Electrical Engineering Answers

A 11 kV, 50 Hz, star connected cylindrical rotor alternator gave the following data on open circuit:
If in Amp 0 10 15 20 31 39 50 55
Ef in kV 0 5.00 7.50 9.00 11.00 12.00 12.80 13.40
An excitation of 20 A was required to circulate a full load current of 160 A on short-circuit. For zeropower factor test, an excitation current 66 A was required to circulate 1.25 times the full load current at 11 kV. Estimate the voltage regulation at full load 0.8 p.f lagging by z.p.f method. Neglect armature resistance.

A 415 star-connected, 3-phase,4-pole synchronous generator has 36 slots carrying double layer 3-phase windings formed through uniformly distributed coils each short-pitched by one slot. The diameter at the air gap is 20 cm and the effective axial length is 60 cm. The rotor driven at 1500 rpm is excited to result in a sinusoidally varying air gap flux density distribution in space with a peak value of 0.5 T.Calculate the number of series turns per phase to generate rated no-load voltage.

A 3-phase salient pole, synchronous motor , with Xd= 1 p.u and Xq=0.8 p.u, is connected
to an infinite bus-bar of rated voltage 1.0 p.u. Calculate the percentage of rated output
that the motor can deliver without losing synchronism with zero field current .Calculate
the p.u armature current and p.f under these conditions.

A salient –pole synchronous generator has the following per-unit parameters; Xd = 1.00, Xq=
0.60, ra= 0.02Ω. If the generator is delivering rated KVA at rated voltage and at 0.8 p.f leading,
compute the power angle and the excitation e.m.f. Draw the phasor diagram also.

A 3-phase, 30 kW, 433 V, 50 Hz, star-connected, salient-pole synchronous motor is operating at
0.8 p.f leading and taking 40A from mains, If the direct and quadrature- axis reactances are 5Ω
and 3 Ω respectively, calculate the maximum power the motor can develop if its excitation is
maintained constant.

A three-phase, 415 V load takes a line current of 800 A from a 3300/415V delta – star transformer. The 3300V system is supplied from an 11000/3300V star – star transformer. Draw the circuit diagram and, assuming no losses, find both line and phase values of voltages and currents in each part of the circuit. What will be the turns ratios of both transformers?

A three-phase, 415 V load takes a line current of 800 A from a 3300/415V delta – star transformer. The 3300V system is supplied from an 11000/3300V star – star transformer. Draw the circuit diagram and, assuming no losses, find both line and phase values of voltages and currents in each part of the circuit. What will be the turns ratios of both transformers?

1. A single-phase ac voltage regulator supplies power to a purely resistive load. The input
voltage is V and the load resistance is R.
(a) If phase-angle control is used and the delay angle is α, obtain an expression for
(i) the rms value of the output voltage [6 marks]
(ii) the rms value of the SCR current [3 marks]
(iii) the average value of the SCR current [4 mark

A three-phase, 415V load takes a line current of 800A from a 3300/415V delta-star transformer. The 3300V system is supplied from an 11000/3300V star-star transformer. Draw the circuit diagram and, assuming no losses, find both line and phase values of voltages and currents in each part of the circuit. What will be the turns ratios of both transformers?

A three-phase, 415 V load takes a line current of 800 A from a 3300/415V delta – star transformer. The 3300V system is supplied from an 11000/3300V star – star transformer. Draw the circuit diagram and, assuming no losses, find both line and phase values of voltages and currents in each part of the circuit. What will be the turns ratios of both transformers?