Parallel Running of Generators

Good day readers!
Today, I will write about parallel running and synchronization of generators. This article is intended for individuals who are interested in power generation, engineering, electro-technician and generators. But, all readers are welcome too. Hope you will find this information very helpful.

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What is Parallel Running Operation of Generators?

Synchronization or parallel running of generators is an activity that uses two or more generators to run simultaneously. Synchronization is carried often on ship and it is a prerequisite for every engineer on ship to know the procedure. In maritime law, it is require to a ship to have at least two generators and nowadays ships have 2 to 3 generators on board.

What are the Advantages?

1. Reliability

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Paralleling or synchronizing generators also means adding power to it. So, this system ensures that there is always an enough and constant power to critical loads. In case of one generator will fail, at least we still have another running generator and the load supplied by the failed generator will be supplied by other generator.

2. Cost Effective

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As the generator size increases, its cost of generation also increases. This is because of law of demand. The market of smaller generators (engines in general) is higher than larger generators. In result, manufacturers cost it in lower price. Using multiple small generators is more economical than a single unit of large generator

3. Efficiency

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In most cases, load varies in time and it is common for generators to run at 30% of its full capacity when the load is low. It may cause wet stacking. The efficiency is normally higher when its load is from 75% to 100% and light load cause the operation of generator inefficient. So, if the load is low, you can take out the other generator to match the load requirement. Efficiency increases when using smaller generator, results to cost reduction.

4. Expandability and flexibility

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For varying load condition, supplying it is only possible with several generators. Using a costly unit or spending much on a big generator is inappropriate and inefficient. For time with lower load, you can use only one small generator and you can expand your generator usage when load expands. In other words, add generator gradually as load demand increases. Small generators are flexible because you store it in a smaller area.

Requirement for Parallel Running

Ideally, any type of generators are can connected in parallel running as long as they have the same voltage, frequency and phase. However, there are limitations due to the compatibility of new and old models.

These are thing to consider

1. Speed control
2. Load balance
3. Voltage regulation
4. Synchronization

Compatible generators
Generators are compatible when they shared some properties like engines, speeds, controls in load sharing, interfaces to control, compatible alternators and monitoring systems. The best way to know if compatible is to use the same or sets with similar alternator pitch, output voltage, and frequency.

Incompatible generators
Paralleling generators with different characteristics are complex. Aside from compatibility, some problems may occur. If the sizes are not the same, the maximum output of large generator is limited by the smallest one. Otherwise, this large generator will overload the smaller one. In this case, design should ensure that larger loads must dropped first in event of failure of large generator. It ensures the smaller one will be left with load it can support.

Must be Check Before Synchronising

1. Frequency - generators must have the same frequencies
2. Voltage - generators must produce with the same voltages
3. Phase - must have the same phases (single or three phase)
4. Current - generators must have the same output current

Methods of Synchronizing

1. Using Synchroscope

Synchroscope

2. Using Synchronizing Lamps or Three Bulb Method

Synchronizing Lamp

Procedures Before Synchronizing

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1. Before taking the synchronization, inform the personnel involve.
2. Start the generator to be synchronized. Before start, prime the engine with fuel using hand pump. Make sure the engine block heater is turned off.
3. Air valve must be open and engine block must be off.
4. Check the oil pressure and cooling water pressure if adequate once the engine is started.

Procedures in Synchronizing using Synchroscope

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1. Check the pressure gauges in engine control room.
2. Check ground lights if working properly with enough brightness.
3. Check the synchronizing relays to open position.
4. Set the running generator to desired output voltage (480 or 240 volts)
5. Set the running generator to 60 Hertz
6. Bring the incoming generator to the parameters the same with running generator (480 or 240 Volts and 60 Hertz)
7. Synchroscope needle will move at a varying speed. Adjusting speed of generator to obtain the steady slow motion of needle in the clock wise direction.
8. Once the needle is moving steady, close the breaker when the needle has traveled three-fourth of its way.
9. Energize breaker when needle is in 11 o’clock position
10. Check parameter of the incoming generator, must be the same with leading generator.

Procedures Using Synchronizing Lamps or Three Bulb Method

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This method is only if there is a failure in synchroscope. For emergency only.

1. Check the pressure gauges in engine control room.
2. Check ground lights if working properly with enough brightness.
3. Check the synchronizing relays to open position.
4. Set the running generator to desired output voltage (480 or 240 volts)
5. Set the running generator to 60 Hertz
6. Bring the incoming generator to the parameters the same with running generator (480 or 240 Volts and 60 Hertz)
7. Two lamps will be bright and one lamp will be dark when incoming generator is in phase.
8. Movements of bright and dark lamps indicates the incoming generator either running fast or slow.
9. Clockwise movement indicates fast and anti clockwise indicates slow.
10. When the movement is almost steady, energize the breaker

Here are my sources
source 1
source 2
source 3

Thank you and have a great day.

Best wishes,
@thinkingmind