Functions
2.7 Motor Protection (Motor Starting Protection 48, Motor Restart Inhibit 66, Load Jam Protection)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
138
Motor Standstill and Motor Startup
Due to the threshold setting below the motor startup current, the load jam protection during motor startup must
be blocked. Via parameters 212 BkrClosed I MIN the open circuit breaker is detected during current-flow
measurement (motor standstill). In this condition the load change protection is blocked. After having closed the
circuit breaker, the blocking is maintained during motor startup by the setting 4406 T Start Blk.. In order
to avoid malfunctioning, the T Start Blk. is set to the double startup time.
Motor Protection Example
Figure 2-42 illustrates an example of a complete motor protection characteristic. Such characteristic usually
consists of different protection elements, and each element is responsible for special motor malfunctions.
These are:
• Thermal overload protection: to avoid overheating of the motor due to inadmissible load
• Load jam protection: to prevent overheating and mechanical damage due to a locked rotor
• Motor starting protection: protects the motor against prolonged startup procedures and the consequent
thermal overload of the rotor
• Overcurrent and high-current elements: for motor shutdown due to electrical faults
Figure 2-42 Example of a complete motor protection characteristic
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