Electrical Machines

A 440 V, 25 hp, 4-pole, Y-connected three-phase wound-rotor induction motor has the following circuit parameters: R1 = 0.46 02, R2 = 0.33 0, x1 = 1.10, X2 = 0.46 02, and Xm = 250. (stator referred) Rotational losses (including core loss) = 500 W (constant). (1) At a slip of 0.04, use the complete equivalent circuit model to calculate: (a) Motor speed (b) Stator current (c) Input power factor (d) Efficiency (2) Use the simplified Thevenin's equivalent circuit to calculate: (a) The developed maximum torque (b) The speed at which the maximum torque is developed. (c) The starting current (d) The starting torque (3) If an external resistance equal to the rotor resistance is added to the rotor circuit, then calculate: (a) The developed maximum torque (b) The speed at which the maximum torque is developed. (c) The starting current (d) The starting torque (4) If the supply frequency is reduced to 50 %, calculate the stator current, the developed air-gap torque, and the maximum torque at a slip Of 0.04. (5) If the supply frequency is reduced to 50 %, calculate the stator current, the developed air-gap torque, and the maximum torque at a slip of 0.04. (6) If the terminal voltage and supply frequency are simultaneously reduced to 50%, calculate the stator current, the developed air-gap torque, and the maximum torque at a slip of 0.04.

A 13 kV, 40-MVA, 0.8-power-factor-lagging, 60-Hz, 8-poles Y-connected synchronous generator has a synchronous reactance of 2.5 2 and an armature resistance of 0.2 2. At 60 Hz, its friction and windage losses are 1 MW, and its core losses are 1.5 MW. The field circuit has a de voltage of 120 V, and the maximum field current is 10 A. The current of the field circuit is adjustable over the range from 0 to 10 A. 1. Draw the open circuit characteristics [OCC] for this generator. Assume that this characteristics is represented by the following relation: 2. Draw the short circuit characteristics [SCC] for this generator. Assume that this characteristics is represented by the following relation: I(If) = 35If, 3. Draw the synchronous impedance (Xs) of this generator as a function of the armature current. 4. Draw the per phase equivalent circuit of the 3-Phase synchronous generator. 5. Draw the terminal voltage (V₁) versus the armature current (1) of this generator up to the rated load current for the following cases [One graph]: A. Rated MVA with 0.8-PF-lagging load. B.Rated MVA with 0.8-PF-leading load. C.Rated MVA with unity load. 6. Draw the voltage regulation (VR) versus the armature current (I) of this generator up to the rated load current for the following cases [One graph]: A. Rated MVA with 0.8-PF-lagging load. B. Rated MVA with 0.8-PF-leading load. C. Rated MVA with unity load. 7. Draw the losses of this synchronous generator as a function of the armature current (IA). 8. Draw the efficiency of the synchronous generator (n) as a function of the load current (IA) up to the rated current. 9. Draw the developed torque of this synchronous generator as a function of armature current (IA). 10.Draw the rotor angle (8) of this synchronous generator as a function of armature current (I).

a. Provide a screenshot of your Simulink Block Diagram and controller. Provide your PID gains. c. Provide a screenshot of your output (using a scope). 1 Provide a screenshot of your control input (using a scope). Provide your overshoot in percentage and degrees. f. Provide your 1% settling time. Comment on the above process. What was easy and what was difficult? B(s)-For a system with the transfer function given by q(s)/v(s) = 50/2s+20sdesign a PID controller252+20sto rotate the system to a desired set point of 8 = 150°. Due to system constraints, you are only allowed to have an overshoot of 4% and need to have a 1% settling time of 0.5seconds. You will likely have to tune the PID gains of the controller to make this happen.

Open- and short-circuit tests of a single-phase transformer yielded the following data: Find the equivalent cirçuit parameters.

Draw the phasor diagram of a synchronous motor operating at leading power factor. What can you infer for the motor characteristic looking at the drawn phasor? Answer in not more than 2 sentence.

What are the advantages and disadvantages of AC and DC motors?

An 'iron ring has a cross sectional area of 5 cm? and a mean diameter of 30 cm. An air gap of 0.5 mm is cut across the section of the ring. The magneto-motive force (mmf) produced by the winding on the ring is 500A-turns and it is found that the flux produced in the ring is 0.3 mWb. Find the relative permeability of the iron.

Three phase, 480V 40 Hz, 6 pole induction motor R_{1}=R_{2}^{\prime}=0.1 \Omega, X_{1}+X_{2}^{\prime}=X_{e q}=0.5 \Omega Full load slip is 3% η = 90% Starting current (ignore magnetizing current) b. Starting torque c. Maximum torque d. Rotor resistance to be added to the rotor circuit to reduce the starting current by 50% e. Starting torque at case d. f. Rotor resistance to be added to the rotor circuit to increase the starting torque tomaximum g. Starting current at f.

To protect a house from electrical hazards, all household circuits should have a household electrical protecting circuit: mention one of them and explain how does it work?

3.15. The three-phase power and line-line ratings of the electric power system shown in Figure 3.34 are given below. (a) Draw an impedance diagram showing all impedances in per-unit on a 100-MVA base. Choose 20 kV as the voltage base for generator. (b) The motor is drawing 45 MVA, 0.80 power factor lagging at a line-to-line terminal voltage of 18 kV. Determine the terminal voltage and the internal emf of the generator in per-unit and in kV.