Alternating Current (Part 1)
Alternating Current is called Alternating Current because it keeps changing the direction in which it moves.
Alternating Current is called Alternating Current because it keeps changing the direction in which it moves. That happens because it’s made by turning an magnet round inside a coil of wire. Not exactly like the picture, but something like that.
When the magnet points straight up, the voltage will be high. When it’s tilted sideways and not pointing so much up, the voltage is less. And when it points down, the current flows in the opposite direction. But the magnet doesn’t make current unless it’s moving.
A voltmeter is used to the voltage constantly moving, so it shown you only the average voltage. This means the voltmeter usually always shows the same reading.
In my place, after the rains, the voltmeter sometimes doesn’t stay at the same reading. It moves up and down, sometimes quivering between two similar voltages, and sometimes swooping wildly up and down. If the needle suddenly goes right to the bottom and stays there, we’re all hopeful because it means the Electricity Board could be fixing the line to bring the voltage back to normal.
One day, the power supply was a truly alternating current. It was alternating between being okay when we were not using it, and changing to a dim supply the moment we switched something on. Luckily, Valagapattu (the village whose supply-line we get our power from) was having the same problem, too. This meant there would soon be a lot of people complaining so it would get fixed soon.
But two days later, our milkman informed us that Valagapattu’s power-supply had been fixed — and, when we checked, ours still hadn’t! There must have been an additional problem on the line between Valagapattu and our house, which wasn’t affecting the village.
When electricity is made in a power station, there are not one but three sets of power lines coming out. The electricity in these lines are of three different “phases”. For most things, any one of the phases can be used to run them, so houses are only supplied with one set of the phase-lines. But for pumping water to fields, there are some more powerful “three-phase” motors that need supply from all three lines to run.
It so happened that our line was connected to one phase, and Valagapattu was supplied by a different one. So if the problem was only on our phase then Valagapattu wouldn’t be affected. The people using motors would get affected, but since it had been raining frequently they wouldn’t be watering their fields for some time.
In Tamilnadu, the government gives free electricity to farmers for irrigation. To make sure they don’t use it too much, one of the phase-lines is switched off some of the time. That way, only the motors are stopped because they need all three phases. And the other two lines remain on to continue supplying the houses.
Once there was a long-drawn-out problem in the Valagapattu line, which was affecting us as well — we were on the same line at that time. The E.B. eventually switched our line to a different phase so that at least we would get proper current. The current came properly — but then it went off again and didn’t come back until the next day. It turned out that they had accidentally switched us to the motors-only third phase, which only gave current for 6 hours a day!
Finally we were switched to the middle phase — not Valagapattu; not motors-only — which is where we’ve been for some time. The advantage is that Valagapattu-specific issues don’t affect us, but the disadvantage is that, when we do have a problem, it’s us alone who have to give the complaint.
The main problem was: how to explain the problem? It wasn’t a simple case of dim-supply. The current was there, with a perfect voltage. Sometimes it would go dim or start flickering, but most of the time it was there.
When we put on a light-bulb, the voltage would drop by 5 volts or so. But that didn’t cause a noticeable change in the brightness. So the E.B. people may think it’s our voltmeter that’s faulty.
It was only when we switched on something more, lie a mixie or laptop, that the voltage would suddenly go down by 100 volts or more. But if we demonstrated the laptop to the E.B., they would say the laptop was faulty. And a mixie would be even more suspicious.
We could hope that the E.B. came when the current was actually dim. But that happened mainly when it was raining, and the E.B. wouldn’t be coming when it was raining. Firstly, they wouldn’t want to get wet. And secondly, the electricity-poles would be too slippery to climb up and repair anything. What we needed was for the lights to dim when a not-suspicious bulb was switched on. And so we hatched a plan….
This is the first of a two part article. It was originally published in Sirius, issue #204 11–24 October 2015 “The Defeat Device”. You can read the second part of the article here.