non-linear loads?

Traditional loads such as motors and incandescent light bulbs are linear loads. There is a direct correlation between the voltage supplied and the current drawn by the device. Non-linear loads use solid state devices, often with microprocessor control, to switch current on and off. Current is drawn discontinuously and not directly dependant on the voltage.

What are harmonic solutions?

The best solution is to look at the source of harmonics and correct the problem at the source, if possible. Harmonic distortion can often be mitigated by good design. The next best option is the use of filters to minimize the problems caused by harmonic sources.

is Electromagnetic Interference (EMI)?

Electromagnetic Interference is high frequency noise (thousands, hundreds of thousands, or millions of hertz and upward), which is caused by, and ironically can negatively effect, the operation of electronic equipment. Special filters tuned to specific frequencies, or bands of frequencies, are used to remove unwanted frequencies.

Wiring

What is daisy chaining and why shouldn't I use this practice?

Daisy chaining is the practice of using only one neutral to act as a return for single phase circuits on different phases of a three phase circuit. What's the problem? With linear multiphase circuits with somewhat balanced loads there is no problem. Neutral currents from the various phases tend to cancel each other. Currents stay well within wire design limits. With multiphase circuits with non-linear loads however, because of the additive properties of triple harmonics, neutral currents can easily exceed wire capacity. In a classic display of this problem some of the first cubicle divider walls used daisy chaining to reduce costs. The overloaded neutrals, the result of harmonic load in the form of computers, caused fires. To avoid this problem either provide separate neutral returns for each phase or upsize the neutral.

I have Aluminum wiring in my facility. Is this a problem?

Although Copper wire is the main stay for building wiring, Aluminum wire is found in many businesses. With good electrical and thermal properties Aluminum does, however, have several differences from Copper. The conductivity of Aluminum is about 61% of Copper. It has a higher temperature coefficient of resistance than copper, meaning its physical dimensions undergo greater change with heating and cooling. Aluminum also reacts readily with oxygen. Because of this the metal is always covered with a thin, invisible film of oxide which is impermeable, protective, and not as conductive. Aluminum, in the presence of water and limited air or oxygen, rapidly converts into aluminum hydroxide, a whitish powder.

What does all this mean?

Aluminum can be used with good results but generally needs more attention to detail. Wire must be sized larger than Copper. Due to the higher thermal expansion coefficient connections can more easily work loose. Conductors must be well cleaned and an anti-oxide grease applied before tightening connections. Damp locations must be avoided. In short, if you have Aluminum wire you need to pay more attention to the condition of the wire and the security of the connections.

What is a neutral-to-ground bond?

A neutral-to-ground bond is the intentional connection of one system conductor at the power supply. This is done by bonding the grounded conductor (the neutral) and the metal parts of the service entrance equipment to a grounding electrode. This is done to promote the prompt tripping of a circuit breaker or fuse to isolate the problem from the power system and to limit voltage due to lightning, line surges, or unintentional contact with higher voltage lines. For a system having a single power source, there should only be one neutral-to-ground bond in the system, and this bond should exist only at the service entrance equipment. A good indicator of multiple neutral-to-ground connections is current flowing on the ground conductors.

My electrician is telling me I need an isolated ground. What is it and when is it needed?

Although the primary purpose of a ground is safety, digital equipment uses ground as a reference point for their logic circuits. In the general purpose grounding system in any facility you will find a small amount of current flowing. This current is the sum of small amounts of "leakage current" from all the equipment that is connected and operating. (Note, if you have upwards of an amp flowing in your ground look for illegal neutral/ground bonds). The changing current flow makes the ground voltage level vary based on where you are connected. This movement does not make the use of the facility ground system the best reference. An isolated ground is a dedicated ground tied back to the origin of the building ground or a separately derived system. As a ground wire dedicated to one or two pieces of equipment the current flow is practically zero. This allows the ground connection system to act as a very stable reference for the digital system.

When do you need an isolated ground?

Computers, Programmable Logic Controllers, and other critical pieces of digital equipment should have isolated grounds. Isolated ground outlets are identified by the bright orange faceplates.

If an isolated ground is good, should I install a separate ground rod at my digital equipment?
No! Installing a separate ground rod that is not bonded to the service entrance ground will cause a ground loop and is a violation of the National Electrical Code.

What is the problem with undersized wire?

Undersized wire can lead to excessive voltage drop in the wire, low voltage at the point of use, and can present a fire hazard from over heating. Electrical systems are analogous to plumbing systems. Current flow, just like water flow, causes a pressure drop as it moves through the wire or pipe. The smaller the wire, the greater the voltage drop (pressure drop) for a given amount of current. Many electronic loads are very sensitive to low voltage. Circuits carrying electronic loads should be designed for plenty of capacity.

How common are loose connections and what problems do they cause?

It has been said more electric reliability problems can be fixed with a screwdriver than any other method. Loose connections are extremely common and are one major reason why electrical maintenance, on an ongoing basis, is necessary to maintain electrical system safety and operation. As conductors carry varying amounts of current, they expand and contract. This is due to heating and cooling caused by the current and the thermal properties of the conductor. This expansion and contraction of the metals eventually results in a loose connection. If the conductor is not making solid contact, the resistance of the connection increases. More heating results. This condition can eventually result in a fire. Check any panel that hasn't been looked at in a while and you will invariably find

Safety

What is the role of equipment grounding?

Grounding is the intentional solid connection to ground from one or more of the noncurrent-carrying metal parts of the wiring system or apparatus, such as: metal conduits, metal raceways, switch boxes, motor frames, and metal enclosures. The main purpose of equipment grounding is personnel safety.

What is the purpose of the National Electrical Code?

The National Electrical Code (NEC) was developed as a minimum safety code to prevent lost of life due to electrical hazards and loss of property due to fires. As the Code specifically states in Article 90, systems built to code will not necessarily ensure proper operation of electrical equipment attached.


