OPERATIONAL PLANNING FOR KENYA POWER GRID...

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1.0 CHAPTER ONE-INTRODUCTION

1.0.1 Project Title: operational planning for Kenya power grid system

1.1 Project Aim.

The project aims at determining operational planning for Kenya power grid system done

by KPLC based on the available resources, the objectives, rules and policies governing its

operation.

1.2 Objectives of the project I. Determine the available power generating plants feeding the KPGS.

II. Determine various planning criteria used to ensure grid stability and load

balancing.

III. Research on operations and operational planning done by KPLC which enable the

company meet its objectives.

IV. Use load flow analysis for KPGS and analyze it and draw comments and

conclusion from it.

1.3 Scope of the Project Computation of power flow is one of the major tasks facing power system planners.

Deterministic power flow studies require specific values of loads, generation inputs and

network conditions. In an open access environment, the data will not be as certain as in

the ideal case.

Given the importance of the planners’ decisions that evolve from the power flow studies,

it appears most desirable to know the possible ranges of the power flow over transmission

lines and the transformers corresponding to the known range of generation and loads.

Operational planning of Kenya power grid system load flow models generation and loads

and network outages in a probabilistic way and enable calculation of the probabilistic

distribution function of the line flows. This gives system planning engineers a better feel

of future systems conditions and provides more confidence in making judgement on the

future transmission investments.

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Transmission grid is a network of power stations, transmission circuits and substation.

Energy is usually transmitted within the grid with three phase AC.DC systems require

relatively cost conversion which might be economically justifiable for particular project.

Single phase AC is used only for distribution to end users since it is not usable for large

polyphase induction motors.

The capital cost of electric power station is so high and electric demand so variable, that

it is often cheaper to import some portion of variable load than to generate it locally.

The web of interconnections between power producers and consumers ensure that power

can flow even if a few links are inoperative. The unvarying portion of the electric demand

is known as the base load and is generally served best by large facilities (and therefore

efficient due to economies of scale) with low variable costs for fuel and operations, i.e.

nuclear, coal and hydropower plants. Renewable such as solar wind, tidal etc are not

considered “base load” but can still add power to the grid.

This chapter (chapter one) will cover the background information on grid system and the

significance of operational tool for Kenya power grid system.

Chapter two will give an overview of the grid system operations, electric power

transmission, grid input and output, grid stability and load shedding on the grid system,

load balancing, failure protection and protection of the system from outages, effects of

power factor on the efficiency, single line diagram and transmission efficiency will also

be analyzed, Kelvin’s economy law, methods of load flow analysis will also be a

discussed.

Chapter three (methodology and description); discussion on what to plan for and how

to come up with the operational plan is covered. In this chapter network planning

methodology taking into consideration business plan, short term and long term plan,

planning criteria used in grid system will also be discussed. Load forecast as an

operational tool and operational maintenance of the overhead transmission line for KPGS

will also be covered.

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Chapter four (results and analysis), in this chapter results on findings on various

operations carried out by KPLC will be discussed and analyzed.

In chapter five, conclusions made from data analysis will be done and possible

operational plans suggested. This chapter will also include recommendations for further

work.

1.4 Background

Electrical energy generated at various generating plants in Kenya is put in a national

power grid system and then transported to remote local centres. Between the generating

station and the point of demand we have, transmission, sub transmission and distribution

levels of voltages.

-At transmission level, the voltage is at a higher level than sub transmission and

distribution. It supplies only large blocks of power to bulk power stations or very big

consumers (e.g. Bamburi).

-Transmission level interconnects the neighbouring generating stations into a power grid.

-Sub transmission level has a higher voltage level than distribution system; it supplies

only bigger loads, supplies a few substations compared to distribution system which

supplies a number of loads.

In Kenya the generation voltage is usually 11kV.This voltage is too low for transmission

and thus has to be stepped up for transmission over long distance.

The interconnection of various generating stations in a grid system provides the best use

of power resources and ensures greater security of supply if there is good operational plan

for the power in the grid.

1.5 Why Operational Planning for Kenya Power Grid System. A good operational tool has the following benefits to KPLC;

1. It enables mutual transfer of energy from surplus zone to deficit zone economically.

2. Enables lesser overall installed capacity to meet the peak demand.

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3. It permits the generation of energy at the most efficient and cheapest generating station

at every time.

4. It reduces the capital cost, operating cost and cost of energy generated.

5. Enables supply with minimal interruption of power in case of a major breakdown of a

generating system.

Planning of grid system operation is focused for the following benefits to the operators:

• Controlled separation and system restoration help system operators improve

restoring capability and reduce outage cost.

• Online stability and control help system operators improve real time analyzing

and controlling capabilities.

• Situational awareness helps system operators improve monitoring and

visualization capability.

In general, a good operation planning tool for power flow may improve overall

transmission reliability and performance.

1.6 Limitations of operational planning of the grid sytstem.

Even with the best coordinate control of AC power flow system, the operation of the grid

system suffers from the following problems:

1. AC network interconnection is a synchronous tie. Frequency disturbance will be

transferred to the others.

2. There is an increase in the faulty level if an existing system is interconnected

with AC tie line. Additional parallel lines reduce the equivalent reactance of

interconnected system.

3. Large power swing might result to frequency tripping.

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2.0 CHAPTER TWO: TECHNOLOGICAL REVIEW

2.0.1 Introduction

Power system losses result from transmission line characteristics and transmission lines

loading. Whereas the transmission line characteristics are constants as far as operations

are concerned, lines loading are a function of the system load and generation dispatch. In

cases where there are no generation and transmission constraints, it is possible to

optimize transmission lines loading through careful selection of generation alternatives at

various system load levels. This will significantly reduce the transmission lines losses

and therefore increase the overall transmission efficiency for KPLC.

2.1 Grid input, losses and exit At generating plants the current is produced at relatively low voltages about 1100 Volts

to 33,000 Volts, depending on the size of the unit plant. The generator terminal voltage is

then stepped up by the power station transformer to higher voltages for transmission over

a long distance.

i) LOSSES

For a given amount of power, a higher voltage reduces the current and thus the resistive

losses in the conductor. Transmitting electricity at high voltages reduces the fraction of

energy loss due to Joule heating (I2R).

In alternating current circuit, inductance and capacitance of phase conductors are

significant. The current that flow in these components of the circuit impedance

constitutes reactive power which transmits no energy to the load. Reactive current flow

causes extra losses in the transmission circuit. The ratio of real power (transmitted to the

load) to apparent power is the power factor. Systems with low power factor have higher

losses compared to systems with high power factors.

ii) Transmission grid exit

At the substations, transformers are again used to step the voltage down to a lower

voltage distribution to commercial and residential users.

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2.2 Grid stability Voltage instability is a phenomenon that causes the electric power grid to fail due to

collapsing (decrease) voltage which propagates across the grid. Voltage stability is well

understood yet challenges remain, including devising ways to best manage the electric

grid to prevent such an event, or to stop it quickly and effectively should one occur.

A system experiences voltage instability when there is progressive or uncontrolled drop

in the voltage magnitude after a disturbance, increase in load demand or change in

operating conditions. The main factor which causes this unacceptable voltage profile is

the inability of the distribution system to meet the demands of reactive power.

Under a normal condition, the bus voltage magnitude (V) increases as Q injected at the

same bus is increased. However, when V of any of the systems decrease with an increase

in Q for the same bus, the Grid system is said to be unstable.

Although the voltage instability is localized, its impact can be widespread for it depends

on the relationship between the transmitted Power, injected Q and receiving end V, this

relationship plays an important role in the stability analysis.

i. PV CURVE

Fig.2.1;P-V curve

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The relationship between transmitted P and receiving end V is of interest when

considering voltage stability of the grid system. The voltage stability analysis involves

the transfer of P from one region of the system to another, and monitoring the effect to

the effect to the system voltages.

Fig.2.1 shows a typical PV curve. It represents the variation in voltage at a particular bus

as a function of the total active power supplied to the loads or sinking areas. It can be

seen that at the “knee” of PV curve, the voltage drops rapidly when there is an increase in

the load demand. Load flow solutions do not converge beyond this point; this indicates

the system has become unstable. This point is the critical point for the system. The curve

can be used to determine the system’s critical operating voltage and collapse margin.

Operating points above the critical point signify a stable system. If the operating points

are below the critical point, the system is diagnosed to be in an unstable condition.

ii. Q-V CURVES

Voltage stability depends on how the variation in Q and P affect the voltage at the load

buses.

Fig.2.2;Q-V curve

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The influence of reactive power characteristic devices at the receiving and is more

apparent in a QV relationship. It shows the sensitivity and variation of bus voltages with

respect to reactive power injections or absorptions.

Fig.2.2 shows a typical QV curve which is usually generated by a series of load flow

solutions. Voltage stability limit is at point where the derivative dQ/dV is zero. This point

defines the minimum reactive power requirements for stable operation. An increase in Q

will result in an increase in voltage during normal operating conditions. If the operating

point is at the right hand side of the curve, the system is said to be stable.

2.2.1 Load balancing Transmission systems provides for base load and peak load capability, with safety and

fault tolerance margin. The peak load times vary by region due to the industry mix, in

very hot and very cold climates on the overall load. This makes the power requirements

vary by the season and the time of the day. Distribution systems designs usually take the

base load and the peak load into consideration.

Transmission system usually does not have a large buffering capability to match the loads

with the generation. Thus generation has to be matched to the load to prevent overloading

failures of the equipment. Multiple sources and loads can be connected to the

transmission system and should be controlled to provide orderly transfer of power.

In centralized power generation, only local control of the generation is necessary, this

involves synchronization of the generating units to prevent large transient and overflow

conditions.

In distributed power generation, the generation is geographically distributed and the

process to bring them online and offline should be carefully controlled. The load control

signal can either be sent on separate line or the power lines themselves. To load balance

the voltage and the frequency can be used as a signalling mechanism.

In voltage signalling, the variation of voltage is used to control generation, the power

added by any system increases as the voltage decreases. This arrangement system is

stable in principle. Voltage based regulation is complex to use in the mesh networks,

since the individual components and set points would need to be reconfigured every time

a new generator units match the frequency of the power transmission system. In the Drop

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Speed Control, if the frequency decreases, the power is increased. The drop in the line

frequency is an indication that the increased load is causing the generator to slow down.

2.2.2 Failure protection

Under excess load conditions, the systems can be designed to fail gracefully rather than

all at once. Brown outs occur when the supply power drops below the demand, blackouts

occur when the supply fails completely.

