-SQA-SCOTTISH QUALIFICATIONS AUTHORITY HIGHER NATIONAL UNIT SPECIFICATION GENERAL INFORMATION PRINCIPLES OF TRANSFORMERS AND MOTORS

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1 -SQA-SCOTTISH QUALIFICATIONS AUTHORITY HIGHER NATIONAL UNIT SPECIFICATION GENERAL INFORMATION -Unit Number Superclass- -Title- XJ PRINCIPLES OF TRANSFORMERS AND MOTORS DESCRIPTION- GENERAL COMPETENCE FOR UNIT: Explaining the basic principles of operation and performance of single phase transformers, d.c. motors and threephase induction motors. OUTCOMES 1. explain the basic principles of operation of a single-phase transformer;. evaluate the performance of a single-phase transformer; 3. explain the basic principles of operation of d.c. motors and three-phase induction motors. CREDIT VALUE: 0.5 HN Credit ACCESS STATEMENT: Access to this unit is at the discretion of the centre. However, it would be beneficial if the candidate had a knowledge of basic electromagnetism and a.c. theory, both single and three-phase. This may be evidenced by possession of NC Module: Electrical Fundamentals Single Phase A.C. or similar qualifications or experience For further information contact: Committee and Administration Unit, SQA, Hanover House, 4 Douglas Street, Glasgow G 7NQ. Additional copies of this unit may be purchased from SQA (Sales and Despatch section). At the time of publication, the cost is 1.50 (minimum order 5.00).

2 HIGHER NATIONAL UNIT SPECIFICATION STATEMENT OF STANDARDS UNIT NUMBER: UNIT TITLE: PRINCIPLES OF TRANSFORMERS AND MOTORS Acceptable performance in this unit will be the satisfactory achievement of the standards set out in this part of the specification. All sections of the statement of standards are mandatory and cannot be altered without reference to SQA. OUTCOME 1. EXPLAIN THE BASIC PRINCIPLES OF OPERATION OF A SINGLE-PHASE TRANSFORMER PERFORMANCE CRITERIA (a) (b) (c) (d) A basic transformer is described clearly as consisting of a laminated iron core and primary and secondary windings. The principles of operation of an ideal transformer on no-load are explained clearly with reference to Faraday s Law. Relationships between primary and secondary voltages and currents and turns ratio are stated correctly. The principles of operation on-load, neglecting losses and regulation, are explained clearly in terms of magnetomotive force (m.m.f.) balance. RANGE STATEMENT The range for this outcome is fully expressed in the performance criteria. EVIDENCE REQUIREMENTS Written and/or graphical and/or oral evidence, that the candidate can explain the basic principles of operation of a single-phase transformer, as specified in PCs (a)-(d).

3 OUTCOME. EVALUATE THE PERFORMANCE OF A SINGLE-PHASE TRANSFORMER PERFORMANCE CRITERIA (a) (b) (c) Calculations using the transformer electromotive force (e.m.f.) equation are correct. Calculations involving turns ratio and primary and secondary voltages and currents are correct. Primary and secondary voltages are measured and recorded accurately for a given transformer. RANGE STATEMENT The range for this outcome is fully expressed in the performance criteria. EVIDENCE REQUIREMENTS Written evidence consisting of two calculations for performance criterion (a) and two calculations for performance criterion (b) respectively. For each performance criterion the steps in the solution of each calculation must be correct and clear, but it is only necessary for one problem to be 100% correct. Written and graphical evidence in the form of a clear and concise report to satisfy performance criterion (c). OUTCOME 3. EXPLAIN THE BASIC PRINCIPLES OF OPERATION OF D.C. MOTORS AND THREE-PHASE INDUCTION MOTORS PERFORMANCE CRITERIA (a) (b) (c) The basic constructional features of the motors are described accurately. The basic principles of operation of the motors are explained accurately. The torque-speed characteristics of the motors are measured and recorded accurately in graphical form. RANGE STATEMENT Motors: d.c.; three-phase induction. 3