Standards

What is IEEE 519 and how is it used?

IEEE (Institute of Electrical and Electronics Engineers) 519 is also known as a Guide for Applying Harmonic Limits on Power Systems. The guide provides procedures for controlling harmonics on the power system along with the recommended limits for customer current harmonic injection and overall power system harmonic levels. It provides specific methods for evaluating harmonic levels at the point of common coupling (PCC) as well as providing examples of measurement procedures for evaluating harmonic voltages and currents. It also illustrates methods of harmonic control at the customer level and on the utility system.

What is the point of common coupling (PCC)?

PCC is the point on the electrical system, which defines, where the utility responsibility ends and end user begins. Normally this is the metering point.

What is Rule 2 and what does it cover?

Electric utilities provide voltage. End users draw current. Rule 2, the tariff governing utility voltage standards, describes the electric utility's responsibility for voltage, voltage tolerances, and under what conditions voltage may range outside these tolerances. Under normal conditions, we are required to maintain the secondary supply voltage levels to +/- 5% of nominal levels. Rule 2 does provide several exceptions to these voltage limits. These exceptions are conditions that: 1. Are infrequent, momentary fluctuations of a short duration. 2. Arise from the temporary action of the elements. 3. Arise from service interruptions. 4. Arise from temporary separation of the parts of the system from the main system. 5. Are causes beyond our control.Rule 2 also addresses the responsibility of customers in their use of electricity. These responsibilities include allowable motor starting currents and protection, maximum current waveform distortion, electrical interference with other services, and power factor requirements.
What is flicker?

Flicker refers to the human sensitivity to changes in light levels. This sensitivity is a function of the degree of change in the light level, the length of time for the change, and how often it occurs. Voltage fluctuations, generally caused by electrical equipment turning on and off, cause many electric light sources to vary light output. The larger the piece of equipment and the smaller the service and wire size, the bigger the change in voltage. Everyone varies in their threshold of perception and level of irritability with flicker.

What is UL 1449?

UL 1449, second edition, is a standard from Underwriters Laboratory for testing Transient Voltage Surge Suppression (TVSS) devices. The test documents the limits of safe operation and provides categories of voltage suppression based on testing.

Protection

What is a Surge Suppressor?

A surge suppressor is designed to protect equipment from voltage transients. It does this by turning on when the voltage exceeds a certain threshold and providing an additional path for electricity to flow. Just like opening a second faucet the additional flow reduces the overall pressure. When the transient passes the surge suppressor turns off and resets.

I have been told I should install surge suppression to save energy. Is this true?

No. Surge suppressors are designed to reduce voltage transients. Surge suppressors will not save energy. They are, however, an excellent idea to protect sensitive equipment.

What is a UPS (Uninterruptible Power Supply)?

A UPS provides an alternative, short term (minutes) power supply should the utility voltage drop below a preset level or disappear all together. The alternative power is generally supplied from batteries. The transfer is designed to be fast enough that sensitive equipment is not impacted. There are three main types of UPS; Standby, Line Interactive, and On-line unit. Standby provides minimum protection. Line Interactive is appropriate for most sensitive loads. On-line units are typically used for critical applications.

What is a voltage regulator?

A voltage regulator is designed to maintain voltage within a narrow output voltage with a widely varying input voltage.

What is a harmonic filter?

Harmonic filters designed to filter or attenuate harmonics on the power system. They are generally passive devices consisting of capacitors, inductors, and resistors. Newer technology is beginning to introduce active harmonic filters. Active filters work by injecting a current of equal and opposite value with the intent of reducing the undesirable harmonic components.

How does a Uninterruptible Power Supply (UPS) work?

A UPS senses voltage and switches to an internal power source (typically batteries) if the input voltage strays outside a specified tolerance. There are several different UPS designs: the Standby, Line Interactive, and On-Line. Each design has its own combination of advantages and disadvantages.

Equipment

I have installed a variable speed drive and am experiencing premature motor failures. What is happening?
If you are using a Pulse Width Modulated Drive (PWM) you may be experiencing amplified voltage peaks at the motor leads as a result of the drive output and long cable length between the drive and motor. To reduce problems keep motor lead length to 50 feet maximum, and use inverter rated motors (NEMA MG-1, part 31). If you must use long cable lengths consider a lower drive carrier frequency and/or output filters for the drive.

What is a line reactor and why is it an important component with my PWM drive?

A line reactor is impedance (typically 3% recommended) that is installed or is integral to the power front end of your drive. The reactor will reduce the impact of transients on your drive as well as reducing the harmonic current drawn by your drive.

I have heard some variable speed drive applications can cause early motor bearing failure. What's going on there and what can I do to avoid this potential problem?

High carrier frequencies used with Insulated Gate Bi-Polar Transistors (IGBT) in many drives create a voltage potential between the rotor shaft and motor case with the bearings in the voltage discharge path. When the voltage discharges through the bearing the resulting current spike vaporizes some metal leading to pitting and fluting of the bearing. The bearing deformation leads to premature bearing failure. Solutions include grounding the motor shaft, conductive bearing grease, and Faraday shields. None of these methods eliminate the problem. By far the best approach is to keep the carrier frequency low.

Do I need to use a special motor if I want to use a variable speed drive?

Variable speed drive applications can be hard on motors if drive carrier frequencies are greater than 10kHz and/or if cable lengths are long. The high frequency voltage output pulses, in concert with long cable lengths, can create high voltage pulses at the input to the motor. These pulses can begin to affect the insulation separating wire turns in the motor. The insulation between turns eventually breaks down causing a short. For added reliability, consider an inverter grade motor. Inverter grade motors incorporate better wire insulation, in-slot wire wound methods, and higher service factors.

My computer screen image is "wavy". What can be causing this?

