GE Multilin 745 Instruction Manual

Protection Schemes 745Transformer Management RelayCommissioninghttp://www.GEindustrial.com/multilin 7ñ35GE Multilinthat the Trip LED is still on. The trip message stays on if the OVERFREQUENCYTARGET setting is ìLatchedî; if it is ìSelf-resettingî, the message resets whenfrequency 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 onlya few milliseconds. Connect the Signal Source and Timer Start triggers asshown in FIGURE 7ñ12: Frequency Element Testing on page 7ñ31.8. Set the current to rated CT secondary value, no voltage connection, and thepre-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 theelement 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 bedesirable to repeat this test several times and average the results. If there is awide scatter, verify the test setup and ensure the signal source behaves in aconsistent manner.The blocking from logic input, if enabled, can be tested as described inearlier tests for other elements.e) Frequency Decay RateA high-quality programmable function generator is required to verify this element.Since the frequency rates of change are measured over a narrow range, the testinstrumentation must accurately simulate frequency decay rates without anysignificant jitter. It is the experience of GE Multilin that some commercial dedicatedrelay test equipment with built-in frequency ramping functions is not accurateenough to verify the 745 performance.Disable all protection functions except the Frequency Decay function. Verify thatsettings match in-service requirements. The settings are entered and modified inthe S4 ELEMENTS !" FREQUENCY !" FREQUENCY DECAY setpoints menu.The following procedures are for the Frequency Decay Rate 1 element. They can beapplied to the Frequency Decay Rate 2, 3, and 4 elements as well, making thenecessary changes where appropriate.Voltage Input Function (Voltage Input Enabled):1. Use a frequency-ramping programmable voltage/current source connected toterminals 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 tothe 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 isnot required for the tests). Monitor the appropriate trip and auxiliary relays.Reset all alarms and indications on the relay. The relay display should remainunchanged with no trip indications.2. Program the function generator to simulate a frequency rate-of-change justabove 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 isto operate. Note that operation occurs if the rate criterion is satisfied and thefrequency is below the threshold.3. Initiate ramping action and verify element operation once the frequency dropsbelow the threshold.4. Check that the Trip and Pickup LEDs are on and one of the following tripmessages is displayed:LATCHED: Freq Decay Rate 1 or OPERATED: Freq Decay Rate 1If the target was selected as ìLatchedî, the Trip LED and the message remainon.NOTENOTE