Question

In open circuit test for synchronous generator we measured Ea؟

1-صح

2- خطا

Answer 1

Answer:

the alternator is run at rated synchronous speed and the load terminals are kept open. That is, all the loads are disconnected. the field current is set to zero,this condition is called open circuit test condition.

Explanation:

The field current is gradually increase in steps, and the terminal voltage Et is measure at each step, The excitation current may be increased to get 25% more than rated voltage of the alternator. A graph is plotted between the open circuit test voltage Ep and field excitation current If.the characteristic curve so obtain is called open circuit characteristic (O.C.C.). it take the shape of a normal magnetization curve. the extension of linear portion of an O.C.C. is called the air gap line are show in figure.

Short Circuit Test

The armature terminals are shorted through three ammeter.Care should we taken performing this test, and the field current should first decreased to zero before starting the alternator. Each ammeter should have range greater than the full rated value. the alternator run at synchronous speed. then the field current gradually increased in step, and the armature current is measured at each step.

The field current may be increased to get armature current upto 150% of the rated value.The field current If and the average of three ammeter reading at each step is taken.A graph is plotted between the armature current Ia and field current If. The characteristic so obtained is called short-circuit characteristic (SCC). the characteristic is a straight line as shown in figure.