The image on your computer screen is created by an electron "gun" that "paints" an electron beam on your screen in a controlled pattern. When the electrons strike the screen they cause coatings to emit light to generate the images you see. Electrons have very little weight and are attracted or repelled by magnetic fields. One source of Electro-magnetic fields is electrical current flowing in wires and transformers. If electrical wires or a transformer is close enough to your screen the Electro-magnetic fields produced may be high enough to cause the electron beam to be pulled off course resulting in a wavy screen. Although it is hard to shield your monitor from outside magnetic fields, their strength falls off very rapidly. Generally moving the screen a few feet away from the source of an Electro-magnetic field is enough to reduce the effects to a manageable level.

What is a Powerline Carrier System and what are the electric reliability issues concerning their installation and operation?

A Powerline Carrier System is a method of sending information over an electrical power distribution system within a building or facility. In the past, Powerline Carrier Systems have been limited in their applications due to unreliable signal transmission caused by electrical noise. Electrical noise is caused by the normal use of appliances and machinery in homes, offices, and factories. Although many new technologies promise to give error free service, solutions presented vary in their effectiveness.

Other

What is a separately derived system?

A separately derived system is a facility wiring system which is powered from a battery, solar photovoltaic system, generator, transformer, or converter windings that has no direct electrical connection, including a solidly connected neutral, to another system.
My company does not understand why we have to spend time and money on maintenance of our electrical system. Can you help?

Enormous amounts of energy flow silently through our electrical systems. We never think about this unless it gets out of control causing fires, or even injury or death. Electrical systems are governed by the laws of physics. Wires move, connections expand and contract, contacts pit and vaporize, insulation cracks. Without maintenance the system will fail. With emergency equipment, such as generators or Uninterruptible power supplies, maintenance is even more important. These pieces of equipment are called into play when your other options fail. Ongoing maintenance and testing should be an important part of any electric reliability effort.

Do power factor correction capacitors save energy?

Yes, but not much. Their main function is to free up electrical capacity. Power factor correction capacitors are often installed to supply VARS for motor loads. VARS (Volt-Amperes Reactive) are the electrical component that fuels the magnetic fields in motor operation. The creation of the magnetic fields requires energy from the utility. This energy is later returned as the magnetic field collapses. This exchange occurs one hundred and twenty times every second. Capacitors can be substituted for the utility as a supplier of VARS. Think of capacitors and motors as Ying and Yang. When motors are drawing VARS, capacitors are releasing them, and visa versa. Mixed in the correct amounts, capacitors and motors can balance each other's need for VARS. Capacity is freed up because the utility no longer has to supply this component. However, the motor still requires power for the electrical component that is converted to other forms of energy (motion and heat). Any savings are the result of reducing the transportation losses associated with not having to supply VARS from the utility, but rather supplying them on the site.

Electrical Disturbances

Electrical disturbances, a form of distorted electrical power, come in many shapes and sizes. Electricity as it comes from the generator is smoothly flowing and shaped like successive waves cycling up and down and up 60 times per second. Distorted electricity can be caused by electrical equipment in your building or in neighboring buildings, as well as events on the utility system.

Research by the Electric Power Research Institute and others has confirmed seventy to eighty percent of the disturbances originate in your building or factory. These disturbances are caused by equipment interaction and are often exacerbated by wiring and grounding problems.
The other twenty to thirty percent of the electrical disturbances that affect equipment originate on the utility system. These disturbances are caused by a number of factors including weather (lighting, rain, or fog), accidents (dig-ins, car pole), and utility equipment failure.

Electrical disturbances interact with the system in several ways. First, something must cause the electrical disturbance such as a large motor starting or a lightning strike. Next the wiring network, which carries the disturbance to other equipment, may aggravate the disturbance. Finally the disturbance reaches electronic equipment which reacts to the disturbance. Listed below are the most common types of disturbances, typical causes, and impacts.

Transients:Also known as surges or spikes, these are caused by lightning, appliances such as printers and copiers, as well as utility activities such as circuit breaker operation and switching. Transients of sufficient energy can upset computers, corrupt data, or even cause damage.

Sag: A brief drop in the voltage (electrical pressure). Sags can be caused by equipment such as motor starting, and heaters in printers and copiers cycling, as well as utility events. Sags often cause computer equipment to lock up or lose memory. This is one of the most common causes of electric problems for computers.

Swell: A brief increase in the normal voltage level. Most swells are caused when a motor stops. Although not generally a problem they have been known to cause failure of marginal components in electronic equipment.

Over and Undervoltage: Longer-term increases or decreases in the normal voltage. These disturbances often indicate an overloaded transformer or circuit, or inappropriate tap adjustment on a transformer.

Interruption: Also called a momentary power outage. An interruption is generally caused by short circuits from downed trees or wires, or damaged equipment. These unsafe conditions cause a circuit breaker or fuse to trip and de-energize the circuit.

Harmonics: Harmonics are a regular distortion of the voltage waveform often caused by the power supplies of electronic equipment. Harmonics can cause over heating in transformers, building wiring, and motors.

Noise: Electro Magnetic Interference (EMI) is electrical interference caused by electric and magnetic fields emanating from electrical equipment, typically transformers or wiring. One often seen impact is a wavy computer screen.

Noise - Radio Frequency Interference (RFI) is electrical interference from equipment that radiates high frequency electrical energy such as TV/radio transmitters and cell phones. Interference can also be caused by arcing sources (switches) or switching power supplies such as those found in electronic ballasts and adjustable speed drives. This kind of noise often causes interference to control circuits.

