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SYSTEM DATA
50
Unbalance Alarm and Trip:
The unbalance settings are determined by examining the motor application and motor
design. The heating effect of unbalance will be protected by enabling unbalance input to
thermal memory; described in details in Chapter 5, Thermal Model. A setting of 10% for the
Unbalance Alarm with a delay of 10 seconds would be appropriate and the trip can be set
to 20% with a delay of 5 seconds.
Stopped and Running Cool Times:
The motor manufacturer usually supplies this information as either cooling times, or
cooling time constants. In this case they are not part of the data that was given with this
motor. Since RTDs are present and will be wired to the relay, biasing of the thermal model
will be used so it is not critical to have these cooling times from the manufacturer. The
default values of motor cooling time constants are 15 and 30 minutes, and can be used for
the running and stopped cool times respectively. If the manufacturer provides cooling
times instead, the approximate values of the cooling time constants is 1/5 the cooling
times provided by the manufacturer.
Acceleration Trip:
This setpoint should be set higher than the maximum starting time to avoid nuisance
tripping when the voltage is lower or for varying loads during acceleration. If reduced
voltage starting is used, according to the acceleration curves, a setting of 18 seconds
would be appropriate, or if across the line starting is used, a setting of 13 seconds would
be appropriate.
Enable Start Inhibit:
This function will limit starts when the motor is already hot. The relay learns the amount of
thermal capacity used at start. If the motor is hot, thus having some thermal capacity
used, the relay will not allow a start if the available thermal capacity is less than the
required thermal capacity for a start.
Starts/Hour:
Starts/Hour can be set to the # of cold starts as per the data sheet. For this example, it is
not given.
Time Between Starts:
In some cases, the motor manufacturer will specify the time between motor starts. In this
example, this information is not given so this feature can be disabled. However, if the
information is given, the time provided on the motor data sheets should be programmed.
Stator RTDs:
RTD trip level should be set at or below the maximum temperature rating of the insulation.
This example has a class F insulation which has a temperature rating of 155°C, therefore
the Stator RTD Trip level should be set to between 140°C to 155°C, with 155°C being
maximum. The RTD alarm level should be set to a level to provide a warning that the motor
temperature is rising. For this example, 135°C would be appropriate since this motor is
designed for class B rise, 130°C is it's normal hot operating temperature.
QUICK REFERENCE GUIDE
469 MOTOR MANAGEMENT RELAY – QUICK REFERENCE GUIDE
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