Ayele Nigussie

Accurate electric load forecasting is crucial for power system planning and operation.

The forecasted load should be close to the load demand on the power system.

Load forecasting is always associated with some uncertainty.

Power systems, however, are to be planned in such a way that changing load developments can be accommodated by the expansion of the system .

load forecasting helps a company to decide◦ Purchasing electric power◦ Generating electric power ◦ Load switching◦ Infrastructure development

Three types of forecasts:1. short-term forecasts- which are usually from one hour

to one week2. Medium-term forecasts- which are usually from a

week to a year3. long-term forecasts- which are longer than a year

Some load forecasting methods are:1. Load forecast with load increase factors2. Load forecast based on economic characteristic

data3. Load forecast with estimated values4. Load forecast with standardized load curves.5. Regression6. Modern forecasting methods

The precise application of the different methods cannot be determined exactly.

And combinations of the methods are usually applied.

This method is based on the existing load and the increase in the previous years and estimates the future load increase by means of exponential increase:

s=rate of increase per year P0 = previous load Pn=load at the nth year n=year

This method is simple but cannot consider externally measured variables and is hardly suitable to provide reliable load and energy predictions.

Example: Assume the pick load on Haramaya substation is 5

MW and the annual growth rate is 7%. What will be the pick load after 10 solid years?

Ans: P10=9.84 MW

An increase in accuracy is obtained if the load forecast is carried out separately for the individual consumption sectors, such as households, commercial, public supply and industrial sectors.

Then the individual results are summed for each year to obtain the total system load.

Another model for load forecasting is based on the phenomenological description of the growth of electrical energy consumption as shown next:

With this model, adjustments can be combined with the process of load development of the past with different increases and saturation effects for the future.

Load forecast calculated with the load development model (curves for various values of k and l ).

As the economy of a country grows, so does the power demand.

Load forecast with economic characteristic data obtained from energy statistics assumes different relations between economic growth, availability of energy resources, energy consumption and requirements in general, such as the increase in energy consumption due to growth of population, and in special applications, such as energy requirements of industry.

The requirement for electrical energy per capita of the population is determined to a large extent by the standard of living and the degree of industrialization of a country.

However, high consumption of energy can be also an indicator of high waste of energy.

The increase of electrical energy consumption in industrialized countries is less affected by the growth of population and predominantly by the growth of the gross domestic product ( GDP ) and/or the gross national product ( GNP ).

Example: In the GTP, the GDP of Ethiopia is supposed to grow at 15%.

Before the GTP period, the power demand was growing at a rate of 23% (GDP growth=11%). Assuming a direct relationship between the economy and the power demand,

a. What is the rate of power demand growth in the GTP period?b. In 2002 E.C, the national power demand was approximately

1500 MW. What will be the expected power demand in 2007 E.C?

In power system expansion, development plan is vital in forecasting the power requirement.

For instance, we can use the table on the next slide in power system planning.

Example: Near Addis, a business area of 10km-squared is to be

electrified. Forecast the power demand.

Land development plans contain general information about the area development and use of land, and the size, location and types of residential, industrial and commercial areas, without allowing one to be able to derive detailed individual measures from them.

Another way of load forecasting is based on the annual energy consumption of individual consumer or consumer groups, which can be taken from the annual electricity bill.

The system load can be determined by means of standardized load curves for different consumer groups such as◦ Residential◦ Commercial◦ Public sectors◦ industrial

As consumption profiles of the particular customer groups not only change with time of day but also show day - of - week and seasonal changes, characteristic days are defined, such as working - day, Saturday, Sunday (or Friday in Islamic countries) and holiday as well as seasonal differences in winter, summer and transition periods.

Based on the load curves we can forecast the future load for a particular hour, a particular day and a particular year.

Summer sunday

Summer working day

Regression is also used in forecasting loads. Read this at your home.

Nowadays, fuzy logic, ANN, and other algorithms are used in power system planning to forecast load.

These algorithms have artificial learning capabilities.

And thus, by taking the past into consideration, they can predict the future.

