General
Causes of Power Problems
Wiring and Grounding Problems
Equipment Problems
Power Disturbances
Should Your Facility Have a "POWER QUALITY STUDY"?
Advantages
Literature
GENERAL
Power quality has become more of an issue in recent years because of the growth of computer based loads within buildings.
In the past, loads were mostly resistive and inductive. Today's loads include a proliferation of electronic equipment with components that are more sensitive to the power supplied. In addition, many of these new loads have characteristics that produce power aberrations that adversely effect equipment and wiring
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CAUSES OF POWER PROBLEMS
There are really four basic sources of power problems:
1. BUILDING WIRING, GROUNDING AND DISTRIBUTION SYSTEMS
2. BUILDING EQUIPMENT (variable frequency drives, elevators, A/C)
3. OTHER EQUIPMENT (copiers, diagnostic equipment, PC's)
4. EXTERIOR (power company, lightning)
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WIRING AND GROUNDING PROBLEMS
The #1 cause of power quality problems is related to wiring, grounding and distribution within buildings. So the first step in a power quality audit should be an evaluation of these items.
Traditionally the grounding system has been a safety issue. Now it serves as a zero-reference for digital electronics. Therefore, excessive ground currents can cause information/memory loss, software damage/errors, equipment lock-ups and common mode noise.
Some examples of poor grounding:
- Improper ground-to-neutral connections (Th4is is a code violation and can cause circulating currents and magnetic fields.)
- Missing grounds
- Neutral and ground reversals
- Undersized grounds
- Excessive ground currents (This can cause common-mode noise.)
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EQUIPMENT PROBLEMS
Because computer based loads draw current over only a portion of the cycle, they generate high peak current demands at multiples of the fundamental line frequency of 60Hz. These are called harmonic currents. When these harmonic currents occur at odd-multiples of three (e.q. triplen currents such as 3rd., 9th., 15th. ...), they do not cancel one another on neutrals, but instead algebraically add together to produce current that can be as much as 1.73 times the line current.
Some problems relating to harmonics include:
- Overloaded neutrals
- Overheated transformers
- Excessive voltage distortion
- Misoperation of equipment
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POWER DISTURBANCES
Because modern electronic loads are more sensitive, they are now being effected by the imperfections that have always existed in the power supplied to them. These power aberrations can enter from Power Company lines or may be generated by equipment within the building. They include: Transients, sags, surges, spikes, undervoltages and overvoltages.
Some problems related to power disturbances include:
- Equipment/component failures
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- Reduced equipment/component life
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SHOULD YOUR FACILITY HAVE A "POWER QUALITY STUDY"?
Some people refuse to go to their doctor for a check-up, until they feel sick. Others feel that it is wiser to be pro-active rather than re-active.
In today's business, every expense must be justified. The important thing to realize is that: "Things have changed." We now have new kinds of loads that are more sensitive to power imperfections. Some of these new non-linear loads are introducing harmonics and transients into electrical distribution systems that may be causing damage to the facility or damage to equipment and may be a safety concern.
New buildings are now being designed differently. Neutrals and panel busses are being oversized; feeders and branch circuits are being derated; K-FACTOR rated transformers are being specified; and grounding systems are being more carefully detailed. Buildings designed just a few years ago do not have the advantages of these new design measures and, in many cases, cannot adequately cope with these new electronic loads. Therefore, it makes good business sense to evaluate existing facilities and correct deficiencies, so that equipment will operate properly and damage will be avoided.
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ADVANTAGES
a. Identifies wiring/grounding problems for permanent correction.
b. Records harmonics and waveforms and provide a base line for comparison, if future problems develop.
c. Measures power anomalies (transients, sags, swells, etc.) to determine if problems currently exist.
Gaskell Associates are Consulting Engineers. We do not sell products or represent manufacturers. This allows us to offer our clients independent, unbiased advice. We have the expertise and experience to investigate and solve your power quality problems.
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LITERATURE
Power Quality Studies & Solutions
Power Quality Monitoring
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