Question 1:

A three-phase 225kV:24kV, 60 Hz, transformer with Δ-Δ connection is supplying a load of 24kV, 325MVA, with 0.93 PF (lagging). The transformer impedance is neglected but the feeder to the transformer has an impedance of 0.11+j2.2 Ω per each line connected to its high voltage terminal. Find the following:

a) The input current from the feeder
b) Line-to-line voltage applied to the feeder.
c) The load current on the secondary side of the transformer
d) The transformer winding currents (primary and secondary)

Question 2:

An elementary machine with a smooth air gap has the following flux linkages on its stator and rotor:

λ_s = L_ss·i_s + L_sr·cos?(poles⁄2·θ_m )·i_r

λ_r = L_rr·i_r + L_sr·cos? (poles⁄2·θ_m )·i_s

Find expressions for the coenergy, W'_fld and the torque, T in terms of

L_ss, L_rr, L_sr, poles, θ_m, i_s and i_r

Question 3:

An 8 pole, 400Hz, three-phase synchronous generator has rotor radius of 0.15m, a length of 0.3 m and an air-gap length of 1.5 mm. The field winding has 1000 turns and a winding factor of 0.95 If the stator winding factor is assumed to be 0.93 and the stator is wye-connected, what would be the turns per phase required to achieve 460V LL, keeping the peak air-gap flux density below 1 T (round to the nearest turn)?What is the field current?

Question 4:
 
A 60Hz, three-phase wye-connected synchronous generator has the following ratings:

V(LL_Rated) = 460 V rms

VA_Rated = 150kVA

V_Base = 266 V rms

I_Base = 188 A rms

Open circuit and short circuit tests are performed and the Short Circuit Ratio, SCR, is found to be

SCR=1.1

Assume that the stator resistance is negligible.

What is the base impedance?

What is the synchronous reactance, X_s in ohms?

If the generator is feeding a load of 120kVA with a power factor of 0.9 lagging, what is the magnitude and phase of I_a and E_af?

Draw the phasor diagram either using per unit values