This document summarizes sources of electricity generation and electrical distribution systems. It discusses the three major classifications of power production: thermal, nuclear, and hydroelectric. It then describes how electricity is distributed from power stations at high voltages through transformers before reaching consumers at lower voltages. The document outlines different earthing systems used in electrical installations and components like meters, consumer units, and circuit breakers used for protection.

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ELECTRICAL
INSTALLATION
Prepared by Tan Hee Chai

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Sources of Electricity

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3 major classifications for power production in
reasonably large scale are :-
1) Thermal power generation
2) Nuclear power generation.
3) Hydro-electric power generation.

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Electrical supply and distribution
•Fuel converted to steam at high temperature and pressure, to
drive turbines which generate electricity at 25kV alternating
current.
•AC changes polarity from positive to negative at 50 cycles per
second (50 hertz)

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Electrical supply and distribution

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Electrical supply and distribution
Reasons power is supplied in Alternating Current (AC) at 50
Hertz:
•Facility of generating machines
•Ease of transformation
•Use of electricity powered AC motors

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Electrical supply and distribution
132, 275 or 400 kV: National transmission
33 000 V: Large/Heavy industries, cities, towns and railways
11 000 V: Light Industries, hospitals, towns and villages
400 V: Small industries, offices, farms etc
230 V: Housing, schools, small commercial premises.

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Electrical supply and distribution
• All but 230 V is supplied with 3 phases: domestic
appliances and standard office equipment are designed
to operate from only one phase.
• 33 000 V, three phase supply to railway operators via
sub-station where it is transformed to 25 000 V DC

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Local
distribution-
Three phase
and single
phase supply

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Local
distribution-
Three phase
& single
phase
Generators at power station are wound
with three conductors.
•Each generate one phase
•Three phases into 3 wires
Called ‘three phase three wire’ supply

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Local
distribution-
Three phase
form
At secondary side of transformer at sub-
station:
•Any pair of three wire is 415 volts
•Any of three conductors is 240 volts
Called ‘three phase four wire; supply

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Local distribution
Service cable
supply to
external meter
cupboard

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Local
distribution
Incoming cable

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Local
distribution
Overhead
cable

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Local
distribution -
TT System

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TT System
• Supplied overhead without earth terminal
• Consumer to provide earth electrode.
• Residual current circuit breaker (or trip switch) provided
between meter & consumer unit.
• RCCB operate on imbalance between the phase or live
conductor and the neutral.
• A fault will energise the core coil to effect the
electromagnetic trip.

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TN-S
System

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TN-S System
• Applied to underground supplies
• Metal sheathed and/or armoured cable.
• Consumer’s terminal connected to metal sheath

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TN-C System
• Earth and neutral
conductors
combine to provide
a protective earth
and neutral (PEN)
or Protective multi
earthing(PME)

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Consumer unit

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Electrical Meter
• One rate (tariff) – domestic
consumers
• Off peak & on peak meters

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Electrical Meter
•Two coils: current coil connect to
phase and & voltage coil across phase
& neutral
•Interaction of two energises a dics
which rotates at speeds proportional
to power consumed
•Gears driven disc effect a digital
display of energy consumed in KWh

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Overload Protection
• Need to prevent current leaks from electrical installation
due to insulation failure in the electrical circuit.
• Earth Leakage circuit breaker detects earth leakage
current and makes the power supply off by opening the
associated circuit breaker.

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Overload Protection
This can be provided by:
1. Semi-enclosed rewirable fuses
2. Cartridge fuses
3. Miniature circuit breakers (MCB)

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Overload
protection

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Overload
protection

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1. Semi-enclosed rewirable fuses
• Advantages
• Low capital cost
• Cheap to replace element
• Simple in concept
• No moving parts

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Disadvantages
•Prone to abuse. Incorrect wire can be used
•Deterioration with age
•Reliability can vary, with temperature & fixing method.
•Cannot be tested
•Cannot be replaced quickly
•Fusing factor higher than current rating

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2. Cartridge fuses
Advantages
•Small and compact
•No moving parts
•Accurate and consistent to declared rating
•Will not deteriorate in protective tube

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2. Cartridge fuses
Disadvantages
•Cannot be repaired or reset, must be replaced
•Prone to abuse (with metal foil)
•Much more expensive than fuse wire

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3. Miniature Circuit breaker
Advantages
•No moving parts
•Accurate and consistent to declared rating
•Durable
•Can be reset

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3. Miniature Circuit Breaker
Disadvantages
•Cannot be repaired, must be replaced
•Much more expensive than fuse wire

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The End