Asst.Prof.Dr.Reza SIRJANI

Components of Electrical

Power Systems

Introduction

Power and Energy are buzz words in today’sworld.

Electricity is emerged as basic necessity withFood, Shelter and Clothing for human being.

Life without electricity has become highlyunimaginable.

Electric locomotives, Heating, Cooling, Fans,Blowers, Motors are some applications thatconverts electrical energy into useful work.

Introduction

Reasons of Popularity of Electricity:

Clean environment for user

Higher efficiency

Better controllability

Quick transfer of power from source to load

Energy conservation is simple

Introduction

Power engineering, also called power systems

engineering, is a subfield of electrical

engineering that deals with the generation,

transmission and distribution of electric power as

well as the electrical devices connected to such

systems including generators, motors and

transformers.

Introduction

Different Fields of Power Engineering

and their related courses in EMU:

Electric Machinery (EENG350 , EENG453)

Power Systems (EENG456, EENG457, EENG458)

High Voltage Engineering (EENG451)

Power Electronics (EENG441,EENG442)

Basic Structure of Power Systems

A power system is an interconnected network

with components converting nonelectrical

energy continuously into the electrical form and

transporting the electrical energy from

generating sources to the loads/users.

A power system serves one important function

and that is to supply customers with electricity

as economically and as reliably as possible.

Power System Components

Power System Components

Generation : Generating and/or sources of

electrical energy.

Transmission: Transporting electrical energy

from its sources to load centers with high

voltages (115 kV and above) to reduce losses.

Distribution : Distributing electrical energy

from substations (11 kV ~ 44 kV) to end

users/customers.

Power System Components

At power generating station (generating

voltage) 11 – 20kV and frequency of 50

Hz

Transform to higher voltage (transmission

voltage) 132kV, 275kV and 400kV

Transform to lower voltage (distribution

voltage) 66kV , 33kV or 11kV

The generator converts nonelectrical energy to

electrical energy. The devices connecting

generators to transmission system and from

transmission system to distribution system are

Transformers.

The main transformers functions are stepping

up the lower generation voltage to the higher

transmission voltage and stepping down the

higher transmission voltage to the lower

distribution voltage.

The main advantage of having higher voltage in

transmission system is to reduce the losses in

the grid.

Since transformers operate at constant power,

when the voltage is higher, then the current has

a lower value.

Therefore, the losses, a function of the current

square, will be lower at a higher voltage.

Power System Components

Power System

Generation

Sources Of Elec. Power Gen.

A.Conventional SourcesThermal (Coal)NuclearGasWater

B.Non conventional SourcesWindSolar- PVBiomass

Power Generation

Disadvantages Of Conventional Sources :

Fossil fuels shall be depleted, forcing us to

conserve them and find alternative resources.

Toxic, Hazardous gases, Residues pollute

environment.

Overall conversion efficiency is very poor.

Sources are located at remote places with

reference to load, increasing transmission cost.

Maintenance cost is high.

Transmission

Transmission System

Lines/transformers operating at voltages above115 kV are usually called the transmission system.

Consists of Transmission Line and Sub-stations

Transmission Line◦ Overhead Lines

◦ Cable Underground Cables

Submarine Cables

Sub-stations

Transmission Towers

Insulators

Overhead Line Conductors•Aluminum conductor steel-reinforced

cable (ACSR cable) is a specific type of

high-capacity, high-strength stranded

cable typically used in overhead power

lines.

•The outer strands are aluminum,

chosen for its excellent conductivity,

low weight and low cost. The center

strand is of steel for the strength

required to support the weight without

stretching the aluminum due to its

ductility. This gives the cable an overall

high tensile strength.

Substations

Size of substation

◦ Depends on transformer size

Types of Sub-station

◦ Conventional outdoor

Require bigger space

◦ GIS (gas insulated switchgear)

Less space

Outdoor or indoor

Sub-station Components

Transformer

Circuit Breaker / Switch Gear

Isolator Switches

Busbar

Protection Relay & Control Equipment

Power Transformer

Sub-station Components

Circuit Breaker / Switch Gear

Busbar

Distribution

Lines/transformers operating at voltages below

115 kV are usually called the distribution

system.

Part of the electric utility system between the

bulk power source and the customer service

entrances (loads).

33kV, 22kV, 11kV, 6.6kV, 415V and 240V

Distribution System

Distribution Intakes (33kV, 22kV)

Distribution Substations (22kV, 11kV, 6.6kV)

◦ Indoor substation

◦ Outdoor substation

◦ Pole mounted substation

◦ Compact substation

◦ Underground substation

Transformer capacity

◦ 100kVA, 300kVA, 500kVA, 750kVA and 1000kVA

Distribution Substations

Distribution Intake

Distribution Substations

Indoor Sub-station

Distribution Substations

Underground Sub-station

Distribution Substations

Compact Sub-station

Distribution Substations

Outdoor Sub-station

Distribution Substations

Pole-Mounted Sub-station

Distribution Substations

Types of Load:

◦ Residential

◦ Commercial

◦ Industrial

◦ Public Transportation

◦ Public Lighting

◦ etc.

Power System Loads

Residential Load

Consist of lighting, radio, TV, refrigerator, kitchenappliances, washing machine and etc.

Usually, increases in the evening around 6 p.m. and returnto a nominal value around 12 p.m.

Commercial Load

• Consists of lighting, air-condition and small appliances.

• Shops, business premises, schools, universities etc.

• The load is fairly constant from 9am until 9pm with the

exception of any mid-day break.

Power System Loads

Industrial Load

Mainly consists of motor load, air conditioner, lighting, welding and furnaces etc.

It can be divided into small, medium and large category.

The nature of industrial load curve depends on the number of shifts worked in the industry.

Power System Loads

Power System Loads

Electricity energy cannot be stored.

Generate electricity based on demand.

Total power drawn by consumer fluctuates

depends on the time of day and seasons.

Demand Curve

◦ Plot each demand of electricity by consumer

daily/annually

Demand Curve