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Download 18998 Demonstrate advanced knowledge of alternating
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NZQA registered unit standard 18998 version 4 Page 1 of 4 Title Demonstrate advanced knowledge of alternating current and threephase theory Level 5 Purpose Credits 10 This unit standard is intended for use in the training and assessment of electricians beyond trade level. It covers alternating current (a.c.) and three-phase power theory, at a level more advanced than the requirements for the National Certificate in Electrical Engineering (Electrician for Registration) (Level 4) [Ref: 1195]. People credited with this unit standard are able to demonstrate knowledge of: – resonant alternating current circuits; – power system harmonics; – alternating current voltage dividers and phase-shift circuits; – power in three-phase balanced loads; and – three-phase unbalanced star-connected loads. Classification Electrical Engineering > Core Electrical Available grade Achieved Entry information Recommended skills and knowledge National Certificate in Electrical Engineering (Electrician for Registration) (Level 4) [Ref: 1195] or equivalent trade qualification for electricians. Explanatory notes This unit standard has been developed for learning and assessment off-job. Outcomes and evidence requirements Outcome 1 Demonstrate knowledge of resonant alternating current circuits. The skills Organisation SSB Code 100401 New Zealand Qualifications Authority 2017 NZQA registered unit standard 18998 version 4 Page 2 of 4 Evidence requirements 1.1 Effects of changing frequency on current and impedance of resonant circuits near resonance are explained with the aid of graphs. Range 1.2 Resonant frequencies of reactive circuits are calculated for given data. Range 1.3 resonant circuits – series, parallel. reactive circuits – series circuit, parallel circuit with negligible resistance. Magnification factors (Q) of resonant circuits are calculated for given data. Range series circuit voltage magnification, parallel circuit current magnification. 1.4 Bandwidth of a resonant circuit is calculated for given data. 1.5 Selectivity of resonant circuits is explained in terms of magnitude of inductor resistance. Range high and low values of resistance, series and parallel circuits. Outcome 2 Demonstrate knowledge of power system harmonics. Evidence requirements 2.1 Shapes of repetitive complex waveforms are explained in terms of harmonic frequencies. Range 2.2 square wave, saw-tooth wave, odd harmonics, even harmonics. Devices introducing unwanted odd and/or even harmonics to a power system are identified, with reference to the range of significant harmonics and method of generation. Range devices – transformers, alternators, alternating current motors, single-phase rectifiers, three-phase rectifiers, devices with nonsinusoidal loads. Evidence of five devices is required. 2.3 The result of resonance at harmonic frequency is explained in terms of harmonic current compared with fundamental current. 2.4 Use of selective resonant circuits to reduce harmonics in power systems is explained, with reference to acceptor and rejecter circuits. The skills Organisation SSB Code 100401 New Zealand Qualifications Authority 2017 NZQA registered unit standard 18998 version 4 Page 3 of 4 Outcome 3 Demonstrate knowledge of alternating current voltage dividers and phase-shift circuits. Evidence requirements 3.1 Operation of voltage divider circuits is explained with reference to circuit and phasor diagrams. Range 3.2 voltage dividers – resistive, resistive-capacitive, resistive-inductive, centre-tapped transformer with resistive-capacitive circuit. The effects of varying circuit parameters on the input-output phase difference are explained. Range circuit parameters – resistance, capacitance, inductance, frequency. Outcome 4 Demonstrate knowledge of power in three-phase balanced loads. Evidence requirements 4.1 Requirements for balance are explained in terms of line currents and power factors. 4.2 Principles of power factor improvement of three-phase systems are explained with reference to phasor diagrams or power triangles, equipment used, connection configuration, and voltage rating. Range 4.3 equipment – rotating machinery, static capacitors, harmonic filters; configurations – delta-connected, star-connected; voltage rating – line voltage, phase voltage. Data for three-phase power factor correction are calculated for a given balanced load situation. Range data – volt-amperes reactive; capacitance and voltage rating for both delta and star connections. Outcome 5 Demonstrate knowledge of three-phase unbalanced star-connected loads. Evidence requirements 5.1 Line and neutral currents of unbalanced resistive loads are calculated for given data. The skills Organisation SSB Code 100401 New Zealand Qualifications Authority 2017 NZQA registered unit standard 5.2 18998 version 4 Page 4 of 4 Line and neutral currents of loads having equal impedance but different power factors are calculated for given data, including unity, leading, and lagging power factors. Planned review date 31 December 2014 Status information and last date for assessment for superseded versions Process Version Date Last Date for Assessment Registration 1 26 February 2002 31 December 2012 Review 2 19 June 2009 N/A Rollover and Revision 3 15 March 2012 N/A Revision 4 15 January 2014 N/A 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 Skills Organisation [email protected] if you wish to suggest changes to the content of this unit standard. The skills Organisation SSB Code 100401 New Zealand Qualifications Authority 2017