Harmonic Detection - GE Multilin 850 Instruction Manual

CHAPTER 4: SETPOINTS

Harmonic Detection

NOTE:
NOTE:
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
The Harmonic detection 1(6) element monitors the selected 2
Harmonics Distortion (THD), which is present in the phase currents. The relay provides six
identical Harmonic Detection elements.
During transformer energization or motor starts, the inrush current present in phase
currents can impact some sensitive elements, such as negative sequence overcurrent.
Therefore, the ratio of the second harmonic to the fundamental magnitude per phase is
monitored, while exceeding the settable pickup level, an operand is asserted, which can be
used to block such sensitive elements.
During startup or shutdown of generator connected transformers, or following a load
rejection, the transformer can experience an excessive ratio of volts to hertz, that is,
become overexcited. Similarly, the ratio of the fifth harmonic to the fundamental
magnitude can be monitored to detect the overexcitation condition.
The harmonics monitored in this element is calculated from the phase currents, unlike the
second or fifth harmonic differential current used in the transformer differential element.
The harmonics are updated every protection pass. The THD is updated every three cycles,
which is not recommended as a blocking signal.
Path:
Setpoints > Monitoring > Harmonic Detection > Harmonic Detection 1(X)
FUNCTION
Range: Disabled, Alarm, Latched Alarm, Configurable
Default: Disabled
HARMONIC
Range: 2nd, 3rd, 4th, 5th, THD
Default: 2nd
This setting selects the specified harmonic or THD to be monitored. The harmonic or THD
is expressed in percent relative to the fundamental magnitude.
PICKUP
Range: 0.1 to 100.0% in steps of 0.1%
Default: 20.0%
PICKUP DELAY
Range: 0.000 to 60000.000 s in steps of 0.001 s
Default: 0.000 s
PHASES FOR OPERATION
Range: Any One, Any Two, All Three, Average
Default: Any One
This setting defines the phases required for operation, and the detail is explained below:
– ANY ONE: At least one phase picked up.
– ANY TWO: Two or more phases picked up.
– ANY THREE: All three phases picked up.
– AVERAGE: The average of three-phase harmonics or THDs picked up.
If set to AVERAGE, the relay calculates the average level of the selected harmonic and
compares this level against the pickup setting. Averaging of the selected harmonic
follows an adaptive algorithm depending on the fundamental current magnitude per-
phase. If the fundamental magnitude on any of the three phases goes below the current
cut-off level, the selected harmonic current from that phase is dropped (zeroed) from the
equation for averaging, and the divider is decreased from 3 to 2. The same happens if
MONITORING
nd th
to 5 harmonic or Total
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