GE TRANSFORMER MANAGEMENT RELAY 745 Instruction Manual page 252

8.5 PROTECTION SCHEMES
3. Close the switch and record operating time of relay.
f) SLOPE MEASUREMENTS
The auto configuration processes the currents to correct for phase shifts, CT mismatch, and zero sequence component
removal. As such, it more complex to measure the slope from an external single phase injection. Therefore, the use of dis-
played actual values is recommended.
The differential and restraint currents are displayed the
and
TIAL CURRENT A2 METERING
1. To measure the slope, connect current signals to the relay as shown in the figure below:
8
= 1.5 × CT and I
2. If I
1
3. The slope is calculated from the values of I
4. Slowly increase I
2
pickup.
5. As I continues to increase, the element operates again when both the initial slope and the minimum pickup conditions
2
are satisfied. Calculate the initial slope 1 value at this point.
6. As I increases further, the element may reset again, depending on the setting of the slope kneepoint. This is caused
2
by the current values moving into the slope 2 region.
7. Continue increasing I
8-14
Courtesy of NationalSwitchgear.com
Figure 8–5: TIMER TEST CIRCUIT
CURRENT RESTRAINT
Figure 8–6: CURRENT SIGNAL CONNECTIONS
= 0, the element is operated as all the current appears as a differential current.
2
differential
. As I is increased, the element will reset when the differential current drops below the minimum
2
until the element operates again. Compute the slope 2 value at this point.
2
745 Transformer Management Relay
A2 METERING CURRENT
PHASE A RESTRAINT CURRENT
and I as follows: %slope
restraint
8 COMMISSIONING
DIFFERENTIAL PHASE A DIFFEREN-
actual values:
I
differential
------------------------- - ×
100% .
=
I
restraint
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