Rolling blackouts, or load shedding are intentionally engineered electrical power

outrages used to distribute insufficient power when the demand for electricity exceeds the

supply. Rolling blackout is the last result measure used by Kenya power and lighting

company in order to avoid a total black out of the power system.

Rolling blackout usually result from two causes:-

-Insufficient generation capacity

-Inadequate transmission infrastructure to deliver the sufficient power to the area

where it is needed.

These blackouts are scheduled at fixed times of the day and week allowing people to

work around a known interruption. KPLC does put the scheduled interruption in the

media.

2.2.3 Power outage.

Also known as power cut, power failure, power loss or blackout, this refers to long or

short term loss of electric power to an area.

Some of the causes of power outage include:-

-Fault at power stations

-Substation or other parts of the distribution system

-Damage to power lines

-Short circuit

-Overloading of electricity mains.

Power outages are categorized into three different phenomenons, relating to the duration

and effects of the outage.

A drop out:-is momentary (milliseconds to seconds) loss of power caused by a

temporary fault on a power line. Power is quickly restored once the fault is cleared.

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A brown out:-is a drop in voltage in electrical power supply, so named because it causes

lights to dim. Systems supplied with 3 phase electric power also suffer from brown outs if

one or more phases are absent, as reduced voltage or incorrectly phased.

Blackouts:-refers to the total loss of power to an area and is the most severe form of

power that can occur.

2.2.4 Protecting the system from outages

The power generation and the electrical load must be very close to equal every second to

avoid overloading of network components which can severely damage them. In order to

prevent this, parts of the system will automatically disconnect themselves from the rest of

the system, to shut themselves down to avoid damages. This is analogous to the role of

relays and fuses in households.

Under certain conditions network component shutting down can cause current

fluctuations in neighbouring segment of the network, though this is unlikely, leading to

cascading failure of a large network section. This may range from a building, to a block

to entire electrical grid.

2.2.5 Restoring power after a wide-area outage

Restoring of power after a wide-area outage can be difficult, as a power station need to be

brought back online. Normally, this is done with the help of power from the rest of the

grid. In the total absence of grid power, black start needs to be performed to bootstrap the

power grid into operation. Typically, transmission company will establish a localized

“power islands” which are then coupled together. To maintain supply frequencies within

tolerable limits during this process, demand must be reconnected at the same pace that

the generation is restored, requiring close co-ordination between power stations,

transmission and distribution.

2.3 Effects of voltage on transmission efficiency

Let us suppose that a power of (W) watt is to be delivered by a 3-phase transmission line

at a line voltage of V and power factor ��

The line current I = �√��

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Then A=��

= �√�.�.��

I = length of the line conductor

�= current density in ampere/m3

A = cross section of conductor

Now R=��

=√��

� = Specific resistance of conductor material

Line loss =3× loss per conductor = 3I²V

=3 � ²��²��²�

×√��

=√��

(2.1)

Line intake or input = Output+ Losses = W+√��

= W (1+ √��√��

)

Efficiency of transmission = Output/input= �

� (�� √�� )

(1− √��

) approx (2.2)

Voltage drop per line = IR=√��

× �√��

=��I (2.3)

Total Volume of copper = 3IA= �� √��

= √��

(2.4)

• From equation (2.1), line losses are inversely proportional to V. it is also inversely

proportional to the power factor, ��.

• Transmission efficiency increases with the voltage of transmission and power

factor as seen in equation (2.2).

• As seen from equation (2.3), for a given current density, the resistance drop per

line is constant (since �and I have been assumed fixed in the present case).

Hence, percentage drop is decreased as (V) is increased.

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• The volume of copper required for a transmission line is inversely

proportional to the voltage and power factor as seen from equation (2.4)

It is clear from the above that for a long distance transmission of an AC. Power, high

voltage and high power factor are essential. Economical upper limit of voltage is required

when the saving in cost of copper or aluminium is offset by the increased cost of

insulation and increased cost of transformers and high-voltage switches.

2.4 Power factor

The power factor has an effect on the efficiency of an AC power system. The power

factor is the real power per unit of apparent power. A power factor of one is perfect, and

99% is good.

Where the waveforms are purely sinusoidal, the power factor is the cosine of the phase

angle (φ) between the current and voltage sinusoid waveforms. Equipment data sheets

and nameplates often will abbreviate power factor as "cosφ" for this reason.

The power factor equals 1 when the voltage and current are in phase, and is zero when

the current leads or lags the voltage by 90 degrees. Power factors are usually stated as

"leading" or "lagging" to show the sign of the phase angle, where lagging indicates a

negative sign. For two systems transmitting the same amount of real power, the system

with the lower power factor will have higher circulating currents due to energy that

returns to the source from energy storage in the load. These higher currents in a practical

system will produce higher losses and reduce overall transmission efficiency. A lower

power factor circuit will have a higher apparent power and higher losses for the same

amount of real power transfer.

A lagging power factor is one in which the current is lagging behind the voltage and is

characteristic of an inductive load. A leading power factor is one in which the current is

leading the voltage and is characteristic of a capacitive load.

The Lagging Power Factor: Consider an inductive load as shown in Figure (2.3). In this

circuit, both watts and VARs are delivered from the source. The corresponding phasor

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diagram is shown in figure (2.3). The power factor angle in this case is negative, and

therefore the power factor is lagging.

Figure 2.3; the concept of lagging power factor

The Leading Power Factor: Consider a capacitive load as shown in Figure (2.4). In this

circuit, the watts are delivered from the source. The reactive power (VARs) is delivered

from the load to the source. The corresponding phasor diagram is shown in figure (2.4).

The power factor angle in this case is positive, and therefore the power factor is leading.

Purely capacitive circuits cause reactive power with the current waveform leading the

voltage wave by 90 degrees, while purely inductive circuits cause reactive power with the

current waveform lagging the voltage waveform by 90 degrees. The result of this is that

capacitive and inductive circuit elements tend to cancel each other out

2.4.1 Power Factor Improvement:

Many utilities prefer a power factor of the order of 0.95. Since industrial equipment such

as an induction motor operates at a much lower power factor, the overall power factor of

the industrial load is low. In order to improve the power factor, synchronous condensers

or capacitors are used. The synchronous machines, when operated at leading power

factor, absorb reactive power and are called synchronous condensers. These machines

need operator attendance and require periodical maintenance.

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Figure 2.4; the concept of leading power factor

Power factor capacitors are static equipment without any rotating parts and require less

maintenance. Therefore, shunt capacitors are widely used in power factor correction

applications. The shunt capacitors provide kVAR at leading power factor and hence the

overall power factor is improved.

2.5 Methods of voltage control

Voltages at different buses of power system vary with changes in load. The voltage is

normally high at light load conditions and low at heavy-load conditions. To keep voltages

within permissible limits, means must be provided to control the voltage, i.e. to increase

the voltage when it is low and to reduce it when it is too high. The following methods are

used for voltage control in a power system:

• Tap changing transformers

• Shunt reactors

• Synchronous modifiers

• Shunt capacitors

• Series capacitors

• Static VAR system(SVS)

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Tap changing transformers

The change in voltage is affected by changing the number of turns with taps. For

sufficiently close control of voltage, taps are usually provided on the high voltage

winding of the transformer. There are two types of tap-changing transformers:

a) Off-load tap-changing transformers

b) On-load tap-changing transformers

For off-load tap-changing transformers, the transformer is disconnected from the main

supply when the tap setting is to be changed. On-load tap changing transformers are used

in order not to interrupt the supply during the tap setting. Such a transformer is known as

tap-changing under load (TUCL) transformer.

Adjusting the voltage by means of shunt reactive elements is known as shunt

compensation. Shunt compensation consists of static shunt compensation and

synchronous compensation. Static shunt compensation uses shunt reactors, shunt

capacitors, and static var system (SVS).in synchronous compensation, synchronous phase

modifiers are used. Adjusting the system voltage by connecting capacitors in series with

the line is called static series compensation.

2.6 Kelvin’s economy law

Several factors are considered in designing a line. Economy is also one of the factors

which should be taken into consideration to select a conductor for the line. The cost of

conductor material forms a substantial part of the total line cost. A design is considered to

be more efficient if the total annual cost is minimum. The total annual cost consists of

two parts:

• the fixed standing charges

• the running charges

The fixed charges consist of the interest on capital cost of the conductor, the allowance

for depreciation, and the maintenance cost. The running cost consists of cost of electrical

energy wasted due to losses during operation. But the capital cost and the cost of

electrical energy wasted in the line is governed by the size of the conductor. A bigger size

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of conductor would be more costly, but due to its lesser resistance the cost of energy due

to �� loss will be smaller.

Annual interest and depreciation cost

�� ∝ � or �� = �� (2.5)

And annual cost of energy dissipated in the line

�� ∝ �� or �� = ��

� (2.6)

Where �� and �� are constants, and � represents the area of cross section of conductor.

The total annual cost may therefore be given by,

� = �� + �� = �� + ��

(2.7)

From economical design there will be one size of the conductor at which the total cost is

a minimum. For the most economical cross-section, the total annual cost is differentiated

with respect to the cross section and the result is equated to zero. That is,

��

= 0: (2.8)

��

(�� + ��

)=0: �� − �� = 0 and �� = ��

� (2.9)

That is,�� = �� and � = � ��

(2.10)

From the above equations the most economical cross section area of the conductor is that

which makes use of the annual cost of energy loss equal to the annual interest and

depreciation on the capital cost of the conductor material. Kelvin’s law is itself not

sufficient to estimate the cross section area of the conductor. It gives the most economical

current density. The most economical cross section area is given by the last equation

(2.10).

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2.7 Fault analysis

Fault analysis is also known as short circuit study or short circuit analysis. Fault analysis

includes the following:

i. To determine the values of voltages and currents at different points of the system

during fault.

ii. Determine the rating of the required circuit breakers

iii. Selection of appropriate schemes of protective relaying.

Generally, the purpose of fault analysis is to save the system from abnormal conditions

within a minimum time.

2.8 Single Line Diagram

Single line diagram is a simplified notation for representing a three-phase power system.

