GE Digital Energy Multilin 239, Instruction Manual

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CHAPTER 5: MONITORING
239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL 5–63
• A: B: C: CURRENT: Actual current flowing in each of the three phases at the moment of
trip is displayed. By comparing these values to the motor full load current after an
overload trip, it should be easy to determine in which phase the fault has occurred. A
high current in one phase and ground indicates a phase to ground fault. A high
current in 2 phases suggests a phase to phase fault. High current in all three phases
indicates a running overload or possible short circuit. The current resolution is 0.1 A if
the
CT PRIMARY
setting is
≤
50 A. The resolution is 1A if the
CT PRIMARY
setting is
> 50A.
• GROUND CURRENT: If excessive ground current was present at the time of trip, an
insulation failure is likely. With the motor off-line, check the insulation resistance in all
three phases and cable wiring.
• CURRENT UNBALANCE: Excessive unbalance can be caused by loose terminal
connections, faulty utility supply, a blown fuse, or faulty contactor. Check for these
before restarting the motor.
• STATOR (BEARING) RTD 1-3 (OPTION): If any stator RTDs shows a high temperature,
check that the ventilation to the motor is clear. Repeated starting using the
Emergency Restart feature will cause the motor to overheat and should be avoided.
After an overload trip, the RTD temperature may be elevated. Verify that the motor has
cooled before restarting by checking each RTD temperature using the messages
A2:
METERING\TEMPERATURE
. If the RTD is installed on a bearing, an excessive
bearing temperature usually indicates a need for lubrication or a fault with the
bearing itself. Lubricate the bearing then monitor its temperature closely after starting
the motor.
• SETPOINTS GROUP IN USE: Alternate setpoints (i.e.
PHASE CT PRIMARY
,
FULL
LOAD CURRENT
, etc.) can be selected using the Option Switch 1 and Option Switch 2
inputs as explained in Section 4.6: Switch Inputs on page –46. One of four possible
groups of setpoints can be selected at once. This message displays the selected group
at the time of the last trip.
• 2nd (3-5) LAST TRIP: A trip record of the last 5 causes of trip is retained for diagnosing
persistent problems. Each new trip is added to the trip record and the oldest (fifth)
cause of trip is erased. No trip data is saved in this trip record. However, by observing
repeated trips of the same type, an indication of an inherent fault is obtained for
maintenance purposes.
5.2.3 Motor Statistics
The total motor running time (including start conditions) and the maximum average
current present during the last successful start are monitored here.
5.2.4 Switch Status
To assist in troubleshooting, the state of each switch can be verified using these messages.
A separate message displays the status of each input identified by the corresponding
name as shown in FIGURE 2–3:
Typical Wiring Diagram on page 2–20. For a dry contact
closure across the corresponding switch terminals the message will read closed.