GE 339

6–102 339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
S3 PROTECTION CHAPTER 6: SETPOINTS
Two-speed motor
Two-speed motors have two windings wound into one stator. These motors rely on
contactors to accomplish speed changes by altering the winding configurations. The
339 motor relay provides a complete set of protective functions for each speed.
The 339 motor relay provides proper protection for a two-speed motor where there are
two different full-load values. The 339 algorithm integrates the heating at each speed into
one thermal model using a common Thermal Capacity Used Register for both high and low
speeds.
In the figure below, contactor L and H are interlocked so that only one contactor can be
energized to select either low speed or high speed. This figure shows the AC connections
for a two-speed motor where CTs connected to low and high speed are paralleled, such
that the 339 relay can measure the motor current when the motor is running at either low
or high speed, and it will switch CT Primary and motor FLA settings as per the motor
running speed. This function is accomplished by detecting the input status from the motor
speed switches.
Figure 6-44: Two-speed motor connections
896LH.CDR
C1
C2
C3
C10
C11
CONTACT INPUTS
52a (C1 #1)
52b (C1 #2)
COMMON
E5
D5
E6
D6
E7
D7
I
A
I
A
I
B
I
B
I
C
I
C
339
Motor Protection System
52a
A
B
C
MOTOR
CURRENTINPUTS
ASSIGNABLE
INPUTS
+
-
DC
L
L
L
H
H
H
L
H
H
T1
T2
T3
T4
T5
T6
H
52