reservoir, emergency, starting, diesel, electrical, generators, motors, pumps,
propulsion, compressor, equipment, lighting, batteries, battery, collision
Diesel generator sets are started with compressed
Main air reservoirs for starting main engine
Reciprocating air compressors can achieve pressures up to 30 Bar
3 units of diesel generators
Synchronizing 2 or more generators running in parallel
Blackout - loss of electrical power
Have you ever wondered what would happen if all the electrical generators were stopped?
Or tripped due to abnormal operating conditions?
If that were to happen, there will not be any electricity on board, and all the motors on board will stop. This means that all the pumps driven by motors will also stop. The main propulsion engine, boilers, steering gear, air compressors and other equipment will be stopped.
All the lighting and ventilation fans will also be off. There will only be some small amount of light from battery supplied emergency lights.
What to do then?
The engine room will be very dark. The engineers will move around using
torch lights. They have to work fast. The batteries for the lighting have quite a limited charge. The ventilation is off, and the engine room can become stuffy and hot in a short while. The sea outside may be rough. The ship may be in danger of being blown to one side by strong winds. If the ship is near to land, there is a real danger of collision or grounding because the engine for propulsion stopped and the steering gears are stopped.
If the air reservoirs are full of compressed air, then it is relatively easy to start back the generator engines. In fact it is very important to keep the air reservoirs full all the time.
What if the air reservoirs are also empty? It can happen!
Engineers sometimes overlook the fact that compressed air is always being used in pneumatic control systems. Bit by bit, the compressed air in the reservoirs becomes depleted unless somebody has the presence of mind to close off the air valves.
Let's say due to abnormal circumstances, the air reservoirs have become empty! That's a big problem!
Luckily, marine systems are built with that possibility in mind.
Usually tucked away in an obscure corner in the engine room, is a tiny diesel engine that can be started by hand cranking. Although tiny in size, and seldom, if ever used, this piece of equipment is of prime importance. It's called the emergency air compressor. The diesel engine drives a small air compressor. The compressed air from this small compressor will slowly fill up a small emergency air reservoir.
When sufficient air pressure is achieved in this small air reservoir, the engineers will get everything ready and prepare to start one of the normal diesel generator engines.
Once a normal diesel generator engine can be started, then it is put on load to supply electricity to the main switchboard. The engineers have to be careful and selective in supplying the electrical power. The cooling seawater pump for the diesel generator has to be started up to prevent overheating of the diesel generator. The engineers will watch the load as they start the main air compressors, pumps and other machines to prevent overloading the generator.
The air compressors have the priority here. Perhaps 2 or 3 compressors will be operated to pump in the compressed air into the main air reservoirs as fast as possible. Normally, one diesel generator is sufficient to supply power for the whole ship. However in emergencies like this, it is good to have more power available. If the emergency air reservoir has built up sufficient air pressure, then another diesel generator will be started up; the electrical supply synchronized and run in parallel to the existing supply.
Once the main air reservoir has built up sufficient air pressure, and with the entire main engine cooling water and lubrication pumps running, the main engine is ready to be started.
With a starting air lever, or a push button, the main engine can be started and the ship could then continue on its journey.
Basically, that is what happens when starting up a diesel generator from scratch. With no compressed air supply, the generator engines could not be started.
This is usual when the ship is in dry-docking or repair yard, when all the generators and all other equipment have been stopped. At the repair yard, there is electrical supply available at the shore. Sometimes, it is too troublesome (or costly or time consuming) to connect to this supply. Some countries use alternating current with different frequencies from the ship. Moreover, when the ship is free floating again, the connection to shore supply is usually dismantled.