The one-line diagram has its largest application in power flow studies. Electrical

elements such as circuit breakers, transformers, capacitors, bus bars and conductors are

shown by standardized schematic symbols. Instead of representing each of three phases

with a separate line or terminal, only one conductor is represented. The theory of three-

phase power systems tells us that as long as the loads on each of the three phases are

balanced and the lines, transformers and bus bars are symmetrical, we can consider each

phase separately. In power engineering, this assumption is usually true (although an

important exception is the asymmetric fault), and to consider all three phases requires

more effort with very little potential advantage. A one-line diagram is usually used along

with other notational simplifications, such as the per-unit system. A secondary advantage

to using a one-line diagram is that the simpler diagram leaves more space for non-

electrical, such as economic information to be included. A presentation of a single line

diagram KPLC grid system is shown appendix3. This gives a picture of a typical

electricity power system.

2.8.1 Concept of bus

Concept of bus in single line diagrams is essentially the same as the concept of a node in

an electrical circuit. Just keep in mind that there is one bus for each phase.

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Figure 2.5; bus concept

Buses are shown in SLDs as short straight lines perpendicular to transmission lines and to

lines connecting equipment to the buses. In actual substations, the buses are made of

aluminium or copper bars or pipes and can be several meters long. The impedance of

buses is very low, practically zero, so electrically the whole bus is at the same potential.

Of course, there is line voltage between the buses of the individual phases.

Single line diagrams like in figure 2.5 are used to illustrate the layout of buses in a

substation. The arrangement of figure two is called a “breaker and a half”. There are three

breakers for every two connections of lines or transformers to the bus, i.e. 1 ½ breakers

per termination.

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2.9 Load Flow Calculation Method

The goal of a power flow study is to obtain the complete voltage angle and magnitude

information for each bus in a power system for specified load and generator real power

and voltage conditions. Once this information is known, real and reactive power flow on

each branch as well as generator reactive power output can be analytically determined.

Due to the non-linear nature of this problem, numerical methods are employed to obtain a

solution that is within an acceptable tolerance.

The solution to the power flow problem begins with identifying the known and unknown

variables in the system. The known and unknown variables are dependent on the type of

bus.

Ø A bus without any generators connected to it is called a Load Bus.

Ø With one exception, a bus with at least one generator connected to it is called a

Generator Bus.

Ø The exception is one arbitrarily-selected bus that has a generator. This bus is

referred to as the Slack Bus. Slack Bus at which:

P = ∞

Q = ∞

V =constant

The table 2.1shows classification of load buses: Either the bus self and mutual

admittances which compose the bus admittances matrix Y bus may be used in solving the

load flow problem. We confine to methods using admittances. Operating conditions must

always be selected for each study.

In the power flow problem, it is assumed that the absorbed real power and reactive power

at each Load Bus are known. For this reason, Load Buses are also known as PQ Buses.

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Table 2.1; classification of load buses

Bus type Known variable Unknown variable

1 SL,Slack V,theta Pg,Qg

2 PV,Voltage

controlled bus

Pg,V Qg,theta

3 PQ,Load bus Pg,Qg,Pd,Qd V,theta

Where;

V =voltage magnitude

Theta =voltage angle

Pg, Qg =MW, MVar generation

Pd, Qd =MW, MVar demand

For Generator Buses, it is assumed that the real power generated Pg and the voltage

magnitude V are known. For the Slack Bus, it is assumed that the voltage magnitude V

and voltage angle are known. Therefore, for each Load Bus, both of the voltage

magnitude and angle are unknown and must be solved for; for each Generator Bus, the

voltage angle and Q must be solved. In a system with N buses and R generators, there are

then 2(N − 1) − (R −1) unknowns. In order to solve the 2(N − 1) − (R − 1) unknowns,

there must be 2(N − 1) − (R− 1) equations that do not introduce any new unknown

variables. The possible equations to use are power balance equations, which can be

written for real and reactive power for each

bus, for the bus k is given. The real power balance equation is:

0= − ��+ ∑ �� + ��

�� = net power injected at bus i

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�� = real part of the element in the Y bus corresponding to the �� row and �� column.

�� = imaginary part of the element in the Ybus corresponding to the �� row and kth

column

�� = difference in voltage angle between the �� and �� buses.

�� = net reactive power injected at bus i.

N = total number of buses

�� = voltage at bus i

�� = voltage at bus k

k = varying index

V = voltage magnitude

Figure 2.6 Typical scheme of load flow characteristic where Pi is the network power

injected at bus i,�� is the real part of the element in the Ybus corresponding to the

��row and �� column, �� is the imaginary part of the element in the Ybus

corresponding to the �� row and �� column and �� is the difference in voltage angle

between the ith and ��buses.

Figure 2.6; typical scheme of load flow characteristic

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The reactive power balance equation is:

0= − ��+ ∑ �� (2.11)

Where Qi is the network reactive power injected at bus i. Equations included are the real

and reactive power balance equations for each Load Bus and the real power balance

equation for each Generator Bus. Only the real power balance equation is written for a

Generator Bus because the network reactive power injected is not assumed to be known

and therefore including the reactive power balance equation would result in an additional

unknown variable. For similar reasons, there are no equations written for the Slack Bus.

2.9. I Power Flow Methods

Load flow can be calculated with,

1. Newton-Raphson method.

2. Gauss-seidal method.

1. Newton-Raphson method

Newton's method (Newton–Raphson method or the

Newton–Fourier method) is perhaps the best known method for finding successively

better approximations to the zeros (or roots) of a real-valued function.

Unlike Gauss-Seidel, which updates the bus voltage one at a time, Newton Raphson,(NR)

solves a voltage correction for all the buses and updates them. Comparing NR with GS,

GS has problems when the system becomes large. One reason is the presence of negative

impedances as a result of 3-winding transformer representation. GS tends to increase in

iteration count and is slow in computer time.

Most production-type power-flow programs use the power equation form with polar

coordinates, for any bus k we have:

�� = �� + �� = �� (2.12)

Since�� = ��

∗ (2.13)

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�� = �� . ��

��∗�� − �� = �� . �� . (2.14)

�� = ∑ �� (2.15)

Substitution of�� given by Equation (2.15) in Equation (2.12) yields

�� + �� = �� ∑ (�� − �� )��∗�

� �� (2.16)

n = unknown

ki = bus

V = Voltage vector

P = Power

Q = reactive power

θ= phase angel

��=is the phasor voltage to ground at node i

��= is the phasor current flowing into the network at node i

The product of phasor �� and ��∗ may be expressed as;

��∗ = V�V� �cos θ�� + j sin θ��

Where �� = �� − ��

Therefore, the expressions for�� and�� may be written in real form as follows:

�� = �� ∑ (�� V� cos θ�� + �� V� sin θ�� )�� (2.17)

�� = �� ∑ (�� V� sin θ�� − �� V� cos θ�� )�� (2.18)

Thus, P and Q at each bus are functions of voltage magnitude V and angle θ of all buses.

24

The process continues until a stopping condition is met. A common stopping condition is

to terminate if the norm of the mismatch equations are below a specified tolerance.

A rough outline of solution of the power flow problem is:

• Make an initial guess of all unknown voltage magnitudes and angles. It is common to

use a "flat start" in which all voltage angles are set to zero and all voltage magnitudes are

set to 1.0 p.u(per unit value).

• Solve the power balance equations using the most recent voltage angle and magnitude

values.

• linearize the system around the most recent voltage angle and magnitude values

• solve for the change in voltage angle and magnitude.

• update the voltage magnitude and angles

• Check the stopping conditions, if met then terminate.

2. The gauss-seidal method

Solutions of load flow analysis follow an iterative process by assigning estimated values

to the unknown bus voltages and calculating a new value for each bus voltage from the

estimated values from other buses, the real power specified and the reactive power

specified or voltage magnitude new set of values for voltages is thus obtained for each

bus and used to calculate still another set of voltages. Each calculation of a new set is

called iteration. Iterative process is repeated until the changes at each bus are less than a

specified minimum value.

Consider solution based on expressing voltage of a bus as a function of real and reactive

power delivered to a bus from generators or load connected to the bus, the estimated

voltages at the other buses, the self and mutual admittances of the nodes. Consider three

bus systems, with swing bus designated number 1, computation starts at bus 2.if P2 and

Q2 are the scheduled real and reactive power entering the system at bus 2,

25

��∗ = �� + �� (2.19)

Where,

�� = ��

∗ (2.20)

In terms of self and mutual admittances of the nodes, with generators and loads omitted

since the current into each node is expressed as in equation (2.20)

��

∗ = �� + �� + �� (2.21)

Solving for �� gives,

�� = ��

{��

∗ − �� + �� + ��} (2.22)

This gives corrected value for�� based upon scheduled �� and �� when the values

estimated originally are substituted in for the voltage expressions on the right hand side

of the equation. The calculated value for �� and the estimated value for ��∗ will not agree.

Substituting the conjugate of the calculated values of �� for��∗ in eqn (2.22) to calculate

another value for ��,agreement is reached to a good degree of accuracy after several

iterations and would be the correct value for ��with the estimated voltages and without

regard to power at the other buses. Two successive calculations of ��,the second being

like the first one except for the correction of ��∗ are recommended at each bus before

proceeding to the next one.

As the corrected voltage is found at each bus, it is used in calculating the corrected value

of the next. The process is repeated at each bus consecutively throughout the network

(except at the swing bus) to complete the first iteration. Then the entire process is carried

out again and again until the amount of correction in voltage at every bus is less than

some predetermined precision index.

An erroneous solution may result to convergence if the original voltages are widely

different from correct values, this can be avoided if original values are of reasonable

magnitude and do not differ too widely in phase, any unwanted solution is usually

26

detected easily by inspection of the results since the voltages in the system do not

normally have a range in phase wider than 45 degrees and the difference between nearby

buses is less than about 10 degrees and often very small.

If there are N buses the calculated voltages at any bus k where�� and�� are given is

Solving for �� gives,

�� = ��

{��

∗ − ∑ ��}�� (2.23)

Where n≠ �, values for the voltages are the most recently calculated values

corresponding to buses. Excessive number of iterations is required before the corrections

are within an acceptable precision index if the corrected voltage at a bus merely replaces

the best previous value as the computation proceeds from bus to bus. The multipliers that

accomplish this improved convergence are called acceleration factors.

At the bus where voltages magnitude rather than reactive power is specified, the real and

imaginary components of the voltages for each iteration are found by first computing a

value for the reactive power. From eqn (2.23)

�� − �� = (�� + ∑ �� )��

∗ (2.24)

Where n≠ �,if we allow n=k then,

�� − �� = ��∗ ∑ ��

�� (2.25)

�� {��∗ ∑ ��

�� } (2.26)

Where IM means imaginary part of the equation, Equation (2.26) gives reactive power

for the best previous values at the buses, this value is substituted in equation (2.23) to

find a new ��.The result is the corrected complex voltage of the specified magnitude.

