Siemens SIPROTEC 7SJ62 Handbuch Seite 26

Extension of Time
Constants
Resetting the
thermal profile
26
When applying the protective relay for protection of explosion proof motors and using
the standardized tripping classes according to IEC 60947–4–1 (VDE 0660, Part 102),
the rated transformer current is taken as the basic current for overload detection.
The setting value 49 K-FACTOR (address 4202) is determined by the ratio of the
rated motor current I
NMotor
(parameter 0204 CT PRIMARY) according to the following formula:
Setting value 49 K-FACTOR
with I Motor Nominal Current
NMotor
Nominal primary CT current (parameter 0204)
I
NCT prim
The factor 1.06 is preset (selection according to IEC 60255–8). Calculation is to be
carried out to the third decimal place and the resulting value is increased by 0.01.
To implement the standardized tripping classes at address 4203 TIME CONSTANT
the following τ –values must be set:
th
TIME CONSTANT τ
Tripping class
Class 2
Class 3
Class 5
Class 10a
Class 10
Class 20
Class 30
Class 40
Class 50
The time constant programmed at address 4203 TIME CONSTANT is valid for a
running motor. For cycling motors without external cooling, the motor loses heat more
slowly. The 7SJ62/63/64 takes the reduced heat loss into account by increasing the
by a programmable factor (Kτ-FACTOR, set at address 4207A).
time constant τ
th
The motor is considered off if the motor currents drop below a programmable minimum
current setting (BkrClosed I MIN).
The thermal overload protection feature may be reset via a binary input
(">RES 49 Image"). The current-induced overtemperature value is reset to zero. The
same is accomplished via the binary input. The same is accomplished via the binary
input (">BLOCK 49 O/L"); in that case the overload protection is blocked completely,
including the current warning stage. The thermal profile is also reset if the overload
protection feature is newly configured, this protection function is deactivated, and if
any parameter relevant for the thermal profile is changed. The behaviour in case of a
power supply failure is described further below.
to the primary rated transformer current I
I
NMotor
---------------------- - 1.06
k =
⋅
I
NCT prim
/min
th
1.0
1.5
2.5
4.5
5.2
9.7
14.5
19.3
23.6
NCT prim
The factor 1.06 is
preset!
7SJ62/63/64 Additional Information
C53000-B1174-C170-1