-ETHOD OF OPERATION
3*
6
# ' #
/VERVOLTAGE PROTECTION
4HE OVERVOLTAGE PROTECTION HAS TO PROTECT ELECTRICAL
EQUIPMENT FROM IMPERMISSIBLE OVERVOLTAGES AND
THUS FROM PROBLEMS WITH THE INSULATION
/VERVOLTAGES MAY OCCUR FOR EXAMPLE ON LONG %(6
TRANSMISSION LINES WITH LOW LOAD IN ISLAND NETWORKS
DUE TO FAILURES OF THE GENERATOR VOLTAGE REGULATION OR
AFTER FULL LOAD SHUTDOWN OF A GENERATOR IN GENERA
TORS DISCONNECTED FROM THE NETWORK
7HEN THE VOLTAGE TRANSFORMERS ARE CONNECTED AT THE
INCOMING BUS BAR SIDE THE VOLTAGE PERSISTS AFTER
OPENING OF THE CIRCUIT BREAKER OR EVEN GOES UP
CAUSED BY LOAD DROP )N SPECIFIC CASES IT MAY THEN BE
REASONABLE TO ENFORCE RESET OF THE OVERVOLTAGE PRO
TECTION 4HE CRITERION IS THE CURRENT WHICH DECREASES
TO ZERO AFTER THE CIRCUIT BREAKER IS OPEN SO THAT THE
CURRENT CRITERION IS NO LONGER FULFILLED
4HE OVERVOLTAGE PROTECTION IS FED BY THE FUNDAMEN
TAL WAVE OF THE HIGHEST OF THE THREE MEASURED VOLT
AGES
4HE OVERVOLTAGE PROTECTION HAS ONE STAGE !FTER EX
CEEDING THE THRESHOLD WHICH CAN BE PARAMETERIZED
THE PROTECTION PICKS UP 7HEN THE PARAMETERIZED
TIME IS EXPIRED A TRIP COMMAND IS GIVEN 4HIS TIME
DOES NOT DEPEND OF THE MAGNITUDE OF THE OVERVOL
TAGE
&IGURE SHOWS THE LOGIC DIAGRAM OF THE OVERVOL
TAGE PROTECTION
/&&
3 1
2
5
## )
4 5
5 4RIP
5 CC <
5 &AULT
RESET MEASUREMENT
/.
/&&
#522%.4
#2)4%2)/.
OV ANNUNCI
ATIONS ONLY
OV OFF
OV ON
BLOCK OVERVOLTAGE
PROTECTION
/.
!,!2- /.,9
/6%26/,4
OV ANNUNC
OV OFF
OV BLK
ANNUNCIATION
4RIP
0ARAMETER
&.O
&UNCTION NUMBER
&.O
&.O
&.O
&.O
&.O
"2+
#,/3%$
&IGURE ,OGIC DIAGRAM OF OVERVOLTAGE PROTECTION
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