GE 745 - 6.3.3 Frequency; 6.3.4 Tap Changer; 6.3.5 Voltage

6–12 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
A2 METERING CHAPTER 6: ACTUAL VALUES
The harmonic derating factor for each of the windings shows the effect of non-sinusoidal
load currents on power transformer’s rated full load current. The calculations are based on
ANSI/IEEE standard C57.110-1986. The actual values messages display the harmonic
derating factor for windings 1 through 3.
6.3.3 Frequency
PATH: ACTUAL VALUES  A2 METERING  FREQUENCY
The SYSTEM FREQUENCY is calculated from the voltage input provided that voltage
sensing is enabled and the injected voltage is above 50% of VT. If these criteria are not
satisfied, then it is determined from winding 1 phase A current provided that it is above
0.05 × CT. If frequency still cannot be calculated, “0.00 Hz” is displayed, though the
sampling rate is then set for the
S2 SYSTEM SETUP  TRANSFORMER  NOMINAL
FREQUENCY setpoint. The FREQUENCY DECAY RATE can only be calculated if system
frequency can be calculated.
6.3.4 Tap Changer
PATH: ACTUAL VALUES  A2 METERING  TAP CHANGER
This message displays the actual tap position. If tap position sensing is disabled, “n/a” will
be displayed.
6.3.5 Voltage
PATH: ACTUAL VALUES  A2 METERING  VOLTAGE
For phase-to-neutral input voltages, the SYSTEM LINE-TO-LINE VOLTAGE displays its line-
to-line equivalent.
 FREQUENCY [] SYSTEM FREQUENCY:
0.00 Hz
MESSAGE
FREQUENCY DECAY
RATE: 0.00 Hz/s
 TAP CHANGER [] TAP CHANGER
POSITION: n/a
 VOLTAGE [] SYSTEM LINE-TO-LINE
VOLTAGE: 0.00 kV
MESSAGE
VOLTS-PER-HERTZ:
0.00 V/Hz
MESSAGE
LINE-NTRL VOLTAGE:
0.00 kV at 0° Lag