This 6-module course covers key topics in power systems including: 1. Per unit systems and fault calculation methods 2. Power system overcurrent protection, including the equipment and their functions 3. Switchgear technologies and their operations 4. Earthing and grounding systems 5. Illumination engineering fundamentals 6. Single line diagrams and typical power system components like generators, transformers, and circuit breakers as well as their functions.

1. ECNG 3015 - COURSE OUTLINE
This course comprise the following modules:
1. Per Unit System (reasons and importance of its use)
2. Fault calculation on ‘small’ systems (types of faults how to analyze
them)
3. Power System and Overcurrent Protection (reasons for protection,
equipment used and how they work together)
4. Introduction to Switchgear technology (types of switchgear and how
they work)
5. Earthing and System Grounding (reason for earthing and grounding)
6. Illumination Engineering (the eye and how it responds to light as
well as basic lighting design)

2. Introduction – Need to Know
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Passive Element Impedance
R Z = R
L Z = jXL = jL = L 90° (where XL = L)
C Z = 1/ jC = -jXC = 1/C -90° (where XC = (1/C)
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circuit,inductiveFor
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3. Phase voltages:
Star Connection
Figure 1 – Star (Wye) connected system
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
120or240
120
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anan
VV
VV
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4. Determination of Line – Line (or simply Line) voltages:
Where:
Vab is the Line – Line voltage and
Vph is the magnitude of the phase voltage
 Note: In a star-star connection, the line current = phase current
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1200
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phca
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phab
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5. Where Vph is phase voltage referenced to the system in Fig. 2
Figure 2 – Delta connected system
Delta Connection
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6.   
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Fig. 3a
Delta to Star Conversion

7.   
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1
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2
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2112
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3bFig.Refer to

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Fig. 3b
Star to Delta Conversion

8. Typically, a three-phase power system:
- is considered balanced
- is represented on a single line diagram
- easy to analyze using single line representation
In reality, the transmission system is typically balanced but not the
distribution system.

9. Consider a system comprising five (5) generators, transformers, circuit breakers and a
common bus ring as shown in figure 4.
SINGLE LINE REPRESENTATION
Fig. 4 – Single line representation of a power system

10. Typically, a power system comprises:
- Generators – V, MVA, per unit impedance, short circuit rating
- Transformers – MVA, V, per unit impedance, transformer ratio, short circuit
rating Cooling method (ONAN, ONAF, OFAF)
- Circuit breakers – MVA, continuous rating, short-circuit rating, principle of
arc extinguishing (eg. Air, Oil, Vacuum and Gas)
Functions of the equipment :
- Generators generate the power
- Transformers are used to bring the voltage of the generators
to a common voltage for the common bus ring, i.e. step up or down.
- The circuit breakers are used to isolate equipment in case of a
fault.
TYPICAL COMPONENTS OF A POWER SYSTEM & THEIR FUNCTION

15. Power system typically utilize either fuses or relays for protection against faults.
Fuses – used to isolate fault once fuse rating is exceeded
Protection relays - to detect fault condition and ‘relay’ signal to circuit breaker to
open and isolate the faulted equipment.
Since short-circuit rating of the power system equipment is ‘time-rated’, if the
protection system fail to clear the fault then equipment damage can occur.
In such instances, back-up protection is imperative.
POWER SYSTEM PROTECTION