On the engine block or on components such as the fuel injection pump, you often find oil stains leaking or splashing from the join between the exhaust manifold and the engine block or from the manifold gasket. This is basically due to the fact that this type of engine is not subjected to normal working loads, usually being operated infrequently and under loads below its nominal power and optimal operating power.
It needs to be borne in mind that the engineers' design for the engine block has been conceived for operation under optimal working loads, which are normally around 80% of the nominal load for a diesel, to withstand tensions, temperatures and dilations of materials calculated for this functioning and prepared to support greater efforts. This being the case, we find that engines that present these oil losses or leaks never or almost never work under these conditions, meaning that the materials never undergo the dilation for which they were designed. For this reason, small leaks of oil occur between the components joined by screws and seals at points where the temperatures are high and the largest dilation occurs. In such cases it is not a matter of tightening the screws, which will be properly tightened to the torque specified by the manufacturer. Nor is it a problem affecting the seals. It is solely a problem of DILATION, which means the only way of avoiding these leaks is to subject the diesel to loads of more than 60% of the nominal power and to be close to 80%, where will have optimal performance.
It is extremely important to disconnect power from the auxiliary service battery charger power supply or floating battering voltage power supply before replacing the starter batteries of emergency generators. This charger or power supply converts the alternating current from the grid into direct current to maintain the batteries topped up and avoid battery discharge due to constant current on the unit or the controller card managing the generator's PLC. If this voltage is present it is possible to produce a SERIOUS RISK OF SHORT-CIRCUIT when the battery positive is disconnected, as the 12 or 24 Vdc positive being supplied to the battery charger will be present on the battery terminal. In such cases it is customary to leave this positive on the ground or support it somewhere, and if the precaution of insulating it is not taken, it may touch a metal surface, closing the circuit to ground and producing a short-circuit.
The routine preventive maintenance operations on emergency generators include three main groups of tasks depending on their frequency and thoroughness and another three groups divided up according to the parts of the unit.
Thus, in the first GROUP:
Thorough servicing, mainly according to the recommendations of the equipment manufacturer. Overhauls are usually ANNUAL or after 1000 hours operation.
Intermediate servicing, SIX-MONTHLY or every 500 hours operation, to check general components of the unit and that, superficially, they work correctly.
Operations to continually check how well the generator starts. This is carried out WEEKLY to check the immediate starting of the generator and the correct state of the components involved in the load management system.
In the SECOND GROUP:
Work to be done on the DIESEL ENGINE
Work to be done on the ALTERNATOR.
Work to be done on the GENERATOR CONTROL PANEL AND AUTOMATIC GRID-GENERATOR SWITCHING SYSTEM.
For reasons of space, given that the servicing work varies according to the generator model, we list here the basic preventive maintenance tasks that can be considered part of a WEEKLY check on the constant fitness for starting and note that during ANNUAL service normally involves changing the oil and filters (fuel and oil filters), coolant and air, provided the predetermined or recommended number of hours between changes has not been reached.
WORK TO BE DONE DURING THE WEEKLY CHECKS:
Check correct oil level in engine sump.
Check correct coolant level in the expansion tank.
Check correct fuel level or that there is sufficient fuel in the daily tank and in the feed tank, if fitted.
Check that the temperature of the engine block is over 45ºC and/or the pre-heater system is working correctly.
Check the starter battery voltage, and the level and density of the electrolyte.
Check that the battery charger is working properly.
Check the presence of auxiliary service voltage (primarily) to power the heater and battery charger.
Check the state of the air inlets/outlets, the exhaust, and that the room or location of the generator is properly ventilated.
Check that the generator starts without a load and runs for at most five minutes.
Check correct starting by simulating a grid failure and drawing a load from the generator, checking that the grid/generator switch-over works properly when the grid is reconnected.
It often happens that the emergency generator starts automatically for no apparent reason and switches from grid to generator, thus supplying power to the installation. In many instances, independently from the unnecessary fuel consumption this causes, this results in the nuisance of the noise and exhaust fumes, and the uncertainty of staff not used to this kind of equipment and the greater inconvenience of going from ZERO (voltage) on each change over from grid to generator and generator to grid.
The most common causes of this are:
Absence of a grid controller with a timer or other filter to eliminate power glitches. (interruptions to the power supply lasting less than 1 second), these glitches are usually imperceptible. The grid watchdog usually incorporates a timer. If it does not, the generator's switches can be set to give a delay.
If there is an increase or decrease in the company's input voltage above or below the grid watchdog's control threshold. This can lead to any of three cases arising:
Incorrect adjustment of the over or under voltage settings for the grid being monitored, producing continual starting.
Correct starting to protect loads, outside the range of limits set for over/under voltage.
Manipulation of wiring by the company and changing the sense of rotation of the phases. (somewhat uncommon) provided the voltage watchdog has this control function.
Leave the stop or manual key pressed. Leave the generator out of service in automatic mode.
Leave outside emergency stop button (enclosed units) or panel control button pressed.
Low fuel level, due to fault on the level probe, the alert or alarm is not shown. The generator does not start, or once it has started, it oscillates and stops. It will be necessary to restore the levels and purge the circuit.
The generator fails or has difficulty starting, due to low temperature of the engine block. This may be caused by a fault in the warming system or triggering of the magnetic/thermal cut-out on the auxiliary services line.
Failure to start due to low density of battery electrolyte. In this case it will be necessary to check the functioning of the battery charger and auxiliary power supply. Even if the battery indicates a correct operating voltage of approximately 13.2 Vdc it will be necessary to isolate the battery from the charger and measure the voltage on the battery alone. Once this has been done, check the electrolyte with a densitometer and if necessary replace the batteries.
Failure of the grid/generator switchover due to triggering of control line protection or the switchover system.
Triggering of generator circuit breaker or low speed triggering. Caused by powerful load impact during starting. It should be borne in mind that a diesel engine does not usually allow a load impact of over 50% of the nominal load without a drop in the frequency or voltage.
Engine oscillations. Basically due to a low diesel flow, impurities or dirt in the diesel filters, poor electronic speed regulator adjustment.
The most common types of fault with this type of operation are:
Fault with the grid contactor windings, due to their being excited for long periods.
Failure of the auxiliary timer relays (if any).
Triggering of a fuse or magnetic/thermal cut-out protecting the switching controls.
Failure of end-of-run contacts or safeties on automatic circuit breakers with motorised control, preventing operation of the primary circuit breaker or of the secondary circuit breaker if there is an internal control panel.
Failure of circuit breaker load spring due to motor failure or wear.
Failure of control orders from the generator set.
Triggering of circuit breakers due to very rapid load transients between the opening of one circuit breaker and the closing of another or a change in the switching contacts.
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