Electrical Energy

Why Electrical Energy?

The most important form of energy in our daily life is Electrical Energy. The branch of engineering which deals with producing, managing and utilizing of this energy, is referred as Electrical Engineering.

It was June 1752, when Benjamin Franklin (founder of USA) first tried to catch electricity from clouds during a heavy storm with the help of a flying kite.

DC vs AC

Early power systems developed by Thomas Edison generated and delivered Direct Current (DC).

However, DC power systems had many limitations, most important that power typically could not be practically transmitted beyond a distance of about one mile.

George Westinghouse’s (AC) power system—invented by Nikola Tesla and used with transformers developed by William Stanley, Jr., proved to be far superior technically and economically. The voltage of AC could be stepped up or stepped down to enable long distance power transmission and distribution. Edison fought against the use of alternating current based systems, which he claimed would be dangerous because of the high voltage at which power would need to be transmitted over long distances.

Other theories

Most of the theories, on which this field of engineering is built, are related to electromagnetism. The law of electromagnetism was invented by Michael Faraday in the year 1831. This law is popularly known as Faraday’s law of Electromagnetic Induction. The relation between current and voltage in a conductor was already stated by Georg Ohm, in 1827. Ohm’s law….. Based on these two theories development of electrical technology began.

Electrical Power System

• In the Power Industry, Power System is a term used for an Electricity Network.
• It is considered as most complex man made system.

Electricity Network  [pic 1]

• Electricity Generation
• Electric Power Transmission
• Electricity Distribution

Electricity Generation

Generating plants are usually located near a source of water, and away from heavily populated areas. They are usually quite large in order to take advantage of the economies of scale.

Electric Power Transmission

The transmission network will move the power long distances‐often across state lines, and sometimes across international boundaries until it reaches its wholesale customer.

Electricity Distribution

Upon arrival at the substation, the power will be stepped down in voltage —from a Transmission-level-voltage to a Distribution-level-voltage. As it exits the substation, it enters the distribution wiring. Finally, upon arrival at the service location, the power is stepped down again from the distribution voltage to the required service voltage(s).

[pic 2]

Limitations of Current Grid

• Obsolete system layout   – Increasing population, more substation, right of way.

• Aging Infrastructure of Current Grid    – Older equipment, higher failure rate

• Outdated engineering of Current Grid   – New power delivery planning needed

[pic 3] [pic 4]

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Economics of Power Generation

Load curves

• The load on power plants will always be changing with time and will not be constant because consumer of electric power will use the power as and when required.

• Load curve is graphical representation between load in KW and time.

• It shows variation of load on the power station.

• If the time is in hours then the load curve is known as Daily Load Curve.

• If the time is in days, the load curve is known as Monthly Load Curve and

• If the time is in months, the load curve is known as Yearly or Annual Load Curve.

• The Daily Load Curve will be different for different type of consumers and different localities. These load curves may show different pattern during summer, winter and rainy season.

[pic 5]   [pic 6]

• The combined DLC for all types of consumers is shown in figure (a) and the Theoretical curve for simplicity is shown in figure (b).

[pic 7]

Load Duration Curves

• LDC is simply a re-arrangement of DLC with loads set up in descending order of magnitude.

• The LDC indicates for how many hours a certain load is required in a day.

[pic 8]

Terms and definitions

1. Connected load: Connected load is the sum of ratings in kilowatts (kW) of equipment installed in the consumer’s premises.

The connected loads in the premises of a consumer are shown in figure.

Total load connected in the consumer’s premises: = 40 + 1000 + 60 + 40 + 20 + 500 + 25 + 60 = 1745 W

[pic 9]

2. Demand: The demand of an installation or system is the load that drawn from the source of supply at the receiving terminals averaged over a suitable and specified interval of time. Demand is expressed in kilowatts (kW) or other suitable units.

3. Maximum demand or Peak load: It is the Max. Load which a consumer uses at anytime. It can be less than or equal to connected load.

4. Demand Factor: It is defined as the Ratio of Max. Demand to Connected-Load.

5. Average Load: It is calculated by dividing the area under the load curve (energy in kWh) by the time period (24 hrs) considered to draw the load curve.

Avg. Load = Area under the Load Curve / 24 hrs  = Energy consumed 24 hrs / 24 hrs

6. Load Factor: It is defined as the Ratio of Avg. Load to Max. or Peak Load.

• Load-Factor and Demand-Factor are always less than unit.
• Load-Factor plays an important part on the cost of generation per unit.
• The higher the Load-Factor the lesser will be the cost of generation per unit for the same Max. Demand.
• Load-Factor = Avg. Load / Max. Load

7. Diversity Factor: It is the ratio of sum of Max. Demand of individual consumer and simultaneous Max. Demand of the whole group during the particular time.

• DiF = Sum of Max.-Demands / Simultaneous Max.-Demand at a Given Time
• Diversity Factor is always greater than unit.

8. Plant Capacity Factor: It is defined as the ratio of actual energy produced in kWh to the Max. Possible Energy that could have been produced during the same period.