With good load flow analysis, the company providing power delivery is expected to

provide (electrical energy) in sufficient quantities to areas that need electricity through

the grid system.

27

2.10 Transmission line Insulators and Supports

Overhead line insulators are used to separate line conductors from each other and from

the supporting structures electrically. In designing line insulators the following should be

taken into consideration:-

1) Should have high permittivity so that it can withstand high electrical stress.

2) Should posses high mechanical strength to bear the conductor load under worst

load conditions.

3) It needs to have high resistance to temperature changes to reduce damages from

power flashover.

4) The leakage of current to earth should be minimum to keep the corona loss and

radio interference within reasonable limits.

5) The insulator material should not be porous and should be free from impurity and

cracks which may lower the permittivity.

2.10.1 Electrical Failure of Insulators

Electrical failure of insulators occurs either by puncture or flashover. In the case of a

puncture the arc passes the body of the insulator. Flashover is caused by an air discharge

between the conductor and earth through air surrounding the insulator. It is either due to

line surges or due to the formation of wet conducting layers over the insulator

surface.Normally, the insulator is not damaged by flashover but it becomes useless after

the puncture.

Sufficient thickness of material is used in the insulators to prevent the puncture under

surge conditions. Flashover is reduced by increasing the resistance to leakage currents.

The length of the leakage path is made large by constructing several layers called

petticoats or rainsheds.This keeps the inner surfaces relatively dry in wet weather and

thus provides sufficient leakage resistance to prevent flashover.

28

For satisfactory operation, the flashover should occur before puncture. The ration of

puncture voltage to flashover voltage, called the factor safety is kept as high as possible.

The flashover voltage is reduced considerably by moisture and surface deposits.

2.10.2 Line supports

Transmission line support perform the following

• Keep proper spacing between the conductors.

• Keep the conductors at prescribed distances from its grounded parts.

• Maintain specified ground clearance.

Line supports may be inform of poles or towers.

i) Wood poles

Of the various types of support wood poles is the cheapest. When properly treated with a

preservative such as creosote a very satisfactory service is obtained. A wood pole has the

limitation of height and diameter. Double pole structure of “A” or”H” shape- type are

used where greater strength is required.

ii) Concrete pole

Concrete pole is reinforced to give greater strength and is alternative to a wood pole. It

has longer life than that of wood pole because of little deterioration. The maintenance

cost is low. Reinforced concrete poles are very heavy and are liable to damage during

loading, unloading transportation and erection due to their brittle nature.

iii) Steel poles

The use of tubular steel poles or girder steel masts is favoured for low and medium

voltage distribution work. Longer spans are possible with steel poles. The poles need be

galvanized or painted periodically to prevent them from corrosion. The maintenance

expense is therefore more.

29

iv) Supporting towers

Steel towers are developed for high voltage and where very long spans are estential.The

long spans cuts the insulation cost considerably as fewer supports are to be provided for.

The possibilities of breakdown for steel towers are low. The towers are either made of

steel or aluminium.

30

3.0 CHAPTER THREE: METHODOLOGY AND DESCRIPTION

3.0.1 Introduction The ability of secure and sufficient electrical energy for consumers in a perfect condition,

beside power production needs to have, enough transmission and distribution capacity of

the network. With these considerations, while keeping in mind that electrical energy

needs increase with time due to industrial growth and varies from time to time, an

expansion of the network in stages is necessary, so that neither bottleneck in the supply,

like by congestion of transmission connection or overload of transformers, nor

uneconomical investments are made. For this reason, operational planning and

maintenance for KPGS is paramount.

3.1 Transmission planning.

The purpose of transmission system planning is to develop a reliable and efficient

transmission system for transforming power from areas of generation to areas of demand

(load) under varying system conditions while operating equipment within accepted rate.

The system conditions should include changing demand patterns, generation changes and

equipment outages (planned or unplanned).KPLC operates on scheduled dispatch to meet

the load demand without failure and with the maximum efficiency thus to reduce cost per

unit of kWhr to its customers and reduce their operation cost.

3.2Network planning

Power system planning is the recurring process of studying and determining which

facilities and procedures should be provided to satisfy and promote appropriate future

demands for electricity. The electric power system as planned should meet or balance

social goals. These include availability of electricity to all potential users at the lowest

possible cost, minimum environmental damage, high levels of safety and reliability, etc.

Plans should be technically and financially feasible. Plans also should achieve the

objectives of KPLC, including minimizing risk. KPLC should ensure that no transmission

lines passing over building , ensuring clear access to the region of transmission lines, any

risk to people like transmission lines leaning on plants is taken care of by “clearing the

31

way”. Line inspection is done through thermal vision inspection to determine hot spot at

the joining points at substation and thus avoid instances of sparking or fire resulting from

“hot spots” thus good maintenance for substation.

Network losses

To start planning any network, it is important for KPGS operators to know if the network

losses are related to population density and electricity use, or do they rather depend on

network design. If so, is there a large scope for improvement by changing network

topology and the specification of network components such as cables and transformers.

3.2.1 Technical criteria for planning purpose

Technical criteria used by KPLC in transmission system planning can be divided into

three main categories; System reliability, Steady state performance and Stability

Transmission system Rolling blackouts, or load shedding are intentionally engineered

electrical power outrages used by KPLC to distribute insufficient power when the

demand for electricity exceeds the supply. Rolling blackout are last result measure used

by Kenya power and lighting company in order to avoid a total black out of the power

system. These blackouts are scheduled at fixed times of the day and week allowing

people to work around a known interruption. KPLC does put the scheduled interruption

in the media.

For Kenya power grid to be said stable, KPLC should work to ensure the following:

§ Satisfactory state-the transmission system is said to be in a satisfactory state if

it can supply aggregate electrical demand and energy requirements of their

customers at all times.

§ Adequacy-the ability of the electric systems to supply aggregate electrical

demand and energy requirements of their customers at all times, taking into

account scheduled and reasonably expected unscheduled outages of system

elements.

§ Security-the ability of the electric systems to withstand sudden disturbances

such as electric short circuits or unanticipated loss of system elements.

32

§ Secure state-the transmission system is said to be in a secure state if it can

satisfy the test for system adequacy for all reasonably expected conditions

including scheduled outages of system elements and return to a satisfactory

state after a sudden disturbance. KPLC uses a deterministic approach to

planning. This approach is consistently applied in most transmission in the

world.

The main interconnection transmission system should be planned and developed to

maintain N-1 security criterion, meaning that the system is in a secure state with all

transmission facilities in surface and in a satisfactory state following credible single

contingency events.

The single contingencies to be considered under N-1 are:

• Loss of a single transmission circuit

• Loss of a single bus section

• Loss of interconnecting transformer

• Loss of a single generating unit provided that the system can be

maintained in a secure state.

The loss of an element could either be planned i.e. as part of scheduled maintenance or

unplanned either by in advertent disconnection or as a consequence of a fault occurring in

the affected element.

The assumption of the N-1 criterion is that maintenance is carried out in times of light

load or using “live line techniques” so that the risk and consequence of interruption due

to unforeseen event during a period of maintenance is minimized.

3.2.2 Steady state criteria

Steady state performance is the normal operating condition of the system with all

scheduled plants in the service or the condition of the system following a disturbance.

In planning a network, KPLC assess the reactive power requirements under light and

heavy load to ensure that the reactive demand placed on the generators, be it to absorb or

generate reactive power, does not exceed the capability of the generators. MVAR in the

33

grid is produced by generators and transmission lines, slightly loaded line has high

capacitive effect. KPLC uses compensators to reduce the impact of reactive power to the

functional power supplied. KPLC has four compensators, two at Lassos and two at Rabai

each of 15 MVAR inductive, “plans are under way for more compensator to be installed

at various substations in Kenya”, planning Engineer KPLC-Juja control centre.

Network frequency will fall if there is insufficient total generation to meet demand.

Although the reduction in frequency will cause a reduction in power demand, it is

unlikely that this will be sufficient and loads should be disconnected until the frequency

rises to an acceptable level.

• Steady State Voltage Limits:

High Voltage;

The network is designed to achieve a continuous network voltage at a user's

Connection not exceeding the design limit of 108% of nominal voltage and not falling

below 92% of nominal voltage during normal and maintenance conditions for KPGS.

• Frequency Limits: Under emergency conditions the network frequency may vary

between 49.7 – 50.2 Hz,(this is the region of frequency at which KPGS is allowed to

operate at) until the under frequency load shedding schemes operate to reduce the load on

the network.

3.2.3 Network Planning Methodology

Network planning for KPLC involves the following:

• Business planning

• Long-term and medium-term network planning

• Short-term network planning

• Operations and maintenance

34

Operating planning of KPGS cannot be carried out without taking into consideration the

various Agencies involved and their roles:

Ø KenGen (Kenya Electricity Generating Company)

KenGen is the major Electricity Generating Company in Kenya and Generates over

80% of the country power. KenGen Generates and sale power to KPLC.

Ø Kenya Power and Lighting Company (KPLC)

KPLC purchases bulk power from Generating companies transmits and distributes

electricity. KPLC is responsible for retailing electricity to customers. It is the only

licensed public electricity supplier in Kenya.

Ø Electricity Regulating Board (ERB)

ERB Regulates the electricity power sector. It protects consumer interests and guarantees

the economic and financial viability of sub-sector utilities .It reviews and adjusts tariff for

everyone who transmits and distributes electricity for sale.

In doing operational planning for KPGS, KPLC need to consider various power

generators, with IPPs associated with higher cost of power, plans have to be put into

consideration to seek other sources of power during drought which affects the over-

reliance on hydropower.

Because KPLC has a monopoly on network functions, ERB calculates on Tariffs, weigh

KPLC’s revenue requirements heavily.

In addition ERB determines a reasonable rate of return on the capital invested to provide

electricity services .ERB is currently working with KPLC to reduce transmission and

other system losses to less than 15%, this will reduce overall costs to the consumer for

electricity power.

The Power Purchase Agreements (PPAs) that KPLC has with IPPS are long-term,

bilateral take or pay contracts. Each agreement has a bulk tariff structure that includes

35

capacity charge, energy charge, fuel pass through, and a clause to increase prices based

on indexed rates of inflation.

Business planning layer determines the planning that the operator must perform to ensure

that the network will perform as required for its intended life-span. The Operations and

Maintenance layer, however, examines how the network will run on a day-to-day basis.

