GATE Electrical Engineering (EE) 2020 Solved Paper

Question : 49 of 65

Marks: +1, -0

The figure below shows the per-phase open circuit characteristics (measured in A) of a 14 kVA, 400 V, 50 Hz, 4-pole, 3 -phase, delta connected alternator, driven at 1500 rpm. The field current, if is measured in A. Readings taken are marked as respective

(x, y)

coordinates in the figure. Ratio of the unsaturated and saturated synchronous impedances

(Z_{s}(unsat){/}Z_{s}(sat))

of the alternator is closest to :

$2.025$
$1.000$
$2.000$
$2.100$

Validate

Solution:

Z_{s}(

Sat

)=\;{I_{o c}}/{I_{s c}}

- Extend Seg OAB to Point C.
Coordinates of

{C}(8,810)

- Extend OE to

{F}

Coordinates of

{F}(8,20)

Now,

Z_{s}

(unsat)

=\;{G C}/{\;\text " GF "\;}=\;{810}/{20}

Z_{s}

(sat)

=\;{G D}/{\;\text " GF "\;}=\;{400}/{20}

\;{Z_{s} \;\text " (unsat) "\;}/{Z_{s} \;\text " (sat) "\;}=\;{810}/{400}=2.025

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