GE Multilin 745 Instruction Manual Download

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Protection Schemes

745

Transformer Management Relay

Commission

ing

http://www.GEindustrial.com/multilin

7–35

GE Multilin

that the Trip LED is still on. The trip message stays on if the

OVERFREQUENCY

TARGET

setting is “Latched”; if it is “Self-resetting”, the message resets when

frequency is below the setpoint.

7. For timing tests, the signal generator must be capable of triggering into step-

wise changing of frequency or ramping down to a pre-selected frequency in only
a few milliseconds. Connect the Signal Source and Timer Start triggers as
shown in FIGURE 7–12: Frequency Element Testing on page 7–31.

8. Set the current to rated CT secondary value, no voltage connection, and the

pre-trigger frequency to the nominal frequency (60 or 50 Hz).

9. Set the post-trigger to 0.5 Hz above the setting of the Overfrequency element.

Reset all targets and relays, if necessary. Reset the timer.

10. Initiate the frequency step and timer start. The Interval Timer records the

element operating time. Compare this time to the

S4 ELEMENTS

FREQUENCY

OVERFREQUENCY

OVERFREQUENCY DELAY

setting:

11. Provided that the operate times are not scattered over a wide range, it may be

desirable to repeat this test several times and average the results. If there is a
wide scatter, verify the test setup and ensure the signal source behaves in a
consistent manner.

The blocking from logic input, if enabled, can be tested as described in
earlier tests for other elements.

e) Frequency Decay Rate

A high-quality programmable function generator is required to verify this element.
Since the frequency rates of change are measured over a narrow range, the test
instrumentation must accurately simulate frequency decay rates without any
significant jitter. It is the experience of GE Multilin that some commercial dedicated
relay test equipment with built-in frequency ramping functions is not accurate
enough to verify the 745 performance.
Disable all protection functions except the Frequency Decay function. Verify that
settings match in-service requirements. The settings are entered and modified in
the

S4 ELEMENTS

FREQUENCY

FREQUENCY DECAY

setpoints menu.

The following procedures are for the Frequency Decay Rate 1 element. They can be
applied to the Frequency Decay Rate 2, 3, and 4 elements as well, making the
necessary changes where appropriate.

Voltage Input Function (Voltage Input Enabled):

1. Use a frequency-ramping programmable voltage/current source connected to

terminals C11 and C12 for the voltage signal and H1 and G1 for the current sig-
nal. Set the frequency to 60.00 Hz (or 50.00 Hz) and the voltage amplitude to
the rated VT secondary voltage. Set the current amplitude to rated CT second-
ary (

Note: if current sensing is disabled for this element, the current signal is

not required for the tests).

Monitor the appropriate trip and auxiliary relays.

Reset all alarms and indications on the relay. The relay display should remain
unchanged with no trip indications.

2. Program the function generator to simulate a frequency rate-of-change just

above Rate 1. The start frequency should be the nominal frequency of the relay;
the end frequency must be below the Frequency Decay Threshold if the relay is
to operate. Note that operation occurs if the rate criterion is satisfied and the
frequency is below the threshold.

3. Initiate ramping action and verify element operation once the frequency drops

below the threshold.

4. Check that the Trip and Pickup LEDs are on and one of the following trip

messages is displayed:

LATCHED: Freq Decay Rate 1

OPERATED: Freq Decay Rate 1

If the target was selected as “Latched”, the Trip LED and the message remain
on.

NOTE