This product does not use the above techniques for directionalisation. This product uses an innovative patented
technique called Transient Reactiv
e Power protection to determine the fault direction of earth faults in
compensated networks.
5.1 TRANSIENT EARTH FAULT DETECTION IMPLEMENTATION
Transient Earth Fault Detection (TEFD) in this device comprises three modules:
● Transient Earth F
ault Detection module (TEF)
● Fault Type Detector (FTD)
● Direction Detector (DD)
5.1.1 TRANSIENT EARTH FAULT DETECTOR
To establish that there is some kind of earth fault on the system somewhere is straightforward. A simple residual
ov
er
voltage comparison can determine this. Therefore a TEF> Start signal is produced by comparing the neutral
voltage with a threshold voltage set by TEF VN> Start in the TEF DETECTION column. The difficulty comes with
establishing the type of fault and its direction.
5.1.2 FAULT TYPE DETECTOR
The FTD uses a Fundamental analysis (FA) technique to establish whether the fault is an intermittent fault or a
steady state faults. For Transient Ear
th F
ault Detection, the detector counts the Residual Voltage bursts within a
specified time window. With some clever signal processing the detector module creates pulses by comparing the
bursts with a settable threshold, then counts these pulses. If the number of pulses exceeds the number specified
by the FTD> Fault Count setting, within the time window specified by FTD> Time Window, the fault is deemed to
be intermittent and the TEF> Intermit DDB signal is asserted. If there are fewer pulses than this number, this
indicates either a disturbance or a permanent fault. To establish which, we need to look at the RMS value of the
residual voltage.
If there are fewer pulses than specified and the RMS value does not draw back within the specified time window,
the fault is deemed to be permanent. In this case the TEF> Steady DDB signal is asserted.
If there are fewer pulses than specified and the RMS value does draw back, this indicates that a disturbance has
been detected but it is not a fault. In this case, the TEF> Steady DDB signal is not asserted.
The inputs to this module are:
● The residual voltage
● FTD> VN (defines the threshold which converts the residual voltage burst into a pulse
● FTD> Time Window (defines the time window - default is 2 seconds)
● FTD> Fault Count (defines the fault count)
The FTD outputs two signals to indicate whether the fault is steady state or intermittent.
5.1.3 DIRECTION DETECTOR
The Direction Detector uses a patented technique based on Transient Reactive Power to establish the direction of
the fault
. Unlik
e traditional methods, this TRP method does not require high resolution CTs or special analogue
filtering hardware and is therefore cheaper to implement.
It can be shown that the residual voltage and residual current components are largest at 220 Hz. Also, in the
forward direction, the residual voltage leads the residual current by 90°, and in the reverse direction the residual
voltage lags the residual current by 90°. These criteria can be used to directionalize the fault.
The residual voltage (Vres) is passed through a bandpass filter tuned to 220 Hz, which also adds 90° to it. The
residual current (Ires) is also passed through a 220 Hz bandpass filter, but no phase shift is applied. The resulting
components which we shall call V
H1
and I
H2
are therefore in antiphase with each other for forward faults and in
phase if the forward line is not faulted.
P14x Chapter 12 - Power Protection Functions
P14xEd1-TM-EN-1 271
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