GE 745 Instruction Manual page 257

CHAPTER 7: COMMISSIONING
7.5.2.7 Slope Measurements
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
 Re-open the switch and reset all targets on the relay.
 Ensure that timer circuit functions correctly.
 Close the switch and record operating time of relay.
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 displayed actual values is
recommended.
The differential and restraint currents are displayed the
DIFFERENTIAL PHASE A DIFFERENTIAL CURRENT

RESTRAINT PHASE A RESTRAINT CURRENT

To measure the slope,
 Connect current signals to the relay as shown in the figure below:
FIGURE 7–6: Current signal connections
= 1.5 × CT and I
If I = 0, the element is operated as all the current appears as a differential
1 2
current.
The slope is calculated from the values of I
FIGURE 7–5: Timer test circuit
A2 METERING
and A2 METERING
actual values:
and I
differential restraint
I
differential
------------------------ -
%slope × 100%
=
I
restraint
PROTECTION SCHEMES
CURRENT
 
CURRENT
 
as follows:
7–19