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Field Handbook for Power Quality Analysis

The book is comprised of five chapters and a glossary of terms:

1. Fundamentals of Power Quality

2. Planning and Performing a Power Quality Survey

3. Waveforms

4. PQ Express

5. Appendices

- Power monitor setups

- Case studies

- International voltages

Types of Power Problems

Most users equate the quality of power with the number of power problems they experience. If there are no problems, power quality is good. If there are a large number of problems, power quality is bad. This is an appropriate level of assessment for a power user; however, for professionals responsible for power quality, the definition of a power problem and power quality are more complicated.

  • A power event is a recorded (or observed) current or voltage excursion outside of predetermined monitoring equipment thresholds.
  • A power disturbance is a recorded (or observed) current or voltage excursion (event) which results in an undesirable reaction or condition in the electrical environment or electronic equipment or systems.
  • The term power problem refers to a set of disturbances or conditions which produce undesirable results for equipment, systems or a facility.

There are no hard and fast rules to determine if a variation from the power norm is a power event, disturbance or problem. Identical circumstances may produce a power event for one user and a power problem for another. Similarly, there is no steadfast definition of good or acceptable power quality. In reality, power quality and definition of a power problem depend on:

  • The nature and source of the power event.
  • The susceptibility of the load to the event.
  • The effect on the end activity or process.

Power problems appear in the system in two ways, one internal and one external. They are produced within the electrical system by the generation, transmission and distribution, or use of electrical energy. If the problem is produced externally, they enter the system through direct injection, electromagnetic coupling or inductive coupling.

Utility as the Source of Problems

The user perception is that all, or at least a large percentage, of power problems enter the facility from the utility. This is probably true for some locations, but on average the bulk of power problems which plague the user are generated within the user's own facility.

The problems entering a facility from the utility tend to have a greater impact on the site than most facility-created events. Typical utility generated events include:

  • Power factor correction (impulse and surge).
  • Breaker clearing (sag, undervoltage and outage).
  • Lightning (impulse, surge and sag).
  • Grid switching (impulse, dropout).
  • Arcing contactors (impulse).

The place to stop or limit utility generated events is at the electrical service entrance. Once the interference enters the facility's distribution system it is much more difficult to control. High energy suppression equipment (building service entrance protection) can be installed in conjunction with the main switchgear. A more closely alternative is the installation of a filter which would have dv/dt (frequency) filtering capabilities.

Building as the Source of Problems

The building (facility) is a source rich in power problems and potential power problems. The normal utilization of electrical energy creates any number of power line events which may effect other sensitive equipment within the facility.

Typical building or facility problems include:

  • Loose connections (impulse).
  • Overloaded circuits and transformers (distortion).
  • Wiring errors (neutral-to-ground voltage).
  • Ground loops (neutral-to-ground voltage, high frequency).
  • Arcing connections (high frequency).

Power problems generated within the facility are more difficult to control. There is no substitute for a comprehensive maintenance program to identify and repair loose connections, wiring errors and other physical problems within the distributions system. The use of transformers (with some output filtering) can be effective in creating areas of electrical interest and prevent interference from one source or section being transmitted to other areas.

Equipment as the Source of Problems

Equipment, through its normal operation, may inject undesirable events into the facility electrical distribution system. Typical equipment (load) activities which cause power problems include:

  • Equipment turn-on/off (impulse, sag, surge).
  • Equipment operation (voltage distortion)
  • Phase angle controlled loads (distortion and repetitive disturbances).

Equipment generated power disturbances are generally corrected at the equipment or by introducing mitigation equipment between the load and the facility wiring. Filters and transformer-based conditioning products are used in these situations.

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