Application Examples; Relay Powered From One Of Motor Phase Inputs; Loss Of Control Power Due To Short Circuit Or Ground Fault; Example Using Flc Thermal Capacity Reduction Setpoint - GE MULTILIN 269 MOTOR MANAGEMENT RELAY Series Instruction Manual

6.1 269 Relay Powered from One of
Motor Phase Inputs
If a 269 relay is powered from one of the three motor
phase inputs , a single phase condition could cause
control power to be removed from the relay. In order to
ensure that the motor is taken off-line if this condition
arises, the 269 output relay (eg. TRIP, AUX. 1) used to
trip the motor must change state when control power is
removed from the 269. This is accomplished by mak-
ing this output relay fail-safe. Factory defaults are:
TRIP: Fail-Safe
ALARM: Non-fail-safe
AUX. 1: Non-fail-safe
AUX. 2: Fail-safe
These can be changed using the RELAY FAILSAFE
CODE in page 5 of SETPOINTS mode.
6.2 Loss of Control Power Due to Short
Circuit or Ground Fault
If the input voltage (terminals 41-43) to a 269 relay
drops below the low end specification (80 VAC on 120
VAC units), the 269 output relays will return to their
power down states. If the input voltage drops due to a
short circuit or ground fault on a motor, the 269 relay
protecting the motor may or may not be able to trip out
the motor. For example, if a 120 VAC 269 relay is set
to trip after 0.5 seconds of an 8.0×FLC short circuit
current, the input voltage must remain above 90 VAC
for at least 0.5 seconds after the short circuit has oc-
curred or else the 269 relay will not be able to trip. As
explained in section 6.1 above, in order to trip the mo-
tor when control power for the 269 is lost, the 269 out-
put relay used to trip the motor must be configured as
fail-safe.
6.3 Example Using FLC Thermal Ca-
pacity Reduction Setpoint
The purpose of the FLC Thermal Capacity Reduction
Setpoint is to accurately reflect the reduction of thermal
capacity available (increase the thermal capacity used)
in a motor that is running normally (100% of FLC or
less). This setpoint allows the user to define the
amount of thermal capacity used by their motor running
at 1 FLC. A motor that is running at 10% of FLC will
obviously use less thermal capacity than a motor at
100% FLC.
For example, if the FLC Thermal Capacity Reduction
Setpoint is set at 30%, then with the motor running at 1
FLC, the thermal capacity used will settle at 30%. Us-
ing the same example, with the motor running at 50%
FLC, the thermal capacity used will settle at 15% (50%
of 30%). A practical example of implementation of this

6 APPLICATION EXAMPLES

setpoint to coordinate hot/cold damage curves is illus-
trated below.
Assume the motor manufacturer has provided the fol-
lowing information:
1. Maximum permissible locked rotor time (hot motor) =
15.4 seconds.
2. Maximum permissible locked rotor time (cold motor)
= 22 seconds.
3. Recommended thermal limit curves are as shown in
Figure 6-1.
Note: Hot motor is defined as a motor that has been
running at 1 FLC, but not in an overload, for a period of
time such that the temperature remains constant (typi-
cal 90°C). Cold motor is defined as a motor which has
been stopped for a period of time such that the tem-
perature remains constant (ambient temperature is
defined by NEMA standard as 40°C).
From the formula:

(Hot Motor Stall Time)

TCR = 1 -

(Cold Motor Stall Time)
TCR = [1 - (15.4/22)] × 100
Thermal Capacity Reduction = 30%
The hot motor locked rotor time is 30% less than the
cold motor locked rotor time. Therefore the FLC Ther-
mal Capacity Reduction Setpoint should be set to 30%.
The overload curve selected should lie below the cold
thermal damage curve. Once the motor has been run-
ning for a period of time at 1 FLC the thermal capacity
used will remain constant at 30%. The time to trip at
any overload value will correspondingly be 30% less.
Once a motor comes out of an overload condition, the
thermal capacity used will discharge at the correct rate
which is exponential and settle at a value defined by the
FLC Thermal Capacity Reduction Setpoint and the pre-
sent current value. Using the example above if the
motor came out of an overload and the present current
value was 50% FLC the thermal capacity used would
discharge to a value of 15% (50% of 30%).

 ×
100

6-1