GE 745 Instruction Manual page 291

CHAPTER 7: COMMISSIONING
7.5.18.2 Fifth Harmonic Scheme
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
LATCHED: Volts-Per-Hertz 1 or OPERATED: Volts-Per-Hertz 1
 For timing tests, prepare a table of expected operating time versus
applied V/Hz signal from the selected timing curve for the element.
 Using the variable frequency function generator to simulate the different
V/Hz ratios, apply suddenly to the relay and measure the operating time.
The 5th harmonic scheme operates if the 5th harmonic content of any current signal
connected to the relay exceeds the threshold setting, for the set time, provided that the
level is above the set threshold.
 Disable all protection functions except the 5th harmonic function.
The 5th harmonic scheme settings are in the
OVEREXCITATION
This test requires a current generator capable of producing a fundamental and 5th
harmonic component.
 Connect the current signal to H1 and G1 and set the fundamental
component level above the threshold setting.
 Slowly increase the amplitude of the 5th harmonic component until the
element operates.
 Calculate the ratio of 5th harmonic to fundamental at which operation
occurred and compare this value to the setting of the element.
 Check that the Trip, Pickup (and if selected, Alarm) LEDs are on, and
one of the following is displayed:
LATCHED: 5th Harmonic Level or OPERATED: 5th Harmonic
Level
 Reduce the 5th harmonic component until the element resets.
The reset level should be 97% of the operate level.
 Reset indicators and clear messages.
 Repeat the above steps with a fundamental current level below the
threshold setting.
 Ensure that the element does not operate.
 For timing tests, simulate an operating condition as above and apply
suddenly to the relay and measure the operating time.
The time should be the same as the setting in the element.
S4 ELEMENTS
5th HARMONIC LEVEL

PROTECTION SCHEMES

setpoints menu.
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