The network planning process begins with the acquisition of external information. This

includes:

Forecasts of how the network/service will operate; the economic information concerning

costs; and the technical details of the network’s capabilities. Because of the complexity of

network dimensioning, this is typically done using specialized software tools. Whereas

researches typically develop commercial software to study a particular problem, network

operators in KPLC typically make use of commercial network planning software

(pss/e).The available generating plants in Kenya can be summarized as shown on the

table 4.1to 4.3.

Some other factors taken into consideration in operational planning and affect the cost of

power are also taken into consideration. These factors are:

a) Diversity factor

This is the ratio of sum of the individual maximum demand to simultaneous maximum

demand.

Diversity factor (DF) = ��

Usually, the maximum demands of various consumers do not occur at the same time and

simultaneous maximum demand is less than their total maximum demand. A large

diversity factor has the effect of reducing the maximum demand. Consequently, lesser

plant capacity is required. This reduces the capital investment on the plant and the cost of

generation is reduced. KPLC used to improve diversity factor by giving incentives to

industries and farmers to use electrical energy at night or during light-load

periods.Currently ,there are no special tariffs to consumers for peak and off -peak. As

36

part of their business plan national control centre determines the value of diversity factor

and this information is used by the management in determining short and long-term plans

for the grid.

b) Annual plant factor

The ratio of actual energy generated per annum to the energy that would have been

produced if the plant had operated continuously at the maximum rating.

Most of the generating plants feeding into the KPGS are hydropower plants and they

produce more than 50% of the power fed into the grid. KPLC needs to plan for failure of

most of these plants during dry span when most of the rivers have low water levels and

the plants cannot provide to the required capacity. Alternative sources which exist should

be considered. These include provision of more diesel and gas power plants to substitute

for low power producing hydro plants, this is part of the long-term plan which should be

taken into consideration for KPGS to meet its grid demands.

c) Load factor

This is the ratio of the average load to the maximum load on the system during period in

consideration. It is a measure of the extend to which the necessary total investment is

being utilized, the lower the load factor ,the more expensive and thus less returns hence

the more the cost of electrical energy .High load factor means better utilization of the

installed capacity and hence better use of the capital expenditure on plant thus the cost is

low. From the national control centre, load factor for KPGS can be obtained because of

load data availability, KPLC uses load factor to determine the cost of generation per unit

(kWhr) and maintenance cost. The higher the load factor the lesser will be the cost of

generation per unit for the same maximum demand.

d) load curve as an operational tool

With the load curve for KPGS, the following information is obtained

• Load variation during various hour of the day.

• The maximum load demand for the grid system

37

• Total energy utilized for the period under consideration.

• Average load

• Load factor

Higher load factor means more uniform load pattern with less variation in load.

Load curves are useful operational tools for the following reasons:

• It enables the KPGS operators to choose the most economical sizes of the various

generating plant units.

• Estimation of the generating cost can be done using the information obtained from

load curve.

• It enables KPGS operators to determine the operating schedule of the power

station i.e. the sequence in which different generating units should run.

• It enables selection of the base load and peak load plants to supply the power grid.

In Kenya power grid system, base plants are basically of two types i.e. hydro plants

and geothermal plants; this is because their running cost is the lowest. Peak load

plants are diesel and gas plants.

3.2.4 Planning Criteria

Planning criteria is a practical approach to select a predetermined number of the best

network system, expansion, alternatives according to the given multiple criteria and

accounting for uncertainty factors and proposed decision. In general case, the number of

optimization criteria is unlimited. They are used as a planning and design tool to protect

the interests of all network users in terms of reliability and quality of supply.

3.2.5 Contingency Criteria

Contingency criteria relate to the ability of the network to be reconfigured after a fault so

that the unfaulted portions of the network are restored. contingency plan for KPLC

involves determining line to ground fault current, this helps them to put the right over

current relay to trip incase of line fault. Determination of the effects of plant failure to the

grid system stability is also an important parameter for it helps the operator to come up

with plan of action in case this happens.

38

• Urban High Voltage Distribution Feeders: High voltage distribution feeders in urban

areas are planned and designed so that, for a zone substation feeder circuit or exit cable

fault, the load of that feeder can be transferred to adjacent feeders by manual network

reconfiguration. Where practical, the network shall be planned and designed so that, in

the event of a failure of a zone substation transformer, all of the load of that transformer

can be transferred to other transformers within the same zone substation and adjacent

zone substations.

Rural High Voltage Distribution Feeders: The radial nature of rural distribution

feeders normally precludes the application of contingency criteria to these feeders.

However, where reasonably achievable, interconnection between feeders should be

provided, and reclosures and sectionalizes shall be installed to minimize the extent of

outages.

• Low Voltage Distribution Networks: Where practical, low voltage distribution

networks in urban areas are constructed as open rings to provide an alternative supply to

as many customers as possible.

3.3 Load forecasting as an operational tool

Load forecasting explains the drivers, factors and uncertainties influencing future

electricity demand in the country. A low load forecasted load leads to an under expanded

power system which can lead to brownouts or black outs in the power system. On the

other hand, an over forecasted load leads to an over expanded power system. In the latter

case, the unnecessary costs are passed on to the power consumers through a higher power

tariff. KPLC takes into consideration factors that affect electricity demand. The key

factors are electricity price, number of the electricity appliances, income,temperatures

and consumer patterns which differ by region and consumer groups. Meanwhile, KPLC

has to take into consideration econometric forecasting series data for vision 2030 into

consideration for any future developments.

3.4 KPGS Operational maintenance of Overhead Power line.

For line maintenance, KPLC has annual inspection which is done by both ground patrol

team and also aerial inspection by air mobile crew using the company chopper. Current

39

detailed aerial inspection approach uses trained inspectors who fly aboard helicopters to

inspect the lines with binoculars and cameras, while recording the data in a logbook. The

procedure is performed while the helicopter hovers over and around power lines and

structures, creating an element of danger for the pilot and the inspector. Information on

observed or potential overhead line defects is thus of great value.

A wide variety of items need to be inspected for defects, which generally depends on the

size of the item and the level of details required;

1) Large scale items: sagging spans, leaning poles, broken or slack stay wires, and tree

encroachment.

2) Medium scale items: equipment mounted on the poles, high voltage and low voltage

fuse units, air break switches, and anti-climbing guards.

3) Small scale items: broken or chipped insulators, discoloration due to corroded joints on

conductors, and traces of arcing on fuse gear or switches.

After inspection, the necessary maintenance required is carried out on the lines.

With the data analysis system, it is possible to build a profile database for each overhead

power line, including its more accurate position, some related images, and possible

defects or warnings.

Thermal vision inspection of substations and connection points of transmission lines is

also carried out to determine the hotspots.

3.5 Responsibilities of National Control Centre (NCC)

Monitoring of the Kenya transmission network is done at the national control centre

located along Juja road Nairobi.

The national control centre is specifically responsible for the following:

• Long, medium and short term planning of the future operation of the power

system.

• Proper functioning and administration of the Power System.

40

• Control and monitoring of the entire transmission network consisting of all

220kV and 132kV transmission lines and substations as well as the infeeds into

the sub-transmission and distribution networks.

• Voltage control in the 220kV, 132kV network and the voltages at the infeed

points to the 66kV and 33kV networks (bus voltage).

• Security analysis of the overall network and applying control actions that

achieve the goal of system security and economy.

• Supervision and monitoring of system and frequency and initiating corrective

measures as necessary.

• Determination of spinning reserve for large and medium size PS

• Coordination of power plants in the country. Control of the plants is under the

responsibility of KenGen and the owners of the IPPs.

• Co-ordination of generation plant and transmission line equipment

maintenance (outage scheduling).

• Restoration of the system after partial or total black-outs.

• Analysis of outages affecting the Power System and equipment.

• Preparation of system operation statistics.

• Preparation of management reports together with other reports related to

operation and performance of the power network.

Prior to the restructuring / unbundling of the Kenyan power sector into transmission

(KPLC) and Generation (KenGen), the NCC was also responsible for the control of the

power stations. Now the responsibility of the NCC is limited to short, medium and long

term operational planning and real time coordination.

41

4.0 CHAPTER FOUR: RESULTS AND ANALYSIS

4.0.1 Introduction

The entire 220 and 132 kV transmission system is supervised from the National Control

Centre (NCC). At 220/132 kV, 220/66 kV and 132/66 kV substations, the NCC also

controls the 66 kV busbar voltage. In case of SCADA system disturbances, the 220kV

and 132kV substations can also be controlled from the Regional Control Centres (RCCs)

.The National Control Centre (NCC) located at Juja Road in Nairobi is responsible for

operation of the Kenyan power system as a whole.

Fig. 4.1 Photograph of Engineer Kibet NCC operator

4.1 Network monitoring and control

The availability of information about the actual status and loading of the transmission

network at any given time is a precondition for effective and optimum operation of the

Kenyan Power System. Monitoring of Kenya power grid system is done by use of

42

SCADA (Supervisory Control and Data Acquisation).Monitoring of the power enables

planning for dispatch to the grid. The dispatcher must always be informed about:

• The network topology, which is the switching status of the network and includes

the position indication of all circuit breakers and isolators.

• The voltage level at each 220/132 and 66kV busbar of the transmission system

and the voltages at the in feed points to the distribution networks.

• The actual loading of each network element including all major generators,

220 kV, 132kV and 66 kV lines, all reactors and capacitors at all transmission

system substations as well as all 220/132 kV, 220/66kV, 132/33kV and 66/33 kV

transformers,

• The energy exchanged with power producers synchronized to the Kenyan Power

system as well as energy supplied to distribution networks and large customers.

• Any event or disturbance that occurs in the network under the control of KPLC

including information of its cause and the sequence of disturbances.

4.2 Power Generating plants contributing to KPGS

Table 4.1KenGen installed capacity as at 15th April, 2009.

