BE MY STUDENT IN EEE433
BY
ENGR. UWUIGBE O. EMMANUEL
2019/2020
1.0 INTRODUCTION
Hello, my name is Engr. Uwuigbe O. Emmanuel. Welcome to “Be My Student in EEE433:
“Energy Generation, Distribution and Utilization”. Did you notice that something is missing from
the course title? Of course! there is no “transmission”. The correct sequence is generation,
transmission, distribution and then utilization. Anyway, do not worry! Transmission is covered in
a separate course, “EEE531: Energy Transmission “and when we get to that river, we will cross it.
For your present level, I am going to take you on a fun filled trip in certain electrical principles in
EEE433. Now, saddle your horse and let us begin.
1.1 COURSE CONTENT
I have broken this entire tour into the outline shown below.
EEE433: ENERGY GENERATION DISTRIBUTION & UTILIZATION
(3 CREDITS)
GENERATION STATIONS: Advantages, disadvantages, schematic diagram and component parts
of Hydro-electric power station; Steam power plants; Gas power station, Nuclear power plants.
Siting of power stations. Comparison between power stations. Economic dispatch. ELECTRICAL
LOAD: Load forecast, effect of variable loads on power stations, load curves, spinning reserve,
connected load, maximum demand, demand factor, average load, load factor, diversity factor, plant
capacity factor, plant use factor, load duration curve. Load types: domestic, commercial, industrial,
municipal, irrigation and traction loads. Interconnected generating stations, advantages of
interconnected systems. ECONOMICS OF POWER GENERATION: cost of electrical energy,
fixed cost, running cost, depreciation. TARIFFS: types of tariff, features of a good tariff,
calculations. POWER FACTOR, power angle, cause of low power factor, disadvantages, power
factor improvement, static capacitors, synchronous condenser, phase advancers, calculations. The
Nigerian power grid UTILIZATION: Electric Heating, Electric Welding, Electrolytic Process.
DISTRIBUTION SYSTEMS: feeders, distributors, service mains. Classification of distribution
systems, overhead versus underground system, radial connection, ring main system,
interconnected system. DC Distribution: 2-wire system, 3-wire system, distributor fed at one, both
ends, fed at the center, ring distributor, current distribution in 3-wire dc system, boosters, ground
detectors. AC Distribution: voltage drops in ac system,4-wire star connected unbalanced load,
unbalanced delta connected load, unbalanced 3-wire Y-connected load, calculations.
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THE NIGERIAN POWER GRID
I want to believe that this course has been interesting and you have learnt a lot about the basics of
power generation. You know that electrical energy can hardly be stored in bulk; hence it must be
put to use to save cost due to wastage. However, the site of electric power generation is usually
several kilometres from where the bulk of the consumers are. For instance, in Nigeria, the
hydropower plant in Kainji in Niger State generates part of the electric power that is used all over
the country. You can imagine how far away Kainji dam is from Uniben in Edo State! The processes
involved in conveying power from Kianji to Uniben is called transmission and distribution. By
definition:
Electric power transmission is the bulk movement of electrical energy from a generating site, such
as a power plant, to an electrical substation. The interconnected lines which facilitate this
movement are known as a transmission network.
In Nigeria, the transmission network is commonly referred to as the National Grid. The schematic
and layout are shown in the pictures below.
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Fig. 1: Schematic of the National Grid
At the transmission substations, the electric power is transformed to lower voltage at a fixed
frequency of 50Hz. For some other countries, 60Hz is used. After the transformation, the power
is further transmitted or distributed.
In Nigeria, transmission starts at the generating stations and ends at injection substations. Electric
energy is generated at about 6.6kV or higher and then stepped up to 330kV usually at the site of
generation. The 330kV is the voltage level for our transmission grid which is commonly referred
to as “National Grid” as shown in Fig.1 above. This is the first tier of transmission or primary
transmission and energy is carried on conductors and towers.
Fig.2: Transmission Towers.
At transmission stations usually several kilometres away from the generating stations, the voltage
is stepped down to 132kV and then further transmitted to secondary substations where it is further
stepped down to 33kV. Feeder lines at 33kV are radiated from the secondary substation and used
to feed injection substations. At the injection substations, the energy is further stepped down to
11kV and distributed through “11kV feeders” to consumers who utilize energy at this voltage level.
