GE 745 - 7.5.3 Instantaneous Differential Protection; 7.5.3.1 Overview; 7.5.3.2 Minimum Pickup

CHAPTER 7: COMMISSIONING PROTECTION SCHEMES
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 7–23
 Apply the current signal and measure the operating time.
The time should be equal to ‘energization period’ plus approximately 50
ms.
 Disable the energization detection scheme and repeat the timing test.
The operate time should be the normal operating time of harmonic
restraint differential element.
7.5.2.12 Target, Output, Contact, And Display Operation
 Verify the correct operation of all targets, output contacts, and display
messages during the percent differential tests above.
7.5.2.13 Blocking from Logic Inputs
Each element can be programmed to be blocked by a logic input, virtual input, virtual
output, output relay operation, or self-test relay operation. This procedure verifies that the
differential element is blockable by logic input 1.
 Select logic input 1 by setting the
S4 ELEMENTS  DIFFERENTIAL 
PERCENT DIFFERENTIAL
 PERCENT DIFFERENTIAL BLOCK setpoint
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.
7.5.3 Instantaneous Differential Protection
7.5.3.1 Overview
Settings for this element are under the
S4 ELEMENTS  INST DIFFERENTIAL setpoints
group. All other protective elements must be disabled to ensure that trip relay(s) and
auxiliary relays are operated by element under test. Monitor the appropriate contact per
intended settings of the FlexLogic™.
7.5.3.2 Minimum Pickup
The operating level of the phase A element is measured by applying an AC current to
terminals H1 and G1. Monitor the appropriate trip and auxiliary contact(s) as the current is
increased from 0 A. Due to the auto-configuration feature, it may be easier to read the
actual differential current on the relay rather computing it.
 Compare the value of the differential current at which operation is
detected against the
S4 ELEMENTS  INST DIFFERENTIAL  INST
DIFFERENTIAL PICKUP
setpoint.