/PERATING INSTRUCTIONS
3$
6
# ' #
3ETTINGS FOR THERMAL OVERLOAD PROTECTION
ADDRESS BLOCK
4HE RELAY INCLUDES A THERMAL OVERLOAD PROTECTION
FUNCTION 4HIS CAN OPERATE ONLY WHEN IT IS CONFIGURED
TO 4(%2-!, /,
%8)34
UNDER ADDRESS DUR
ING CONFIGURATION OF THE DEVICE FUNCTIONS REFER 3EC
TION
#ABLES ARE PARTICULARLY ENDANGERED BY OVERLOADS OF
LONGER DURATION 4HESE OVERLOADS CANNOT AND
SHOULD NOT BE DETECTED BY THE SHORTCIRCUIT PROTEC
TION !N OVERCURRENT TIME PROTECTION AS BACKUP PRO
TECTION FOR EXAMPLE MUST BE SET SUFFICIENTLY HIGH SO
AS TO ONLY DETECT SHORTCIRCUITS /NLY SHORT DELAYS ARE
PERMITTED FOR SHORTCIRCUIT PROTECTION 4HESE SHORT
TIME DELAYS HOWEVER DO NOT PERMIT MEASURES TO UN
LOAD THE OVERLOADED CABLE NOR TO UTILIZE ITS LIMITED
OVERLOAD CAPACITY
4HE LINE DIFFERENTIAL PROTECTION RELAY 3$ IN
CLUDES AN OVERLOAD FUNCTION WITH A THERMAL TRIP CHAR
ACTERISTIC WHICH CAN BE MATCHED TO THE OVERLOAD CA
PACITY OF THE PROTECTED CABLE 4HIS FUNCTION IS USUALLY
NOT REQUIRED FOR OVERHEAD LINES AS THE CURRENT CARRY
ING CAPACITY OF OVERHEAD LINES IS GENERALLY NOT DE
FINED
4HE PARAMETERS OF THE THERMAL OVERLOAD PROTECTION
ARE SET IN ADDRESS BLOCK 4HE OUTPUT CURRENT OF THE
SUMMATION TRANSFORMER IS DECISIVE SINCE THE RELAY
CANNOT PROCESS THE INDIVIDUAL PHASE CURRENTS /VER
LOADS ARE GENERALLY THREEPHASE SYMMETRICAL OC
CURRENCES THE CURRENT VALUES ARE BASED ON THE SYM
METRICAL CURRENT WITH STANDARD CONNECTION ACCORD
ING TO &IGURE
4HE THERMAL OVERLOAD PROTECTION CAN BE SET TO BE IN
OPERATIVE TO INITIATE ALARMS ONLY OR TO INITIATE TRIPPING
INCLUDING ALARM !DDITIONALLY THE TRIP COMMAND
CAN BE BLOCKED WHILST THE OVERLOAD PROTECTION FUNC
TION REMAINS OPERATIVE ADDRESS
4HE RATED CURRENT OF THE LINE AS PARAMETERIZED IN AD
DRESS REFER TO 3ECTION IS USED AS THE
BASE CURRENT FOR THE OVERLOAD MEASUREMENT 4HE
SETTING FACTOR K IS DETERMINED BY THE RATIO OF THE CON
TINUOUSLY PERMISSIBLE THERMAL CURRENT )
MAX
TO THE
RATED CURRENT OF THE LINE
K
)
MAX
)
. LINE
4HE PERMISSIBLE CONTINUOUS CURRENT DEPENDS ON
CROSSSECTION INSULATION MATERIAL TYPE OF CONSTRUC
TION AND METHOD OF INSTALLATION OF THE CABLE ETC )N
GENERAL THE MAGNITUDE OF THE CURRENT CAN BE TAKEN
FROM WIDELY AVAILABLE TABLES OR OTHERWISE IS TO BE
STATED BY THE MANUFACTURER
4HE HEATINGUP TIME CONSTANT
Ç
DEPENDS ON THE
CABLE DATA AND THE CABLE SURROUNDINGS )F THE TIME
CONSTANT IS NOT READILY AVAILABLE IT CAN BE CALCULATED
FROM THE SHORTTERM OVERLOAD CAPACITY OF THE CABLE
&REQUENTLY THE S CURRENT IE THE MAXIMUM PERMIS
SIBLE CURRENT FOR S DURATION IS KNOWN OR CAN BE TAK
EN FROM TABLES 4HE TIME CONSTANT CAN THEN BE CALCU
LATED ACCORDING TO THE FOLLOWING FORMULA
PERMISSIBLE S CURRENT
CONTINUOUSLY PERMISSIBLE CURRENT
3ETTING VALUE
Ç
;MIN=
|
)F THE SHORTTIME OVERLOAD CAPACITY IS STATED FOR A DU
RATION OTHER THAN S THEN THAT SHORTTERM CURRENT IS
INSERTED INTO THE ABOVE FORMULA INSTEAD OF THE S CUR
RENT (OWEVER THE RESULT IS THEN MULTIPLIED WITH THE
STATED DURATION IE BY IN CASE OF AN S CURRENT
PERMISSIBLE
S CURRENT
CONTINUOUSLY PERMISSIBLE CURRENT
3ETTING VALUE
Ç
;MIN=
|
)T SHOULD BE NOTED THAT THE RESULT BECOMES MORE IN
ACCURATE THE LONGER THE STATED DURATION OF THE CUR
RENT BECOMES
4 ( % 2 - ! ,
/ 6 % 2 , / ! $
0 2 / 4
"EGINNING OF BLOCK 4HERMAL OVERLOAD PROTECTION
Summary of Contents for 7SD502
Page 148: ... PPENDIX 3 6 PPENDIX ENERAL DIAGRAMS ONNECTION DIAGRAMS 4ABLES ...
Page 176: ... 3 6 ...
