Phase Ct Inputs; Table 2-2: Typical Ct Ratings - GE 269Plus Instruction Manual

PHASE CT INPUTS

One CT for each of the three motor phases is required to input a current into the relay proportional to the motor
phase current. The phase sequence must be as shown in Figure 2–7: RELAY WIRING DIAGRAM (AC CON-
TROL POWER) on page 2–8 and Figure 2–10: RELAY WIRING DIAGRAM (DC CONTROL POWER) on page
2–11. The CTs used can have either a 1 A or 5 A secondary and should be chosen so that the motor full load
current is between 75 and 100% of the rated CT primary current. The CT ratio should thus be of the form n :1 or
2
n :5 where n is between 20 and 1500. The ratio of the CT used must be programmed into the 269Plus (see
Section : on page 3–46).
The CT connections to the relay are made between the ":1" and "COM" terminals for 1 A CTs or between the
":5" and "COM" terminals for CTs with a 5 A secondary.
The connections to the 269Plus internal phase CTs are made directly via #10 screws.
CTs should be selected to be capable of supplying the required current to the total secondary load which
includes the 269Plus relay burden of 0.1 VA at rated secondary current and the connection wiring burden. The
CT must not saturate under maximum current conditions which can be up to 8 times motor full load during
starting or up to 20 times during a short circuit. Only CTs rated for protective relaying should be used since
metering CTs are usually not rated to provide enough current during faults. Typical CT ratings are:
TABLE 2–2: TYPICAL CT RATINGS
CSA (Canada):
ANSI (USA):
IEC (Europe):
Refer to Appendix H: CURRENT TRANSFORMERS for details on CT withstand, CT size and saturation, as
well as the safe use of 600 V class window type CTs on a 5 kV circuit.
2-
14
Courtesy of NationalSwitchgear.com
Class10L100 10 = accuracy, L = protection, 100 = capacity, higher is better
Class C 100 B4 C or T = protection, 100 = capacity, higher is better, B4 = accuracy
20 VA Class 5P20 P = protection, 20 VA = capacity, higher is better
269Plus Motor Management Relay
2 INSTALLATION
2.5 PHASE CT INPUTS
GE Power Management