The best tutorial on Parallel operation of Diesel Generators on ships

In this post, I will explain the simplest method of paralleling the generator sets. In a few places, I have mentioned Generators as machines. Though now day’s the entire have an automatic synchronizing facility. But I would advise my readers to learn the manual methods of Synchronization as well for the basic understanding of the process for safe operations.

Parallel operation of Diesel Generators

This post on the Parallel operation of Diesel Generators will explain the simplest method of paralleling the generator sets. In few places, I have mentioned Generators as machines. Though now a day’s the All the Generator panels have an automatic synchronizing facility for the Parallel operation of Diesel Generators. But I would advise my readers to learn the manual methods of Synchronization as well for the basic understanding of the process for safe operations.

What is the parallel operation of generators?

Paralleling generators or operating generators in parallel mode means connecting two Diesel Generators in parallel to increase the power output to supply to grid or end-user.

In most generator applications for Parallel operation of Diesel Generators, multi generators are operating in parallel to supply power to various loads.

A machine previously connected to the system is called a running machine. At the same time, the machine is required to be synchronized to connect, known as an incoming machine. A machine frequency reduces marginally once the active load is applied to it. And an increased frequency assists it to prevent operating as a synchronous motor. A machine is not connected system in standstill condition since it will cause emf in the stator winding of machine and causing short circuit.

Parallel generator theory

A machine is required to be paralleled on bus bars to which other machines are already connected. Following conditions must be fulfilled before preceding the parallel operation.

Conditions for parallel synchronization of generators

Instantaneous voltages of the incoming Generator and the bus bar must be similar.

2. The frequency of the incoming Generator and the bus bar must be identical.

3. The phase of the incoming Generator must coincide with the phase of bus bar voltage.

4. The phase sequence must be similar.

Must match the requirement at above point №1 to 3 during each parallel opera

Necessary operation requirement for paralleling a generator with other generators already running on load

Marine vessels and Industries with heavy power applications are equipped with multi machines with three phases to fulfill the increased output. For two machines to be synchronized, they must satisfy the following requirement.

1. Adjust the incoming voltage of the machine to equal to the bus bar with AVR (Automatic Voltage regulator.)

2. Adjust the speed to match the frequency with the other machine already connected to the bus bar.

3. The paralleling breaker should close as nearly as possible when the above two conditions are met.

How to parallel two Diesel Generators

On Ships and industries, all the present-day control panels are equipped with a facility for auto paralleling. Then, in manual synchronization, the paralleling is carried out with the help of a synchronoscope to close the breaker in time. The following procedure is adopted to perform the paralleling operation

Paralleling 3 Phase Machines Using Synchroscope

1. Start the incoming machine and warm it up. Increase the speed to appropriate the desired operational frequency

2. Monitor the incoming machine’s voltage to match with the bus bar voltage.

3. Ensure the phase sequence of both machines is similar.

4. Carry out the necessary adjustments to accommodate the identical voltage, frequency, and phase sequence.

5. Switch on the synchronoscope and audit the movement of the pointer.

6. Increase or decrease the speed of the machine to stabilize the speed to the desired level.

7. Maintain the speed of the incoming machine to slightly higher than the machine on load for the pointer to move very slowly in a clockwise direction.

8. Engage the breaker just before the pointer reaches to 12’ O clock position. It is the occasion when the incoming machine is in phase with the bus bar.

9. Decide to stop the one machine or run in parallel and take action accordingly.

10. The above action could be completed by decreasing the speed of the running machine while raising the speed of the incoming machine.

11. Switch off the synchroscope.

12. Trip the breaker of the running machine.

Paralleling 3 Phase Machines Using Lamp Method

Another typical method of paralleling the machines is a dark lamp or one dark two bright methods. This method is cheap and alternative to the synchroscope method, which is a costly affair. In the dark lamp method, all three lamps are connected to the same phase. Phases are connected across two phases of the bus bar with a voltmeter, and the terminals of the incoming machine. On the other system of one dark and two bright lamp systems, one lamp is connected to the phase while the other two bright lamps are connected out of phase to the bus bar.

The basic philosophy behind the working of a dark lamp is, when two generators are in parallelism, their net consequence frequency will be zero. In such a case, all three lights will remain dark initially when there is a difference in frequency; the resultant frequency will source the lamp to flicker simultaneously.

If these bulbs don’t flicker simultaneously, then it is indicative of an incorrect phase sequence. In this case, stop the incoming machine and change the terminal location.

The breaker will close during the dark phase of light with a net frequency is close to one.

1. Start the machine and raise the speed to the rated value.
2. Join all three lamps and a voltmeter to the terminals, as shown in the image, by Ensuing two bright and one dark lamp method.
3. Check the voltage of the incoming machine at par with the bus bar. If it is not the same, then raise the voltage until it is at par with terminal voltage.
4. Observe the flickering of the bulb for its clockwise or anticlockwise arrangement.
5. The anticlockwise movement will indicate the slow speed, and the clockwise direction will demonstrate the fast speed concerning the bus bar or the running machine.
6. Reduce the flickering of bulbs nearing zero by adjusting the speed.
7. Now engage the breaker when the bulb connected to the phase is dark while the other two bulbs are bright.
8. Decide to stop the one machine or run in parallel and take action accordingly.
9. The above action could be completed by decreasing the speed of the running machine while raising the speed of the incoming machine.
10. Disconnect the bulb supply and step-down transformer.
11. Trip the breaker of the running machine

Synchronizing single phase Generators

It is possible to synchronize a single-phase generator and connect it in parallel by the dark lamp or bright lamp method of synchronization.

In this case, only two lamps are used for the whole operation. For the dark lamp, method lamps are connected in phase to the terminal and the bus bar. While for the bright lamp method, lights are secured out of phase to each other.

The bright bulb will flicker with alternate bright and dark phases depending on the net conclusive frequency of machines.

When the frequency and voltage of the running machine match with the incoming machine, the bulb will be dark due to the opposite magnitude.

As the three-phase machine engages the breaker in the middle of the dark phase period, the two outputs are in the opposition phase sequence during that point of time. Therefore, if the operation is not carried out properly, machines will not synchronize, leading to a reverse power trip.

Conclusion

in industry, The process of paralleling is to enhance the power output with ease of maintenance and reduced operational cost. A machine can run in parallel by providing proper synchronization and effective load sharing. All the Generator panels have an automatic synchronizing facility. It is exceptional to see backup manual synchronization methods for an emergency.