A 240 V, 60 Hz, Delta connected, 870 r.p.m., Eight poles, Three-Phase Induction Motor has the following per phase parameters: R1 = 0.07, R2 = 0.05, X1 = X2 = 0.2, Xm 6.5, Draw the approximate equivalent circuit and determine the following: I. Starting Torque I. Maximum Torque II. Rated Torque

The resistance and reactance per phase of the rotor of a 3-phase induction motor are 0.6 ohm and 5 ohms respectively. The induction motor has a star-connected rotor and when the stator is connected to a supply of normal voltage, the induced e.m.f. between the slip rings at standstill is 80 V. Calculate the current in each phase and the power factor at starting when (i) the slip-rings are shorted, (ii) slip-rings are connected to a star-connected resistance of 4 ohm per phase.

a)the figure below shows the per-phase equivalent circuit of a two - pole three- phase induction motor operating at 50 Hz . The voltage (E1) across the magnetizing inductance is 210 v , and the slip (s) is 0.05 . What is the developed torque produced by the motor ? b) A 4 poles , 50Hz , Y-connected three phase induction motor has the per phase equivalent circuit parameters of (R1 =R2=0.12 , X1=X2=0.6 , Xm =12 ) ohm and I2 =20 (0 . Use exact equivalent circuit to determine the following at rated slip of 0.03 : I. Stator current II. Magnetizing current III. Power factor IV. Developed torque C) What is the physical meaning for each of the following induction motor parameters : R1 , R2 , Rc , X1 , X2 , Xm d) What is synchronous watt

A compound generator has a lap-wound armature with 200 slots and four turns per coil. It is rotating with a speed of 80 rpm and flux per pole is 100mWb. The armature resistance is 12 and shunt field resistance is 2002. The series field resistance is 22. Determine: (i) Terminal voltage (ii) If a load is connected to the terminals which starts pulling a load current such that the flux that is produced by the series field is added into the shunt field to keep the new induced voltage to be the same as the induced voltage at no load, what will be the new terminal voltage if the shunt field current is dropped to 90% of the shunt field current at no load? (iii) Power dissipated in the load Draw equivalent circuits

Explain the conditions for parallel operation of synchronous generators. A three phase, wye connected, synchronous generator is rated 150 MW, 0.85 lagging power factor, 12.6 kV, 60 Hz, and 1800 rpm. Each winding has an armature resistance of 0.05Q and a synchronous reactance of 0.6Q. Draw the phasor diagram with values, show torque angle and determine the induced voltage for the condition of rated load.

4. Chorded windings are used in induction motors because theyA. have better mechanical characteristics.B. are made with less wire and are therefore cheaper.C. are made with smaller wire and are therefore cheaper.

Problem #2: A 3-phase induction motor has a star-connected rotor. The rotor emf (between slip rings) at standstill is 50 V. The rotor resistance and standstill reactance are 0.5 and 3 2, respectively. Find rotor current per phase (a) at starting with the slip rings short circuited (b) at starting with a star-connected rheostat of resistance 6 ohms per phase connected across the slip rings. (c) if the motor is running at a slip of 4%.

With the aid of diagrams describe the basic topology of a wound field 3 phase synchronous generator and outline the relationship between the excitation voltage and rotor current. Q2 (a) (b) Outline with the aid of a suitable diagram the necessary power conversion stages required to interface a small permanent magnet (PM) generator to a stand alone DC system. A star connected 3 phase wound field synchronous generator with a synchronous reactance of 20 N is connected to a 6.6 kV (phase voltage) grid and supplies 1.5 MW at 0.95 lagging power factor at its terminals. Calculate the phase current and resultant voltage across the synchronous reactance (Vxs), and from a scaled phasor diagram graphically determine the required excitation voltage (Eph) and load angle (8). (c) The load is now increased to 3 MW with the Excitation Voltage kept constant. Using the phasor diagram drawn in part (c) graphically determine the resultant phase current, power factor and load angle. (d)

The maximum torque of 3-phase induction motor occurs at a slip of 11 percent. The motor has anequivalent secondary resistance of 0.08 ohm/phase. Calculate the equivalent load resistance RL theequivalent load voltage VL and the current at this slip if the gross power output is 8 kW.

3.An induction motor has a rotor resistance and reactance at standstill of 0.1 ohm and 3.5 ohm respectively. At standstill the voltage induced to the rotor is 60volts per phase. If the slip is 5%, determine the rotor current