Motor Protection; Motor, System And Soft Starter Protection Mechanisms; Protection Coordination; Motor Overload Protection - AuCom MVE Series User Manual

MOTOR PROTECTION

8. Motor Protection
8.1

Motor, System and Soft Starter Protection Mechanisms

The MVE incorporates extensive protection features to ensure safe operation of the motor, system and soft starter.
Most protection features can be customised to suit the installation. Use parameter group 4 Protection Settings to
control the situation where the protections will activate and parameter group 16 Protection Action to select the soft
starter's response. The default response is to trip the soft starter.
8.2

Protection Coordination

Check protection settings on the supply side of the starter to ensure correct coordination with the parameters of the
soft starter.
When using fuse and main contactors, set the upstream circuit breaker protection parameters according to the
ratings for fuse and contactor. The contactor must not open if the current is above its maximum breaking current
value. The fuse must act first or the upstream breakers instantaneous trip level must be less than the contactor's
maximum breaking current level.
If using circuit breakers only, set the soft starter's maximum instantaneous trip time < 150 ms. Always use a suitable
external protection relay with a circuit breaker to ensure instantaneous overcurrent trip functionality.
Voltage must not be continuously maintained on the phase arms while the motor is off. Short circuit protective
equipment must be installed in all cases.
8.3

Motor Overload Protection

The MVE offers motor overload protection based on an advanced I
monitors the performance of the motor at all stages of operation and constantly calculates its temperature.
The thermal model adjusts itself according to the motor's recent operating history (including temperature rise from
previous operation).
Motor thermal model
The motor thermal model has two components:
• Motor windings: These have a low thermal capacity and affect the short-term thermal behaviour of the
motor. This is where the heat is generated by the current.
• Motor body: This has a large thermal capacity and affects the long-term behaviour of the motor.
The motor thermal model includes considerations for the following:
• Motor current, iron losses, winding resistance losses, motor body and winding thermal capacities,
cooling during run and cooling at standstill.
• The percentage of the rated capacity of the motor. This sets the displayed value for the thermal model
and is affected by factors such as the motor FLC and motor service factor.
Thermal model overload protection has a number of advantages over thermal relays.
• The percentage of motor thermal capacity used during each start is stored in memory. The starter can
be configured to automatically determine whether or not the motor has sufficient thermal capacity
remaining to successfully complete another start.
• The memory function of the model means that the motor is fully protected in "warm start" situations.
The model uses data from the real-time clock to account for elapsed cooling time, even if control power
has been removed.
The actual full load current, locked rotor current, locked rotor time and motor service factor can be
•
used to more accurately tune the model.
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| MVE User Manual (710-17074-00H)
t thermal model. The motor thermal model
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