GE 239 Instruction Manual page 26

ORGANIZATION CLASS TYPE
5P15 0.2VA
IEC (Europe)
5P15 2.5VA
NOTE: The sizes shown above may not be standard CT ratings. The numbers are merely used to indicate what size
CTs can be used with the 239.
2–20
Courtesy of NationalSwitchgear.com
Table 2–3: Typical CT Ratings
239 CT
INPUT
P = Protection class
5 = Maximum %voltage error at limiting factor
15 =
1 Amp
0.2 = Maximum amount of continuous burden allowed for
5 Amp same as 1 Amp input
GROUND CT INPUT (10/11/12)
Ground sensing terminals are labeled 5A, 50:0.025, and COM. Connection depend on the
grounding system and sensitivity required. For high resistance grounded systems that limit
the ground current or in mines where low levels of ground leakage must be detected, use a
separate CT to sense ground current. In this configuration, referred to as zero sequence or
core balance detection, all three phase conductors must pass through the CT window. If
the phase conductors are bundled in a cable with a ground, the ground wire must either
pass outside the ground CT window or be routed back through the window if it passes
through as part of the cable. Shielded and unshielded cable installations are illustrated in
the TYPICAL WIRING DIAGRAM. A ground CT with a ratio of 50:0.025 for sensing primary
ground currents from 0.05 to 15 A is available from GE. Connect this CT to terminals
50:0.025 and COM. If a conventional 5 A secondary CT is used for zero sequence ground
sensing, connect it to the 5A and COM terminals. A 1 A secondary CT can also be used;
however, to prevent readings from being off by a factor of 5, the ground CT primary
setpoint must be adjusted. See Section 4.3.1 CT Inputs on page 4–21 under
for suitable settings in this situation. Due to the low secondary currents, it is
PRIMARY
recommended that the ground CT secondary leads be twisted together and routed to the
239 away from high current carrying conductors. NOTE: The 50:0.025 input is only
recommended for resistance grounded systems. Where the system is solidly grounded
or high levels of current are to be detected use the 5A ground input.
For low resistance or solidly grounded systems where higher ground fault currents will
flow, the phase CTs can be residually connected to provide ground sensing levels as low as
20% of the phase CT primary rating. For example, 100:5 CTs connected in the residual
configuration can sense ground currents as low as 20 A (primary) without requiring a
separate ground CT. This saves the expense of an extra CT however 3 phase CTs are
required. If this connection is used on a high resistance grounded system verify that the
DEFINITIONS
Limit factor, determines max. voltage CT can deliver to load
burden without exceeding the %voltage error
rated CT secondary
239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
CHAPTER 2: INSTALLATION
GROUND CT