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ABB

Figure 7: Nomograph for PBA2 Potential Device

Capacitance C2 similarly measured will contain an

insignificant percentage of stray capacitance.

Capacitance C1 is then:

C1=

C2 x 0.85C4

C2 – 0.85C4 (1)

Approximate adjustments may be calculated using the

nomograph (Fig. 7) and the instructions on the following

pages or the equations below.

First calculate the bushing tap voltages as if no potential

device burden were present. This is determined from the

relation:

e = E

C1 + C2 + C3 (2)

Where e is the open circuit tap voltage in volts and E is the

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 = 10

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

same value of reactance determine whether the device

reactance switch is to be in the BUCK or BOOST position

and further determine the number of turns required in the

phase angle adjustment. Now set the rotary switches and

toggle switch of the phase angle adjustment so that the

total turns are the same as that determined from the curve.

ABB PBA2 User Manual

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