Indications of Voltage Disturbances
1. Selected pieces of electronic equipment fail or malfunctions for no apparent reason.check logs for other coincident failures or malfunctions
2. Electronic clocks or timing devices lose or gain time.my be evidence of harmonics
3. Timekeeping system such as that by Simplex, which use power line carrier systems, fail inexplicably.evidence of high frequency noise
4. Incandescent lamps dim/flicker for extremely brief moments.probably a very short interruption or deep sag.
5. Computer monitors/video displays have wavy or jittery pictures.evidence of nearby Electric or Magnetic Fields
6. Electric motors run extremely hot.symptom of prolonged low voltage
7. Printed Circuit Boards (PCB) or Metal Oxide Varistors (MOV) burned.due to voltage transients
8. Arcing or burn marks evident in panels and around electrical connections.evidence of loose connection or damaged insulation
9. Control equipment misoperates due to voltage transient from capacitor switching
10. Alarm or warning lights activate on an Uninterruptible Power Supply (UPS) evidence of voltage sags or over voltage transients

Troubleshooting, First Steps

One of the first steps in troubleshooting a reliability problem is collecting information.
A disturbance or outage log is invaluable for noting what happened, when, and what else was happening that might be related to the problem.

Next, you need confirmation that the equipment problem was the result of an electrical phenomenon. To verify electrical activity you need the appropriate kind of electrical monitoring equipment. The monitor should be hooked up as close as possible to the impacted equipment.
Next, consult your electric utility to see if they have any information on electrical activity on the utility system that may have impacted your equipment.

Before solutions can be examined you will need to know about the equipment and the electrical environment.

Do you have an up-to-date one-line diagram, a map of the electrical layout and equipment connected?

Have you checked the wiring and grounding to verify it is adequate for the job?

Do you know the electrical specifications for the equipment in question?

The next steps involve looking at the potential solutions and evaluating their economics. This is covered under the section entitled "The Bottom Line."

Top 10 Tips for Reducing Electric Reliability Problems
1. Tighten loose connections and fittings.
2. Protect sensitive equipment with Uninterruptible Power Supplies (UPSs) and Transient Voltage Surge Suppressors (TVSSs).
3. Separate sensitive and non-sensitive equipment.
4. Position video display away from current-carrying conductors.
5. Avoid the use of Power Line Carrier (PLC) systems.
6. Ground and bond in accordance with the National Electrical Code (NEC).
7. Limit current and voltage harmonics.
8. Ensure power factor is greater than or equal to 0.9.
9. Balance electrical loads (voltage imbalance less than or equal to 3%).
10. Minimize distance between Adjustable Speed Drives (ASDs) and motors (less than 75 feet).

Reliability Solutions

Finding solutions to power reliability problems generally involves a multi-faceted approach. Concentrating on only one or two areas may often lead to solutions that are not optimal, resulting in higher cost and/or less effectiveness. The main elements of a whole systems approach include:

Electrical Infrastructure - The physical wires and electrical components that feed electricity to the equipment in the facility.

Enhancement Devices - Equipment that cleans and conditions power for sensitive equipment.

Equipment Specifications - Specifying equipment designed to reliably operate in the electrical environment in which it is placed.

Electrical Maintenance - The ongoing upkeep of the electrical system.

Electrical Infrastructure

Electrical systems are similar to plumbing systems. The components of the system, the wires (plumbing pipe), the location of the transformers (pressure reducers), and the types, sizes, and locations of appliances, all interact and determine how well the system performs.
Just as small plumbing pipes and a larger water-using appliance, such as a washer, can cause the pressure at the shower to vary, wiring, transformers, and electrical equipment can interact and cause pressure variations (electrical disturbances).

Although the National Electrical Code (NEC) is generally used as the design guide for electrical installations, the code was designed primarily as a safety code, protecting human life and preventing fires. Building to Code, as is most often done, will not necessarily guarantee optimum performance, particularly of sensitive electronic equipment.

Two key tenants of good electrical design are source and separation.

Source involves maintaining constant voltage (pressure) at the equipment. This is often done by placing the transformer (pressure reducer) as close as possible to the equipment to be served and ensuring the wiring (plumbing) is more than adequate for the flow.

Separation is about keeping equipment that causes electrical disturbances (motors, printers, and copiers) electrically separated from equipment sensitive to electrical disturbances (computers).

An often recounted but true example is that of the computer plugged into a wall outlet with a refrigerator plugged into the same circuit on the opposite wall. Every time the refrigerator motor operates, it would cause a voltage disturbance causing the computer to stop functioning. By plugging the computer into a different outlet served by a different circuit the problem is often cured.

Reliability Enhancement Devices

Reliability enhancement devices are designed to help recreate the perfect electrical signal. Although there are many types of equipment fitting this description, this page will focus on three major categories: surge suppression, uninterruptible power supplies, and back-up generators.

Surge Suppressors are designed to divert excess energy away from sensitive electronic equipment. Just like a pressure relief valve, if the electrical pressure exceeds a predetermined threshold, this electrical "relief valve" operates to reduce the electrical pressure (voltage) and then resets. To provide adequate protection surge suppression needs to be installed on any outside connection to sensitive electronics. This includes phone, cable, and local area networks, as well as power connections.

Uninterruptible Power Supplies (UPS) are designed to provide continuous, but short term back-up power for sensitive electronics. If the supplied power drops below a preset level the UPS draws power from batteries to maintain the proper voltage. The battery size and equipment power requirements determine how long this back-up source can supply power. To keep costs down, battery back-up is typically designed to carry equipment through a short power outage (minutes), allowing back-up generation to be started and switched into service should an outage persist.

Back-Up Generators are designed to provide long term back-up power for all kinds of equipment. Most types of generators can not be switched into service quick enough to avoid disruption of sensitive equipment unless UPS support or other schemes are employed. Key issues with generators are sizing, load transfer systems, and maintenance.

Emergency Preparedness for Your Electronic Equipment

Emergencies can strike at any time. Many things can cause loss of electrical power or fluctuations in power that could be damaging to your equipment. Before something happens consider this - what equipment is critical to your business and what is the risk of not providing adequate protection?

Facts about Surge Suppression

What's the problem? All homes and businesses experience power disturbances. The microprocessors and other sensitive circuitry in modern appliances and equipment make them easily damaged by power surges. Equipment can be ruined by one hit of lightning or little by little over time.