Station Machine Rating (MW)

Installed Capacity (MW)

Effective Capacity (MW-Normal)

Hydropower plants Masinga No.1&2 = 20 40 40 Kamburu No. 1,2,3 = 31.4 94.2 88 Gitaru No. 2&3 = 72.5

No.1= 80 145 80

216

Kindaruma No.1&2 = 22 44 40 Kiambere No.1 = 72

No.1 = 84 72 84

72 84

Turkwel No.1&2 = 53 106 106 Sondu No.1&2 = 30 60 60 Tana No. 1&2 = 2

No.3 = 2.4 No. 5&6 = 4

Retired 2.4 8

10

Wanjii No. 1&2 = 2.7 No. 3&4 = 1

7.4

7.4

Gogo No. 1&2 = 1.125 2.25 2

43

Ndula No. 1&2 = 1.0 2 2 Sagana No. 1,2&3 = 0.5 1.5 1.5 Mesco 0.38 0.38 0.36 Sossiani No. 1&2 = 0.2 0.4 0.4 Total Hydro 745.53 729.66 Steam/Geothermal Ol-Karia 1 No. 1,2&3 = 15 45 45 Ol-Karia 2 No. 1&2 = 35 70 70 Kipevu Steam No.6 = 29

No.7 = 33 Retired Retired

Total Steam/Geothermal

115 115

Gas GT Kipevu KVN No. 1&2 = 30 60 60 GT N/South Fiat 13.5 13.5 10 Gas Total 73.5 70 Diesel Kipevu DP1 No. 1 to 6 = 12.5

Effective = 10.0 75 60

KenGen Total 1009.03 974.66

0perational IPPs and EPPs

At present, there are four Independent Power Producers (IPPs) in Kenya that generate and

sell electricity in bulk to the Kenya Power and Lightning Company (KPLC), which is the

country’s only public electricity supplier.

Table 4.2 shows installed plant capacity for IPPs as at 15th April, 2009.

Station Machine Rating (MW) Installed Capacity (MW)

Effective Capacity (MW)

N/South Iberafrica No. 1to 8 = 5.46 No. 9&10 = 6.0

55.68 55.68

Orpower4 No. 1,2&3 = 4.33 No. 4, 5 & 6 =12

12.99 36.00

12.99 36.00

Tsavo No. 1 to 7 = 10.77 75.39 75.39 Mumias Sugar 2 2 2 IPPs Total 182.6 182.6

44

The four IPPs are as follows:

Iberafrica Power Ltd (55.68 MW), Tsavo Power Company (75.39 MW) , Orpower (49

MW) and Mumias (2MW) currently being upgraded to reach 25MW.In1997, in response

to a severe shortage of power three IPPs were negotiated as 7-year Power Purchase

Agreement (PPAs). Three of the original IPPs have signed follow up contracts. In 2001,

Tsavo Power Company signed a 20-year PPA, and, in 2004, Iberafrica Power signed a

20-year PPA and has increased its capacity from 13MW to now 55.68MW.

Following a dry spell and increased power demand especially in Nairobi region, KPLC

has contracted Emergency Power Producers (EPPs) with total capacity of 146MW to

contribute to the national power grid following low dam levels being experienced in

Kenya. These includes: Aggreko Embakasi1, Aggreko Embakasi2 and Aggreko Eldoret.

Table 4.3 shows installed plant capacity for EPPs as at 15th April, 2009.

Station Installed Capacity (MW)

Effective Capacity (MW)

Aggreko Embakasi 1 60 60 Aggreko Embakasi 2 50 50 Aggreko Eldoret 36 36 EPPs Total 146 146

4.3Maximum demand at bulk supply

The knowledge of maximum demand is very important for KPGS operators’ .It helps in

determining the installed capacity of generating plants to satisfy the loads at maximum

demand. The generating stations must be capable of meeting the maximum demand for

the nation.

Kenya power grid system (KPGS) operators do take into consideration up to date peak

demand in order to determine the capability of the available generating plants to meet the

peak value in case of such demands.

45

Table 4.4; Maximum Demand at bulk power supply.

4.4 Plant capacity factor

From table 4.5, it is clear that geothermal power plants can be run up to and above 97%

of the time. Their operating and maintenance costs range from Ksh.1.01 to Ksh.3.5 per

kWh, depending on how often the plant runs. Higher priced electricity justifies running

these plants at high capacity factor because the resulting higher maintenance costs can be

recovered.

Orpower steam daily plant has a plant capacity factor of 91.20%, the average factor for

hydro plants and UETCL is 58.35%.

In consideration for the power dispatch KPLC gives priority to available geothermal

power plants due to low operation cost and thus reduces pass over cost of fuel to its

SYSTEM GROSS Max. demand

march 2009

Date Time Up to date max. demand

Date Time

Morning 878.40 6/03/09 10.00 929.42 7/12/07 09.30 Afternoon 848.89 6/03/09 16.30 895.35 27/11/08 17.00 Evening 1043.98 23/03/09 19.30 1070.37 26/11/08 19.30 Nairobi region 554.60 4/03/09 20.00 568.06 26/11/08 20.00 Ruaraka: 2*60 MVA Txs.

105.17 MW 2/03/09 20.00 125.75 MW 7/09/04 19.30

Embakasi: 2*90 MVA Txs.

156.01 MW 12/03/09 00.30 193.79MW 19/08/05 09.30

Juja: 255MVA ( 7 Txs.)

147.0MW 4/03/09 20.00 219.60 MW 10/12/02 20.00

Nairobi North: 2*90 MVA Txs

96.20MW 20/03/09 20.00 100.0 MW 14/07/08 20.00

Ulu 1.84 MW Mar-09 - 1.84 MW Mar-09 - SultanHamud:1*5

MVA Tx 1.88 MW Mar-09 - 2.641 MW Jan-06 -

Kiboko: 1*5 MVA Tx

3.53MW Mar-09 - 3.53MW Mar-06 -

Makindu 1.81 MW Mar-09 - 1.86 MW Jan-09 - Coast region 182.80 18/03/09 19.30 205.40 10/10/08 20.30 West region 201.76 Mar-09 20.30 217.13 Oct-08 20.00 Mt. Kenya region 104.01 Mar-09 20.00 117.91 Jul-08 20.00

46

consumers. This is a very important measure to the KPGS operators in ensuring low cost

of power per KWh and maximization of company’s profits. In its operation, KPLC takes

into consideration the PPAs with IPPs because of penalty if breached.

Table 4.5 units (kWh) generated by power generating plants and daily plant capacity

factor of 22nd march, 2009(Sunday.)

STATIONS ENERGY

UNITS kWh Station CAPACITY PLANT

Hours FACTOR (MW) RUN AVAIL. GROSS IMP FROM UETCL 89,500 24.00 28.32% WANJII 0 0.00 0.00% 0.00 0.00 TANA 38,100 24.00 11.02% 6.40 1.60 MASINGA 210,000 20.17 21.88% 10.00 10.00 KAMBURU 890,250 24.00 39.38% 94.20 80.00 GITARU 1,656,000 24.00 30.53% 225.00 216.00 KINDARUMA 448,000 24.00 46.67% 20.00 20.00 KIAMBERE 1,387,000 24.00 40.13% 72.00 72.00 NDULA 243 1.25 0.51% 1.00 0.00 MESCO 3,656 18.50 40.09% 0.38 0.20 SAGANA 5,050 24.00 14.03% 1.00 0.21 SOSIANI 0 0.00 0.00% 0.00 0.00 GOGO 17,630 19.32 36.73% 1.00 0.91 SONDU MIRIU 145,000 7.50 10.07% 30.00 28.00 TURKWEL 1,715,000 23.63 67.41% 106.00 106.00 TOTAL HYDRO+UETC IMP 6,605,429 24.00 58.35% 566.98 534.92 IBERAFRICA 836,800 24.00 61.14% 45.00 45.00 N/S FIAT GT 35,983 3.50 11.11% 13.50 10.00 OLKARIA 1 1,101,000 24.00 101.94% 45.00 45.00 ORPOWER4 STEAM 1,079,310 24.00 91.20% 48.00 47.38 KIPEVU GT1 651,000 0.00 90.42% 30.00 30.00 KIPEVU GT2 3,900 0.28 0.54% 30.00 30.00 KIPEVU DIESEL 610,000 24.00 33.89% 62.50 42.00 TSAVO 1,521,200 24.00 85.65% 74.00 63.40 OLKARIA 2 1,603,000 24.00 95.42% 70.00 66.00 AGGREKO (Embakasi) 1 604,780 24.00 42.00% 60.00 60.00 AGGREKO (Embakasi) 2 392,090 24.00 32.67% 50.00 50.00 AGGREKO(Eldoret) 30,630 8.00 3.55% 18.00 18.00 MUMIAS POWER 0 0.00 0.00% 0.00 0.00

47

4.5 Dispatch merit order for KPLC

Table 4.6; KPLC merit order for March 2009 based on cost for February 2009 data

STATION (A) 1

(B) 2

(C) 3

A+B+C 4

(A+B) 5

(D) 6

(C+D) 7

(E) 8

(E-D) 9

β(A+B) 10

Orpower4 2.019 0.000 13.429 15.448 2.019 1.661 15.090 3.894 2.233 1

Geothermal 2.690 0.000 0.000 2.690 2.690 2.360 2.360 3.894 1.534 2

Hydro 2.690 0.000 0.000 2.690 2.690 2.360 2.360 3.894 1.534 2 Wind (Ngong) 2.690 0.000 0.000 2.690 2.690 2.360 2.360 3.894 1.534 2

Mumias 2.133 1.027 0.000 3.160 3.160 1.793 1.793 3.894 2.101 3

Tsavo 0.739 5.441 2.755 8.935 6.180 0.809 3.564 3.894 3.085 4 Kipevu Diesel 1 2.690 7.484 0.000 10.173 10.173 2.637 2.637 3.894 1.257 5 Aggreko (Embakasi) 1.760 9.376 0.000 11.136 11.136 1.795 1.795 3.894 2.099 6 Aggreko -Eldoret 1.760 10.005 0.000 11.765 11.765 1.818 1.818 3.894 2.076 7

Iberafrica 0.685 11.961 2.051 14.697 12.646 1.006 3.057 3.894 2.888 8 UETC Day &Peak 4.873 11.092 0.000 15.965 15.965 4.420 4.420 3.894 -0.526 9 UETC Night 4.873 11.092 0.000 15.965 15.965 4.420 4.420 3.894 -0.526 9 Thermal KVNGT1 2.690 18.213 0.000 20.903 20.903 3.034 3.034 3.894 0.860 10 Thermal KVNGT2 2.690 18.213 0.000 20.903 20.903 3.034 3.034 3.894 0.860 10

Fiat GT 2.690 49.597 0.000 52.287 52.287 4.195 4.195 3.894 -0.301 11 The costs are for a unit kWh and;

A=energy cost KVN= Kipevu North

B=fuel cost

C= capacity cost converted to energy at contractual load factor.

