Functions
2.7 Motor Protection (Motor Starting Protection 48, Motor Restart Inhibit 66, Load Jam Protection)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
132
For ratios deviating from nominal conditions, the motor tripping time changes:
At 80% of nominal voltage (which corresponds to 80% of nominal starting current), the tripping time is:
After the time delay (4104 LOCK ROTOR TIME) has elapsed, the binary input becomes effective and generates
a trip signal. If the locked rotor time is set just long enough that during normal startup the binary input „>48
Rot. locked“ (FNo. 6805) is reliably reset during the delay time LOCK ROTOR TIME, faster tripping will be
available during motor starting under locked rotor conditions.
Threshold Values "cold" / "warm" Motor
Parameter 4106 TEMP.COLD MOTOR determines the threshold value. It is derived from the number of cold
(n
cold
) and warm (n
warm
) motor startups.
Unless specified otherwise, three cold and two warm startups (n
cold
= 3; n
warm
= 2) will be sufficient. These are
typical motor data. The limit value is thus derived:
A recommended setting value with consideration of a safety margin for TEMP.COLD MOTOR = 25%.
Should the technical data of the motor make reference to four cold and two warm startups (n
cold
= 4; n
warm
= 2),
the following limit value can be determined:
The setting value should fall below the limit value. A value of 40% is recommended for that purpose.
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