The London College

Programme - Higher National Certificate/Diploma in Engineering

Unit Number and Title - Unit 21: Electrical Machines

Assignment Title - Electrical Machines

Unit Learning Outcomes
LO1: Assess the constructional features and applications of transformers.
LO2: Analyse the starting methods and applications of three-phase induction motors and synchronous machines. LO3: Investigate the types of generator available in industry by assessing their practical applications.
LO4: Analyse the operating characteristics of electromagnetic transducers and actuators.

Assignment Brief and Guidance

Scenario:

LO1 ASSESS THE CONSTRUCTIONAL FEATURES AND APPLICATIONS OF TRANSFORMERS.

a. Describe the main core types of transformers and how they operate

b. What are the main applications of transformers

c. Discuss the main connections of three-phase transformers

d. A transformer has 500 turns in the primary windings and 100 turns in the secondary side. The resistances in the primary and secondary sides are 0.3 ? and 0.1 ? respectively and the reactances are 2.0 ? and 0.1 ? respectively.

Find:
1. The equivalent resistance referred to the primary
2. The equivalent reactances referred to the primary
3. The equivalent impedance referred to the primary
4. The phase angle of the impedance
e. A 200 kVA rated transformer has a full-load copper loss of 1.5 kW and an iron loss of 1 kW.
1. Determine the transformer efficiency
i. At full load and 0.85 power factor.
ii. At half full load and 0.85 power factor
2. Determine the maximum efficiency at power factor 0.89

LO2 ANALYSE THE STARTING METHODS AND APPLICATIONS OF THREE-PHASE INDUCTION MOTORS AND SYNCHRONOUS MACHINES.

a. Analyse the operation of induction and synchronous motors and the main applications of these motors.
b. A 400V, 4 Pole, 3 Phase, 50 Hz star connected induction motor has a rotor resistance and reactance/phase = 0.01? and 0.1? respectively and stator resistance and reactance/phase of 0.641? and 1.106 respectively and Xm=26.3. The equivalent circuit is referred to the stator. Determine i) Starting Torque ii) Slip at which maximum torque will occur. iii) Speed at which maximum torque occurs iv) The value of maximum torque v) Full load torque if full load slip is 4%. Assume ratio of stator to rotor turns as 4.
c. Analyse the different methods of starting induction motors and synchronous machines
d. Justify the selection of a motor for a specific industrial application.
e. Critically evaluate the efficiency of a number of available motors and make a recommendation for a specified operational requirement.

LO3 INVESTIGATE THE TYPES OF GENERATOR AVAILABLE IN INDUSTRY BY ASSESSING THEIR PRACTICAL APPLICATIONS.

a. Explain the types and constructions of generators (direct current, alternating current and excitation)
b. Identify a generator for a specific application, considering their characteristics.
c. A 3Φ, 16 pole, star connected salient pole alternator has 144 slots with 10 conductors per slot. The alternator is run at 375 rpm. The terminal voltage of the generator found to be 2.657 kV. Determine the frequency of the induced emf and the flux per pole
d. Justify the application of a specific type of generator.
e. Assess the efficiency of a number of available generators and make a recommendation for a specified operational requirement.

LO4 ANALYSE THE OPERATING CHARACTERISTICS OF ELECTROMAGNETIC TRANSDUCERS AND ACTUATORS.

a. Describe in general terms the parts and operation of a magnetic actuator and transducer
b. Explain fully the different types of transducers ( passive, active and sensors)
c. Explain fully the different types of actuators (solenoid, linear and rotary)
d. The magnetic circuit shown in the figure below has dimensions Ac = Ag= 10 cm2, g =
0.05 cm, lc = 50 cm, and N = 600 turns. Assume the value of the relative permeability, μr = 70,000 for core material. (a) Find the reluctances Rc and Rg. For the condition that the magnetic circuit is operating with Bc = 1.0 T, find (b) the flux and (c) the current i.

e. Justify the selection of suitable transducers for specific industrial applications
f. Analyse the practical application of transducers and actuators in an industrial situation and make recommendations to improve the operating efficiency of the units in use.

Learning Outcomes and Assessment Criteria

LO1 Assess the constructional features and applications of transformers

P1 Examine the types of transformers available.
P2 Discuss suitable applications for available transformers.
P3 Discuss the different methods of connections available for three-phase transformers.

M1 Illustrate the operation of the transformer, considering the equivalent circuit.

D1 Assess the efficiency of a number of available transformers and make a recommendation for an actual operational requirement.

LO2 Analyse the starting methods and applications of the three-phase induction motors and synchronous machines

P4 Analyse the types of electrical motors available, discussing suitable applications.
P5 Analyse the different methods of starting induction motors and synchronous machines.

M2 Justify the selection of a motor for a specific industrial application.

D2 Critically evaluate the efficiency of a number of available motors and make a recommendation for a specified operational requirement.

LO3 Investigate the types of generators available in the industry by assessing their practical application

P6 Explain the types and construction of generators.
P7 Identify a generator for a specific application, considering their characteristics.

M3 Justify the application of a specific type of generator.

D3 Assess the efficiency of a number of available generators and make a recommendation for a specified operational requirement.

LO4 Analyse the operating characteristics of electromagnetic transducers and actuators

P8 Analyse the operation, types and uses of electromotive transducers and actuators, examining features that support their suitability for specific applications.

M4 Justify the selection of suitable transducers for specific industrial applications.

D4 Analyse the practical application of transducers and actuators in an industrial situation and make recommendations to improve the operating efficiency of the units in use.

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