GE Digital Energy Multilin 239 Instruction Manual page 61

CHAPTER 4: PROGRAMMING
239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
LRT Cold = Locked Rotor Time Cold, is defined as the locked rotor time when the
motor has been stopped for a time sufficient for the motor temperature to reach
ambient.
LRT Hot and LRT Cold are usually determined from the motor specifications. If this
information is not known, enter a typical value of 85% for the
.
RATIO
The
HOT/COLD CURVE RATIO
motor when the average phase current is at or below the FLC setpoint. When the
motor is cold (motor temperature at ambient) the thermal capacity used will be 0%.
When the motor is hot (motor running at FLC for a time sufficient to reach a steady
state temperature) the thermal capacity used will be calculated as 100% –
, or 100 – 85 = 15% using the example value given above. In
COLD CURVE RATIO
between these two extremes there is a linear relationship; the 239 thermal model
covers the entire range of motor temperatures: cold—cool—warm—hot. The steady
state value of thermal capacity used for any phase current level can be calculated as:
Thermal Capacity Used
For example, if LRT Hot = 7.0 s, LRT Cold = 10.0 s, FLC = 100 A, and the actual motor
current is 80 A, then the steady state thermal capacity value will be:
Thermal Capacity Used
• DISABLE STARTS: In some applications start protection may not be required.
Therefore, by setting this setpoint to
defeated. If the setpoint is set to
overload curves will be employed to protect the connected load.
This setpoint can also be used in conjunction with a switch input. If the
setpoint is programmed to
STARTS
setpoint described on page 46 is assigned to
protection will be defeated if the respective switch input is closed. The
setpoint must be programmed to
STARTS
inputs.
setpoint is used by the 239 to thermally model the
Actual Current
----------------------------------- - × (
100% HOT/COLD CURVE RATIO
= –
FLC Setpoint
Actual Current
× (
----------------------------------- - 100% HOT/COLD CURVE RATIO
= –
FLC Setpoint
80 7.0
 
× ×
-------- - 100% --------- - 100%
= –
 
100 10.0
20%
=
, the start protection on the 239 can be
YES
, the 239 will go directly into run condition and
YES
and
YES OPTION SWITCH 1-2 FUNCTION
DISABLE STARTS
for the feature to work via the switch
YES
HOT/COLD CURVE
HOT/
)
)
 
 
DISABLE
, the 239 start
DISABLE
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