For other consumers, it is conveyed to “mini-substations” where it is stepped down once more to
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415V and distributed on 3-phase, 4-wire overhead systems along streets and roads to various
consumers. This is the general voltage level for most consumers in Nigeria. The 240V used by
the appliances in the home is actually a single phase (line-to-neutral) equivalent of the 415V.
Exercise: (i) why is it not stupid to generate electrical energy at 6.6kV, step up to 330kV and then
start stepping it down again? (ii) What are the voltage levels of the Nigerian power system from
generating station to your father’s house?
Transmission system is covered in details in another course, “Be my Student in EEE531”. Our
focus here is distribution systems and utilisation.
STAKEHOLDERS IN THE NIGERIA POWER SECTOR
There are some major players in the Nigeria Electricity Supply Industry (NESI) that we
must have an understanding of there roles in order to grasp both the technical and financial
aspects of power supply in Nigeria. Some of these organisations includes, NERC, NBET,
TCN, NEMSA, DisCos, IPP amongst others.
NERC
The Nigerian Electricity Regulatory Commission (NERC) is an independent body, established by
the Electric Power Sector Reform (EPSR) Act of 2005 to undertake technical and economic
regulation of the Nigerian Electricity Supply Industry (NESI). NERC, though independent, is a
Federal Government
ROLE OF NERC
The role of the Commission includes but not limited to:
1. Licensing of operators,
2. Determining operating codes and standards,
3. Establishing customer rights and obligations and
4. Setting of cost reflective industry tariffs.
The Commission has its headquarters in Abuja, and has currently six zonal offices in the six
geopolitical zones of the country. Since inception, NERC has recorded significant achievements
including the expansion of capacity and network by the issuance of licenses for electricity
generation, transmission and distribution, as well as the development of industry codes and
standards, market rules and a multi-year tariff order. In addition, the Commission has issued
various regulations and orders that have created an attractive and stable electricity market in
Nigeria. These achievements have been made possible by ensuring that market transactions are
rule based and regulatory interventions are preceded by robust consultative and stakeholder
engagement
processes
to
ensure
transparency,
fairness
and
accountability.
These qualities of transparency, fairness and accountability are critical to NERC as an independent
regulator. The EPSR Act was thorough in ensuring this independence.
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NBET
The Nigerian Bulk Electricity Trading (NBET) Plc. is the manager and administrator of the
electricity pool in the Nigerian Electricity Supply Industry (NESI). It was incorporated on the 29th
day of July 2010 and is fully owned by the Federal Government of Nigeria.
NBET purchases electricity from the Generating Companies through Power Purchase
Agreements (PPAs) and sells to the Distribution Companies through Vesting Contracts. The
Generating Companies include the privatized PHCN successor companies, the Niger Delta Power
Holding Companies (NIPPs), the already existing Independent Power Producers (IPPs) and the
new IPPs.
ROLE OF NBET
1. Management and administration of the financial flows for the physical supplies on the network.
2. Operation of a competitive market that encourages efficient value discovery for commodity
and capacity.
3. Promotion of a contracts-based market that allocates risks efficiently to parties responsible for
them.
4. Formulation and advisory on polices for efficient system settlement and least possible cost
incentives for maintaining the transportation network within its acceptable energy, frequency
responses and voltage tolerances.
TCN
Transmission Company of Nigeria (TCN) was incorporated in November 2005. TCN emerged
from the defunct National Electric Power Authority (NEPA) as a product of the merger of the
Transmission and Operations sectors on April 1, 2004. Being one of the 18 unbundled Business
Units under the Power Holding Company of Nigeria (PHCN), the company was issued a
transmission License on 1st July, 2006. TCN is mandated to plan, build, operate, and maintain a
reliable and efficient transmission grid.
ROLE OF TCN
TCN licensed activities include:
1. Transmission of electricity,
2. System operation and electricity trading in collaboration with NBET.
DISTRIBUTION SYSTEMS
Electric power distribution refers to the movement of electrical energy from injection substations
to points of utilization like mills, factories, residential and commercial buildings, pumping
stations, schools, etc.
