November 2014
Beginner
288 pages
7h 52m
English
Content preview from Electrical Estimating Methods, 4th Edition
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CHAPTER 17 Power Systems and Capacitors
Power systems are standby or emergency generator sets for providing power to essential services during a loss of normal power. Capacitors are used for power factor correction to increase efficiency, thus reducing electrical utility bills. Definitions are provided for each of the components in this chapter. Units for measure, material and labor requirements, and a takeoff procedure are also provided.
CAPACITORS
Power factor (PF) is a measurement of the ratio between true power and apparent power, that is, PF = W/VA. It is a measure of how effectively the power is being used. The ideal PF is 1.0. In industrial and commercial buildings, reactive loads, such as motors, can cause phase shifts between the voltage (V) and the current (A) which, in turn, create undesirable power factors (0.51–0.80). By installing a capacitive load in the system, the PF can be adjusted toward 1.0.
Industrial capacitors are metal-clad units that include one (single-phase) or three (three-phase) capacitors and discharge resistors. Industrial capacitors may be connected to the loads of each individual motor or to the main incoming lines. Capacitors are sized in terms of kVAR at a specific voltage and according to the number of phases.
Units of Measure. Capacitors are taken off and quantified by counting as individual units each (EA).
Material Units. The following items are generally included per unit:
- Capacitor
- Fasteners
Additional items that may be required ...
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