Planning and Design of hydro generation stations

Ayele Nigussie

1. Introduction2. Layout 3. Environmental Effects of HPPs4. Economic Aspects of HPPs5. Designing HPPs6. Summary

Hydroelectric power captures the energy released from falling water.

Potential Energy Kinetic energy Electrical Energy

Hydroelectric power plants are categorized as◦ Micro hydropower plants [<100 kW)◦ Mini Hydropower Plants [100 kW – 1 MW]◦ Small Hydropower Plants [1 MW – 30 MW]◦ Large Hydropower Plants [>30 MW]

In Ethiopia, more than 96% of the electricity is hydro.

The effects are: Physical - ◦ change the ecosystem, ◦ effect on downstream,◦ Loss of habitat◦ Loss of farms◦ Deforestation◦ Effect on micro-climate level

Biological-◦ Flora◦ Fauna◦ Humans

High initial cost of construction. Electricity is cheap. Energy is green. In an HPP construction, costs to be considered:◦ land/land rights, ◦ structures and improvements, ◦ equipment, reservoirs, dams, waterways, roads, railroads, and

bridges. ◦ protecting fish and wildlife. ◦ Operation and maintenance costs ◦ hydraulic expenses, electric expenses, and rents.

When designing a hydroelectric power plant a number of elements and equipment need to be taken into consideration.

Dam size, retention basin size and depth, inlet valves, weir and control gates, penstock length and diameter, turbines, generators, transformers and excitation equipment, and efficiency all have to be examined.

Elevation or head and stream flow have to be established as well.

Firm power:

Based on the firm power:◦ Mechanical Engineers design the hydraulic

turbines.◦ Electrical engineers design the generators,

transformers, the switch yards and the protection system.◦ Dams, canals, intakes, penstocks, tailraces and

power houses are designed by civil engineers. Firm power is also one of the main factors that

decides the feasibility of an HPP.

Feasibility study contains:

◦ Site visit and selection

◦ Capacity analysis

◦ Economic analysis

◦ Environmental impact analysis

Feasibility study is the first step in HPP construction.

In planning an HHP, the general requirements are:◦ Determining location of the powerhouse , location of

switchyard , ◦ Laying out the highway and railroad access, other site

features, ◦ Determining types of powerhouse, structures, ◦ selection of type of powerhouse, ◦ location of main transformers, powerhouse and

switchyard, equipment, powerhouse Auxiliary Equipment

Architectural design requirements are:◦ Exterior Design ◦ Exterior Details◦ Interior Design◦ Interior Details◦ Schedule of Finishes◦ Painting ◦ Design memorandum ◦ Drawings

The structural requirements are:◦ All the civil works are under this category.

Ayele Nigussie

3.1 Introduction3.2 What is a substation?3.3 Important points3.4 Classification of substations3.5 Substation equipments3.6 Substation Configurations3.7 Substation design3.8 Planning of substations3.9 Conclusion

A substation is a nodal point in a power system.

Internationally standardized voltage level for substations:

66 kV, 110 kV, 132 kV, 150 kV, 220 kV, 380 kV,

For very long transmission distances : 500 kV, 800 kV

Tasks of substation: Distribution of power towards load circuit Separation of different network groups (reduction

of short circuit power) Coupling of different voltage level via power

transformers Measuring, signaling and monitoring of network

data (e.g. U, I, P, Q, f)

3.2 What is a Substation ?

The assembly of apparatus used to change some characteristics (e.g. voltage, a.c. to d.c. ,freq, p.f. etc..) of electrical supply is called a substation.

It should be located at a proper site(i.e. at the center of gravity of load).

It should provide safe and reliable arrangement.

It should be easily operated and maintained.

It should involve minimum capital costs.

Substation

According to service requirement According to constructional feature

According to Service requirement: Transformer Substation: Transformers are installed to

transform voltage from one level to another as per needs. Switching Substations: This substations mean for switching

operation of powerlines with out transforming the voltage. Power factor correction Substation: This substations are

installed to increase the power factor to minimise losses. Frequency Changer Substation: This substations are installed

where speed control of motors is required. Converting Substation: This substations convert a.c to d.c or

vice versa. Industrial Substation: This substations are installed to supply

power only to an industries.

