GE 745 Instruction Manual page 262

PROTECTION SCHEMES
Note
NOTE
7.5.3.3 Operating Time
Note
NOTE
7.5.3.4 Target, Output Contact, and Display Operation
7.5.3.5 Blocking from Logic Inputs
7–24
 Check that the Trip and Message LEDs are flashing and the following
trip message is displayed:
LATCHED a (bc) Inst Differential.
The message may show OPERATED instead of LATCHED if the TARGET setpoint is "Self-
Reset".
To measure the basic operating time of the instantaneous differential elements,
 Connect an AC current signal to terminals H1 and G1 through a double-
pole, single-throw switch.
The second pole of the switch starts a timer circuit that will be stopped
by the operation of the relay trip contact. Refer to FIGURE 7–5: Timer
test circuit on page 7–19.
 Close the switch and set the current level to two times the pickup value
measured earlier.
 Re-open the switch and reset all targets on the relay.
 Ensure that the timer circuit functions correctly.
 Close the switch and record operating time of relay.
All differential currents are calculated using the same principal shown in Transformer
Type Selection on page 7–11. The differential current derivation is affected by phase
shift compensation and zero sequence removal.
 Verify the correct operation of all targets and output contacts and
display messages during testing.
Each element is programmable to be blocked by a logic input, virtual input, virtual output,
output relay operation, or self-test relay operation. This test verifies that the differential
element can be blocked by logic input 1.
 Select Logic Input 1 by setting the
PERCENT DIFFERENTIAL
to Logc Inpt 1.
 Apply current to operate the differential element then assert logic input
1.
 Verify that the element has reset and that all targets can be reset.
 With logic input 1 asserted, remove the current and reapply.
 Verify that the element did not operate.
CHAPTER 7: COMMISSIONING
S4 ELEMENTS
PERCENT DIFFERENTIAL BLOCK

745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
DIFFERENTIAL
 
setpoint