Imagine a day without electricity! Irritating! disgusting!! and you feel so much helpless. Picking up your phone and gadgets and suddenly you remember "Oh! there is no electricity" It's disheartening right? We shout, blame the provider but don't try to understand why our loads are being shaded. To grab an idea, let's try to understand how the generated electricity is at our door; the concept of Grid System.

What is Grid?

You must have seen generators in shops, complexes, offices, markets, etc. When the electricity is out, they are used to provide a backup. But where is the generator that provides electricity to the whole country? Is there only one generator or several? The answer is, there are numerous generators connected together to serve the country. And the way they are connected to each other and to the users' end is known as grid. Therefore, grid is an interconnected network with different components working together.

How does grid works?

As we all know there are 3 blocks of operation generating station to users' end i.e. Generation, Transmission, Distribution. Let's discuss one by one.

☛ Generation: Electrical energies are generated, actually not generated but transformed from other sources (water, coal, gas, nuclear, etc.) by mechanical means.

Hydro-electric Power Plant

There are numerous power plants all over the country like this. The output from these stations are connected to different nodes create a common energy bus. The transmission system starts from here.

☛ Transmission: The generated electricity is stepped up to a higher potential of about 33 KV through transformers for transmitting to a long-distance without a severe drop in the transmission line.

Transmission

☛ Distribution: These high voltage transmission wires end in substations outside the towns. There, with the help of step down transformers, the potential is stepped down to 11 KV Again they are stretched to the substations inside the town and stepped down to 220 V (3 phase 4 wire), and then single-phase supply is provided to the houses. The three-phase supply (11 KV) is given to the industries on demand. 

Power system 

This diagram shows the entire system from producer to consumer. And the entire network with all these components is called Grid. All the generating stations contribute to the grid and also work as a backup for other stations. Many interesting topics are related to this grid. Or do you think it's so simple as stated above! 

When I studied Grid System, a number of questions came in my mind that why it is necessary to interconnect so many generators together? Can't a single generator serve the purpose? And why different countries have separate grids? Why not a single grid is created all over the world that connects all the countries?

Do you also have these questions in your mind? If so,  stay with us and find your answers. 

Image Source:

* Circuit Globe

* Giphy

B.D.H. Tellegen

Tellegen’s Theorem is the very first theorem that initiates the journey of EEE. In 1952, Dutch engineer B.D.H. Tellegen proposed this theorem which goes something like this,

‘‘In any electrical network, the summation of instantaneous
 power in all the branches is equal to zero provided that the network 

satisfies Kirchhoff’s Laws’’

Eventually, this theorem has become an important circuit analysis tool. But what is so special in this theorem? It simply looks like another form of energy conservation law, isn’t it?

Power Is Everything
Engineers throughout the world are much more concerned about power. Why? Let us take a device (electrical or mechanical) for example. You will see we never care about the voltage or current specifications of the device while buying. Rather we want to know the power rating or how efficient the device is. So power is an important term to define the sustainability of a system and it requires measuring power associated with each element of an electrical system.

Absorbed or Supplied?
The theorem clearly says that absorbed power has to be equal to supplied power. Here we encounter some facts;
· How to find out which element is supplying power and which one is absorbing? Is it always the source (voltage/current) that supplies power?
· How to differentiate between the absorbed power and the supplied power?

Sign Convention
It’s a general convention that current comes out from the positive terminal of active components (battery and discharging capacitor), flows through the passive component, and flows back into the negative terminal of the active component.

A simple circuit

Following this convention we have,

Active Sign Convention states that if current comes out from the positive terminal of an active element, power is being supplied to the network and it has a negative sign.

Passive Sign Convention states that if current enters into the positive terminal of a passive element, power is being absorbed by that element and it has a positive sign.

Sign Convention

Throughout the calculation, signs of power will vary according to the current direction and the sign of the component’s terminal. But the question is, does a passive element (i.e. resistor) have specified positive or negative terminals?  Think it yourself.

Network Solving
It is very simple to solve the electrical network using Tellegen’s Theorem. We just need to find the values of branch voltages and current through the element. Using the appropriate sign of powers, this theorem can be verified and the circuit can be solved for unknown parameters.

Another question remains; why is this theorem so important? Apart from solving electrical networks, Tellegen’s theorem is used for filter designing in digital signal processing; in areas of biological & chemical processes; in determining the stability of complex systems.

Image Source:

* edubilla.com