According To Constructional Features: Indoor SubstationsIndoor Substations: In this substations, the apparatus are

installed with in the substation building. Till 66 kV. Outdoor SubstationsOutdoor Substations: this substations are installed in open land.

This substations are employed for voltage levels beyond 66k.v. Underground SubstationsUnderground Substations: This: This substations are installed under

ground in densely populated cities where cost of the land is more.

Pole-Mounted SubstationsPole-Mounted Substations: This substations are erected for distribution of power in localities. This is employed for transformers up to 250 kVA.).

Foundation Mounted SubstationsFoundation Mounted Substations: This substations are installed for transformers which are too heavy.(rating beyond 250Kva).

3.4 Classification of Substation …

Busbar: is a conductor connecting power line to substation equipment.

Insulators & fittings: fix and isolate the busbar system.

Isolating Switch: is used for disconnecting equipment for maintenance and repair.

Relays & Circuit Breaker: open and close a circuit under normal and fault conditions.

Power Transformers: are used in substations to step up or step down the voltages.

Instrument Transformers: used for measuring .

Metering & Indicating Instruments: used to watch over the circuit quantities.

Power line carrier communication systems: used for SCADA.

Coupling capacitors and wave traps

AC/DC supply: is used for auxillaries and DC supply for relay operation.

Oil handling system: used for purifying oil from moisture.

Illumination: should be properly illuminated for safety.Compressed air system: for functioning of CB.Service bay: to carry the equipments to installation side.Fire extinguishers

Lightning/Surge Arresters

Isolating switches:

• Circuit Breakers

3.5 Substation equipments …

3.5 Substation equipments …

3.5 Substation equipments …

3.5 Substation equipments …

Piezoelectric motorsPiezoelectric motorsPiezo GeneratorsPiezo GeneratorsActuatorsActuatorsUltrasonic TransducersUltrasonic TransducersAnd many more…And many more…

What are to be considered? Site selection Design of structures Design of foundation for transformers &

structures(IE Rules 64) Control room building Cable trench & drainage Design of earthing Protection schemes & interlocks

Conventional substations (AIS): Construction according to standardized minimal

distances (clearance) between phase and earth Normally used for outdoor substations, just in very few

cases used for indoor substations Based on single power system equipments◦ Replacement of single equipment by equipments from other

manufacturers is possible. Simple to expand (in case that space is not an issue) Excellent overview, simple handling and easy access

Minimum clearance in air according to IEC 61936-1

Minimum clearance in air according to IEC 61936-1

Basis requirements for new substations: Optimal location of substations within power system (load flow, short

circuit, customer requirements, long term planning, land space) Selection of substation design Calculation of short-circuit currents and long term development

(ratings) Selection of power system requirements Adaption of design according to available space, fixing of busbar

configuration (e.g. using wire conductor or tubular conductor) Detailed planning of: primary and secondary equipment, auxiliary

equipment, basement, steel structure, building, earthing system

You can find important standards for power system installations:

Planning and Design of a substation normally starts with the development of the electrical single line diagram.

A single line diagram shows number of busbars and substation bays including the relevant equipment.

Selection of substation layout depends on◦ Its importance within the power system

(power system reliability in case of failures and maintenance activities)◦ Power system operation

Substation is the heart of a power system. Hence, its design should be such that it will provide continuous , quality & desired power with safety.

Read further on substations.

THANK YOU

Electrical Considerations for T.L. Design: Low voltage drop Minimum power loss for high eff iciency of

power transmission. The l ine should have suff icient current

carrying capacity so that the power can be transmitted without excessive voltage drop or overheating.

