GE 745 Instruction Manual page 289

CHAPTER 7: COMMISSIONING
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
 Reset all alarms and indications on the relay.
The relay display should remain unchanged with no trip indications.
 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.
 Initiate ramping action and verify element operation once the frequency
drops below the threshold.
 Check that the Trip and Pickup LEDs are on and one of the following
trip messages is displayed:
LATCHED: Freq Decay Rate 1 or OPERATED: Freq Decay Rate 1
If the target was selected as Latched, the Trip LED and the
message remain on.
 Reduce the voltage to below the
FREQUENCY DECAY
supervision level.
 Repeat ramping action and verify that element does not operate.
If the voltage supervision level has been set to 0.00, the element
continues to operate correctly down to approximately 2% or nominal.
 Return voltage to nominal value.
 If current sensing is enabled, set the current level below the
ELEMENTS
OPERATING CURRENT
 Repeat ramping action and verify that element does not operate.
 For timing tests, an approximate operate time is obtained if a timer is
triggered at the same time as the ramping action and the time interval
between the trigger point and the relay operation measured.
From that measured time, subtract the time required for the frequency to
reach the threshold value.
Current input function (voltage input disabled):
 Using a frequency-ramping programmable voltage/current source
connected to terminals H1 and G1 for the current signal, set the
frequency to 60.00 Hz (or 50Hz). Set the current amplitude to rated CT
secondary.
 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.
 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
S4 ELEMENTS
MINIMUM OPERATING VOLTAGE

FREQUENCY FREQUENCY DECAY
 
value.
PROTECTION SCHEMES
FREQUENCY
 
voltage
S4
MINIMUM

7–51