“On 3rd April, Prime Minister of India, Shri. Narendra Modi had appealed to Indians to turn off their lights and light a lamp (Diya) at 9:00 pm on 5th April to mark India’s fight against Corona Virus. Just after the announcement, there was big chaos on social media saying that this would result in a complete blackout due to failure of the electric grid.
I, being an electrical engineering student, wanted to see the effect of a sudden reduction of load on the electric grid. One of the parameters which gets affected is Frequency. So, I decided to make a device to measure the frequency of voltage from a power outlet in my house. Please note that for this little experiment precision of the measured value is not important as I just wanted to observe the changes in the frequency.
In this Instructable, I will quickly explain how a grid can fail and then show you how I measured frequency.
An electric grid can fail due to many factors one of which is a sudden reduction of load. I will try to explain it in the simplest way possible such that a person with no electrical background can understand it.
What is Frequency? It is the number of times an AC wave repeats in one second. Frequency in India is 50Hz which means that an AC wave is repeated 50 times in one second.
In any power plant, there is a turbine which is a rotary mechanical device that extracts energy from fluid flow (steam, water, gas, etc) and converts it into useful work (mechanical energy). This turbine is connected (coupled) to a generator. A generator then converts this mechanical energy into electrical energy which we get at our home.
Let us consider a steam power plant for this explanation. Here, high-pressure steam is used to rotate a turbine which in turn rotates the generator and electricity is generated. I won’t be discussing how a generator works but just remember that the frequency of the generated voltage is directly related to the speed at which the generator rotates. If speed increases, frequency increases, and vice versa. Assume that the generator is not connected to any load. The generator is brought to speed by increasing the steam input to turbine until the frequency becomes 50Hz. The generator is now ready to deliver power. As soon as the generator is connected to the load (or grid), current starts flowing through its winding and its speed decreases and so the frequency. But as per regulation standards, the frequency should be within a specific band. In India it is +/- 3% i.e. 48.5Hz to 51.5Hz. Now, to compensate for the reduced frequency due to a decrease in speed, the steam input is increased until the frequency becomes 50Hz again. This process goes on. Load increases, speed decreases, frequency decreases, steam input is increased and the generator is brought to speed. All this is done automatically using a device called Governor. It monitors the speed (or frequency) of the generator and adjusts the steam input accordingly. Since most of the part is mechanical it takes few seconds (i.e. high time constant) for changes to take effect.
Now, let us consider that the entire load on the generator is suddenly removed. The generator speeds up above its normal speed since we had earlier increased the steam input to compensate for the increased load. Before the governor can sense and change the steam input, the generator speeds up so fast that the frequency crosses its upper limit. Since this is not permitted as per the regulatory standards, the generator trips (or is disconnected) from the grid due to over-frequency.
In India, we have One Nation - One Grid which means that all the generators in India are connected to one single grid. This helps in sending power to any part of the country. But there is one disadvantage. A massive fault in any one part of the country can spread quickly to other parts which results in the tripping of the entire grid. Thus, an entire country is left with no power!”