AC Electrical.

AC Electrical.

Learning outcome (LO)    Assessment Criteria    In this assessment you will have the opportunity to present evidence that shows you are able to:    Task no.
(Page no)
LO 4

Be able to apply single phase AC theory to solve electrical and electronic engineering problems.    4.1
Recognise a variety of complex waveforms and explain how they are produced from sinusoidal waveforms.
4.2    Apply AC theory to solve problems on R, L, C circuits and components..
4.3    Apply AC theory to solve problems involving transformers.

Learner declaration
I certify that the work submitted for this assignment is my own and research sources are fully acknowledged.


In addition to the above PASS criteria, this assignment gives you the opportunity to submit evidence in order to achieve the following MERIT and DISTINCTION grades

Grade Descriptor
Indicative characteristic/s
Take responsibility for managing and organising activities    Activities have been effectively  managed.
Autonomy / independence has  been  demonstrated    All tasks have been accurately and concisely completed within the given time constraints. (All Tasks)
Demonstrate convergent/lateral/creative
Effective thinking has taken place in unfamiliar contexts.     Complex waveform generation in electric circuits by non-linear electronic components has been clearly presented and explained.

Please note that for unit assignments assessors should use these or other exemplar indicative characteristics for the individual grade descriptors from Annexe C of the HN specification or any other relevant indicative characteristics for the particular assignment. The indicative characteristic should then be contextualised. Only one indicative characteristic per grade descriptor, M2, M2, M3, D1, D2, D3 is required.

Assignment brief
Unit number and title    21881C Engineering Science
Qualification    Pearson BTEC Level 4/5 HN Engineering  Streams

Start date
Deadline/hand-in     29/1/15
Assessor    Dr Warren Kent PhD CMath MIMA CSci MIET AKC PGCE QTS

Assignment title    AC Electrical
Purpose of this assignment

To develop the students knowledge and application of AC Theory and complex waveforms and their application in AC electrical circuits and systems.

This Assignment has been designed to allow students to show evidence of the application of AC Theories in realistic AC electrical circuits and systems and supporting the learning outcome.

Task 1 : (LO4:4.2) D2

A resistor of 45 ? is in series with a pure inductor of 105.3 mH.
This circuit is connected across a 100 V rms, 100 Hz voltage supply.

the inductive reactance,

the circuit impedance,

the current flowing,

the potential difference across the resistor,

the potential difference across the inductor,

the phase angle between the supply voltage and current.

All the circuit components remain unchanged but a 25 µF
capacitor is placed in series with the resistor and pure inductor. Find:

the current flowing,

the voltage across the resistor,

the voltage across the coil,

the voltage across the capacitor,

the phase angle between the supply voltage and current.

Task 2 (LO4: 4.2) D2

An electric motor has an output power of 5.75 kW and an efficiency
of 85%. It has a power factor of 0.725 lagging when operated
from a 230 V 50 Hz supply.

It is required to improve the power factor to 0.925 by connecting a capacitor in parallel with                                                                                         the motor.


The current taken by the motor,

the supply current with the power factor correction,

the current taken by the capacitor,

the capacitance of the capacitor,

the kvar rating of the capacitor.

Task 3 (LO4: 4.1)  D2 D3

Explain when a sinusoidal electrical waveform conducted through
A pn junction diode to a resistive load, does not appear sinusoidal
across the resistor. Draw a circuit diagram and also show the waveforms
from source and across the load.

A complex voltage waveform is composed of harmonics and is
described by the following expression:

is applied to the following circuits comprising of pure components of:

i) 25 ? resistor,
ii) 25×10-3 H inductor,
iii) 25×10-6 F capacitor.

The fundamental frequency is 500 Hz. Determine the current expression
flowing in each separate circuit.

Task 4 (LO4: 4.3)  D2

A 10 kVA on full-load single phase transformer has a turns ratio of 25:1
and is fed from a 5.0 kV supply. Neglecting losses (ie. assuming the ideal
transformer) determine:

the full-load secondary current,

the minimum load resistance which can be connected across the secondary
windings for full-load,

the primary current at full-load,

the input impedance seen at the primary windings,

the power dissipated across the load resistance.

Evidence checklist    Summary of evidence required by student    Evidence presented
Task 1    Circuit diagram showing the application of AC theory to R, L, C circuits.
Task 2    Circuit diagram showing the application of AC theory to AC systems.
Task 3    Understand and analyse complex waveforms in electrical/electronic systems.
Task 4    Understand the principles of transformers and analyse them with AC theory.
Sources of information:

Achievement Summary

Qualification    Pearson BTEC Level 4/5 HN Engineering  Steams

Assessor name

Unit Number and title    21881C Engineering Science
Student name

Criteria Reference    To achieve the criteria the evidence must show that the student is able to:    Achieved?

4.1    Recognise a variety of complex waveforms and explain how they are produced from sinusoidal waveforms.

4.2    Apply AC theory to solve problems on R, L, C circuits and components.

Apply AC theory to solve problems involving transformers.

Higher Grade achievements (where applicable)

Grade descriptor

Grade descriptor
D2: Take responsibility for managing and organising activities
D3: Demonstrate convergent/lateral/creative thinking

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