In general, distribution system covers the network of power lines and associated equipment
between the injection substation and prepaid or post-paid power meter at the consumers’ premises.
It consists of Feeders, Distributors and Service mains.
Feeders – are conductors (3-phase, 3-wire) which connect an injection substation to minisubstations. A mini-substation is one that has a step-down transformer (usually 200kVA, 300kVA
or 500kVA), feeder pillar or distribution box, line isolator, etc. from which 3-phase, 4-wire
overhead systems are used to distribute power through roads, streets, etc to the consumers. In
Nigeria, mini-substations are found at street junctions along major roads. In recent times, some
mini-substations are now pole mounted commonly seen at banks or along the streets.
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33kV transmission lines which connects a transmission substation to and injection substation is
sometimes referred to as 33kV feeder, however, the term “feeder” is best suited for 11kV lines
which connects the injection substation to mini-substations along road and streets. Ideally, no
tappings are taken from feeders so that current in it remains the same from injection substation to
mini-substation. But in practice in Nigeria, you find a single feeder connected to several minisubstations. This is due to the fact that injection substations are few and inadequate, so each feeder
is used to supply power to a large area. This cannot be done without making tappings to several
mini-substations.
The figure below shows a typical mini-substation in Nigeria.
Food for thought: Have you ever wondered why the set-up in the picture below is called a minisubstation?
Distributors – are conductors (3-phase, 4-wire overhead systems) from which tappings are taken
for supply to the consumers. The power output from mini-substations is at 415V line-to-line or
240V line-to-neutral which is very suitable for consumer appliances. The current through a
distributor is not constant because of the tappings at various points along its length. Also, there
will be voltage drops along the line as it stretches farther away from the source. This drop along
the line must be put into consideration while designing distributors to ensure that the voltage at the
receiving or consumer end does not drop below ±5% of the rated value; usually 240V.
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Fig.xx : 3-phase, 4-Wire 415V distributor at the
source point. The upriser cable from the
distribution box (feeder pillar) is attached firmly to
the LV pole. Minimum clearance is 25cm.
Sometimes, the same pole is used to convey both
11kV and 415V lines as shown below:
Figure 1: 3 phase 4-wire Distributors.
Methods of Electric Power Distribution
(i) Overhead distribution
(ii) Underground
distribution
Overhead Distribution
Overhead distribution as a method of conveying electrical energy from one location to another
involves the use of bare conductors of copper or aluminium which are strung between poles or
towers erected or mounted at convenient distances along a route. The bare copper or aluminium
wire is fixed to an insulator, which is itself mounted onto a cross-arm (33kV)
Line supports consist of poles (wooden, reinforced concrete or steel) or tower structures. Poles are
used for 33kV lines and below while towers are employed for voltages above 33kV.
Underground Distribution
The use of underground cable is ordinarily confined to the short lengths required in congested
urban areas. The cost of underground cable is much more than that of aerial conductors.
Underground cables take up less right-of-way than overhead lines, have lower visibility, and are
less affected by bad weather. However, costs of insulated cable and excavation are much higher
than overhead construction. Faults in buried transmission lines take longer to locate and repair.
Underground lines are strictly limited by their thermal capacity, which permits fewer overloads or
re-rating than overhead lines. To improve underground cable power-handling capability, research
is being done in forced cooling techniques, such as circulating-oil and compressed-gas insulation.
Another Possible method is the use of cryogenic cables or superconducting cables.
Long underground AC cables have significant capacitance, which may reduce their ability to
provide useful power to loads beyond 80 km. Long underground DC cables have no such issue
and can run for thousands of miles.
Generally, a good distribution system, whether underground or overhead should meet the
following requirements:
1. The voltage at the consumer end must be maintained at not more than ±5% of the declared
voltage.
2. The insulation resistance of the whole system must be very high so that there is no undue
leakage or danger to human life.
3. The distribution cost must be minimal and affordable.
4. The loss of power in the system itself should not be in excess of 10% of the distributed power.
5. The maximum current flowing through the conductor should be limited to such a value as not
to overheat the conductor or lead to insulation failure.
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