How to Commission a Generator Section
This article describes the process of electrically commissioning (or re-commissioning) a generator section for a Ross Hill or Hill Graham SCR system. It could be adapted to other makes and models because many of the basic principles are the same between manufacturers, and is serves as a useful troubleshooting guide.
It is assumed that all safety and mechanical checks have been completed satisfactorily and that the engine-generator is safe to run. The generator section itself should have been previously operational, commissioned or thoroughly tested. This is a job for an experienced engineer and not to be undertaken by unqualified individuals.
- Remove the generator and busbar safety fuses from the generator section. These are the fuses which directly connect to the generator incoming connections and the main busbars.
- Visually check inside the generator cubicle for misplaced tools and other debris and remove or clean as required.
- Perform a minimum 1500VDC insulation check on the generator power cables. Check the resistance of each cable to ground as well as between phases.
- Check that the magnetic sensor on the engine flywheel is correctly spaced from the flywheel teeth as per the manufacturer’s recommendation, and that the sensor head is clean.
- Turn the engine control switch to the IDLE position (or RUN if no IDLE). Disconnect the throttle wires from the AC Module (terminals 533 and 545) and check the resistance between the wires. It should be between 30 and 40 ohms. Re-connect the wires.
- Disconnect the AC Module Tach inputs (terminals 526 and 527) and check the resistance between the wires. The resistance will vary depending on the sensor, but should be between 50-300 ohms. If open circuit or short circuit there may be a problem which should be investigated. Re-connect the wires.
- Disconnect the AC Module generator exciter connections (terminals 555 and 556) and check the resistance between the wires. It should be between 3 and 50 ohms depending on the make and model of the generator. Re-connect the wires.
- Check the Hands-Off-Start (HOS) batteries are connected and switched on. Check for +12V approximately between AC Module terminals 510(+) and 501(-), and -12V between terminals 511(+) and 501(-). If the batteries are flat it may be necessary to manually lift the actuator on the first start.
Phase Rotation Check
The following tests ensure that the phase connections to the generator control cubicle circuit breaker are correct. It is also useful to check that there is sufficient residual magnetism in the generator to generate sufficient voltage for the generator to self-excite and build up voltage. No residual magnetism is rarely a problem unless the generator has been stationary for a long period of time.
- If possible, rack out the generator circuit breaker (to the TEST position if available).
- Use a 2-channel oscilloscope with 1000V probes (differential probes preferred if available). Connect the ground lead of the scope to ground, the channel 1 probe to the A phase generator connection and the channel 2 probe to the B phase generator connection. Set the timebase to 200ms/div and the channel voltages to +/-50V to start with (the timebase and voltages can be adjusted to get the clearest display during the test). Set the scope trigger to trigger on channel 2.
- Ensure the STOP-IDLE-RUN switch is in the STOP position and turn the generator over on the starter. If there is residual magnetism in the generator a small voltage will be generated which can be used to check the phase rotation. Leave the channel 2 probe connected and move the channel 1 from the A-phase to the C-phase and ensure the A-phase leads the B-phase (Fig 1) and the C-phase lags it (Fig 2). The trick here is to get the scope display stable by adjusting the triggering so that the B-phase (channel 2) is stationary.
Fig 1: A leads B
Fig 2: C lags B
Flashing the GeneratorIf there is insufficient residual magnetism to perform the test, there is a likelihood that there will be problems getting the generator voltage to build up and it may be necessary to ‘flash’ the generator. To do this :
- Disconnect the exciter control wires at one end (cubicle or generator).
- Connect the positive terminal of a 12V car-type battery to F+.
- Momentarily (5-10 seconds) connect the negative terminal of the battery to F-. There may be sparks, so take precautions.
- Once this is complete, re-connect the exciter control wires and perform the test.
Start UpHaving established the phase rotation is correct, the generator can be run up.
- Fit the generator section safety fuses.
- Monitor the output of the Generator Exciter PCB with an oscilloscope set to a timebase of 50 ms/div and voltage range +/-100V by connecting the ground lead to PC1 terminal 1 and channel 1 probe to PC1-10 (assuming the standard designation that PC1 is the Generator Exciter PCB).
- Turn the engine control switch to IDLE.
- Set a Digital Multimeter to monitor mA (200 or 500mA range) and insert the meter in series with the throttle control circuit by disconnecting the wire to AC Module terminal 533.
- Turn the generator over with the starter and observe the throttle current rise to about 20mA, and observe a full wave rectified DC output on the oscilloscope build up (Fig 3) until the build-up relay is heard to click at which point the waveform should switch to a thyristor-controlled output (Fig 4).
