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 6

ABB

Adjusting

General

The Type PBA2 is a ‘resonant’ or ‘in-phase’ device having
Class’“A” performance, and hence it must be adjusted or
tuned to match a specific bushing and a specific burden. A
reference voltage of known value and phase angle position
is required to make this initial adjustment. This reference
voltage is usually supplied from the secondary voltage of a
potential transformer of the desired ratio, which is connected
line-to-ground to the same phase of the transmission line
as the bushing to which the potential device is mounted.

However, the reference voltage may be taken from another
potential device which has been previously adjusted, or it
may be taken from the low voltage secondary of the power
transformer provided it is known that voltage is in phase
with the line-to-ground voltage of the transmission line. The
object is to have a reference voltage for comparison, this
reference voltage to be approximately 115 volts (or this value
divided by 1.73) as may be decided upon for the device
output, and this voltage to be in phase with the transmission
line-to-ground voltage.

There are three adjustments provided on the device adjusting
panel; these are power factor correction of the burden, phase
angle adjustment of the transformer to series tune the
bushing reactance, and voltage adjustment to control the
burden voltage. The phase angle adjustment shows its
effect by shifting the phase angle of the secondary or output
voltage. The controls on the adjusting panel are marked
power-factor correction, volt-amperes, phase-angle, and
inductive reactance, and voltage adjustment.

The numbers on the respective adjustments are in terms of
volt-amperes of power factor correction; active turns of
reactance winding and volts-primary of the ratio transformer.
The values are useful in making the device adjustment.

It is desirable to adjust the device with the final burden in
place. If this is not possible then a synthetic burden shall be
used having the identical volt-ampere and power factor
characteristics of the actual burden.

The adjustment procedure requires a voltmeter of fairly high
impedance to check the magnitude of the output voltage,
whether 115 volts or 66.4 volts (note that the ratio of these
two voltages in the output is fixed so that only one of them
need be adjusted and checked). To check the phase angle
of the output voltage requires either a phase angle meter
having two voltage coils, a low voltage voltmeter, or an
oscilloscope. The oscilloscope is probably the most
satisfactory for phase angle adjustment.

If the reference voltage being used is the exact magnitude
desired then the entire adjustment can be made by using
two voltmeters (one reading about 150 volts, and the other
about 5 volts) by connecting the ground of the reference
and the ground of the device output together and then
checking voltage between the line terminals, first with the
150 scale voltmeter and finally with the 5 scale voltmeter.
The device will be correctly adjusted when the voltage
between line terminals is a minimum (less than 1 volt).

Procedure

Power Factor Correction

Correct the power factor of the burden to unity, or to a slightly
leading angle. This is the first step and may be done by
switching in an amount of capacitive volt-amperes, to match
the reactive volt-amperes of the burden. In the case of
delta-connected burdens operating from a bank of three
potential devices, it may be simplest to excite the total burden
from a separate voltage source and to adjust the capacitors
to secure unit power-factor in each phase. This can be done
by grounding terminal S3 (Fig. 3) of each device and applying
the three-phase test voltage to the three S1 terminals, or
the three S2 terminals, depending on the voltage. The primary
shall be de-energized for this test and the ground switch
open.

If in this test the protective gap flashes over this may be
stopped by making a radical change in the phase angle
setting, such as by reversing the BUCK-BOOST switch, or
by changing large sections of turns in the tapping arrangement.

As an alternative, the reactive volt-amperes can be calculated
and the corresponding capacitive volt-amperes set on each
device.

Phase Angle and
Voltage Adjustment

There is some interdependence between the phase angle
and voltage adjustment and so these will be considered
together. These are the final adjustments and are best made
with the final burden (power factor corrected) connected in
its final form to the potential device.  The device adjustment
is basically a single-phase procedure, even when connected
into a 3 phase group.

Summary of Contents for PBA2

Page 1: ...Bushing Potential Device Type PBA2 PTAE APD903 IZUA 7711 210 Instructions for Installation and Maintenance ...

Page 2: ...tenance and all details and variations of this equipment do not purport to be covered by these instructions If further information is desired by purchaser regarding his particular installation operation or maintenance of his equipment the local ABB Inc representative should be contacted ...