Conductivity of Conductor:R = ρ.L/A , orR = L/Ϭ. A

Where:L: Conductor length.A: Conductor cross sectional area.ρ: resistivityϬ: Conductivity (Ϭ= 1/ρ)

The conductor conductivity must be very high

to reduce Conductor resistance R and hence reduce losses

P L= 3 I 2 .R

Mechanical Considerations for T.L. Design:

The conductors and l ine supports should have suff icient mechanical strength:

- to withstand conductor weight, Conductor Tension and weather condit ions (wind, ice).

- The Spans between the towers can be long.

- Sag wil l be small.- Reducing the number and height of towers

and the number of insulators.

• Heat expansion coefficient must be very small.

R t = R 0. (1 + α 0 .t)

α t = α 0/(1+ α 0.t)

α t is the heat expansion coefficient at t.

TYPES OF CONDUCTORS

MATERIALS

lowest cost – low mechanical strength

Used for small span

1- Steel strands2- Aluminum strands ACSR (26/7)

• High mechanical strength can be uti l ized by using spans of larger lengths.

• A reduction in the number of supports also include reduction in insulators and the risk of l ines outage due to f lash over or faults is reduced.

• losses are reduced due to larger diameter of conductor.

• High current carrying capacity.

Wooden Poles

Reinforced Concrete Poles

Steel Poles

Latt ice Structure Steel Towers

Wooden Poles

Reinforced Concrete Poles

Steel Poles

1- Suspension Tower

2- Tension Tower

3- Angle Tower

4- End Tower

This type of towers exist in the beginning and at the end of the l ine which exposed to tension in one side.

Sag of T.L depends on:

- Conductor weight.- Span length, - Tension in the conductor, T- Weather condit ions (wind , ice).- Temperature.

kV C (m)0.4 5.5

11 5.533 6.066 6.2132 6.2220 7.0400 8.4

Spacing = (S ) 0 . 5 + V/150Where:S: Sag in meters.V: Line voltage in kV.

Electrical Considerations for T.L. Design: Low voltage drop Minimum power loss for high eff iciency of

power transmission. The l ine should have suff icient current

carrying capacity so that the power can be transmitted without excessive voltage drop or overheating.

Conductivity of Conductor:R = ρ.L/A , orR = L/Ϭ. A

Where:L: Conductor length.A: Conductor cross sectional area.ρ: resistivityϬ: Conductivity (Ϭ= 1/ρ)

The conductor conductivity must be very high

to reduce Conductor resistance R and hence reduce losses

P L= 3 I 2 .R

Mechanical Considerations for T.L. Design:

The conductors and l ine supports should have sufficient mechanical strength:

- to withstand conductor weight, Conductor Tension and weather conditions (wind, ice).

- The Spans between the towers can be long.- Sag wil l be small.- Reducing the number and height of towers and

the number of insulators.

• Heat expansion coefficient must be very small.

R t = R 0. (1 + α 0 .t)

α t = α 0/(1+ α 0.t)

α t is the heat expansion coefficient at t.

TYPES OF CONDUCTORS

MATERIALS

lowest cost – low mechanical strength

Used for small span

1- Steel strands2- Aluminum strands ACSR (26/7)

• High mechanical strength can be uti l ized by using spans of larger lengths.

• A reduction in the number of supports also include reduction in insulators and the risk of l ines outage due to f lash over or faults is reduced.

• losses are reduced due to larger diameter of conductor.

• High current carrying capacity.

Wooden Poles

Reinforced Concrete Poles

Steel Poles

Latt ice Structure Steel Towers

Wooden Poles

Reinforced Concrete Poles

Steel Poles

1- Suspension Tower

2- Tension Tower

3- Angle Tower

4- End Tower

This type of towers exist in the beginning and at the end of the l ine which exposed to tension in one side.

Sag of T.L depends on:

- Conductor weight.- Span length, - Tension in the conductor, T- Weather condit ions (wind , ice).- Temperature.

kV C (m)0.4 5.5

11 5.533 6.066 6.2132 6.2220 7.0400 8.4

Spacing = (S ) 0 . 5 + V/150Where:S: Sag in meters.V: Line voltage in kV.