Unit 63 Electrical Power


Unit 63:

Electrical Power

Unit code:

QCF level:

Credit value:


This unit will develop learners’ understanding of electrical power systems and power distribution and the advantages and disadvantages of alternative energy sources.

Unit abstract

Our modern world increasingly relies upon electrical power to supply our industries, commercial centres and homes with a convenient, flexible and reliable source of energy.

To meet the client’s expectations, electrical energy must be provided at a reasonable cost and transmitted to the point of need, at the appropriate voltage and current levels. The client’s utilisation of the energy source needs to be appropriate, without undue complexity, to facilitate energy generation and transmission.

This unit takes the learner through the complex process of analysing three-phase systems with consideration being given to harmonics and their effects. The methods of power distribution through the National Grid are then discussed with final economic considerations taken into account to enhance generation, transmission and distribution, with acceptable costs to clients.

Throughout their working careers, modern engineers will have to consider new technologies and be able to evaluate the options available to make appropriate selections. With our global resources of fossil energy reserves decreasing and concerns over protecting the environment growing, alternative sources of energy are considered. Evaluative considerations will be made to inform the engineer of the issues associated with this topic, which may need to be considered far more at local and regional levels. Additionally, self-generation of electrical energy is now possible for a broad range of users throughout the world, utilising local environmental facilities.

Learning outcomes

On successful completion of this unit a learner will:

1       Be able to analyse three-phase systems

2     Understand the sources and effects of harmonics in power systems

3       Understand methods of power distribution

4       Understand the economics of components, power systems and alternative energy.

Unit content

1      Be able to analyse three-phase systems

Fault free three-phase systems: use of j-notation (complex numbers) in the analysis of un-faulted three-phase systems eg phase sequence, balanced star supply, balanced delta supply, 4 wire and 3 wire balanced star loads, unbalanced 4 wire star loads, balanced delta loads, unbalanced delta loads

Measurement of power: methods of determining power in three-phase balanced and unbalanced systems eg Blondel’s theorem, integrated three-phase wattmeters, real power, reactive power, apparent power

Faulted three-phase systems: connection errors and faults eg loss of neutral, loss of one line, reversed supply phase, unbalanced supply voltages, reversed phase sequence

Three-phase transformers: construction eg three single-phase transformers, shell and core type; connections eg terminal marking BS 171, phasor diagrams, star, delta, zig-zag, clock number and group, parallel operation

Characteristics: methods of operation of a three-phase induction motor; starting methods; current; torque and control techniques; torque speed characteristics of motor and load; steady state; operating point

Load dynamics: eg dynamic stability, crawling, inertia, friction, acceleration time

2      Understand the sources and effects of harmonics in power systems

Harmonics: pitch; wave theory; natural frequencies, harmonic series; resonance

Sources of harmonics: transformer magnetising current; direct current power supply units; general non-linear loads

Effects of harmonic: increased root-mean-square currents; zero sequence; triple-n neutral currents in star systems; triple-n currents trapped in delta transformers; overheating in neutral; overheating in motors and transformers; failure of power factor correction capacitors; harmonic resonance; skin effect losses

Mitigation of harmonics: methods of mitigation such as oversized neutral, de-rating, circuit separation, K factor and factor K, isolation transformers, passive and active filters, total harmonic distortion, standards G5/4

3      Understand methods of power distribution

Topology: system integrity; radial feeders; parallel feeders; open and closed rings; inter-connector

Operating parameters: load distribution eg radial, ring, parallel feeders, voltage and current profiles, permissible, voltage drop, power losses, power efficiency

4      Understand the economics of components, power systems and alternative energy

Economics: economic considerations eg power factor correction, energy tariffs, Kelvin’s law, compact fluorescent lighting; comparisons of single and three-phase systems; high and low efficiency motors

Alternative energy: geothermal; solar; wind; water; biomass eg liquid biofuel, solid biomass, biogas

Evaluation: cost (capital, operating); efficiency; energy storage; environmental impact; feasibility on large and small scale

Learning outcomes and assessment criteria

Learning outcomes
Assessment criteria for pass

On successful completion of
The learner can:

this unit a learner will:

1   Be able to analyse three-

solve problems involving fault free three-phase systems

phase systems

measure power in three-phase systems

solve problems involving faulted three-phase systems

describe three-phase transformers

describe the characteristics of a three-phase induction


assess the effect of load dynamics

2   Understand the sources and

identify typical sources of harmonics in a power system

effects of harmonics in

explain the effects of harmonics in power systems

power systems

evaluate at least four different methods of mitigation of


Understand methods of

compare different power system topologies

power distribution

analyse the operating parameters of a radial and a ring

distribution system

Understand the economics

compare the economics of single-phase and three-

of components, power

phase distribution

systems and alternative

compare and evaluate the different forms of alternative





This unit may be linked with Unit 1: Analytical Methods for Engineers and Unit 5: Electrical and Electronic Principles. Unit 35: Further Analytical Methods for Engineers would support the use of j-notation (complex numbers) required in learning outcome 1.

Essential requirements

Learners will need access to appropriate laboratory and test equipment (for example three-phase supply, transformer and loads, three-phase induction motor and starters, power analyser, etc).

Employer engagement and vocational contexts

Delivery of this unit would benefit from visits to a power station or wind farm or the attendance of guest speaker(s) with relevant experience of power generation and transmission.