7–56 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
AUXILIARY PROTECTION AND MONITORING FUNCTIONS CHAPTER 7: COMMISSIONING
7.6 Auxiliary protection and monitoring functions
7.6.1 THD Level Scheme
7.6.1.1 Minimum Pickup
Testing of this element uses with the same setup used in testing the harmonic restraint
percent differential elements (see FIGURE 7–1: Test setup on page 7–4).
To test the winding 1 THD element,
Connect the composite current signal to terminals H1 and G1.
Since the DC component actually consists of a half-wave rectified
signal, it contains all even harmonics which the relay measures and
operates on.
Note that the fundamental component is required to prevent saturation
of the input CTs. Monitor the output relays as per the relay FlexLogic™
assignment.
Set the fundamental component to rated CT secondary (1 or 5 A).
Gradually increase the DC component to produce even harmonics until
the THD level element operates.
Display the total harmonic content under A2 METERING
HARMONIC CONTENT
THD W1 THDa (2nd-21st).
The displayed value of THD at which operation took place should be the
same as the programmed value.
Check that the Trip, Pickup (and Alarm if selected) LEDs are on and
one of the following is displayed:
LATCHED: W1 THD Level or OPERATED: W1 THD Level
Lower the DC component until the element resets.
The reset value should be approximately 2% less than the operate value.
Verify that the Phase, Pickup, and Alarm LEDs reset if the target
function is set to Self-resetting.
The Trip LED should remain latched.
7.6.1.2 Operating time
To measure the basic operating time of this element,
Preset a fundamental and DC component composite current signal to
cause the element to operate.
Using the setup of Figure 10-1, apply the current suddenly, at the same
time as you trigger the timer.
The measured operating time should correspond to the time delay
setting for the element.
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