Instrument Transformer Data; Motor Protection - GE 469 Instruction Manual

CHAPTER 1: GETTING STARTED
1.4.2

Instrument Transformer Data

1.4.3

Motor Protection

469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
• RTDs
The motor is fitted with the following RTDs:
– RTD type: 100 Ω Platinum
– 6 Stator RTDs, 2 per phase
– 2 Bearing RTDs
– 1 Ambient RTD
Use the above data to set the output relays to achieve breaker control; to set digital inputs
for breaker status, remote operations, remote status, and alarm indication. Assume that
the communications between the station and the master control center will be done by the
RTU. Alarms, status indication, and breaker commands will be hard-wired from the relay to
the RTU. Similar information could be exchanged between the RTU and the relay via an
RS485 or RS422 Serial Link using the Modbus RTU protocol. Refer to GE Publication GEK-
106491C: 469 Communications Guide for additional information.
• Voltage Transformers
– 2 × Open Delta connected, ratio = 600:120 V
– Motor System Voltage = 575 V
• Phase CTs
The phase CTs should be chosen such that the FLC is 50% to 100% of CT primary.
Since the FLC is 347.5A a 350:5, or 400:5 CT may be chosen; 400:5 is a standard
available size and so would probably be selected.
• Ground CT
For high resistive grounded systems, sensitive ground detection is possible with the
50:0.025 CT. Use a 1 A or 5 A secondary CT on solidly grounded or low resistive
grounded systems where the fault current is much higher. If a residual connection is
chosen, pickup levels and timers must be set with respect to the acceleration time.
The chosen zero-sequence CT must be able to handle all potential fault levels without
saturating. In this example, 50:5A CT is selected.
• Motor FLC
Set the motor full load current to 348 A, as specified by the data sheets.
Use the above data to set the relay system parameters, such as CT and VT
connections, VT secondary voltage, and CT and VT primary to secondary ratios.
• Overload Pickup
The overload pickup is set to the maximum allowed by the service factor of the motor.
Since this motor has RTDs and the relay will be using the RTD bias feature for
enhanced protection, set the overload pickup to the highest setting of 1.25 x FLC for
the motor service factor of 1.15. If service factor is unknown, assume 1.0.
• Overload Curve
1–25