Siemens SIPROTEC 7SJ531 - Page 65

-ETHOD OF OPERATION3*
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 /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
/&&
31
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5 4RIP
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5 CC &LT
5 &AULT
RESET MEASUREMENT
/.
/&&
#522%.4
#2)4%2)/.
OV ANNUNCI
ATIONS ONLY
OV OFF
OV ON
BLOCK OVERVOLTAGE
PROTECTION
/.
!,!2- /.,9
/6%26/,4
OV ANNUNC
OV OFF
OV BLK
ANNUNCIATION
4RIP
0ARAMETER

&.O 
&UNCTION NUMBER
&.O 
&.O 
&.O 
&.O 
&.O 
"2+
#,/3%$
&IGURE  ,OGIC DIAGRAM OF OVERVOLTAGE PROTECTION
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