GE MM3, Instruction Manual, Page: 98 / 230

5–18 MM3 MOTOR MANAGER 3 – INSTRUCTION MANUAL
S2 PROTECTION CHAPTER 5: SETPOINTS
The motor protection options settings are programmed as follows:
• MINIMIZE RESET TIME : The MM3 Motor Manager 3 measures the motor thermal
capacity used during a start. This data can be used to minimize the lockout time
following an overload trip. This allows the motor to be restarted after it has cooled to a
safe starting temperature. When set to “DISABLE”, the lockout time after an overload
trip will be the time required for the thermal memory to reduce to 15%.
For example, if the thermal capacity used during the previous start is 40%, then after an
occurrence of an overload trip, a reset can be accomplished when the thermal capacity
decreases to 58% as shown below:
(EQ 5.3)
• STOPPED MOTOR COOL TIME : The
STOPPED MOTOR COOL TIME
determines how long
it takes for a stopped motor to reach steady state ambient temperature from its
maximum allowable temperature. The maximum allowable temperature occurs when
the thermal capacity used reaches 100% (e.g. at the occurrence of an overload trip).
The thermal capacity value will decrease exponentially to model the cooling
characteristic of the motor. The
STOPPED MOTOR COOL TIME
setpoint thus represents
the time for the thermal capacity value to decay through five time constants. Note
that an overload trip can normally be reset when the thermal capacity value
decreases to 15%.
For example, given a maximum thermal capacity of 100% (overload trip) and a STOP
MOTOR COOL TIME of “30 minutes”, the time to reach thermal capacity is calculated from:
(EQ 5.4)
Therefore, the time that must pass until the thermal capacity reaches 15% is as follows:
(EQ 5.5)
• OVERLOAD TRIP RESET : If this setpoint is set to “AUTO”, an automatic reset of overload
trips will occur after the motor has cooled to a thermal capacity value below 15%.
When set to “MANUAL”, the keypad RESET key must be pressed to reset the trip after
the motor has cooled to a thermal capacity value below 15%.
• RESET LOCKOUT USING RESET KEY : If this setpoint is set to “ENABLE”, the RESET key
on the faceplate of the MM3 Motor Manager 3 will reset all trips providing that the trip
condition is not still present. When set to “DISABLE”, the RESET key on the faceplate
will not reset the three lockout trips (overload, ground fault, and locked rotor); one of
the interlock inputs will have to be used to reset these three trips. Note: when the
lockout reset function is configured, the RESET key will no longer be able to reset the
three lockout trips.
• PHASE UNBALANCE ALARM : When an unbalance in phase currents exceeds the
internally set threshold, an alarm condition will be generated if this value is set to
“ENABLE”. The internal threshold is 15% and the unbalance must be above this
threshold for at least five seconds for the alarm to occur.
RESET ALARMS USING
RESET KEY: DISABLE
Range: Enable, Disable
Thermal capacity 100% TC used during start
–
2% safety margin
– =
100% 40%
–
2%
– =
58%
=
Thermal capacity 100 e
t T
⁄
–
×
=
Thermal capacity 100 e
t T ⁄
–
×
=
0.15
⇒
e
t T ⁄
–
t
T
--
⇒
0.15 ( ) ln
–
t
⇒
T 0.15 ln
– = = =
t
⇒
11.4 minutes
=