TP-6953 7/19134 Section 7 Troubleshooting
Protective Relay Intended Function Potential Causes Troubleshooting
Over Current
(on the Decision-
Makerr 3500
controller:
Generator
Current Average:
High Warning)
To protect the alternator
from excessive heating
due to stator current.
Undersized generator for
application.
Ensure that the load demand is not greater than a single generator can support. This may require
ensuring more than one generator is online before attempting to start a motor load.
Verify Generator Management and Load Management are appropriately configured and system wiring
is correct for operation as determined by a comprehensive coordination study.
Incorrect Soft Start configuration
for motor.
Some Soft Starters transfer the motor to line voltage before it has time to reach rated speed. This will
cause a large current spike on the alternator. Monitor current into the motor with a current clamp and
multimeter to trace the root cause.
Verify appropriate soft starter configuration for generator supplied application.
Simultaneous starting of switching
motor loads.
If multiple motors exist in the application, try ensuring that they all start simultaneously to repeat the
condition. If the condition repeats, it may be necessary to inhibit some motors from starting until others
are up to speed.
Verify Generator Management and Load Management are appropriately configured and system wiring
is correct for operation as determined by a comprehensive coordination study.
Incorrect Protective Relay setting. Ensure that protective relay settings are determined by a comprehensive coordination study using
recent and accurate system data.
Under Voltage
(on the Decision-
Makerr 3500
controller:
Voltage Average:
Low Warning)
To protect the customer
loads from poor quality
power.
System Control mode. System Control mode will force all generators in the system to control reactive power to a target set by
the voltage bias. If the actual reactive power is lower than the target, the voltage will increase. If the
actual reactive power is higher than the target, the voltage will decrease. Make sure that no controllers
are receiving a system load control input. Make sure that no controllers are configured for System
Control mode in software.
System Sync mode. System Sync mode will force all generators in the system to match voltage to a bias level set by the
voltage bias (which could be from 90% to 110% of rated voltage). Make sure that no controllers are
receiving a system sync control input. Make sure that no controllers are configured for System Control
mode in software.
Baseload. Baseload mode on a controller may dec rease the voltage of the paralleling bus if attempting to unload
reactive power when the other generators as configured are not able to support the load. Check for
other nodes configured in Baseload mode. Check if this node is configured for Baseload.
Excessive motor load. Very heavy motor loads may cause the voltage to remain low for long enough to trip the undervoltage
relay. Make sure that the voltage on the generator recovers to rated voltage within 1/2 of the time
specified for the undervoltage protective relay when all motors are started together with a reasonable
preload. If not, it may be necessary to reconsider the coordination study for the system.
Loose wiring between controller
and LED board or wound field
activator.
Failure of any alternator in the paralleling system can cause an undervoltage condition (although it
should be detected by a reverse VAR condition, that time delay is often longer). The failed generator
should be easily detected as it will shut down on undervoltage after the protective relay trips the
breaker.
Activator board failure on
alternator.
Failure of any alternator in the paralleling system can cause an undervoltage condition (although it
should be detected by a reverse VAR condition, that time delay is often longer).
Broken wire or failed w inding in
alternator.
Failure of any alternator in the paralleling system can cause an undervoltage condition (although it
should be detected by a reverse VAR condition, that time delay is often longer).
Voltage Trim disabled. The Voltage Trim corrects the generator output voltage to a nominal level under normal operation. If it
is disabled, the generator voltage could fall anywhere between 90% and 110% of nominal. Make sure
that Trims are enabled on at least 1 of the paralleling generators.
Loss of sensing on a voltage
phase.
The controller uses three-phase sensing to regulate voltage (in a three-phase application). The loss of
a single phase may cause either an overvoltage or undervoltage event. Start the generator to ensure
that all three line voltages are metered accurately.
Incorrect Protective Relay setting. Ensure that protective relay settings are determined by a comprehensive coordination study using
recent and accurate system data.
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