701 Motor Protection Relay Date Code 20010719
Settings Calculation
Basic Motor Protection
4.8
Basic Motor Protection
Thermal Model Element
The SEL-701 Relay motor thermal element provides integrated protection for all
of the following motor operating conditions:
Locked Rotor Starts.
Running Overload.
Unbalance Current/Negative-Sequence Current Heating.
Repeated or Frequent Starting.
This protection is provided using any of the three available relay setting methods.
The Setting Method setting offers three options: Rating, Generic, and User.
Rating Setting Method. When selected, the relay configures a thermal curve
based on the motor Full Load Amps, Service Factor, Locked Rotor
Amps, Hot and Cold Locked Rotor Time, and Locked Rotor Trip Time
Dial settings.
Generic Setting Method. When selected, the relay offers 45 standard motor
thermal limit curves which you can select by curve number.
User Setting Method. When selected, the relay allows you to build a customized
thermal limit curve by directly entering from 5 to 25 time-current points
based on your motor’s published thermal limit curve.
All three thermal element setting methods can provide outstanding motor
protection. In each case the relay operates a thermal model with a trip value defined by
the relay settings and a present heat estimate that varies with time and changing motor
current. The relay expresses the present motor thermal estimate as a % Thermal
Capacity. When the % Thermal Capacity reaches 100%, the relay trips. You can see the
present % Thermal Capacity value using the relay front panel Meter Values\Thermal &
RTD Data function or the serial port METER T command.
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