23 656-500
Capacitor Fuses Each capacitor stage consists of groups of capacitor cells mounted on
modular trays. Each capacitor stage is protected by a semiconductor-
grade fuse.
Inrush-Limiting Reactors Some PureWave AVCs are fitted with detuning reactors. These reactors
prevent resonance-related problems and limit the rate of rise of SCR
current to limits specified by the SCR supplier.
Cooling of SCR/Diode Valves Each SCR/diode heat sink includes a thermostatically controlled cool-
ing fan. The cooling fan is turned on when the temperature at the sur-
face of the heat sink exceeds 60° C. The fan turns off when the heat
sink temperature cools to 45° C.
Heat-Sink Temperature Sensor A temperature transducer, mounted on each SCR/diode heat sink, dis-
ables the triggering signal for that capacitor stage if the temperature
reading on the surface of the heat sink exceeds 85° C, which is indica-
tive of fan misoperation. Normal operation will resume when the heat
sink temperature cools.
Surge Arresters The PureWave AVC is provided with high-energy MOV surge arresters
that offer protection against transient overvoltages in the power sys-
tem. The arresters are placed at the cable entrance.
Frequency Scan Synchronization of the SCR triggering times, set by the control pro-
gram, is based on the zero crossing of the phase-to-neutral voltages. To
avoid SCR misfires due to voltage waveform distortion, the micropro-
cessor timing block calculates the time between two consecutive zero
crossings. If the duration does not correspond to the 60-Hz power fre-
quency, SCR firing signals are disabled for one cycle, or until the volt-
age waveform returns to normal.
PROTECTIVE DEVICES
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