Where do surges come from? Most surges originate in your building and result from motorized or "noisy" equipment. Some surges originate outside your building and result from factors such as weather, animals, nearby buildings, traffic accidents or utility equipment operations. Surges can enter your business through power or phone lines or cable TV connections.

What's the solution? One solution is to plug your sensitive equipment into a surge suppressor. It's an inexpensive option for your valuable equipment. A surge suppressor diverts excessive electrical energy away from your equipment to an electrical "ground" where it disappears without doing any harm.

Features to Look for in a Surge Suppressor

Look for the following features when purchasing a plug-in surge suppressor:

UL 1449 listing: Signifies the suppressor has been tested by Underwriter Laboratory's for surge suppression ability.

Peak surge current (or maximum transient current or maximum surge): Look for a minimum of 39,000 amps. The higher number the better.

Clamping voltage: The best protection is 330 volts; higher levels offer less protection. Also, look for three modes of protection (often shown as L-N, L-G and N-G).

Energy dissipation: Should be 420 joules or more. The higher number the better.
Appropriate connectors.

Use one outlet for each piece of equipment and have room for AC adapters (transformers). If you are protecting a TV, VCR, telephone, fax or computer, get a surge suppressor with a TV cable connector and/or phone jacks.

Indicators: They should have status or warning lights to indicate when the device is working (and not just on).

Electrical noise protection: For EMI (electromagnetic interference) and RFI (radio-frequency interference).

Why an Uninterruptible Power Supply (UPS) is Important

Many kinds of electronic equipment cannot tolerate even the slightest fluctuation in power. Tiny disturbances can cause microprocessors - the brains of the computers - to reset, and you to lose your work. Computers have to be re-booted and production lines restarted.
How does a UPS help? A UPS can help protect any electronic equipment by isolating it from electrical disturbances. It filters the incoming power and provides additional power, stored in batteries, when the electric power drops or disappears altogether. The UPS does this so quickly that the sensitive equipment doesn't detect a drop in power.

Three Most Common Types of UPS

Standby UPS: Power is normally routed directly to the equipment. Only if the power drops below a certain threshold does the unit switch on and function in a back-up mode. It's the least expensive type of unit.
Line Interactive: This UPS provides some voltage regulation but switches to back-up only when an extended voltage dip is detected.
Online UPS: The UPS is always on and always conditioning power. Although more expensive, they tend to provide more protection than the Standby model.

Other Things to Know Before You Buy

Adjustments: A threshold adjustment lets you adjust how the unit operates. The adjustment may help prevent a UPS from cycling on & off unnecessarily, reducing battery life.
Communications: A communication link can be used to manage the orderly shutdown of connected equipment before batteries are exhausted, alarm a system operator, schedule maintenance or report other parameters.

Capacity: The rating or size of a unit is determined by the electrical demand, in Volt-Amperes, of the equipment it's intended to serve, plus any equipment growth. Battery size is based on the run time desired.

Technology Type: The design determines the distortion (quality) of output power produced. Since some equipment is very sensitive, make sure the unit you purchase meets the requirements of the equipment to be powered.

Filtering and Protection: Additional circuitry will determine how effective the UPS protects your equipment from conditions other than loss of power. You also should determine how your unit will react to abnormal conditions such as depleted batteries, overheating or loss of communications. Some units may turn off power to your equipment or leave your equipment totally unprotected.

Protection Recommendations

Minimal - If you want protection at minimal cost, purchase a Standby UPS with 10 to 15 minutes of back-up.
Critical - If you have critical equipment in an electrical environment with motors and other heavy equipment, purchase an Online UPS with 15 to 30 minutes of back-up.
If you have a computer server or other critical application equipment, purchase an Online UPS with four hours or more of back-up batteries. Or, consider less battery time in combination with a back-up generator to carry the equipment before batteries are depleted.

Equipment Specifications

The old saying, "The best defense is a good offense", certainly applies to sensitive electronics.
One of the best ways to improve reliability is to order and install equipment that has the best chance of operating in the environment in which it will be placed.

Often the most cost-effective approach is to provide protection closest to the sensitive electronics. When this idea is factored into the specification, design, and building of equipment the benefit to cost ratio can be very high. Several industries are now setting their own standard requirements for equipment reliability specifications. In this way manufacturers are being asked to provide equipment that meets optimum cost to performance requirements of their customers.

Guidelines:

Equipment sensitivity to voltage sags is by far the most common problem. To minimize your exposure to equipment problems, follow these guidelines:
1. Have a procedure to establish how critical each piece of equipment is to your operation.
2. Ask for information on voltage sag tolerance from the manufacturer.
3. Decide, based on your electrical environment, where to set the specification for voltage sag tolerance. A seventy-percent tolerance is good. Fifty-percent is better.
4. Support industry standards for your type of business.

Electrical Maintenance

Just like other equipment, electrical systems need to be maintained to keep them in good working order. Although they appear passive, electrical systems transport a highly concentrated form of energy. When things go wrong crippling losses and injury can result. A regular maintenance program can improve safety, improve efficiency, and reduce mis-operation and damage to equipment.


Elements of an Effective Maintenance Program

The elements of an effective maintenance program include:

record keeping,
maintenance procedures, and
measurement and predictive monitoring.

Record keeping should include:
tracking changes in equipment,
an up-to-date one-line diagram, and
current service records.

Maintenance procedures should include:
visual inspections of components on a regular basis, and
a regular program to exercise key mechanical components.

Finally, electrical testing and monitoring can serve as an early warning of developing problems.

Key areas include:
Voltage and current measurements provide an excellent baseline and are recommended yearly on main panels and distribution centers. A measurement check is also important whenever a major load is added or subtracted from the system.
Electrical connections are the single biggest problem area in electrical systems. Major connections should be checked yearly with an infrared scan to determine potential problems. Any suspect connection should be cleaned and torqued.
Breakers and protective devices should be exercised on a regular basis.
Substation class oil-filled transformers should have a dissolved gas analysis performed every five years. The information can provide trending information warning of developing problems.
Generators, transfer switches, and uninterruptible power supplies should be exercised monthly under load. A preventive maintenance schedule should be followed.


