Correct Answer - Option 3 : 5

__Synchronous Impedance of alternator:__

Open Circuit Test:

- In the open-circuit test for determining the synchronous impedance, the alternator is running at the rated synchronous speed, and the load terminals are kept open.
- This means that the loads are disconnected, and the field current is set to zero.

Short Circuit Test:

- The field current should first be decreased to zero before starting the alternator.
- Each ammeter should have a range greater than the rated full load value.
- The alternator is then run at synchronous speed.
- Same as in an open circuit test that the field current is increased gradually in steps and the armature current is measured at each step.
- The field current is increased to get armature currents up to 150% of the rated value.

The synchronous impedance of the alternator is given by

ZS = VOC / ISC

Where,

VOC is the open-circuit voltage per phase

ISC is the short circuit current

__Calculation:__

Given,

V_{OC}(Line) = 1730 V

⇒ V_{OC} (Phase) = (V_{OC}(line) / √3) = (1730 / √3) = **998.82 V**

ISC = 200 A

ZS = VOC / ISC

**ZS = 998.82 / 200 = 4.99 ≈ 5 Ω **