Setting Notes - Siemens siprotec SJ62 User Manual

2 Functions

2.10.2 Setting Notes

General
Overload Parame-
ter k-factor
179
The overload protection is only in effect and accessible if address 142 49 = No
ambient temp or = With amb. temp. during configuration. If the function is not
required Disabled is set.
Transformers and cable are prone to damage by overloads that last for an extended
period of time. Overloads cannot and should not be detected by fault protection. Time
overcurrent protection should be set high enough to only detect faults since these
must be cleared in a short time. Short time delays, however, do neither allow mea-
sures to discharge overloaded equipment nor do they permit to take advantage of its
(limited) overload capacity.
The protective relays 7SJ62/63/64 feature a thermal overload protective function with
a thermal tripping curve which may be adapted to the overload tolerance of the equip-
ment being protected (overload protection with memory capability).
Overload protection may be switched ON or OFF or Alarm Only at address 4201 FCT
49. If overload protection is ON, tripping, trip log and fault recording is possible.
When setting Alarm Only no trip command is given, no trip log is initiated and no
spontaneous fault annunciation is shown on the display.
Note
Changing the function parameters resets the thermal replica. The thermal model is
frozen (kept constant) as soon as the current exceeds the threshold value 1107
I MOTOR START.
The overload protection is set with quantities per unit. The nominal current I
the protected object (motor, transformer, cable) is used as a basis for overload detec-
tion. The thermally permissible continuous current I
k :
prim
The thermally-permissible continuous current for the equipment being protected is
known from the manufacturers specifications. This function is normally not applicable
to overhead lines since the current capability of overhead lines is generally not spec-
ified. For cables, the permissible continuous current is dependent on the cross-sec-
tion, insulating material, design, and the cable routing, among other things. It may be
taken from pertinent tables, or is specified by the cable manufacturer. If no specifica-
tions are available, a value of 1.1 times the nominal current rating may be assumed.
The 49 K-FACTOR to be set in the device (address 4202) refers to the secondary
nominal current of the protective relay. The following data apply for the conversion:
allows to calculate a factor
max prim
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
of
Nom Obj.