The Bottom Line

A recent report from the Electric Power Research Institute (EPRI) suggests that across all business sectors, the US economy is losing up to $175 billion annually due to power outages and other power disturbances. California has the highest annual costs estimated between $13.2 and $20.4 billion.

The reason for the growing costs is businesses are becoming more reliant on digital circuitry for everything from e-commerce to industrial process controllers. With the shift to digital equipment businesses activities have become increasingly sensitive to the usual disturbances in the power supply.

How important is electric power and reliability to your business?

Evaluating an investment in electric reliability should be similar to evaluating any critical investment your company makes. Once you have the information on costs and benefits you can make an informed decision.

Managing Reliability

Managing reliability is all about having specific information on how reliability impacts your company and making decisions and investments based on sound company policy.

Key elements to a reliability plan include:

Assembling Information for Decisions
Evaluating Options
Taking Action
Assembling information for Decisions
What equipment is experiencing problems?
What happens when a problem occurs?
When does the problem occur?
Is equipment or product damaged?
How much time is lost?
What else happened at the time?
Has the problem occurred before?
How do you know the problem is related to power reliability?
How likely is the problem to reoccur and what are the consequences of multiple occurrences?
What does an interruption or outage cost your company?
Evaluating Options
Analyzing possible solutions
Compare cost and effectiveness
What is the life of the solution and the cash flow over that life?

Taking Action

Lack of action has a cost. If your analysis proves satisfactory implement a solution.

Your Electric Equipment

When you plug in a piece of equipment it becomes part of the electric power system, a network of wires connected to thousands of electrical generators on one end and billions of pieces of electrical equipment on the other. You not only access electricity, but also experience the interaction of all of the equipment connected as well as events on any of the delivery system.
All electrical equipment interacts with the system in different ways. Some equipment is very sensitive to any changes or disturbances in the electrical power. Some equipment causes changes and disturbances during their normal operation. Some equipment can be both sensitive to changes and cause disturbances for other equipment.

When a piece of equipment malfunctions or is damaged the impacts to business can be minor or catastrophic. A key part of electric reliability is determining the level of reliability you and your equipment needs and then taking action to secure this needed level. This next section will help you understand how to determine your equipment's reliability needs and the best strategy to meet those needs.

Services we need to provide

For help with services described below, please contact us at…

Utility System Information
Phone Consultation
Field Consultation
Electric System Reliability Check-Up
Education and Training
Brochures
Staff Bios
Links to other resources
Contact Us via Email

Utility System InformationWe track and investigate activity on the utility system. Generally, if there has been an outage or disturbance we can tell you when it happened and why. This information may help confirm that a problem you experienced was due to a power phenomenon.
Phone ConsultationWe are just a phone call away. We will answer your specific questions about electric power reliability and equipment operations. We can help you determine if a more detailed service is needed to resolve any existing electric reliability issues.

Field ConsultationUpon request and at no charge, we can help you identify and resolve persistent power-related equipment problems. Working with your facility personnel, our engineer will:

Review the existing problem with information provided

Tour the electrical room and building to gain an understanding of how the equipment is served and the possible interaction with other electrical equipment

Attach a power monitor at the equipment or at the electric service entrance to capture useful electrical data

Analyze the information and recommend solutions

Electric System Reliability Check-UpDuring this one to three hour review, we will help you determine if your electrical system can support your company's reliability needs. This free service consists of an electric reliability orientation discussion with site personnel and a walk-through of your facility.

The walk-through will concentrate on:
Critical equipment
The electric system serving this equipment
Electrical infrastructure equipment safety and maintenance
Power conditioning
Back-up generation
After completion of the electric reliability check-up, you'll be given a verbal assessment of your facility's electrical system relative to your needs. Within five working days, you'll receive a document that includes recommended action steps to ensure your facility's electrical system can support your company's reliability needs. As a courtesy, we will bring any maintenance or safety concerns identified to your attention.
Education and Training
Seminarswe offer training on electric reliability throughout the year. We also can provide individual training at your facility.

Glossary of Electrical Terms

Alternating current (AC) - An electrical system in which voltage polarity and current flow alternates direction on a regular basis. Your home is an example of a system that is powered by AC.

Amp - A unit of electrical flow. In a water system flow might be expressed as gallons per minute.

Direct current (DC) - An electrical system in which current flows in one direction only. Batteries provide direct current.

Frequency - In an AC system, the value of voltage and current rise from zero to a maximum, falls to zero, increases to a maximum in the opposite direction, and falls back to zero again. This complete set of values is called a cycle. The number of complete cycles passed through in one second is called the frequency. The General Conference on Weights and Measures has adopted the name hertz (abbreviated Hz) as the unit of frequency. The common power frequency in North America is 60 Hz. In Europe and most of Africa and Asia it is 50 Hz. Airplanes typically use 400 Hz systems.

Harmonic - A whole multiple of the basic power frequency. On a 60 Hz system the 2nd harmonic is 120 Hz, the third harmonic is 180 Hz, and so forth

Impedance - Impedance is the opposition offered by a material to the flow of an electrical current and is a characteristic of AC systems. Impedance has two parts - resistance and reactance. Reactance has two components, capacitive reactance and inductive reactance. The properties of these last two components are dependent upon the frequency.

Ohm - A unit of resistance and impedance.

Ohms law - The relationship between voltage, current and impedance. If two values are known the other can be calculated. This relationship is expressed many different ways. The basic relationship is voltage (V) is equal current (I) times impedance (Z).

Phase Relationship - The timing relationship between voltage and current. If voltage and current cross through zero in a cycle at the same time they are said to be in phase. Phase differences are expressed in degrees. A cycle is 360 degrees.

