Table of Contents
Advertisement
10.6 PROTECTION SCHEMES
10.6 PROTECTION SCHEMES
Keep track of modifications/changes made to settings during the course of these commis-
sioning steps and ensure that all settings are returned to the "in-service" values at the end of
the tests.
CAUTION
The harmonic restrained percent differential element setpoint are under:
SETPOINTS/S4 ELEMENTS/DIFFERENTIAL/PERCENT DIFFERENTIAL/...
Disable all other protection elements to ensure that trip relay(s) and auxiliary relays are operated by element
under test only. With a multimeter, monitor the appropriate output contact(s) per intended settings of the Flex-
Logic. Refer to the relay settings to find out which relay(s) should operate when a given element operates.
a) MINIMUM PICKUP
1. The minimum pickup of the A-phase element is measured by applying a fundamental frequency AC current
to terminals H1 and G1, Winding 1 phase A. Monitor the appropriate trip and auxiliary contact(s) as the
current is increased from 0 A. Compare the current value at which operation is detected against:
SETPOINTS/S4 ELEMENTS/DIFFERENTIAL/PERCENT DIFFERENTIAL/PERCENT DIFFERENTIAL PICKUP
Since the operating point is normally set quite low, fine control of the current signal will be required to
obtain accurate results.
2. The currents in the winding may be phase shifted or may have the zero-sequence component removed
due to auto-configuration (see Section 5.2: AUTO-CONFIGURATION on page 5–3). As an alternate to cal-
culating to relation of input current to differential current, the differential current is displayed under:
ACTUAL VALUES/A2 METERING/CURRENT/DIFFERENTIAL/...
Ensure that the displayed value is the same as the minimum pickup setting when the element operates.
3. Check that the TRIP and MESSAGE indicators are flashing and the following trip message is displayed:
SS OPERATED (LATCHED)∅A
SS Percent Differentl
The message will indicate either OPERATED or LATCHED depending on the setting under:
SETPOINTS/S4 ELEMENTS/DIFFERENTIAL/PERCENT DIFFERENTIAL/PERCENT DIFFERENTIAL TARGET
NOTE
4. To independently verify that auto-configuration causes the currents to be as measured, follow the rules
outlined in steps 5 to 9 below.
5. Look up transformer type in Table 5–1: TRANSFORMER TYPES on page 5–10.
6. For the phase shift shown for the particular set of vectors, determine the processing applied to the current
vectors for that winding from Table 5–2: PHASE SHIFTS on page 5–23.
7. Calculate the "dashed" current values using the equations in Table 5–2: PHASE SHIFTS on page 5–23. If
applicable, use the zero-sequence removal computation. This is applicable for all Delta windings and for
both windings of a wye-wye transformer. Compute the processed current vectors to obtain the "dashed"
values for that winding.
8. Calculate the CT correction factor for Windings 2 (and 3 if applicable) and apply as necessary.
10
9. Turn the equations around to compute the threshold differential currents in terms of the applied currents.
10-14
10.6.2 HARMONIC RESTRAINED PERCENT DIFFERENTIAL
745 Transformer Management Relay
10 COMMISSIONING
10.6.1 WARNING
GE Power Management
Advertisement
Table of Contents