D=KPLC incremental cost

E=yield to KPLC at generation terminal

A+B=total incremental generation cost

A+B+C=total generation cost

C+D=KPLC total generation cost

48

E-D=incremental benefit to KPLC

β(A+B)=merit order based on variable total incremental generation cost (A+B)

From table 4.6 it is clear that KPLC takes into consideration the fuel cost for generating

power before dispatching to the grid, thus reduce the fuel costs which is usually passed

to the consumers hence balancing the cost per unit kWh and the company’s profit.

4.6 Load curve as an operational tool

Load curves are important operational tools for KPGS, they give the minimum load

present throughout the given period and this enable selection of base load and peak load

power plants.

Graph 4.1: daily load curve of 22nd, March 2009.

From daily load curve (graph 4.1) the minimum national demand is approximately 535

MW. In deciding the power plants for dispatch, decision should be based on base plants

that can meet this minimum demand.

Load curves differ from day to day and season to season. Flat load curves mean higher

load factor and this is interpreted as uniform load patterns with less variations in load.

This is desirable from the point of view of maximum utilization of associated equipments

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

900.00

1000.00

LOA

D, M

W

TIME, Hr

LOAD CURVES

NationalGen.DemandNairobiRegion

CoastRegion

West Region

Mt. KenyaRegion

49

which are selected on the basis of demand. The higher the load factor, the lesser will be

the cost of generation per unit kWh and thus low cost of power to consumers.

4.7 Load Forecast

The load forecast for the next 10 years is derived from the recommended generation and

transmission expansion program for Kenya.

The table 4.7 only indicates the additional generation and the transmission lines required

to connect the new power stations to the network. It does, however, not show the

additional transmission lines and substations (or substation extensions) within the

transmission and sub-transmission networks required to transfer the additional power to

the consumers.

According to this load forecast, the peak load in Kenya has increased from 829 MW in

2004 to 1043MW in 2008 and is expected to increase to2184 MW in 2019

0

500

1000

1500

2000

2500

3000

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

MW

Year

Graph 4.2;Load Forecast and Generation Expansion

Peak Load [MW] Effective Generation [MW]

50

Table 4.7; load forecast data

.

4.8 Load flow transmission line loss analysis.

The bulk of the system load, maximum peak value so far 568.06 MW, more than 50% of

national demand is concentrated in Nairobi region. In this region, available generation

capacity is 176MW with Nairobi South (Iberafrica) 56MW, AggrekoEmbakasi1&2

60MW and 50 MW respectively; GT N/S Fiat also generates 10MW. Western region up

to date peak value amounts to 217.13 MW (20%) is consumed in the Western region of

Kenya. Generation at Mount Kenya area exceed the regional demands and as such

transmission losses there are expected to be minimal.

In determining the optimal dispatch therefore we establish the best alternatives available

to supply Nairobi region and West Kenya given the generation and transmission

limitations. However, it is recognized that the best alternatives is to invest in generation

in these two load areas both as a means of voltage support and transmission loss

reduction.

Year Peak Load [MW]

Effective Generation [MW]

Load Growth [%]

2004 829 1102 5.3

2005 873 1103 5.3

2006 926 1139 6.1

2007 983 1239 6.2

2008 1043 1289 6.1

2009 1116 1349 7.0

2010 1195 1504 7.1

2011 1280 1564 7.1

2012 1370 1664 7.0

2013 1467 1724 7.1

2014 1567 1831 6.8

2015 1667 1951 6.4

2016 1781 2058 6.8

2017 1914 2186 7.5 2018 2048 2326 7.0

2019 2184 2473 6.6

51

Generally power losses are high in system areas characterized by under voltages. To

minimize losses, it is therefore prudent to operate the system at the best possible voltages

at all demand levels, given the system constraints in the specified regions

Simulations carried out to determine the optimal dispatch for loss reduction at system

peak established the following.

1. Table 4.8; Contribution of Kindaruma Station at system peak to KPGS with reference to Juja control centre

Generation (MW)

Line loading % Transmission losses (MW)

Kind-juja Dand 1 Dand 2 220 132 Total

20 33 80 79 19.47 13.42 32.89

20 42 78 77 18.87 13.64 32.51

40 53 77 75 18.34 14.15 32.49

Transmission system efficiency for the current system can be improved by taking full

advantage of generation at Kindaruma Hydropower plants, Ibera Africa, Aggreko

Embakasi and Ol-Karia stations.

For maximum efficiency in load transfer from hydropower plants to Nairobi, Kindaruma should be operated at full-load. This reduces loading on the heavily loaded Dandora 220 Kv lines hence reduces total system losses. Loading of these lines still remains high and further reloading will increase loss reduction benefits.

2. Table 4.9; Contribution from Iberafrica at system peak

Generation (MW) Line loading % Transmission losses (MW)

Dandora line-1 Dandora L2 220 132 Total

25.3 86 85 21.74 14.44 36.18

50.6 80 79 19.47 13.42 32.89

55.7 79 77 19.08 13.25 32.33

52

(Fiat gas turbine)12

76 75 18.18 13.23 31.41

For maximum efficiency, Iberafrica should be operated at full load to further reduce

loading on Kamburu 220 Kv lines. It should also be noted that further generation in

Nairobi will still be beneficial in loss reduction along the transmission lines.

3. Table 4.10; Contribution from Ol-Karia at system peak


Juja-Naiv Dand 1 Dand 2 220 132 Total

(Orp 4 & 1) 42.8 23 80 79 19.47 13.42 32.89

(Orp 4 & 1) 57.8 18 77 76 18.4 12.87 31.27

(Orp 4 , 1,2) 77.6 19 73 72 17.26 12.65 29.91

(orp 4,1,2) 92.6 22 71 70 16.52 12.84 29.36

For maximum Transmission efficiency KPLC should co-operate with KenGen to operate

all available generation at Ol-Karia. This increases supply to Nairobi hence reducing

loading on Dandora lines significantly. It also enhances supply to West Kenya.

4. Table 4.11; Contribution from Turkwel at system peak


Juja-Naiv Dand 1 Dand 2 220 132 Total

90 27 82 81 19.31 14.44 33.75

100 22 80 79 19.41 13.48 32.89

104 20 79 78 19.49 13.19 32.68

For maximum efficiency Turkwel should be run at full load when there is limited

generation at Ol-Karia. However when all currently available generation at Ol-Karia is in

53

operation Turkwel should be operated at 100 MW for overall system transmission

efficiency.

5. Table 4.12; Contribution from Generation at Kipevu

Generation (MW) Line loading % Transmission losses

(MW)

Kiambere-Rabai Rabai-Juja 220 132 Total

103.2 18 29 20.27 13.2 33.47

113.2 15 33 19.8 13.34 33.14

123 12 36 19.46 13.56 33.02

126.6 11 38 19.36 13.67 33.03

131.6 10 39 19.26 13.83 33.09

Generation optimization in coast region is arrived at through trade off between loading of

Kiambere-Rabai line and Rabai-Juja line.Load along Rabai-Juja line needs to be supplied

via export from Rabai and not from Juja due to the high demand in Nairobi.

6. Table 4.13; Ol-Karia-Dandora and Kiambere-Embakasi transmission lines Power generation and dispatch optimization

Network Power losses (MW)

Estimated Energy losses (MWh)

Energy losses as % of net Generation.

220 kV 9.07 39,948 1.0

132 Kv 10.38 45,717 1.1

Total (132 & 220 kV) 19.45 85,665 2.1

66 kV 6.68 29,421 0.7

54

From table 4.13, Transmission losses are 2.1% of net generation. Transmission system

efficiency is therefore expected to be 97.9% with Ol-Karia-Dandora and Kiambere-

Embakasi transmission lines and Ol-Karia II Power generation and dispatch optimization.

4.9 Thermography inspection results

Thermography inspection by KPLC is one of the operations carried out to maintain

substations in Kenya. Thermogram on photograph 4.3show results obtained for this

inspection at Bamburi 132kv/33kv substation on 7th April, 2009.

Figure 4.2; Identification photograph for Thermography inspection.

From Thermography inspection, the difference in temperature of the hotspot (Ar1) and

normal point (sp1) is 232 degrees Celsius. The results of thermography inspection as

shown on figure 4.3 show that the copper tube connection clamp on the yellow phase has

a serious hotspot. The cause of the heating is the clamp bolt which needs to be replaced

thus immediate action is necessary.

Photo and Identification

Location 33Kv side

Equipment Beyond 1T0

Type Pin insulator

Fault 1

55

thermogram 7/04/2009

Delta T

Sp1

Ar1

17.6

78.6 °C

20

40

60

Object Parameters

Value

Atmospheric Temperature

20.0 °C

Sp1 Temperature 30.8 °C

Ar1 Max. Temperature

262.8 °C

Delta T Value 232.0

Figure 4.3; Thermography inspection for section shown on photograph 4.2

56

5.0 CHAPTER FIVE: Discussion and Conclusion

5.1 Summary of the research on operational planning for KPGS.

All Operations carried out by KPGS operators are aimed at meeting the following:

• Maintain the electric power system frequency within +0.2 and -0.3 range of

50Hz.

• Maintain the transmission busbar voltage levels within 8% error margin of the

nominal value at Juja road, Rabai and Lessos substation.

• Facilitate all planned transmission and generation equipment outage at a monthly

target of 95%.

• Operate the transmission system accident free through compliance with safety and

operational standards.

• Guarantee effective response to all system contingencies.

With aging transmission lines already operating at capacity, and the difficulties involved

in building new ones, KPLC tries to meet increasing customer demands for reliable

power at all times. It must keep existing lines operative at maximum efficiency, which

requires more regular inspection and maintenance.

5.2 Achievements

v Getting to national control centre and obtaining firsthand information on grid

operations.

v Doing research on real time operations and interacting with KPLC engineers.

5.3 Constrains

i. It took a lot of time to be allowed by KPLC to carry out research on their

operations.

ii. Limited time which made me not to visit NCC enough times and learn more on

their operations.

iii. Lack of good transport means to Juja control centre (NCC)

57

5.4 suggestions for further work

Operational planning for transmission line inspection and substation inspection is very

important in maintaining the existing national power grid network .For this reason, I

would recommend for further work by KPLC or any other individual to come up with the

following:

1) Database for line inspection

2) Pattern recognition algorithm for tower top and pole-top of the overhead power

lines.

3) Recognition algorithms for other specific inspection features need to be developed

based on the inspection requirements.

This will help KPLC to analyse the aerial line defects quite easily and thus save time for

straining the inspection engineers and pilot.