Page 3: ...ction 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 ener...

Page 4: ... variance with the foregoing tabulation In this connection it is to be noted that the auxiliary capacitance built into each device varies according to the device application See page 10 Calculation of Approximate Adjustment Performance The Type PBA2 Potential Device is a Class A device as defined by AIEE Standard 31 and NEMA Standards SG4 1968 The regulation characteristics with respect to varying...

Page 5: ...er is removed Discharge the bushing tap layer by touching the socket contact with a grounded wire 1 If the bushing is ABB O plus C or other type that permits addition of transformer oil to the test tap with the tap cover in place you may choose to fill the PBA connector housing with transformer oil In this case do not add the petrolatum to the PBA connector housing 2 Otherwise pack the inside of t...

Page 6: ...66 4 volts note that the ratio of these two voltages in the output is fixed so that only one of them need be adjusted and checked To check the phase angle of the output voltage requires either a phase angle meter having two voltage coils a low voltage voltmeter or an oscilloscope The oscilloscope is probably the most satisfactory for phase angle adjustment If the reference voltage being used is th...

Page 7: ...am for checking the phase angle and ratio using the oscilloscope with vertical and horizontal sweeps each energized at 115 volts 60 hertz The oscilloscope shall be adjusted so that the total deflection in each the vertical and the horizontal directions is roughly the same The reference and the output voltages are in phase when the trace on the oscilloscope is the nearest possible to a single strai...

Page 8: ...rect position of the buck boost switch and then the finer adjustments of the phase angle switches is a straight forward procedure to secure a straight line trace on the oscilloscope Start by first trying the larger steps 192 turns is the largest step and if any step is in excess of that required then drop back to the next lower turns in the same switch For example with the three rotary switches in...

Page 9: ...9 ABB Figure 5 Curve of Ohms versus Turns of Reactance ...

Page 10: ...sted device In the case of delta connected three phase burdens it is necessary to make preliminary or approximate adjustments of each device first and to then re check and trim each device one or more times until the three phase voltages to ground are equal and each in phase with its reference voltage When final adjustment is accomplished with the burden connected check voltage H2 H3 This voltage ...

Page 11: ...e actual system line to ground voltage at the condenser bushing The dial setting of the voltage adjustment should then total dial volts 173 e 44 1 3 For the phase angle adjustment it is necessary to know the capacitive reactance XC which must be series tuned This value in ohms is for 60 hertz XC 1012 377 C1 C2 C3 4 377 2 πf with f 60 hertz Using this value of XC refer to curve Fig 5 and using the ...

Page 12: ...ms for 60 hertz or 104 000 to 670 000 ohms for 50 hertz Let ex maximum permissible reactance voltage then ex 7600 2 e2 5 Max watts ex x e XC K 6 Constant K from empirical equation K 95 078XC 100 000 but not less than 11 Application Notes Heater Each device contains two vitreous enameled resistors of 1200 ohms each These are to be energized from an external source for the purpose of preventing the ...

Page 13: ...75 watts and no more than this amount of burden shall be connected to the Z terminals even though the total rating of the device may be in excess of 75 watts in some cases Operating Tap Voltage The primary of the device transformer is designed for continuous operation at voltages not in excess of 7600 volts Therefore it is necessary to check the voltage H2 H3 after any alteration to be certain thi...

Page 14: ...ay not register correctly if coils are not operated at their rated voltage or current 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 ...

Page 15: ...15 ABB Notes ...

Page 16: ...E AND JUDGEMENT WITH RESPECT TO BUSHINGS THIS INFORMATION SHOULD NOT BE CONSIDERED TO BE ALL INCLUSIVE OR COVERING ALL CONTINGENCIES IF FURTHER INFORMATION IS REQUIRED ABB INC SHOULD BE CONSULTED NO WARRANTIES EXPRESSED OR IMPLIED INCLUDING WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY OR WARRANTIES ARISING FROM COURSE OF DEALING OR USAGE OF TRADE ARE MADE REGARDING THE INFORMA...

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