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Description
Application
The condenser bushing potential device is a means for
securing small amounts of 60 hertz power at 115 volts
and 66.4 volts from high voltage lines through the medium
of the condenser bushing. For 115kV and higher voltages
this device is the most economical means of securing
such small amounts of power.
These devices provide a 115 and 66.4 volt output which
is substantially proportional to the system line-to-ground
voltage and in phase with it. This output is commonly
used to energize synchroscopes, voltmeters, and voltage
responsive relays. The device accuracy is not adequate
for use with metering instruments where revenue is involved.
Construction
The potential device is built in an outdoor, weatherproof,
steel housing arranged for mounting on the side of an oil
circuit breaker or transformer in the vicinity of one of the
condenser bushings. A special cable assembly of
Figure 1: Outline and Mounting
ABB
weatherproof construction, and with a grounded external
shield, connects the potential device to one of the metallic
layers of the condenser bushing.
The device network (see Fig. 6) consists of a main transformer
having adjustable reactance, an auxiliary transformer of
adjustable ratio, a tapped capacitor to correct burden power
factor, a protective spark gap, and a dead-front adjusting
panel.
A grounding switch permits de-energizing the device, and a
heater (to be energized from an external voltage source)
prevents internal sweating of the housing.
Standardized mounting dimensions permit the interchangeability
with most standard ABB or Westinghouse units sold since
the middle of 1934. The standard device is electrically usable
for most bushings having capacitance taps per IEEE
C57.19.01-2000 Type A: Normally Grounded having the tap
on the second metallic layer above ground potential. This
includes substantially all Westinghouse bushings manufac-
tured since the middle of 1935 and having a voltage rating of
115kV or higher. Cable lengths (see Fig. 2) are also standard
for circuit breakers, but special lengths are general for trans-
formers. End fittings of cables are common for all.
3
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