58

APPENDIX

Appendix 1: Aerial power line inspection illustration

59

Appendix 2: Broken insulator unit (photograph taken during aerial line inspection)

60

Appendix 3: Kenya power national grid network

61

Appendix 4;Statements of quality objectives for system control section NCC The following are some of statements of quality objectives;

• Effective dispatch of generating plants

• Reduction of supply interruption time

• Operation of transmission bus bars within stipulated voltage levels

• Operation of power systems at the stipulated frequency

• Maintain power system stability

• Continually review and update ISO 9002:2000 Quality Management Sytems

62

REFERENCES 1) Stevenson William D. Elements of power system analysis, 4th Edition published

by Mc Graw Hill, 1982. 2) Hove, Richard Anthony, Advanced studies in electrical power system design, 1st

Edition, published in London by Chapman & Hall,1966. 3) Pai, M.A, Energy function analysis for power system stability, published by

Kluwer Academic Pub,1989 ISBN 0792390350. 4) Gattecha, Haron, Budgeting system for the Kenya Power and Lighting Company

Limited, published by University Of Nairobi. 5) Mortlock, J.R and M.W Humphrey Davies, Power system analysis, published in

London by Chapman & Hall,1952. 6) Goren, Turan, Modern Power System analysis, published by Wiley, 1988, ISBN

0471859036. 7) Gross, C.A, Power system analysis, published by Wiley, 1979 ISBN 0471018996

Bibliography 1) http://en.wikipedia.org/wiki/Power_flow_study

2) http://en.wikipedia.org/wiki/Network_planning_and_design

3) http://en.wikipedia.org/wiki/Ac_power

http://en.wikipedia.org/wiki/Power_flow_study

http://en.wikipedia.org/wiki/Network_planning_and_design

http://en.wikipedia.org/wiki/Ac_power

63

Dedication

I would like to dedicate this project work to:

• My dear Parents

• My friends

• All those who helped me to write this project

64

Acknowledgements

I would like to express my gratefulness to: My supervisor Dr. Mang’oli for his assistance by providing me with references, encouragement and useful comments.

I also appreciate KPLC engineers especially Engineer Ticha (operation Engineer NCC) and Engineer Bosire (Transmission department –Coast) for taking their time to help me learn about operational planning for KPLC, providing me with data and permission to take photographs within KPLC premises.

I wish to thank my sister Assumpter and my friends Boniface , Susan and catherine who helped with the corrections and who gave other helpful comments and suggestions at the time of preparation for my final copy. Finally, I appreciate all those who helped me in any capacity.

65

ABSTRACT

Power grid operational tool is a device or a mechanism which enables proper planning for

the power in the grid relative to the demands of the power at a given time. To enable

operational planning for the power on the grid at present and future, KPLC takes into

consideration:

• The available generating plant capacity.

• The energy available.

• The distance of the generating plant to the load centres.

• T he energy demand at the load centre.

With this information the suitable generating power plant is dispatched through the grid

system to the load centre. By using the best transmission efficiency, maximum power can

be delivered to customer with minimal loss. Operational tool also enables planning for

future developments such as laying new lines to the grid.

By monitoring the voltage on the grid, deviation from normal operating frequency of the

grid, the power factor and the load flow in general can help KPLC to plan for short term

operation of the grid.

Operational planning in the grid enables high economical use of high generating plants in

case of other generating plant failures.

The project aims at doing research on planning for the power in the grid relative to the

load (demand) for the power, determination of load shedding during contingencies,

voltage stability on the grid system, planning methodologies used by KPLC which enable

them perform effectively and meet the demands for the Kenya power grid system.

66

TABLE OF CONTENTS 1.0 CHAPTER ONE-INTRODUCTION .............................................................................................. 1

1.0.1 Project Title: operational planning for Kenya power grid system ..................................... 1

1.1 Project Aim. ....................................................................................................................... 1

1.2 Objectives of the project.................................................................................................... 1

1.3 Scope of the Project .......................................................................................................... 1

1.4 Background ....................................................................................................................... 3

1.5 Why Operational Planning for Kenya Power Grid System. .................................................. 3

1.6 Limitations of operational planning of the grid sytstem. .................................................... 4

2.0 CHAPTER TWO: TECHNOLOGICAL REVIEW ............................................................................. 5

2.0.1 Introduction ................................................................................................................... 5

2.1 Grid input, losses and exit .................................................................................................. 5

2.2 Grid stability ...................................................................................................................... 6

2.2.1 Load balancing ................................................................................................................ 8

2.2.2 Failure protection ........................................................................................................... 9

2.2.3 Power outage. ................................................................................................................ 9

2.2.4 Protecting the system from outages ............................................................................. 10

2.2.5 Restoring power after a wide-area outage .................................................................... 10

2.3 Effects of voltage on transmission efficiency .................................................................... 10

2.4 Power factor .................................................................................................................... 12

2.4.1 Power Factor Improvement: ......................................................................................... 13

2.5 Methods of voltage control ............................................................................................. 14

2.6 Kelvin’s economy law ...................................................................................................... 15

2.7 Fault analysis ................................................................................................................... 17

2.8 Single Line Diagram ......................................................................................................... 17

2.8.1 Concept of bus .............................................................................................................. 17

2.9 Load Flow Calculation Method ......................................................................................... 19

2.9. I Power Flow Methods .................................................................................................... 22

2.10 Transmission line Insulators and Supports ..................................................................... 27

2.10.1 Electrical Failure of Insulators ..................................................................................... 27

2.10.2 Line supports .............................................................................................................. 28

3.0 CHAPTER THREE: METHODOLOGY AND DESCRIPTION .......................................................... 30

67

3.0.1 Introduction ................................................................................................................. 30

3.1 Transmission planning ..................................................................................................... 30

3.2Network planning ............................................................................................................. 30

3.2.1 Technical criteria for planning purpose ......................................................................... 31

3.2.2 Steady state criteria ...................................................................................................... 32

3.2.3 Network Planning Methodology ................................................................................... 33

3.2.4 Planning Criteria ........................................................................................................... 37

3.2.5 Contingency Criteria ..................................................................................................... 37

3.3 Load forecasting as an operational tool ........................................................................... 38

3.4 KPGS Operational maintenance of Overhead Power line. ................................................. 38

3.5 Responsibilities of National Control Centre (NCC) ............................................................ 39

4.0 CHAPTER FOUR: RESULTS AND ANALYSIS ............................................................................. 41

4.0.1 Introduction ................................................................................................................. 41

4.1 Network monitoring and control ..................................................................................... 41

4.2 Power Generating plants contributing to KPGS ................................................................ 42

4.3Maximum demand at bulk supply ..................................................................................... 44

4.4 Plant capacity factor ........................................................................................................ 45

4.5 Dispatch merit order for KPLC .......................................................................................... 47

4.6 Load curve as an operational tool .................................................................................... 48

4.7 Load Forecast .................................................................................................................. 49

4.8 Load flow transmission line loss analysis. ......................................................................... 50

4.9 Thermography inspection results ..................................................................................... 54

5.0 CHAPTER FIVE: Discussion and Conclusion ........................................................................... 56

5.1 Summary of the research on operational planning for KPGS. ........................................... 56

5.2 Achievements .................................................................................................................. 56

5.3 Constrains ....................................................................................................................... 56

5.4 suggestions for further work ............................................................................................ 57

APPENDIX.................................................................................................................................. 58

Appendix 1: Aerial power line inspection illustration ............................................................. 58

Appendix 2: Broken insulator unit (photograph taken during aerial line inspection) .............. 59

Appendix 3: Kenya power national grid network ................................................................... 60

Appendix 4;Statements of quality objectives for system control section NCC ........................ 61

68

REFERENCES .............................................................................................................................. 62

Bibliography .............................................................................................................................. 62

LIST OF FIGURES

Figure 2.1;P-V curve...........................................................................................................6

Figure 2.2;Q-V curve...........................................................................................................7

Figure 2.3; the concept of lagging power factor...............................................................13

Figure 2.4; the concept of leading power factor...............................................................14

Figure 2.5; bus concept.....................................................................................................18

Figure 2.6; typical scheme of load flow characteristic.....................................................21

Figure. 4.1 Photograph of Engineer Kibet NCC operator................................................41

Figure 4.2; Identification photograph for Thermography inspection...............................54

Figure 4.3; Thermography inspection for section shown on photograph 4.2...................55

LIST OF GRAPHS

Graph 4.1: daily load curve of 22nd, March 2009.............................................................48

Graph 4.2;load- forecast and generation expansion.........................................................49

69

LIST OF TABLES

Table 2.1; classification of load buses...............................................................................20

Table 4.1; KenGen installed capacity as at 15th April, 2009.............................................42

Table 4.2; Installed plant capacity for IPPs as at 15th April, 2009...................................43

Table 4.3; Installed plant capacity for EPPs as at 15th April, 2009..................................44

Table 4.4; Maximum Demand at bulk power supply.........................................................45

Table 4.5 Units (kWh) generated by power plants ,daily capacity factor for22/03/09.....46

Table 4.6; KPLC merit order for March 2009 based on cost for February 2009 data.....47

Table 4.7; load forecast data.............................................................................................50

Table 4.8; Contribution of Kindaruma Station at system peak to KPGS with reference to Juja control centre......................................................................51

Table 4.9; Contribution from Iberafrica at system peak...................................................51

Table 4.10; Contribution from Ol-Karia at system peak...................................................52

Table 4.11; Contribution from Turkwel at system peak....................................................52

Table 4.12; Contribution from Generation at Kipevu.......................................................53

Table 4.13; Ol-Karia-Dandora and Kiambere-Embakasi transmission lines Power generation and dispatch optimization.............................................................................53

70

List of Abbreviations and Acronyms

DP Diesel Plant

EPP Emergency Power Producer

GT Gas Turbine

IPP Independent Power Plant

KenGen Kenya Electricity Generating Company Ltd.

KPGS Kenya Power Grid System

KPLC Kenya Power and Lighting Company Ltd.

Ksh Kenya Shilling

kV Kilovolt

kW Kilowatts

kWh Kilowatt-hour

MVA Megavolt-Ampere

MW Megawatts

MWh Megawatt-hour

P Effective power

PPA Power Purchase Agreement

pu Per Unit

Orp4 Olkaria 3-Naivasha

Q Reactive power

S Apparent power

Tx Transformer

UETCL Uganda Electricity Transmission Company Limited

% Percent

V voltage

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