4 EVIDENCE REQUIREMENTS Written/graphical and/or oral evidence to show that the candidate can meet the requirements of performance criteria (a) and (b) for one type of d.c. motor and one type of three-phase induction motor. Written/graphical evidence to show that the candidate can meet the requirements of pc(c) for one type of d.c. motor and one type of three phase inductor motor. MERIT To gain a pass in this unit, a candidate must meet the standards set out in the outcomes, performance criteria, range statements and evidence requirements. To achieve a merit in this unit, a candidate must demonstrate a superior or more sophisticated level of performance. This may be demonstrated by: (i) (ii) obtaining 100% accuracy in the solution to problems required as evidence for outcome performance criteria (a) and (b). carry out the practical work for outcome performance criterion (c) and outcome 3 performance criterion (c) with little or no supervision and produce a clear, logical report presentation with specific reference to measuring unknown parameters in an industrial situation ASSESSMENT In order to achieve this unit, candidates are required to present sufficient evidence that they have met all the performance criteria for each outcome within the range specified. Details of these requirements are given for each outcome. The assessment instruments used should follow the general guidance offered by the SQA assessment model and an integrative approach to assessment is encouraged. (See references at the end of support notes). Accurate records should be made of the assessment instruments used showing how evidence is generated for each outcome and giving marking schemes and/or checklists, etc. Records of candidates achievements should be kept. These records will be available for external verification. SPECIAL NEEDS Proposals to modify outcomes, range statements or agreed assessment arrangements should be discussed in the first place with the external verifier. 4

5 Copyright SQA 1997 Please note that this publication may be reproduced in whole or in part for educational purposes provided that: (i) (ii) no profit is derived from the reproduction; if reproduced in part, the source is acknowledged. 5

6 HIGHER NATIONAL UNIT SPECIFICATION SUPPORT NOTES UNIT NUMBER: UNIT TITLE: PRINCIPLES OF TRANSFORMERS AND MOTORS SUPPORT NOTES: This part of the unit specification is offered as guidance. None of the sections of the support notes is mandatory. NOTIONAL DESIGN LENGTH: SQA allocates a notional design length to a unit on the basis of time estimated for achievement of the stated standards by a candidate whose starting point is as described in the access statement. The notional design length for this unit is 0 hours. The use of notional design length for programme design and timetabling is advisory only. PURPOSE The purpose of this unit is to give candidates an introduction to the principles of operation and performance of single phase transformers, d.c. motors and three-phase induction motors. It is aimed at those candidates with no previous knowledge of the subject matter. The unit is intended primarily for those candidates from other engineering disciplines who do not require an in-depth treatment of electrical plant subjects. CONTENT/CONTEXT Corresponding to outcomes: Outcome 1 Faraday s Law e = - N d φ dt Relationship between current, voltage and turns; V V 1 N1 = = N I I 1 Principle of m.m.f. balance; Outcome I 1 N 1 = I N Transformer e.m.f. equation; E = 4.44 NfΦ m 6

7 Outcome 3 A simple, descriptive treatment of the principles of operation is intended dealing mainly with the production of torque and the characteristic torque speed curves of the different types of motor. Shunt and series d.c. motors and squirrel cage and wound rotor three-phase induction motors should be covered. APPROACHES TO GENERATING EVIDENCE In addition to more formal teaching and tutorial work candidates should be given the opportunity to examine transformers and motors. This is particularly valuable if the motors can be dismantled. Practical work should be undertaken to demonstrate the operation of transformers and motors and allow performance to be measured. It should be noted that a motor test bed is required. ASSESSMENT PROCEDURES Written tests may be used to assess those performance criteria involving explanations, descriptions and calculations. Practical exercises in the laboratory will be needed to assess performance criterion (c) of outcome and performance criterion (c) of outcome 3. PROGRESSION This unit may lead on to any of the following HN Units: Power Transformers Three Phase Induction Motors D.C. Motors Brushless DC and Stepper Motors REFERENCES 1. Guide to unit writing.. For a fuller discussion on assessment issues, please refer to SQA s Guide to Assessment. 3. Information for centres on SQA s operating procedures is contained in SQA s Guide to Procedures. 4. For details of other SQA publications, please consult SQA s publications list. Copyright SQA 1997 Please note that this publication may be reproduced in whole or in part for educational purposes provided that: (i) (ii) no profit is derived from the reproduction; if reproduced in part, the source is acknowledged. 7