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15858 Demonstrate knowledge of ac motors

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15858 Demonstrate knowledge of ac motors

NZQA registered unit standard 15858 version 4

     Page 1 of 6

Title Demonstrate knowledge of a.c. motors

    Level 4 Credits 7

    Purpose This unit standard covers the principles, construction,

    calculations, and measurement of single-phase and three-

    phase alternating current (a.c.) motors. It is intended for use in

    the training of electricians and related trades.

    People credited with this unit standard are able to:

     demonstrate knowledge of single-phase motors;

     demonstrate knowledge of single-phase multi-speed

    motors;

     compare characteristics of single-phase motors;

     demonstrate knowledge of three-phase induction motors;

     demonstrate knowledge of the factors that affect the

    performance of three-phase induction motors;

     perform a.c. motor calculations and verify by

    measurement;

     reverse direction of rotation of induction motors; and

     diagnose faults in electric motors.

Classification Electrical Engineering > Electrical Machines

Available grade Achieved

Explanatory notes

    1 This unit standard has been developed for learning and assessment off-job.

2 Definitions

    Industry practice those practices that competent practitioners within the industry

    recognise as current industry best practice.

    Specifications machine specifications, maintenance instructions, or bearing

    manufacturers’ recommendations relating to removal, cleaning, testing, and fitting of

    bearings and seals, and the types of lubricants to be used.

3 Assessment

    a Candidates shall be supplied with formulae involving more than three quantities.

    b Use of a calculator during assessment is permitted.

    c Candidates are expected to express calculated values in the relevant Systeme

    Internationale (SI) units, including multiples and sub-multiples (pico, nano, micro,

    milli, kilo, mega, etc) and be able to convert between them.

ElectroTechnology Industry Training Organisation ; New Zealand Qualifications Authority 2012

    SSB Code 100401

NZQA registered unit standard 15858 version 4

     Page 2 of 6

Outcomes and evidence requirements

Outcome 1

Demonstrate knowledge of single-phase motors.

    Range motors universal, shaded-pole, standard split-phase induction, capacitor-start,

    permanently-split capacitor, capacitor start and run.

Evidence requirements

    1.1 Construction is described and all components are identified with the aid of a

    diagram or from physical examples.

    Range components casing, end shields, armature, shaft, bearings,

    mounting plate, commutator, field windings, field poles, centrifugal

    switch, capacitor, start and run windings, integrated over-

    temperature protection (microtherm).

    1.2 Operating principles are described in terms of starting, production of rotating

    magnetic field, and production of torque.

1.3 Speed control methods, where achievable, are described.

    1.4 Method of reversal of rotation is described with the aid of a diagram.

    1.5 A typical application for each type of motor is stated with reasons for the

    suitability of the choice.

    1.6 Types of motor enclosures are identified and the features of each stated.

    Range screen protected, drip-proof, totally enclosed, flame-proof.

Outcome 2

Demonstrate knowledge of single-phase multi-speed motors.

Evidence requirements

    2.1 Multi-speed motors are described with the aid of circuit diagrams with reference

    to principles of operation, winding connections, and speed change methods.

    Range tapped-field universal motor, two-speed split-phase motor.

    2.2 A typical multi-speed motor application is stated with reasons for the suitability

    of the choice.

ElectroTechnology Industry Training Organisation ; New Zealand Qualifications Authority 2012

    SSB Code 100401

NZQA registered unit standard 15858 version 4

     Page 3 of 6

Outcome 3

Compare characteristics of single-phase motors.

    Range motors universal, standard split-phase induction, capacitor-start, permanently-

    split capacitor, capacitor start and run, shaded pole.

Evidence requirements

    3.1 Typical speed versus torque curve is sketched for each motor.

3.2 Single-phase motor properties are compared.

    Range typical properties power, speed, power to mass ratio, starting

    torque, starting current, power factor, efficiency, method of

    reversal, method of starting, starts per hour, radio frequency

    interference, complexity, construction cost. Evidence of five

    properties is required.

    3.3 Electronic speed control methods are described for each motor.

Outcome 4

Demonstrate knowledge of three-phase induction motors.

Evidence requirements

    4.1 Construction of three-phase induction motors is described with the aid of

    diagrams and reference to components.

    Range components casing, end shields, shaft, bearings, mounting, rotor,

    stator, yoke, core, winding, integrated over-temperature protection

    (microtherm) and thermistors.

    4.2 Operating principles of three-phase induction motors are explained in terms of

    the action of the rotating magnetic fields, the interactions of stator and rotor

    fluxes, and methods of starting.

    4.3 Method of reversal of rotation is described with the aid of a diagram.

    4.4 Speed versus torque curves are sketched, and labelled showing starting torque,

    running torque, rated torque, pull-out speed, and rated speed.

    Range motors squirrel cage, wound rotor with slip-rings, double cage

    rotor.

