Electric Machinery Principles - Help

Thread Starter


Joined Jul 22, 2008
(1) A three phase 220 V, 60 Hz induction motor runs at 1140 rpm.
a) Determine the number of poles P,
b) the slip s,
c) the frequency of the rotor current fr.
a) the shaft torque if the motor is rated at 10-hp

(2) A three phase, three-wire, 208 volt system is connected to a balanced three-phase load. The
load is Y-connected. The line currents IA, IB, and IC are in phase with the line-to-line voltages VBC, VCA,
and VAB, respectively. The phase to phase voltages are referenced as follows:
VBC = 208∠0°V;VCA = 208∠ −120°V;VAB = 208∠120°V .
If the line current is measured as 10 A, what is the per-phase impedance of the load?

(3) An autotransformer is used to connect a 13.2 kV distribution line to a 13.8 kV distribution
line. It must be capable of handling 2000 kVA. There are three phases connected Y-Y with the neutrals
solidly grounded.
a) What must the NC/NSE turn ratio be to accomplish this connection?
b) How much apparent power must the windings of each autotransformer handle?
c) If one of the autotransformers were connected as an ordinary transformer how would the ratings