Scenario
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
1.
A resistor of 45 Ω is in series with a pure inductor of 105.3 mH.
This circuit is connected across a 100 V rms, 100 Hz voltage supply.
Calculate:
(a)
the inductive reactance,
(b)
the circuit impedance,
(c)
the current flowing,
(d)
the potential difference across the resistor,
(e)
the potential difference across the inductor,
(f)
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:
(g)
the current flowing,
(h)
the voltage across the resistor,
(i)
the voltage across the coil,
(j)
the voltage across the capacitor,
(k)
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.
Determine:
(a)
The current taken by the motor,
(b)
the supply current with the power factor correction,
(c)
the current taken by the capacitor,
(d)
the capacitance of the capacitor,
(e)
the kvar rating of the capacitor.
Task 3 (LO4: 4.1) D2 D3
(a)
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.
(b)
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 Ω 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:
(a)
the full-load secondary current,
(b)
the minimum load resistance which can be connected across the secondary
windings for full-load,
(c)
the primary current at full-load,
(d)
the input impedance seen at the primary windings,
(e)
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:
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