Question

A 1200 kVA, 11/3.3 kV, 50-Hz, three phase Dyn 11 transformer is subjected to both the open,
and short circuit tests, yielding the following results:
OPEN CIRCUIT TEST SHORT CIRCUIT TEST
Vsupply = 3.3 kV Vsupply = 650 V
Io = 7.3 A Isc = 54.4A
Po = 6.71 kW Psc = 8.89 kW
Determine:
1.1 The no load current per phase, in RECTANGULAR form, referred to the H.V. side.
(5)
1.2 How would you know, without being told, that the short circuit test was probably supplied
on the H.V. side? Support your argument with calculations. (6)
1.3 Was the SCT carried out at rated full load currents? (Note: You must ALWAYS check
this, even if it is not asked!). (1)
1.4 The percentage impedance (or “Impedance Voltage”). (4)
1.5 The full load copper loss, and from this, the %R. (4)
1.6 The equivalent impedance per phase, referred to the l.v. side. (3)
1.7 The efficiency of this transformer under the following conditions:
1.7.1 Full load, at a power factor of 0.9 (2)
1.7.2 40% of full load, at a power factor of 0.75 (3)
1.7.3 The maximum efficiency at a power factor of 0.96 (3)
1.8 The full load terminal voltage on the l.v. side when the transformer load power factor is
0.8 lagging. (5)
1.9 Show how you would connect this transformer according to its designated vector group.
Use Figure 1 to help you. (