- The generator should run up to idle speed (two-thirds full speed) and idle voltage (two-thirds full voltage).
Fig 3: Exciter before
build-up relay energises
Fig 4: Exciter after
build-up relay energises
Ensure that after the build-up relay energises there is a pulse for each phase as shown in Fig 4. If one pulse is missing there may be a faulty thyristor on the Exciter PCB or a missing firing pulse from the AC module.
If the waveform builds up but disappears when the build-up relay cuts in there may be a problem with the Generator Exciter PCB, the AC module exciter firing or control circuit, or the exciter transformer phase relationship with the AC Regulator transformer which provides the synchronising signals for the exciter.
If the waveform continues to build as an uncontrolled, full-wave rectified waveform there may be a problem with the build-up relay and over-voltages from over-excitation will result.
- As the engine idles the throttle current should be around 20mA. If all is well, turn the engine control switch to RUN. The engine speed should ramp up smoothly to full speed, and as the engine approaches full speed the voltage should pick up to around the system voltage.
- At full-speed, no load the throttle mA should be 25-35mA. Much more or less than this may cause load sharing problems at high loads. The only way to get the correct mA reading this is to adjust the actuator linkage. If the current is too high the linkage should be adjusted to open up the fuel rack a little more so that the regulator has to deliver fewer mA for the same amount of fuel. If it is too low the opposite adjustment should be made. Note that this may not apply exactly to very old Ross Hill systems, which may have AC Module with non-integrating KW regulators. If this is the case the actuator adjustment is extremely important for good load sharing across the range whereas later versions have a reasonable amount of compensation built in.
- Verify that the speed of the engine can be adjusted from the cubicle front panel potentiometer by about +/-10% and voltage can be similarly adjusted from the corresponding control.
- Remove the meter from the throttle circuit. Note that if you disconnect it without first connecting wire 533 back on to the module the engine will stall.
Fig 5: Actuator Linkage
SynchronisingIt should never be taken for granted that, because the phase rotation is correct, the synch check panel is OK. The operation of panel should be verified. This requires the bus to be hot, so another generator will be needed on line.
Fig 6: Synchronising Panel
- With the bus hot, select the generator under test for synchronising. Place a multimeter set to 1000VAC (an analogue meter is best) across the main circuit breaker A-phase and observe the voltage rise and fall as the generator and bus voltages drift in and out of synch.
- Adjust the engine speed to slow this drift down so that it is more readily observable. Ensure that as the test meter voltage approaches zero the synchronising panel lights dim and the synchroscope needle approaches the vertical (point upwards) position.
- Check this is true for all 3 phases. If this is not the case there is a problem with phase rotation or the synchronising signals which must be resolved. Ensure that the circuit breaker UV coil is energised (or the circuit breaker permitted to close by other means) only within the synchronising window, which is a few degrees either side of the synchroscope meter pointing vertically upwards.
- If all looks good rack in the circuit breaker, synchronise and close.
- Once on line adjust the generator voltage so that the KVAR reading across all generator on line is balanced. To verify load sharing a substantial load is required. Load tanks are normally only resistive so can only check engine KW load sharing. To check the KVAR load balance a reactive load will be required. The Mud Pumps are usually a good source of steady load for this purpose.
- Confirm that the generator shares across the load range.
- The Ross Hill SCR System scheme dictates that the lowest number generator (or leftmost cubicle) is the KW load sharing master and the others follow, so be sure to check the generator as a master and slave if possible.
Verify voltage and current indication by independent means if possible.
Check all 3 phases are balanced. The KW indication can be checked with a resistive load tank, and once confirmed this can be used to mathematically verify the KVAR reading together with the total current indication.
Note that the standard Ross Hill AC Module KW and KVAR metering outputs are not true indications – they are in fact real or reactive currents, with no consideration of voltage, so the meters can only be accurate at the system voltage.
It is not advisable to perform AC Module undervoltage, overvoltage, underfrequency, overfrequency trip or reverse power checks in a real situation. These are verified using a test simulator, such as those used by Contrelec, during bench testing of the AC Module. If a certifying authority such as Lloyds or ABS wish to see the trips demonstrated then this should be done under the supervision of a Contrelec Service Engineer, or send your module to Contrelec for a health check.
This information is provided in good faith and with no warranties or guarantees. Contrelec Limited accepts no responsibility whatsoever for damages or losses either direct or consequential which may result from following all or part of this procedure, or procedures and advisories derived from it.