Electrical Installation and Workshop Technology
1. ELECTRICAL POWER SUPPLY AND DISTRIBUTION
Electrical power system
An electrical power system is a network of electrical components deployed to supply, transfer, and use electric
power. It consists of;
Generators: supply the power
Transmission systems: carries power from generating centres to load centres
Distribution system: feeds the power to industries and homes
Sources of electrical power supply
Electrical energy is produced from many different energy sources. Some of these energy sources are renewable
and others are non-renewable.
Hydro
Electrical energy created from water stored in huge dams. The energy created by the water released from these
dams is transformed into electricity by hydro-electric turbines and generators. The most famous source of
hydroelectric power in Kenya is seven folks scheme.
Geothermal
The heat found beneath the earth surface heats water, which escapes to the surface in form of steam. This steam
is used to turn generator turbines hence producing electric energy. Geothermal power plants in found in Olkaria.
Wind
Moving air (wind) is used to turn the turbines hence producing electricity. Although wind energy accounts for small
percentage in Kenya, it is still an important source of electric power. Wind turbines are found in Ngong hills.
Sun
Electricity can be generated using an array of solar panels. This power can either be stored in battery banks or
converted directly to AC power.
Biomass
The electric energy can be generated from landfills or rubbish dumps. This waste is collected, dried and burnt to
produce heat for generating steam that turns the turbines. This type of electric power is not available in Kenya.
Non-renewable sources
Nuclear
It uses nuclear fission to generate heat, which in turn heat water to produce steam that drives the turbines.
Nuclear plant is not available in Kenya.
,Fossil fuels
Fossil fuels such as coal are burnt to create steam, which turns the turbines. This non-renewable source produces
large amounts of electricity. This type of power supply is not available in Kenya.
Generators
Diesel/petrol or gas-powered generators is used to produce electricity. Some of the electricity that goes to the
national grid comes from diesel generators.
Types of power supply system
There two types of power supply system, which include;
AC power supply system
DC power supply system
AC Power Supply system
The lines network between Generating Station (Power Station) and consumer of electric power can be divided into
two parts.
Transmission System
Distribution System
The following parts of a typical power supply scheme are shown in the figure below.
,Electrical power is normally generated at 11kV in a power station. This generating voltage is then stepped up to
132kV, or greater voltage. Stepping up the voltage level depends upon the distance at which power is to be
transmitted. The longer the distance, higher will be the voltage level. Stepping up of voltage is to reduce the I 2R
losses in transmitting the power (when voltage is stepped up, the current reduces by a relative amount so that the
power remains constant, and hence I2R loss also reduces). This stage is called as primary transmission.
The voltage is the stepped down at a receiving station to 33kV. Secondary transmission lines emerge from this
receiving station to connect substations located near load centers (cities etc.).
The voltage is stepped down again to 11kV at a substation. Large industrial consumers can be supplied at 11kV
directly from these substations. Also, feeders emerge from these substations. This stage is called as primary
distribution.
Feeders are either overhead lines or underground cables which carry power close to the load points (end
consumers) up to a couple of kilometers. Finally, the voltage is stepped down to 415/240 volts by a pole-mounted
distribution transformer and delivered to the distributors. End consumers are supplied through a service mains line
from distributors. The secondary distribution system consists of feeders, distributors and service mains.
Three phase, four-wire ac supply system
Three phase system is derived from a star connected winding of a transformer, the star point being earthed. From
this point the fourth conductor, neutral is taken to form a three phase four-wire system. The voltage between any
two phase conductors is 415V. The voltage between any phase conductor and neutral is 240V.
Three-phase is supplies are fed to very large consumers where total load exceed 100kW. The voltages are either 11
or 33kV. Also, three-phase is ideal for commercial and industrial premises of medium size such as schools,
hospitals, hotels etc.
DC supply system
Though a.c. is extensively used everywhere, there are few applications like operation of d.c. motors, batteries,
charging where d.c. supply is must. It can be obtained by using rectifiers or by d.c. generators at substations.
The d.c. systems are further classified as,
Two wire d.c. system
Two wire with midpoint earthed d.c. system
Three wire d.c. system
, Two Wire D.C. System
It consists of two wires, one positive and other negative. The positive is outgoing while the negative is return
wire. The two wire d.c. system where loads are connected in parallel is shown below.
Two Wire D.C. System with Midpoint Earthed
In this system, there are two line conductors, the one having voltage of + with respect to midpoint which is
earthed while the other is at potential - with respect to midpoint. Hence the total voltage available between the
two lines is 2V. No connection is taken out from the midpoint, which is earthed at the substation. The loads
requiring high d.c. voltages are connected across the lines. The symbolic representation of this system is shown
below
Three Wire D.C. System
This system is exactly similar to the two wire d.c. system with midpoint earthed. The only difference is,
additional third wire from earth terminal of substation is available for the connections. This wire is also known as
neutral wire. The scheme is shown in the figure below
1. ELECTRICAL POWER SUPPLY AND DISTRIBUTION
Electrical power system
An electrical power system is a network of electrical components deployed to supply, transfer, and use electric
power. It consists of;
Generators: supply the power
Transmission systems: carries power from generating centres to load centres
Distribution system: feeds the power to industries and homes
Sources of electrical power supply
Electrical energy is produced from many different energy sources. Some of these energy sources are renewable
and others are non-renewable.
