Parallel Operation of Alternators

In this article we will learn about the parallel operation of alternators and their advantages. From this article we will know condition of operation of alternator.The process of  connecting an alternator in parallel with another, then alternator is called synchronizing.

Parallel Operation of Alternators

It is rare to find a 3-phse alternator supplying its own load independently except under test condtions. In practice, a very largenumber or 3-phase alternators operate in parallel because the various power stations are interconnected capacity. For example, the total capacity of the interconnected system may be over 40000 MW while the capacity of the biggest single alternator may be 500 MW. For this reason, the performance of a single alternator is unlikely to affect appreciably the voltage and frequency of the whole system. An alternator connected to such a system is said to be connected to infinite bus bars. The outstanding electrical Characteristics of such bus bars are that they are constant voltage, constant frequency bus bar.

Loads are taped from the infinite bus at various load centers. The alternators may be connected to or disconnected from the infinite bus, depending on the power demand on the system. If an alternator is connected to infinite bus bars, no matter what power is delivered by the incoming lternator, the voltage and frequency of the system remain the same. The operation of connecting an alternator to the infinite busbars,the voltage and frequency of the system remain the same. The operation of connecting an alternator to the infinite busbars is known  as paralleling with the infinite busbars. It may be noted that before an alternator is connected to an infinite busbars, certain conditions must be satisfied. These are some condition  of parallel operation of alternators.

Advantage of parallel operation of Alternators

The various advantage of running alternator in parallel

1. Better continuity of power supply-can be maintained running a single unit.

2. It gives maximum efficiency , because of running at full load

3. Repairing of a unit  is more convenient and economical

4. The additional unit can be installed and when required with the increase  of load

5. The cost of stand by unit is less.

The following are the advantages of operating alternators in parallel:

• Continuity of service

The continuity of service is one of the important reqirements of any electrical apparatus. If one alternator fails,the continuity of supply can be maintained through the other healthy units. Ths will ensure uninterrupted supply to consumers.

• Efficiency of Alternator

The load on the power system varies during the whole day; being minimum during die late night hours. Since alternators operate most efficiently when delivering full-load units cn be added or put off depending upon the load requirement. This permits the efficient operation of power system.

• Maintenance and Repair

It is often desirable to carry out routine maintenance and repair of one or more units. For this purpose, the desired unit/can be shut down and the continuity of supply is maintained through the other units. It is some advantage of parallel operation of alternators.

Conditions of paralleling Alternator with Infinite Bus bars

The proper method of connecting an alternator an alternator to the infinite busbars is called synchronizing.  A stationary alternator must not be connected to live busbars. It is because the induced EMF is zero  at standstill and a short-circuit will result. In order to connect an alternator safely to the infinite busbars. The following conditions are met :

1. The terminal voltage (RMS Value) of the incoming alternator must be the same as busbars voltage.
2. The frequency of the generated voltage of the incoming alternator must be equal to the bus bars frequency.
3. The phase of the incoming alternator voltage must be identical with the phase of the bus bars voltage. In other words, the two voltages must be in phase with each other.
4. The phase sequence of the voltage of the incoming alternator should be the same as that of the busbars.The magnitude of the voltage of the incoming alternator can be adjusted by changing its field excitation. The frequency of the incoming alternator can be changed by adjusting the speed of the prime mover driving the alternator. Condition (1) is indicated by a voltmeter. Conditions (2) and (3) are indicated by synchronizing lamps or a synchronoscpe. The condition (4) is indicated by a phase sequence indicator.

Condition for parallel operation of Alternators

1. The voltage of both the alternators must be same. the incoming voltage of the alternator to be synchronized and the running voltage of the bus bar must be same.

2. The frequency must be same

3. The phase sequence must be same

Method of synchronizing or parallel operation of alternator

The following are the method of the parallel operation

1. Dark lamp method

2. Bright lamp method

3. Dark and Bright lamp method

4. synchronoscope method

Equipment required for parallel operation of Alternator

1. Double range voltmeter

2. Double range frequency meter

3. Synchroscope

4. Lamps for Dark and bright lamp method

Load sharing of Alternator

1. By changing the excitation  of current

2. By increasing the steam supply of one Alternator

Why Alternator paralleling ?

1. At the junction point voltage must be same even though not the same at the Alternator

2. At the junction point the phase sequence for three phase must be same

3. The incoming machine must be in phase at the moment of parallel point.

4.  At the paralleling point the line frequencies must be identical. In vast majority of cases,means the same frequency changing is not economic.

5. The prime-movers must have relatively similar and dropping speed-load characteristics.

Hence these are parallel operation of alternators and their advantages. From above article we have studied about condition of parallel operation of alternators.