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14.7.3 Motor protection functions - Full set
The Full protection set provides all the following motor protection functions.
14.7.3.1 Blocked Rotor
The Blocked Rotor protective function detects a rotor blocking condition by sensing the current
increase arising from the loss of synchronism between the revolving rotor and the phase voltages.
An extreme condition is reached when the rotor is not moving and the steady state current equals
the motor start peak value, i.e. several times the rated motor current.
It can be used to monitor the starting characteristics of three-phase asynchronous motors to
check whether the rotor braking is on and other conditions preventing the motor from speeding up.
If this malfunction occurs, the starting current would flow permanently and the motor would be
thermally overloaded.
The protection operates like an Overcurrent Protection function.
Fig. 70
Nominal Motor Current (IMn):
Start Value (Is):
Time (tbr):
Parameter
Values
Start Value Is
1.00 – 20.00 p.u. di IMn
Time, tbr
50 ... 300000
Nominal Motor Current,
50 – 1.20 P.U. di In
The threshold setting range is expressed in primary current Ampere [A], up to 20 IMn with IMn is
the motor nominal current, by default equal to In, the feeder Nominal Primary Current value entered
in the General Settings.
Nominal Motor current
Current threshold for motor start condition detection.
Time delay for Trip condition detection.
Default
100
50
100
Step
Unit
ExplanationType
1
A
Current threshold for BR
condition detection.
50
ms
BR Time delay.
1
A
Nominal Motor Current in
actual application
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