Functions
2.8 Motor Protection
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
171
2.8.2.2 Setting Notes
General
Restart inhibit is only effective and accessible if address 143 48 is set to Enabled. If not required, this function
is set to Disabled. The function can be turned ON or OFF under address 4301 FCT 66..
Note
When function settings of the motor restart inhibit are changed, the thermal replica of this function is reset.
The motor restart inhibit acts on the starting process of a motor that is shut down. A motor is considered shut
down when its current consumption falls below the settable threshold 212 BkrClosed I MIN. Therefore, this
threshold must be set lower than the motor idle current.
The motor restart inhibit concludes the condition „warm motor“ from the thermal replica of the restart inhibit. For
this function, address 4301FCT 66 has to be enabled.
Additionally, the function can trip directly if the rotor temperature exceeds the maximum admissible temperature
(100%). For this purpose address 4311 ROTOR OVERLOAD is set to ON. If only monitoring is desired, set to
Alarm Only, otherwise to OFF.
Characteristic Values
Many of the variables needed to calculate the rotor temperature are supplied by the motor manufacturer.
Among these variables are the starting current I
STARTUP
, the nominal motor current I
MOT. NOM
, the maximum al-
lowable starting time T START MAX (address 4303), the number of allowable starts from cold conditions (n
cold
),
and the number of allowable starts from warm conditions (n
warm
).
The starting current is entered at address 4302 IStart/IMOTnom , expressed as a multiple of nominal motor
current. In contrast, the nominal motor current is entered as a secondary value, directly in amperes, at address
4305 I MOTOR NOMINAL. The number of warm starts allowed is entered at address 4306 (MAX.WARM
STARTS) and the difference (#COLD-#WARM) between the number of allowable cold and warm starts is entered
at address 4307.
For motors without separate ventilation, the reduced cooling at motor stop can be accounted for by entering
the factor Kτ at STOP at address 4308. As soon as the current no longer exceeds the setting value entered
at address 212 BkrClosed I MIN, motor standstill is detected and the time constant is increased by the ex-
tension factor configured.
If no difference between the time constants is to be used (e.g. externally-ventilated motors), then the extension
factor Kτ at STOP should be set to 1.
The cooling with the motor running is influenced by the extension factor 4309 Kτ at RUNNING. This factor
considers that motor running under load and a stopped motor do not cool down at the same speed. It becomes
effective as soon as the current exceeds the value set at address 212 BkrClosed I MIN. With Kτ at
RUNNING = 1 the heating and the cooling time constant are the same at operating conditions (I > BkrClosed
I MIN).
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