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How to parallel generators

how to parallel generators

This post on the how to parallel 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. It is better for my readers to learn the manual methods of Synchronization as well for the basic understanding of the process for safe operations.

Generator Operating Modes

  1. Island Operation
  2. Parallel Operation

Island Operation

In Island operation mode, the Captive Diesel Power plant supplies the power to a system not connected to the public distribution system.

In this mode of operation, the Generators control the frequency and voltage in the system. In Island Operation, the captive Diesel Power plant operates at full load from 0.95leading (Under excitation) to 0.81 lagging (Over excitation). Due to this reason, the power plant can be used as a reactive power compensator on both the leading and lagging within limits mentioned above.

Parallel Operation

What is the parallel operation of generators?

Connecting two Diesel generators in parallel to increase the power output to supply to grid or end user is the process of parallelig generators or operating the generators in parallel mode.

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.

If the Generators are operating parallel with the grid, the grid will regulate the frequency and voltage. Generators will follow the fluctuations of voltage and frequency. Generators’ increase or decrease in output doesn’t affect the system frequency or voltage in a plant smaller than the total network size.

In Parallel mode, the generator power plant has the same operating range at full load as in island operation.

Power Sharing In Synchronized Generators ( Load Sharing)-How To Parallel Generators

Load sharing

  1. The equivalent distribution of the Kilowatt and Kilovolt-Ampere Reactive complete load between numerous generating sets in a Synchronized system is described as Load-sharing.

Load sharing is crucial to prevent overloading and instability on the generating sets

Kilowatt (Active Power) Load sharing

  • When Generating sets are running in synchronized mode, the governor of prime mover resolves the corresponding sharing of the entire Kilowatt (Active power) need of the arrangement.
  • Fuel supply to the prime mover is regulated to accomplish the Kilowatt load sharing.
  • The increase of fuel in one prime mover in an arrangement will not result in a speed increase (Frequency), but it will lead to a rise in the ratio of the complete Kilowatt load. But if the Generating set is running on solo mode, increasing fuel will increase the frequency.
  • The decrease of fuel in one prime mover in an arrangement will not result in a speed decrease (Frequency), but it will reduce the ratio of the complete Kilowatt load.
  • The ECS (Electronic Control System) of a generator set (utilizing Prime mover speed control arrangement) regulates and controls the distribution of the complete load (Kilowatt) in ratio to the associated rating of the prime movers on the arrangements generating sets.

Kilovolt-Ampere Reactive (KVAR ) Load sharing

  • When generating sets run in synchronized mode, each machine’s alternator field excitation arrangement regulates the sharing of complete reactive power requirements of the arrangement in an equal ratio.
  • Increasing or decreasing the field excitation system achieves the kVAR load sharing.
  • An increase in field excitation will not lead to a rise in voltage, but it will increase the ratio of the complete kVAR load delivered and a decrease in PF( Power factor).
  • A reduction in field excitation will not lead to a decrease in voltage, but it will reduce the ratio of the complete kVAR load delivered and an increase in PF( Power factor).

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-How To Parallel Generators

how to parallel generators

.1. 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 No. 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 fulfil 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.

how to parallel generators

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

How To Parallel 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. Always keep the flashlight handy before starting the operation. The procedure is to perform the paralleling operation is described below.

Paralleling 3 Phase Machines Using Synchroscope

3 Phase  synchronoscope
  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. The breaker of the running machine tobe tripped.

Paralleling 3 Phase Machines Using Lamp Method (How To Parallel Generators)

 Lamp dark Method

Dark lamp or one dark two bright methods is another typical method of paralleling the machines. 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.

The procedure of synchronization of the machines with two brights and one dark lamp method

two bright and one dark lamp method
  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

How to parallel single phase Generator? (How to Parallel Generators)

Synch. 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.

While the voltage and frequency of incoming machine matches with the operating machine, the opposite magnitude will turn the bulb in black.

  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.

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