Hydro
Electrical energy created from water stored in huge dams. The energy created by the water released from these
dams is transformed into electricity by hydro-electric turbines and generators. The most famous source of
hydroelectric power in Kenya is seven folks scheme.
Geothermal
The heat found beneath the earth surface heats water, which escapes to the surface in form of steam. This steam
is used to turn generator turbines hence producing electric energy. Geothermal power plants in found in Olkaria.
Wind
Moving air (wind) is used to turn the turbines hence producing electricity. Although wind energy accounts for small
percentage in Kenya, it is still an important source of electric power. Wind turbines are found in Ngong hills.
Sun
Electricity can be generated using an array of solar panels. This power can either be stored in battery banks or
converted directly to AC power.
Biomass
The electric energy can be generated from landfills or rubbish dumps. This waste is collected, dried and burnt to
produce heat for generating steam that turns the turbines. This type of electric power is not available in Kenya.
Non-renewable sources
Nuclear
It uses nuclear fission to generate heat, which in turn heat water to produce steam that drives the turbines.
Nuclear plant is not available in Kenya.
,Fossil fuels
Fossil fuels such as coal are burnt to create steam, which turns the turbines. This non-renewable source produces
large amounts of electricity. This type of power supply is not available in Kenya.
Generators
Diesel/petrol or gas-powered generators is used to produce electricity. Some of the electricity that goes to the
national grid comes from diesel generators.
Types of power supply system
There two types of power supply system, which include;
AC power supply system
DC power supply system
AC Power Supply system
The lines network between Generating Station (Power Station) and consumer of electric power can be divided into
two parts.
Transmission System
Distribution System
The following parts of a typical power supply scheme are shown in the figure below.
,Electrical power is normally generated at 11kV in a power station. This generating voltage is then stepped up to
132kV, or greater voltage. Stepping up the voltage level depends upon the distance at which power is to be
transmitted. The longer the distance, higher will be the voltage level. Stepping up of voltage is to reduce the I 2R
losses in transmitting the power (when voltage is stepped up, the current reduces by a relative amount so that the
power remains constant, and hence I2R loss also reduces). This stage is called as primary transmission.
The voltage is the stepped down at a receiving station to 33kV. Secondary transmission lines emerge from this
receiving station to connect substations located near load centers (cities etc.).
The voltage is stepped down again to 11kV at a substation. Large industrial consumers can be supplied at 11kV
directly from these substations. Also, feeders emerge from these substations. This stage is called as primary
distribution.
Feeders are either overhead lines or underground cables which carry power close to the load points (end
consumers) up to a couple of kilometers. Finally, the voltage is stepped down to 415/240 volts by a pole-mounted
distribution transformer and delivered to the distributors. End consumers are supplied through a service mains line
from distributors. The secondary distribution system consists of feeders, distributors and service mains.
Three phase, four-wire ac supply system
Three phase system is derived from a star connected winding of a transformer, the star point being earthed. From
this point the fourth conductor, neutral is taken to form a three phase four-wire system. The voltage between any
two phase conductors is 415V. The voltage between any phase conductor and neutral is 240V.
Three-phase is supplies are fed to very large consumers where total load exceed 100kW. The voltages are either 11
or 33kV. Also, three-phase is ideal for commercial and industrial premises of medium size such as schools,
hospitals, hotels etc.
DC supply system
Though a.c. is extensively used everywhere, there are few applications like operation of d.c. motors, batteries,
charging where d.c. supply is must. It can be obtained by using rectifiers or by d.c. generators at substations.
The d.c. systems are further classified as,
Two wire d.c. system
Two wire with midpoint earthed d.c. system
Three wire d.c. system
, Two Wire D.C. System
It consists of two wires, one positive and other negative. The positive is outgoing while the negative is return
wire. The two wire d.c. system where loads are connected in parallel is shown below.
Two Wire D.C. System with Midpoint Earthed
In this system, there are two line conductors, the one having voltage of + with respect to midpoint which is
earthed while the other is at potential - with respect to midpoint. Hence the total voltage available between the
two lines is 2V. No connection is taken out from the midpoint, which is earthed at the substation. The loads
requiring high d.c. voltages are connected across the lines. The symbolic representation of this system is shown
below
Three Wire D.C. System
This system is exactly similar to the two wire d.c. system with midpoint earthed. The only difference is,
additional third wire from earth terminal of substation is available for the connections. This wire is also known as
neutral wire. The scheme is shown in the figure below
