CDVR Troubleshooting
Outline
• Troubleshooting
– If operation is not as expected – Excitation loss (reverse kvar) – Generator over voltage
– Generator under voltage – No generator voltage
Outline (continued)
• Troubleshooting
– Over excitation fault – Loss of sensing
– Field over current
– Internal Memory Failure – Internal Watchdog Failure – Unstable Voltage
Troubleshooting
• If Operations is not as Expected:
– Check for Alarms or Shutdown Faults
– If Fault LED is lit Continuously Alarm Output Drive Active – If Fault LED is Flashing Shutdown Output Drive Active
– Open Communications with CDVR to determine what Alarm / Shutdown is active
– Alarm Signal Indicator Visible on all Screens – Go to Metering Screen, look at Alarms area – Check Programmable Settings
Troubleshooting
• If Excitation Loss(Reverse kvar) has Occurred:
– Verify programmable settings are consistent with application – Check wiring of generator voltage (P12 – 10 to 12) and Current
Sensing (P12 – 1 & 2)
– Check phase rotation, if not consistent with wiring diagram, modify connections
– Check other paralleled generators or voltage sources for over voltage (this can cause reverse var flow into generator)
Troubleshooting
• If Generator Over Voltage has Occurred:
– Check wiring of generator voltage sensing (P12 –10 to 12) – Verify that the generator over voltage fault settings are correct – Verify that voltage adjustment is not set too high
– Verify that sensing PT (if used) has correct turns ratio – Verify that sensing PT fuses (if used) have not opened – High voltage may occur if operating in droop mode with
capacitive load or if CT connection is backwards or wrong phase rotation
– High voltage may occur if operating in line drop compensation mode with a large generator load
– Verify auxiliary input voltage is not too high – Replace regulator
Troubleshooting
• If Generator Under Voltage has Occurred:
– Check wiring of generator voltage sensing (P12 –10 to 12)
– Verify that the generator under voltage fault settings are correct – Verify that voltage adjustment is not set too low
– Verify that the generator is running at rated speed
– Verify that the under frequency setpoint (knee frequency) is not greater than generator frequency
– Verify that sensing PT (if used) has correct turns ratio – Check for correct input power
– Low voltage may occur if operating in droop mode with high inductive load
– Verify auxiliary input voltage is not too low – Replace regulator
Troubleshooting
• If No Generator Voltage is Present: – Check wiring
– Verify that the generator is running at rated speed
– Verify that residual voltage applied to the power input is at least 6Vac or greater
– Verify that the fuse is not open
– Verify that CDVR is connected to 24Vdc control power – Verify that common alarm / shutdown LED is not flashing
Troubleshooting
• If No Generator Voltage is Present and an Exciter Diode Monitor Fault has Occurred:
– Stop machine
– Insure power input to CDVR has been removed, unplug P6 – Refer to generator manual for instructions on checking the
rotating exciter diodes
– If no fault is found with rotating exciter diodes, the EDM trip value may be too low
– Increase EDM trip value to a level greater than the ripple current under normal operation
– If rotating exciter diodes are at fault, repair, reinstall P6 then reset the CDVR using the Fault Reset contact input or cycle the 24Vdc control power
Troubleshooting
• If No Generator Voltage is Present and an Over Excitation Fault has Occurred:
– Stop machine
– Check generator and load conditions for a fault that could cause excessive exciter field current
– If no fault is found, reset the CDVR using the Fault Reset contact input or cycle the 24Vdc control power
– Verify the over excitation settings are properly adjusted for the
generator, set slightly above the requirement of the application but not so high as to render the protection ineffective
– If an exciter diode fault has occurred, the instantaneous trip value of
28A may have been reached. The EDM fault will not indicate this, due to a 5 sec time delay
– SR4 &SR4B generator require up to 12Adc for full load. A 10 second setting is required to insure 300% short circuit requirements
Troubleshooting
• If No Generator Voltage is Present and a Loss of Sensing Fault has Occurred:
– Stop machine – Check wiring
– Check generator and load conditions for a fault that could cause sensed voltage to be low
– If sensing potential transformers are used, verify that they are functional and have not blown a fuse
– Once fault is repaired, reset the CDVR using the Fault Reset contact input or cycle the 24Vdc control power
Troubleshooting
• If No Generator Voltage is Present and a Field Over Current Fault has Occurred:
– Stop machine – Check wiring
– Check generator and load conditions for a fault that could cause a field over current
– A field over current fault occurs when output current exceeds 28A (approximately)
– Once fault is repaired, reset the CDVR using the Fault Reset contact input or cycle the 24Vdc control power
Troubleshooting
• If No Generator Voltage is Present and an Internal Memory Failure Fault has Occurred:
– Try resetting the CDVR using the Fault Reset contact input or cycle the 24Vdc control power
– If after resetting the CDVR, if another Internal Memory Failure fault occurs, replace regulator
Troubleshooting
• If No Generator Voltage is Present and an Internal Watchdog Failure Fault has Occurred:
– Try resetting the CDVR using the Fault Reset contact input or cycle the 24Vdc control power
– If after resetting the CDVR, if another Internal Watchdog Failure fault occurs, replace regulator
Troubleshooting
• Unstable Voltage:
– Verify that the governor for the engine is operating properly
– Verify that the sensing and power leads are connected securely – Verify that the CDVR stability range is set to the proper range – Verify that the stability level (Kg) is properly set
Troubleshooting
• Poor Voltage Response to a Transient Load:
– Verify that the governor for the engine is operating properly – Verify that the CDVR stability range is set to the proper range – Verify that the stability level is properly set
Troubleshooting
• CDVR PID Tuning:
– Perform a “step of reference” test with 1 or 2% steps – Look at terminal voltage response with chart recorder – Determine if voltage response is acceptable
• Rise time • Over shoot • Settling time • Damping
– If not acceptable, tune the CDVR for the application
– Once “step of reference” test is suitable, verify load application / rejection performance
Step of Reference Test
Step of Reference Test
Step of Reference Test
Settling Time
Step of Reference Test
Troubleshooting
• CDVR PID Tuning:
– Examples of “step of reference” test results
– Tests performed on 300kW, 240V, 60Hz AREP generator
• Factory defaults • PID calculator
PID Calculator, T’do = 2s, Te = 0.1s
PID &Kg = 25, 43, 2.7 & 50
PID Calculator, T’do = 2s, Te = 0.1s
PID &Kg = 25, 43, 2.7 & 200
PID Calculator, T’do = 1.5s, Te = 0.1s
PID &Kg = 25, 51, 2.6 & 200
PID Calculator, T’do = 1.0s, Te = 0.1s
PID &Kg = 42, 100, 4.5 & 200
“Magic” PID Values = 80, 20, 10
Kg = 50
PID Tuning Conclusion
• Must adjust Kg to achieve best results
• Factory Default Values result in “OK” performance
• PID Calculator gives very good results but must know T’do and Te • “Magic” PID values also very good and it is simple
• Once “step of reference” test is suitable, verify load application / rejection performance
Information Needed If Replacement of CDVR is Selected
• When sending back a CDVR, please provide the following: – Detailed statement of problem including
• Symptoms of the failed CDVR • Genset configuration and ratings
• Operating Conditions (kW, voltage, current … etc) • Run time
• Anything unique about the installation
• Did anything of significance occur just before the failure
occurred? (i.e. sparks, re-wiring, etc.)
