1. Field of the Invention
This invention relates to capacitor units for use in electrical power distribution systems. Capacitor units are used in electrical power distribution systems to improve voltage regulation and to correct circuit power factor when a lagging power factor is caused by inductive loading on the system.
2. Description of the Prior Art
When an electrical power distribution system is operated during periods of heavy load, losses in transmission lines result in decreased voltage at the load. The insertion of a shunt capacitor unit in the system near the load results in a voltage increase at that point to counteract the voltage lost in the transmission lines. Thus voltage can be regulated by inserting or removing shunt capacitor units as required by changes in system loading.
Capacitor units also serve to increase circuit efficiency when inductive loads create a lagging power factor. This is accomplished by connecting shunt capacitor units in parallel with the load to supply part of the lagging component of the current, thereby increasing the circuit power factor.
Prior to this invention, power capacitor units contained a fixed discharge resistor permanently connected in parallel with a capacitive element. This discharge resistor is required to drain the charge off of the capacitive element when the capacitor unit is disconnected from the power distribution system voltage. This provides a safety feature which minimizes the probability of an electrical shock being caused by residual charge on the capacitor when it is disconnected from the distribution system.
When the capacitor unit is connected to the power distribution system, the discharge resistor is connected across the power lines and continually consumes power during normal operation. Since the discharge resistor serves no purpose when the capacitor unit is connected to the power distribution system, any power which it consumes tends to lower the efficiency of the system.