    4.5 A typical application is stated with reasons for the suitability of the choice.

    Range motors squirrel cage, wound rotor with slip-rings, double cage

    rotor.

ElectroTechnology Industry Training Organisation ; New Zealand Qualifications Authority 2012

    SSB Code 100401

NZQA registered unit standard 15858 version 4

     Page 4 of 6

Outcome 5

    Demonstrate knowledge of the factors that affect the performance of three-phase induction motors.

Evidence requirements

    5.1 The effects of reduced supply voltage on a three-phase induction motor are

    described in terms of reduced torque and speed, increased current, and risk of

    over heating.

    5.2 The effect of increasing load on efficiency and power factor is described in

    terms of increased motor current and reduced cooling.

    5.3 The effect of the loss of one phase is stated for star and delta connected motors.

    5.4 The effect of a reversed winding on the operation of a three-phase induction

    motor is stated, and two methods of rectification are explained.

5.5 The effect of multiple starts is explained.

5.6 The effects of voltage surges are explained.

    Range effects may include but are not limited to harmonics, lightening

    strikes, multi-control systems.

Outcome 6

Perform a.c. motor calculations and verify by measurement.

    Range calculations run current, start current, synchronous speed, rotor speed, slip

    speed, input power, output power, efficiency;

     motors single-phase induction, capacitor-start split-phase, three-phase cage,

    three-phase slip-ring.

Evidence requirements

    6.1 Calculations are made in accordance with industry practice.

6.2 Values are measured in accordance with industry practice.

    6.3 Measured and calculated values are compared and variations explained in

    terms of load variations, instrument tolerance, and measurement error.

Outcome 7

Reverse direction of rotation of induction motors.

Range single-phase, three-phase.

Evidence requirements

ElectroTechnology Industry Training Organisation ; New Zealand Qualifications Authority 2012

    SSB Code 100401

NZQA registered unit standard 15858 version 4

     Page 5 of 6

    7.1 Motor is connected to mains and the direction of rotation is reversed by means

    of a reversing switch.

    7.2 Motor is connected to mains and the direction of rotation is reversed by means

    of contactors.

Outcome 8

Diagnose faults in electric motors.

Range motor types single-phase, three-phase.

     Evidence of two types of fault on each motor is required.

Evidence requirements

    8.1 Fault diagnosis includes verification of motor performance against specifications

    or records of previous performance, in accordance with industry practice.

    Range dynamometer or in situ connected-load tests, power factor, line

    current, speed, output.

8.2 Visible and audible defects are identified.

    Range defects may include but are not limited to excessive sparking

    during operation; signs of tracking; overheating indicators such as

    discolouration, burning, melting, or burnt insulation smell;

    excessive vibration and noise; noisy, sloppy, or worn bearings;

    worn, loose, or damaged accessories; damage to casing, foot-

    plate, end plates, terminal box and cover, fan and fan cover.

    8.3 Fault-finding demonstrates a logical technique for analysing symptoms, and

    making electrical measurements where necessary, to locate fault and/or faulty

    components.

    8.4 Assessment of viability of repair takes into account availability of parts, cost,

    time, and supervisor’s instructions.

    8.5 Results are documented in accordance with industry practice.

    Replacement information This unit standard replaced unit standard 1704 and unit

    standard 1705.

Planned review date 31 December 2014

    Status information and last date for assessment for superseded versions Process Version Date Last Date for Assessment

    ElectroTechnology Industry Training Organisation ; New Zealand Qualifications Authority 2012

    SSB Code 100401

NZQA registered unit standard 15858 version 4

     Page 6 of 6

Process Version Date Last Date for Assessment

    Registration 1 10 February 1999 31 December 2013

    Review 2 26 May 2005 31 December 2013

    Review 3 22 August 2008 31 December 2013

    Rollover and 4 15 March 2012 N/A Revision

Consent and Moderation Requirements (CMR) reference 0003

    This CMR can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.

Please note

    Providers must be granted consent to assess against standards (accredited) by NZQA, before they can report credits from assessment against unit standards or deliver courses of study leading to that assessment.

    Industry Training Organisations must be granted consent to assess against standards by NZQA before they can register credits from assessment against unit standards.

    Providers and Industry Training Organisations, which have been granted consent and which are assessing against unit standards must engage with the moderation system that applies to those standards.

    Requirements for consent to assess and an outline of the moderation system that applies to this standard are outlined in the Consent and Moderation Requirements (CMR). The CMR also includes useful information about special requirements for organisations wishing to develop education and training programmes, such as minimum qualifications for tutors and assessors, and special resource requirements.

Comments on this unit standard

    Please contact the ElectroTechnology Industry Training Organisation at reviewcomments@etito.co.nz if you wish to suggest changes to the content of this unit standard.

    ElectroTechnology Industry Training Organisation ; New Zealand Qualifications Authority 2012

    SSB Code 100401

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