-ETHOD OF OPERATION3*
6
#
' #
(IGHLY SENSITIVE EARTH FAULT PROTECTION
4HE HIGHLY SENSITIVE EARTH FAULT PROTECTION CAN BE
USED IN ISOLATED OR ARC COMPENSATED NETWORKS TO DE
TECT AN EARTH FAULT TO DETERMINE THE EARTH FAULTED
PHASE AND TO DISCRIMINATE THE EARTH FAULT DIRECTION )N
EFFECTIVELY GROUNDED OR LOW
IMPEDANCE EARTHED
NETWORKS DETECTION OF HIGH
RESISTANCE EARTH FAULTS
WITH VERY SMALL FAULT CURRENTS IS POSSIBLE )T CAN BE
DELAYED AND RESULT IN ANNUNCIATION OR ALSO IN A TRIP
"ECAUSE OF ITS HIGH SENSITIVITY IT IS NOT SUITED FOR DE
TECTION OF HIGHER EARTH FAULT CURRENTS FROM ! AND
ABOVE AT THE RELAY TERMINALS FOR HIGH
SENSITIVITY
EARTH FAULT PROTECTION &OR THOSE APPLICATIONS USE
THE OVERCURRENT TIME PROTECTION FOR EARTH CURRENTS AS
DESCRIBED IN 3ECTIONS AND
6OLTAGE STAGES
4HE EARTH FAULT PROTECTION FUNCTION COMPRISES THE
EARTH FAULT DETECTION BY MONITORING THE DISPLACEMENT
VOLTAGE 5
%
AND THE RECOGNITION OF THE EARTH
FAULTED PHASE 4HE DISPLACEMENT VOLTAGE MAY BE
CONNECTED DIRECTLY TO THE RELAY TERMINALS OR MAY BE
CALCULATED FROM THE SUM OF THE PHASE
TO EARTH
VOLTAGES )N THE LATTER CASE THE DISPLACEMENT VOLTAGE
CAN ONLY BE DETECTED WHEN THE RELAY IS CONNECTED TO
THREE PHASE
EARTH VOLTAGE TRANSFORMERS THE STAR
POINT OF WHICH IS EARTHED
)F THE RELAY IS CONNECTED TO PHASE
TO PHASE VOLT
AGES EARTH FAULT DETECTION IS NOT POSSIBLE AS THE DIS
PLACEMENT VOLTAGE CANNOT BE CALCULATED 4HE RELAY
IS INFORMED ABOUT THE VT CONNECTIONS DURING CONFIG
URATION
4HE DISPLACEMENT VOLTAGE 5
%
INITIATES EARTH FAULT DE
TECTION AND IS ONE CONDITION FOR RELEASE OF DIRECTIONAL
DETERMINATION ACCORDING TO 3ECTION 5
%
MEANS
THE VOLTAGE AT THE INPUT OF THE DEVICE WITH OPEN DELTA
64 IF THIS INPUT IS NOT USED THE RELAY THEN CALCULATES
5
%
o | 5
5
,
5
,
5
,
o
)N ORDER TO ENSURE MEASUREMENT OF STABLE VALUES
THE EARTH FAULT DETECTION IS DELAYED UNTIL SECOND
ADJUSTABLE AFTER INCEPTION OF VOLTAGE DISPLACEMENT
!FTER RECOGNITION OF DISPLACED VOLTAGE CONDITIONS THE
FIRST OBJECTIVE OF THE DEVICE IS SELECTIVE DETECTION OF
THE EARTH
FAULTED PHASE IF POSSIBLE &OR THIS PUR
POSE THE INDIVIDUAL PHASE
TO EARTH VOLTAGES ARE
MEASURED 4HE AFFECTED PHASE IS THE ONE IN WHICH
THE VOLTAGE IS BELOW THE SETTABLE THRESHOLD 5
PH
WHEN SIMULTANEOUSLY THE OTHER TWO VOLTAGES EXCEED
AN EQUALLY SETTABLE MAXIMUM THRESHOLD 5
PH
0ICK
UP BY THE DISPLACEMENT VOLTAGE CAN BE USED
FOR TIME DELAYED TRIP COMMAND .OTE THAT THE TOTAL
COMMAND TIME IS COMPOSED OF THE INHERENT MEASUR
ING TIME APPROXIMATELY MS PLUS PICK
UP DELAY
PLUS TRIP DELAY TIME
4HE LOGIC DIAGRAM OF THE VOLTAGE STAGES OF EARTH FAULT
PROTECTION IS SHOWN IN &IGURE
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