Multilin 469 Motor Management Relay ... - GE Digital Energy

CHAPTER 5: SETTINGS
5.6.3 Overload Curve Setup
and the MOTOR THERMAL CAPACITY USED should be zero. If the motor is in overload, once
the thermal capacity used reaches 100%, a trip will occur. The THERMAL CAPACITY ALARM
may be used as a warning indication of an impending overload trip.
Overview
The overload curve accounts for motor heating during stall, acceleration, and running in
both the stator and the rotor. The OVERLOAD PICKUP LEVEL settings dictates where the
running overload curve begins as the motor enters an overload condition. This is useful for
service factor motors as it allows the pickup level to be defined. The curve is effectively cut
off at current values below this pickup.
Motor thermal limits consist of three distinct parts based on the three conditions of
operation: locked rotor or stall, acceleration, and running overload. Each of these curves
may be provided for a hot and a cold motor. A hot motor is defined as one that has been
running for a period of time at full load such that the stator and rotor temperatures have
settled at their rated temperature. A cold motor is a motor that has been stopped for a
period of time such that the stator and rotor temperatures have settled at ambient
temperature. For most motors, the distinct characteristics of the motor thermal limits are
formed into a smooth homogeneous curve. Sometimes only a safe stall time is provided.
This is acceptable if the motor has been designed conservatively and can easily perform its
required duty without infringing on the thermal limit. In this case, the protection can be
conservative and process integrity is not compromised. If a motor has been designed very
close to its thermal limits when operated as required, then the distinct characteristics of
the thermal limits become important.
The 469 overload curve can take one of three formats: Standard, Custom Curve, or Voltage
Dependent. Regardless of the selected curve style, thermal memory is retained in the
A1 STATUS MOTOR STATUS MOTOR THERMAL CAPACITY USED register. This register is
updated every 100 ms using the following equation:
100 ms
TCused at t = TCused at t – 100ms + -------------------------- × 100%
time to trip
(EQ 5.1)
where: time_to_trip = time taken from the overload curve at I eq as a function of FLA. The
overload protection curve should always be set slightly lower than the thermal limits
provided by the manufacturer. this will ensure that the motor is tripped before the thermal
limit is reached.
Standard Overload Curves
If the SELECT CURVE STYLE is set to “Standard” in the Thermal Model, only the following
settings will appear:
PATH: SETTINGS S5 THERMAL MODEL OVERLOAD CURVE SETUP
OVERLOAD [
STANDARD OVERLOAD
CURVE NUMBER: 4
Range: 1 to 15 in steps of 1. Seen only if
Standard curve is selected.
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL 5–39