Voltage Input - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

10 COMMISSIONING
6. Verify frequency: 60 or 50 Hz, as per frequency of input current on phase A.
ACTUAL VALUES/A2 METERING/FREQUENCY/SYSTEM FREQUENCY
7. 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.
1
×
I CT Ratio
= -- -
1
3
where a = 1∠120°
1
×
I
= -- - CT Ratio
2
3
All angles will be 0°.
These values are displayed with the following actual values:
ACTUAL VALUES/A2 METERING/CURRENT/POSITIVE SEQUENCE/W1...W2...W3
ACTUAL VALUES/A2 METERING/CURRENT/NEGATIVE SEQUENCE/W1...W2...W3
8. Now, lower the current amplitude while displaying the system frequency. Verify that the frequency is dis-
played correctly with current levels down to approximately 50 mA rms input. Decrease current to 0 A.
1. 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.
2. Remove all current signals from the relay.
3. Verify the voltage reading with the following actual value:
ACTUAL VALUES/A2 METERING/VOLTAGE/SYSTEM VOLTAGE
The reading should be: Input voltage × VT Ratio
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
NOTE
phase-to-phase.
4. With the voltage signal still ON, read the displayed system frequency under:
ACTUAL VALUES/A2 METERING/FREQUENCY/SYSTEM FREQUENCY
5. Lower the voltage amplitude while displaying the system frequency. Verify that the frequency is displayed
correctly with voltage levels down to less than 3 V RMS input (when the lower limit is reached, the system
frequency will be displayed as 0.00 Hz). Verify that at less than 1.0 V, frequency is displayed as 0.00 Hz.
The 745 automatically configures itself to correct for CT ratio mismatch, phase shift, etc., provided that the
input CTs are all connected in wye. The following example illustrates the automatic setting feature of the 745.
a) AUTOMATIC TRANSFORMATION PERFORMED IN THE 745
The automatic configuration routines examine the CT ratios, the transformer voltage ratios, the transformer
phase shift, etc., and apply correction factors to match the current signals under steady state conditions.
Consider the case of a Y:D30° power transformer with the following data (using a 1 A CT secondary rating for
the relay):
GE Power Management
10.5 DISPLAY, METERING, COMMUNICATIONS, ANALOG OUTPUTS
1
2
× ( ) ×
I aI a I CT Ratio
+ + = -- -
a b c
3
1
2
× ( ) ×
I a I aI
+ + = -- - CT Ratio
a b c
3
745 Transformer Management Relay
×
I since I I 0
= =
a b c
×
I since I I
= = 0
a b c

10.5.3 VOLTAGE INPUT

10.5.4 TRANSFORMER-TYPE SELECTION
10
10-9