The synchronous generator is connected to an infinite bus. If its excitation is increased

The synchronous generator is connected to an infinite bus. If its excitation is increased

Right Answer is:

Absorb Reactive power

SOLUTION

The synchronous generators connected to the power system are generally over-excited in order to supply reactive power to the inductive power system loads. A synchronous generator operated without a torque input or load, but instead operated solely to supply reactive power is referred to as a synchronous condenser.

Synchronous Generator connected to an infinite bus

An infinite bus is a system that imposes its own voltage and frequency upon any apparatus connected to its terminals. Once connected to a large system (infinite bus), a synchronous generator becomes part of a network comprising hundreds of other generators that deliver power to thousands of loads. It is impossible, therefore, to specify the nature of the load (large or small, resistive or capacitive) connected to the terminals of this particular generator.

Infinite bus -effect of varying the exciting current of synchronous generator

Immediately after we synchronize a generator and connect it to an infinite bus, the induced voltage Eo is equal to, and in phase with, the terminal voltage E of the system. There is no difference of potential across the synchronous reactance and, consequently, the load current I is zero. Although the generator is connected to the system, it delivers no power; it is said to float on the line.

If we increase the excitation the synchronous generator voltage Vo will increase and the synchronous Reactance Xs will experience a difference of potential Vx.

Current (I) will circulate in the circuit

I = (Eo − E)/Xs

Where

E = Terminal voltage

Because the synchronous reactance is inductive, the current lags 90° behind E. The current is therefore 90° behind E, which means that the generator sees the system as if it were an inductive reactance.

Consequently, when we over-excite a synchronous generator, it supplies reactive power to the infinite bus. The reactive power increases as we raise the dc exciting current. Contrary to what we might expect, it is impossible to make a generator deliver active power by raising its excitätion.

If we increase the excitation the synchronous generator voltage Vo will increase and the synchronous Reactance Xs will experience a difference of potential Vx.

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