Unit of competency: UEENEEG149A - Provide engineering solutions to problems in complex polyphase power circuits


Retrieved from: https://training.gov.au/Training/Details/UEENEEG149A 12/02/2020


Unit Descriptor

Unit Descriptor 

1) Scope: 


1.1) Descriptor 


This unit covers determining correct operation of complex polyphase power circuits and providing solutions as they apply to electrical power engineering work functions. It encompasses working safely, problem solving procedures, including using electrical measuring devices, applying appropriate circuit theorems and providing solutions derived from measurements and calculations and justification for such solutions.

Application of the Unit

Application of the Unit 



This unit is intended to augment formally acquired competencies. It is suitable for employment-based programs under an approved contract of training.

Licensing/Regulatory Information

License to practice 



The skills and knowledge described in this unit require a license to practice in the workplace where plant and equipment operate at voltage above 50 V a.c. or 120 V d.c. However other conditions may apply in some jurisdictions subject to regulations related to electrical work. Practice in the workplace and during training is also subject to regulations directly related to occupational health and safety and where applicable contracts of training such as apprenticeships.


Prerequisite Unit(s) 



2.1) Competencies 


Granting competency in this unit shall be made only after competency in the following unit(s) has/have been confirmed.


UEENEEE125A         Provide engineering solutions for problems in    complex multiple path circuits.


UEENEEG102A        Solve problems in low voltage a.c. circuits


Employability Skills Information

Employability Skills 



This unit contains Employability Skills

The required outcomes described in this unit of competency contain applicable facets of Employability Skills. The Employability Skills Summary of the qualification in which this unit of competency is packaged will assist in identifying Employability Skill requirements.

Elements and Performance Criteria Pre-Content

6) Elements describe the essential        outcomes   of a unit of competency

Performance Criteria describe the required performance needed to demonstrate achievement of the Element. Assessment of performance is to be consistent with the Evidence Guide.


Elements and Performance Criteria




Prepare to provide engineering solutions to problems in complex polyphase power circuits.


OHS procedures for a given work area are identified, obtained and understood.



OHS risk control work preparation measures and procedures are followed.



The nature of the circuit(s) problem is obtained from documentation or from work supervisor to establish the scope of work to be undertaken.



Advice is sought from the work supervisor to ensure the work is coordinated effectively with others.



Sources of materials that may be required for the work are established in accordance with established procedures.



Tools, equipment and testing devices needed to carry out the work are obtained and checked for correct operation and safety.


Provide engineering solutions to problems in complex polyphase power circuits.


OHS risk control work measures and procedures are followed.



The need to test or measure live is determined in strict accordance with OHS requirements and when necessary conducted within established safety procedures.



Circuits are checked as being isolated where necessary in strict accordance OHS requirements and procedures.



Established methods are used for solving circuit problems from measure and calculated values as they apply to complex polyphase power circuits.



Unexpected situations are dealt with safely and with the approval of an authorised person.



Problems are solved without damage to apparatus, circuits, the surrounding environment or services and using sustainable energy practices.


Complete work and document solutions for problem solving activities.


OHS work completion risk control measures and procedures are followed.



Work site is cleaned and made safe in accordance with established procedures.



Justification for solutions used to solve circuit problems is documented.



Work completion is documented and an appropriate person or persons notified in accordance with established procedures.

Required Skills and Knowledge


7)  This describes the essential skills and knowledge and their level, required for this unit.

Evidence shall show that knowledge has been acquired of safe working practices and providing solutions for problems in complex polyphase power circuits.

All knowledge and skills detailed in this unit should be contextualised to current industry practices and technologies.

KS01-EG149A Polyphase power circuit analysis 

Evidence shall show an understanding of polyphase power circuit analysis to an extent indicated by the following aspects:

T1 Polyphase supply system encompassing:

·         advantage of three phase system compared to single phase systems

·         double subscript notation

·         phase sequence

·         120 degree operator

·         given circuit component parameters, solve practically based problems using:

·         equivalent circuits of transformers, lines and loads.

·         component values using rectangular and polar notation.

·         current divider and potential divider rules using complex impedances.

·         The “per unit” values of voltage, current, VA and impedance to a common VA base.

T2 Types of three phase system connections encompassing:

·         supply to balanced star, 3 and 4 wire loads

·         supply to delta connected loads

·         effects of phase reversal

·         representation of currents and voltages as complex phasors for 3 phase and 3 phase and neutral quantities.

·         calculation the values of and draw labeled phasor diagrams, not to scale, to represent complex values of current and voltage for balanced and unbalanced loads for star and delta systems.

·         calculation of values of P, Q and S for balanced and unbalanced systems.

·         draw and label single phase diagrams to represent 1 phase of a complex 3 phase system.

·         represent unbalanced voltages or currents as symmetrical components.

·         Phase to phase currents

·         Phase to neutral/earth currents.

T3 Balanced three phase loads encompassing:

·         calculations of balanced loads connected in star

·         calculations of balanced loads connected in delta

·         calculation of steady state values of fault current for various configurations.

·         evaluation of the symmetrical component impedances for the various distribution system components. Transformers (earthed neutral case). Generators (high impedance earth)

·         calculation of fault currents using the per unit approach.

·         calculation using the “worst case” values based on transformer impedance only (ie., a short circuit fault)

·         estimation of peak values using accepted multipliers.

·         effects of the d.c. component on the instantaneous magnitudes of fault currents in transformers and generators.

T4 Unbalanced three phase loads encompassing:

·         Star – 4 wire systems

·         Delta systems

·         Star – 3 wire systems

·         Star 4 wire with neutral impedance

T5 Power in three-phase circuits encompassing:

·         summation of phase powers and power in balanced loads

·         measurement of power in balanced loads – 2 Wattmeter methods

T6 Reactive three phase power encompassing:

·         power triangle calculation

·         measurement of VAR

·         power factor correction

T7 Fault currents encompassing:

·         symmetrical components

·         positive, negative and zero sequence impedance

·         fault current breaking and let-through energy capacities of circuit breakers, fuses

·         importance of fault/arc impedance

·         calculation of fault currents - phase-to-earth faults

·         calculation of fault currents - phase-to-phase faults

·         analysis of asymmetrical faults currents.

T8 Harmonics in three phase systems encompassing:

·         presence of triple in harmonics in 3 phase systems

·         effects of 3 phase harmonics for different star and delta connections.

·         methods for reducing harmonics in three phase systems.

Software/Hardware Used