Power Factor - The ratio between Watts and Volt-Amperes. This ratio is generally expressed as a decimal fraction. A power factor of 1.00 is unity.

Resistance - The opposition offered by a material to the flow of a steady electrical current. DC systems have resistance only.

Volt - A unit of electrical pressure. In a water system pressure might be expressed as pounds per square inch. The voltage found in most homes is 120 and 240 volts. Businesses will typically utilize voltage at 120 and 208, or 277 and 480 volts.

Volt-Ampere (VA) - The product of volts times amps. A kilovolt-ampere (kVA) is equal to one thousand volt-amperes. VA is also known as apparent power.

Watt (W) - A unit of power equal to the product of the value of current of one ampere flowing in phase with the pressure of one volt. In a water system a comparable measure might be gallons per hour. A kilowatt is a thousand watts. W is also known as real (or true) power.

Watt-Hour (Wh) - A unit of energy equal to the power of one watt for one hour. In a water system a comparable measure might be gallons. A kilo-watt hour is a thousand watt-hours.

Glossary of System Equipment

Distribution System: This system of wires distributes electricity to neighborhoods and communities. The distribution system is comprised of sets of three or four wires which can be suspended or buried underground. The voltage on distribution lines ranges from 4,000 to 12,000 volts and is further stepped down with pole-top or pad-mounted transformers to a customer use level ranging from 480 to 120 volts. There are approximately 15,000 miles of distribution lines in San Diego County.

Electric Meter: Electricity is provided to customers by wires, often called service drops, emerging from distribution transformers. These wires go into electric meters that measure the quantity of electricity used (measured in kilowatt-hours). The meter is typically located where the utility hands off the delivery of electricity to the customer. Generally the customer is responsible for purchasing and maintaining equipment past this point.

Generating Station: This is where electricity is produced. A generator is similar to a water pump. While a water pump creates water pressure causing water to flow, a generator produces electrical pressure to push electricity through the wires. Typically, this pressure is accomplished by converting a mechanical energy source to electrical energy (electricity). Examples of mechanical energy sources used at generating stations include steam under pressure that was heated by burning natural gas, coal, or nuclear fusion, or blades being turned by the power of the wind. This mechanical energy is then converted to electrical energy through a spinning shaft turning large magnets. Stationary coils of copper wire surround these rotating magnets. This rotating action causes electrons (packets of electrical energy) to move from atom to atom in the copper wire of the coils. This motion of electrons in the copper wire is electricity.

Pad-Mounted Transformer: This is the version of a distribution transformer which sits on the ground. Usually green and rectangular in appearance, this transformer is fed from underground lines.

Pole-Top Distribution Transformers: These are the cylindrical gray cans you see mounted on utility poles. They will usually be found alone or in-groups of three depending on whether they serve a single-phase service (typical home or small business) or three-phase service (typical large business or industrial use). These transformers step-down the voltage on the distribution system to a level that can be utilized directly by customers.

Pole-Top Fuses: Fuses, similar to those found in some electrical equipment in your home, disconnect the electrical connection if a short circuit occurs. The fuse must be replaced after the problem has been located and corrected to restore service. Fuses are generally found at branches in the distribution system or ahead of transformers.

Recloser: This rectangular box, found on distribution utility poles, acts as a smart circuit breaker. It can determine if a short circuit occurs ahead or behind it. If the problem is behind the recloser it disconnects service. It can be programmed to try to reconnect after a short time period. This action may cause "blinks" on the line but can drastically reduce the length of the outage. Often short circuits on overhead distribution lines are caused by conditions that will disappear given a little time. Things like animal contacts or tree branches in the line. Many times the recloser can automatically re-energize the line after a very brief time. If the short circuit remains, the recloser will trip and lockout. At that point a service person must be dispatched to locate and repair the problem.

Short Circuit: An unwanted leak in the electrical system. Breakers or fuses act as safety devices to stop the flow should a short circuit occur.

Substations: These sites contain specialized equipment to reduce or step-down transmission line voltage. Typically, the voltage is stepped down from 230,000 to 12,000 volts and is connected to a system of wires called the distribution system described below. Substations also contain large circuit breakers to stop the flow of electricity to transmission and distribution lines should the system develop a short-circuit (an electrical leak).

Switches: Are used to easily reconfigure the electrical feeds on a distribution system should repairs or maintenance be needed. By reconfiguring the circuit the number of customers without power can often be minimized.

Transmission System: The electricity produced at generating stations is connected to a system of wires called the transmission system. This interconnected "spider web" of wires carries electricity across cities, counties, states, and even countries through sets of three wires. The transmission system can carry electricity vast distances because it is done at very high voltages (69,000 to 500,000 Volts). Because of this "high pressure" the wires of transmission lines must be suspended high in the air on very large steel structures or poles to keep it from "leaking away".

Glossary of Utility System Reliability Terms

ANSI C84.1-1982(2) - A standard specifying a steady-state voltage tolerance for the electric utility at the point of service to be within 5 percent of nominal for non-lighting loads. The standard also specifies steady-state voltage tolerances for acceptable performance of end use equipment of plus 6 percent to minus 13 percent.

Average Service Availability Index (ASAI) - The average degree of service continuity experienced by customers served during a year (measured in percent).

Customer Average Interruption Duration Index (CAIDI) - The average forced sustained interruption duration experienced by interrupted customers per year (measured in minutes).

Forced Outage - Interruptions that are not prearranged.

Flicker - A small change in line voltage, which causes a perceptible change in the intensity of electric lights. In some situations people can detect sags as low as a third of a volt.

Frequency Deviation - An increase or decrease in the power frequency. Nominal value in the U.S. is 60 Hz or 60 cycles per second.

Instantaneous Reclosing- A term applied to reclosing of a utility breaker as quickly as possible after interrupting fault current. Typical times are 3 to 6 cycles for transmission breakers to 18 to 30 cycles for distribution breakers.

