GE 745 - Page 248

7–10 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
METERING CHAPTER 7: COMMISSIONING
Since the transformer load is calculated using the maximum current from phases A, B, or C,
the displayed load should be:
where (EQ 7.2)
 Verify the harmonic content display in A2 METERING  HARMONIC
CONTENT
 THD  W1...W2...W3.
It should be zero or equal to distortion of input current.
 Verify frequency shown in A2 METERING
 FREQUENCY 
SYSTEM FREQUENCY.
It should be 60 or 50 Hz, as per frequency of input current on Phase A.
 To verify the positive and negative sequence component values, apply
the current signal to Phase A of each winding in series.
Read the values of positive and negative sequence current displayed by
the relay.
where a = 1∠120° (EQ 7.3)
(EQ 7.4)
All angles will be 0°. These values are displayed in the A2 METERING  CURRENT 
POSITIVE SEQUENCE
 W1...W2...W3 and A2 METERING  CURRENT  NEGATIVE
SEQUENCE
 W1...W2...W3 actual values menus.
 Lower the current amplitude while displaying the system frequency.
 Verify that the frequency is displayed correctly with current levels down
to approximately 50 mA RMS input.
 Decrease current to 0 A.
7.4.3 Voltage Input
 Connect an AC voltage to the voltage input (if the input voltage feature
is enabled) to terminals C11 and C12.
 Set the level at the expected VT secondary voltage on the VT for your
installation.
 Remove all current signals from the relay.
 Verify the voltage reading in A2 METERING
 VOLTAGE  SYSTEM
LINE-TO-LINE VOLTAGE.
The reading should be equal to the input voltage × VT ratio.
NOTE
Note
The displayed system voltage is always the line-to-line voltage regardless of the input
VT signal. Earlier versions of the 745 may display the same voltage as the selected
input, i.e. phase-to-neutral if the input is a phase-to-neutral signal and phase-to-
phase if the input is phase-to-phase.
% Loading
Actual Current
Rated MVA Current
------------------------------------------------
100%×=
Rated MVA Current
MVA
3kV
LL–
-----------------------
=
I
1
1
3
---
CT Ratio× I
a
aI
b
a
2
I
c
++()×
1
3
---
CT Ratio× I
a
× since I
b
I
c
0====
I
2
1
3
---
CT Ratio× I
a
a
2
I
b
aI
c
++()×
1
3
---
CT Ratio× I
a
× since I
b
I
c
0====