What is emergency diesel generator, its purpose and how to safely operate it?

The emergency diesel generator is a self contained diesel engine driven electrical generator set, which is located in a separated room with access from deck. Usually the generator is the self-excited, brushless type and can be set for manual or automatic operation. Auto will be normally selected, with the manual setting being used for testing the generator or in case of auto start failure.

Emergency generator

Upon failure of the main diesel generators the emergency generator set will start automatically and connect to the emergency switchboard to maintain supplies to essential services. It is also used to get the ship under power from dead ship condition and will enable power to be supplied to the essential services without the need for external services such as starting air, fuel oil supply and cooling water.

The engine is normally equipped with a self-contained cooling water system which is circulated by an engine-driven pump and cooled in a radiator. Cooling air is forced through the radiator by an engine-driven fan. The cooling water is mixed with anti-freeze in order to prevent freezing of the cooling water in cold conditions and a thermostatic electrical heater is fitted in the cooling water system to maintain the engine in a condition ready for immediate starting. The engine-driven cooling water pump supplies the LO cooler and after leaving the engine, the cooling water flows to the thermostat and back to the radiator or engine circulation pump.

The engine running gear is force lubricated by an engine-driven gear pump which draws oil from the sump tank and discharges it through the cooler and a filter to the lube oil rail. The system is equipped with a pressure regulating valve to prevent over-pressure of the lube oil supply to the engine.

The generator is supplied with fuel from a dedicated tank which is located in the emergency generator compartment. The fuel level into the tank, as per SOLAS requirement should be enough for 18 hrs in case of cargo ships and 36 hrs in case of passenger vessels of continuous running of the generator at maximum nominal load.

The engine is normally started by means of an electric starter motor with power to the motor being supplied by batteries. The batteries are provided with an isolation switch and are maintained in a fully charged condition by a battery charger which operates continuously and is usually equipped with an alarm which is activated if the charger fails. A back up hydraulic starter is also fitted with the hydraulic power being manually generated via a hand pump. An accumulator charged by the hand pump provides the pressure to drive the hydraulic motor which connects with the flywheel.

Emergency generator hydraulic starter

When in automatic operation only the electric starter motor is utilized. The engine should be started at least once a week and run up to full load monthly.

The emergency switchboard is normally supplied from the main 440V switchboard and when AUTO mode is selected, the emergency generator is started automatically by detecting no-voltage on the emergency switchboard busbar. Usually, three start attempts are available under automatic control, with a start failure alarm in the event of a failure to start.

The emergency generator air circuit breaker (ACB) will connect automatically to the emergency switchboard after confirming the continuation of no voltage and the bus tie breaker on the emergency switchboard, which feeds from 440V main switchboard is opened automatically when no voltage is detected.

Emergency generator air circuit breaker (ACB)

The emergency generator is designed to restore power to the emergency switchboard within 45 seconds as per SOLAS requirement. According to SOLAS regulation an emergency generator must be fully operational for up to 10 degree of trim and 22 and a half degrees of list and need to start anytime at 0°C temperature.

Example of an emergency generator control panel

So, in order to enable the emergency generator to start automatically in the event of a blackout:

  • The mode selector switch at the local control panel must be set to the AUTO position.
  • The fuel tank must always contain sufficient fuel for at least 18 hours of operation at full load.
  • The battery system must always remain on charge and the batteries must be checked to ensure that they are fully charged. If one of the battery systems fails it must be disconnected and must be replaced at the earliest possible time.

Usually, after power has been restored on the main switchboard the generator ACB and tie breaker will automatically operate and engine will stop. If the automatic system fails, the manual procedure to stop the engine after power restoration is as follow:

  • Turn the emergency generator operating mode switch to the MANUAL position.
  • Manually open the emergency generator circuit breaker.
  • Manually close the normal supply circuit breaker (tie breaker) to the emergency switchboard.
  • Manually stop the emergency generator by pressing the STOP pushbutton on the engine panel.
  • After engine stops, turn the emergency generator operating mode switch to the AUTO position.
Example of an emergency generator electrical panel

If for some reason the emergency generators fails to start automatically, then this must be started manually either using battery starter or hydraulic starter mentioned above. The procedure of manual starting of the emergency generator and manual closing of the circuit breaker is, generally as follow:

  • Check that there are no water, fuel or lubricating oil leaks and that the emergency generator is available for starting and ensure that there is no restriction on the engine starting.
  • Ensure that the engine control panel is supplied with electrical power.
  • Ensure that the fuel system is fully primed and that all of the valves from the fuel tank to the engine are open.
  • Check the water level in the radiator expansion tank add water to the tank if necessary.
  • The generator heater and switchboard heater must be switched on.
  • Ensure that the starter batteries are fully charged and that they are able to supply electrical power to the starter motor.
  • Check the oil level in the engine sump and replenish if necessary.
  • Turn the engine control panel mode selector switch to the MAN position.
  • At the engine control panel press the START pushbutton. The engine should turn over on the electric starter motor and should fire. When the engine fires the START pushbutton must be released. The engine governor will regulate the speed to the preset value.
  • Check that the engine runs smoothly without excessive noise or vibration.
  • When the engine is running normally and the generator voltage and frequency are correct, the generator may be connected to the switchboard. The emergency generator circuit breaker is closed by pressing the CLOSE/MAN pushbutton on the same panel.

In order to test the interlock between main switchboard and emergency switchboard the procedure is quite simple but requires attention in order to prevent total power loss during test. In this procedure the bus tie breaker (located normally in ECR and EG’s room) need to be manually open and the emergency switchboard will black out. The emergency generator will start automatically and the generator ACB will close to feed the emergency generator. To return to the normal mode, the tie breaker must be manually closed and emergency generator ACB will open and generator will automatically stop after a preset cooling time. The same test can be performed by turning the E/G SEQ TEST switch, located at the emergency switchboard, inside the emergency generator panel, to the ENG & ACB position. The bus tie breaker will receive an open command. However, during live test in presence of a surveyor or PSC officer , they will always ask to manually trip the tie breaker.

It is very important to avoid frequent consecutive start and stop of the emergency generator without cooling down as this will lead to alternator heater or winding failure. Moreover, running the engine on idle before stop will allow the cooling water and lube oil to carry away heat from the combustion chambers, bearings and turbocharger. It is very important for the turbocharger where frequent sudden stops can result in damage to the bearings and seals.

Generally the idling period before stop is set for 5 minutes and the time period should not be extended, as long periods of idling will result in poor combustion and build-up of carbon deposits in the engine combustion chamber, exhaust manifold and turbocharger.

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