Momentary Average Interruption Frequency Index (MAIFI) - The average number of forced momentary interruptions experienced per customer served per year (measured in outages).

Momentary Interruption - An interruption lasting no longer than 5 minutes.

Nominal Voltage - A nominal value assigned to a circuit or system for the purpose of designating its voltage class. Typical nominal customer service voltages are 120, 208, 240, 277, and 480. Larger facilities may be served at 4160 or 12,000 volts.

Over Voltage - A long duration RMS voltage variation at least 10 percent greater than the nominal voltage for a period of time greater than one minute.

RMS Voltage or RMS Current - Root mean square. The AC value that produces the same heating effect in a resistor as would a DC value of the same magnitude.

Sustained Outage - Those interruptions lasting more than 5 minutes.

System Average Interruption Duration Index (SAIDI) - The average forced sustained interruption duration per customer served per year (measured in minutes).

System Average Interruption Frequency Index (SAIFI) - The average number of forced sustained interruptions experienced per customer served per year (measured in outages).

Transient - A very brief excursion from nominal voltage with durations of a microsecond (millionths of a second) to several hundred microseconds. Transients are classified as impulsive or oscillatory.

Under Voltage - A long duration RMS voltage variation at least 10 percent below the normal (nominal) voltage for a period of time greater than one minute.

Voltage Sag - A decrease of 10 to 90% in the RMS voltage at the power frequency for durations of one-half cycle to 1 minute.

Voltage Swell - A temporary increase in the RMS value of voltage of more than 10% at the power frequency, for durations from one-half cycle to 1 minute.

Links to Other Resources

IEEE - Institute of Electrical and Electronic Engineers
NFPA - National Fire Protection Association
NESF - National Electrical Safety Foundation
NECA - National Electrical Contractors Association
NEMA - National Electrical Manufacturers Association
IAEI - International Association of Electrical Inspectors
Power Quality Magazine

Links to third party web sites are solely for the convenience of our customers and visitors.

Utility Grade Power

How are water and electricity alike? In how they are delivered and used by all of us. There are many similarities between the water you purchase from the local water utility and the electricity purchased from a Utility Company. Water straight out of the tap meets many needs such as irrigating and bathing. For other uses, it may need to be conditioned in some way. Drinking water may be filtered. Water for laboratories may be distilled. Other uses may require heating, cooling, or chemical treatment.

In the same way, electricity straight from the utility "tap" may be adequate to power many of your needs such as lighting and most motorized equipment. For some uses, however, the electricity you purchase may need to be filtered or conditioned to adequately meet the requirements of the equipment. This is especially true for electronic equipment.

Standards defining the quality of utility grade power include the evenness of the average pressure (voltage), the regularity (frequency), and the reliability. We follow national guidelines defined by the American National Standards Institute in designing and operating the utility system for voltage and frequency. Public Utilities Commission sets the reliability goals.

Electric Utility Systems Operations

The electric utility system serving you is one of the largest and most complex machines in the world. Here on the West Coast over 1,000 generating plants in California alone produce electricity. These generators are interconnected by over 12,500 miles of transmission lines (the major electrical highways), which constitute a gigantic, interconnected grid. Billions of pieces of electric equipment plug into this system. All of these pieces, generation, transmission, distribution, and electrical end use equipment, all interact.

A problem in one area can have a rippling effect that affects other parts of the system. The immensity of the system increases reliability but adds to the complexity. The system must be continually coordinated and balanced to meet the changes in electrical demand minute to minute.

In the area served by us, electricity is generated at several key plants as well as a host of scattered smaller sites. Over 16,600 miles of transmission and distribution lines (major and local lines) provide the pathway for electricity.

Operations Tour

This section illustrates how the electric system operates and the kinds of things that can cause power disturbances.

To view the tour you must have the Macromedia Shockwave Player installed on your browser. Download it now.
Begin power system elements tour.
Examples of events that affect customer equipment (click on each event for event demo: (See Glossary of Utility System Reliability Terms)
EVENT
RESULT
Car pole accident
Forced outage
Feeder short circuit due to fires
Voltage sag
Lightning strike
Voltage surge/transient
Air conditioner start-up
Voltage sag
Microwave oven
Under voltage
Printer operation
Voltage swell
Short circuit
Forced outage

What We Can Do and Are Doing to Improve Reliability Performance

We take reliability seriously. Electric reliability is measured against standards established and monitored by the State regulatory board. Our performance goals focus on preventing and mitigating the impact of outages, including reducing their number and duration. Some of those activities include:

Distribution automation improvements - Installing equipment in substations and on distribution circuits to collect real-time information allowing central dispatch to operate switches remotely. This system enables us to quickly identify and isolate problems, and reroute power by remotely opening and closing switches.

Underground cable replacement - Proactively identifying and replacing older cable before it fails. When they do fail, we employ the latest technology and methods to find cable faults quickly.

Vegetation management - A comprehensive effort to reduce tree related outages.
Additional capacity - Adding capacity to circuits and substations to reduce the possibility of overloading equipment and to provide adequate back-up to improve restoration of service.

Monitoring - Installing power monitors on circuits and in substations to assist with the identification of system events other than outages that may impact customer equipment operation.



Voltage Standards

As is the case with any electric utility power supply the voltage on our system will vary throughout the day largely due to the variation in customer electricity use. Under normal conditions, secondary voltage service levels are supplied in accordance with American National Standards Institute (ANSI) standard C84.1 Range A. These levels are +/- 5% of the nominal levels shown in the table below (Steady State Voltage Limits). Rule 2, the tariff governing utility voltage standards, does provide several exceptions to these voltage limits.

These exceptions are conditions that:

Are infrequent, momentary fluctuations of a short duration;
Arise from the temporary action of the weather;
Arise from service interruptions;
Arise from temporary separation of the parts of the system from the main system;
Are causes beyond our control.
Even though we endeavor to maintain constant voltage to your service point your equipment must be prepared to accept occasional deviations outside the nominal ranges.