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Grounding
Any one terminal of either the "S" winding or the "Z"
winding of a device may be grounded (it is not necessary),
if desirable for the purposes of the connected burden.
The primary of the device transformer is grounded to
the device housing and it in turn is grounded to the
transformer or breaker tank by the device mounting
and by the sheath of the lead-in cable. The current,
which flows to ground, is a small fraction of an ampere.
Type of Burden
Burdens having ferro-magnetic cores shall be
substantially linear in impedance to 1.73 times normal
voltage.
Broken Delta Burdens
The burden connected to the Z terminals, under
condition of maximum zero sequence voltage, shall
not exceed 50% of the device rating.
Record of Adjustment
A record of the adjustment setting of a given device in
a given location will consist of a record of the following:
Volt-amperes of power factor correction, "Buck" or
"Boost" of reactance switch, total turns of reactance
tapped in, and total volts on primary of voltage
adjustment transformer.
Trouble Shooting
Inability to make voltage of phase angle adjustment
calls for the following:
1. Recheck the reference voltage for phase angle position.
2. Recheck the circuit being used for adjustment.
3. Check accuracy of voltmeter being used, and also
of phase angle meter if one is being used. Note that
phase angle meters may not register correctly if coils
are not operated at their rated voltage or current.
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4. Recheck degree of power factor correction.
5. Calculate the approximate adjustment in line with
sections on "Calculation of Approximate Adjustment"
and""Unusual Combinations" to be sure device is
applicable to the combination at hand.
6. Check for loose, grounded or open connections within
device.
7. Frequency other than 60 hertz on system, such as
25 hertz or 50 hertz.
Variability in performance of device may be due to some
loose connections, to electrical leakage to ground at
the primary voltage of the transformer, or to shorted
turns of transformer primary. The electrical leakage might
be in the bushing tap, in the lead-in cable or in the
potential device.
Flashing of gap means an overburden on the device, or
a ground or short either inside or outside the device, or
a defective gap. The gap shall flash over in the region
15 to 20 kV 60 hertz.
A shifting of adjustment with passage of time can be
indicative of deterioration of the condenser bushing.
Poor ratio regulation will result from increased losses in
the device, and this may result from poor connections
or shorted turns in transformers.
Maintenance
The bushing potential device is a piece of static
equipment and requires no maintenance other than to
see that the heater is energized when it is required, to
see that the paint finish is kept in good condition, and
to be sure no extraneous objects rest on the lead-in
cable. If there is suspicion of change in voltage output
then see Trouble Shooting above.
ABB
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