How are Generators Synchronized on a Ship?

                        Synchronization of generators is an activity that is carried out quite often on ship. It is a prerequisite that each and every engineer on the ship knows the procedure thoroughly. In emergencies, the engineers are required to carry out the process manually in extremely limited amount of time.

Introduction

                  It's a known fact that marine generators are the heart of any type of ship. Maritime law requires that every ship should have at least two generators. Nowadays all the ships have around 2-3 generators on board. More number of generators are used to facilitate load sharing and to prevent wear down due to excessive load.
             Maintenance of generators at regular interval of time is extremely important. In this article we will learn the process of generator synchronization when multiple machines are required or one of the generators needs to the stopped and the other started in its place
Say for example if a ship has three generators on board, two are used under normal working conditions and one is kept as stand-by.                  
              Whenever a requirement to service a running generator arises , the standby generator is brought in line and the desired generator is taken off line. For bringing the standby generator in line, the generator is synchronised with the other running generators.

The main things that are kept in check for synchronizing a generator are :

• Frequency
• Voltage
• Load
• Phase

Let's have a look how the synchonization of generators is done manually

Generator Synchronization Procedure- Before starting

A step by step method for synchronizing generators in provided below.

1. When a decision of synchronizing generators in taken, first the bridge should be notified about the scheduled activity
2. Start the generator that has to be synchronized. Before starting, prime the engine with fuel using hand pump. Make sure the engine block heater is turned off.
3. Open the air valve and then turn on the engine.
4. Once the engine starts, check if the oil pressure and cooling water pressure is adequate. Check if the cooling water pump is working properly by feeling the pipes. Once the check is done, close the air valves.

Synchronizing procedure

Once the engine starts running properly, synchronization is carried out.

1. In the Engine control room, Check the pressure gauges.
2. On the generator control panel, check if all the ground lights are working properly with adequate brightness.
3. Also check the synchronizing relays for open position. Bring the running or the lead generator to the desired optimum parameters: 480 volts and 60 hertz
4. Bring the generator that is to be synchronized(0n-coming) to the desired parameters. Now turn on the synchronizing relay and keep a close look at the needle.
5. The needle in the synchroscope will move at a varying speed initially. Adjust the speed of the generator by obtaining a steady slow motion of the needle in the clock wise direction.
6. Once the needle is moving at a steady speed, depress the breaker close button when the needle has traveled three-fourth of its way. Energize the breakers when the needle reaches a position similar to the 11' o clock position of a clock.
7. After doing this, check the parameters of the on-coming generator. They should be same as those of the leading generator. i.e 480 Volts and 60 hertz

 

 

 

After synchronizing

After the main job of synchronizing, the following steps are to be carried out.

1. Change the governer control to the off-going generator.
2. Now the load shown in the guages by this generator should be removed off the system as soon as possible before it starts acting as load(reverse power). This can be done by quickly pulling the trip breaker as soon as the generator goes off-line.
3. Once the generator is offline, stop the engine using a toggle switch.
4. After turning off the engine, turn on the engine block heater.
5. At the end, take a proper look at the control panel guages for adequate pressure and even distrubution of load.

           It must also be noted that load distribution can be adjusted by varying the fuel supply to the generator via its governor but for current sharing to be equal you would need to vary the excitation current which changes the power factor of the generator.

Image Credits

http://powergenelectrics.com/yahoo_site_admin/assets/images/synchroscope_2.291110319_std.jpg
http://www.seg-me.com/UNATRAC%20Project1.jpg
http://www.o-t-s.com/synchroscope.jpg