TP-6953 7/19 133Section 7 Troubleshooting
Protective Relay Intended Function Potential Causes Troubleshooting
Reverse VARs
(on the Decision-
Makerr 3500
controller:
Generator Total
Reactive Power:
Low Warning)
Protect the generator
from slipping a pole due
to a low excitation
conditioninthe
alternator.
Incorrect Reactive Load Sharing
configuration.
Check that the engine is able to supply load and maintain normal voltage when running alone. If so,
the Reactive Load Sharing configuration is probably incorrect.
A paralleled unit in a fixed power
mode (Baseload or System Load
Control) or KV AR setting is higher
than the actual load.
Check modes on other controllers. Baseload mode on one generator may result in reverse VARs on
the other generators.
Verify KVAR setting is less than the actual load requires, consider PF sharing.
Incorrect wiring to the CTs on one
or more units on the paralleling
bus (not necessarily the unit that
tripped on reverse power).
Load bank each generator individually. Power should read positive and accurately. Make sure that the
generator controller reads a unity power factor into a resistive load bank. If a load bank is unavailable,
make sure that phase powers are all positive and that phase power factors make sense.
Incorrect current meter calibration
for one or more generators in the
system.
Check the current meter calibration according to the manual.
Loose or broken wiring between
controller and LED board or wound
field activator.
The failed generator should be easily detected as it will shut down on undervoltage after the protective
relay trips the breaker.
Voltage may be unusually unstable.
Check wires and connectors for any failures, intermittent or open connections.
Activator board failure on
alternator.
If alternator produces no voltage, look for bad wires or connections. If no bad connections are found,
continue with Alternator troubleshooting in Section 10 or 11.
Visually inspect the activator board for damage or failure.
Broken wire or failed w inding in
alternator.
If alternator produces no voltage, look for bad wires or connections. If no bad connections are found,
continue with Alternator troubleshooting in Section 10 or 11.
Capacitive load. Verify that the load on the vessel is not capacitive. If a single generator (with the CTs connected
properly) is reading a leading power factor, the load is capacitive. If multiple generators are supplying
the load, check for the total system load under bus metering to determine if the reactive power is
leading (-).
Incorrect Protective Relay setting. Ensure that protective relay settings are determined by a comprehensive coordination study using
recent and accurate system data. Note: Setting the Reverse VARs protective relay above 20% is not
recommended as it may result in slipping a pole under high real loads.
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.
To Next Page
Loading...
