During the 1960’s a new kind of device was introduced into the power system that was so detrimental to the health of the power grid, that it led many to believe that the power grid wouldn’t survive if people continued to use it. You see, up until then, pretty much all loads (devices that consume electric power) were linear, that is, the current drawn by the load was proportional to the voltage and it followed the envelope of the voltage waveform. However, the devices in question had the power to change the waveform of the voltage itself, and these devices were increasingly being used by consumers in their day to day lives.
So what if they can change the voltage waveform? How much harm can it do?
Well, a lot! Take a look at the diagram. The red line represents the normal, fundamental sinusoidal waveform oscillating at 50 Hz (or 60 Hz), that is expected from a power supplier. These ‘new’ and ‘advanced’ could change the voltage waveform and result in harmonics (or smaller waves) that can superimpose itself on the fundamental waveform and result in a waveform that looks a lot like the one in yellow. This resultant waveform, looks nothing like a sinusoidal waveform that you would normally expect, in fact, it isn’t even sinusoidal at all!
Okay, the wave is weird, but so what? What difference will a few bumps do to my devices?
Turns out, it can do a lot of harm if your devices are sensitive to voltage fluctuations like that. Harmonics can cause your devices and wires to run hot, extremely hot! This can, in turn, reduce the life of your devices including household devices and even large motors, generators and transformers! It also degrades the power systems, as devices cannot run under harmonic distortions. This means that although you will be billed for the power you are supplied, a large percentage of that power is unusable by your devices. Harmonics can cause poor power factor, increase current in the neutral conductor, increase losses due to hysteresis and eddy current in motors and it can also sometimes interfere with telephone networks! The effects of harmonics were so great and so devastating, that during the 1960’s many experts believed that no power systems could ever survive!
So what are these devices anyways!?!?!
Power Electronics. The humble transistor and its other heavyweight cousins like the SCR, MOSFET and IGBT are what causes harmonics. With their ability to stop or limit voltages at will, they can pretty much change waveforms to any desirable shape or value. This property was initially seen as useful, especially in making rectifiers (yes, even diodes cause harmonics), inverters (changes DC to AC) and converters (changes AC to AC or DC to DC). These devices, were smaller, easily controllable and were longer lasting as compared to their ancestors, the vacuum tubes and mercury arc valves. They were cheaper too, which fueled their rampant use not only by power suppliers and utilities, but even consumer goods manufacturers.
But things are ok now right? I mean, we still have a power grid, right?
Not really. Power electronics were so useful and cheap, that no one really could stop using them. The big box that is attached to your laptop charger: it causes harmonics. Choke coils in fluorescent lights: causes harmonics. Even phone chargers cause harmonics! In fact, the devices used to control the speed of motors (variable speed drives), cause harmonics, and those harmonics, in turn affect the motors that they are used to run (crazy isn’t it?).
The worst part about harmonics is that it isn’t a supplier issue, it is in fact, a consumer driven issue. And what is worse is that harmonics can actually ‘flow upstream’ to the machines that give us generated power and harm them, they can also harm other loads attached to the grid. Yes, your humble laptop could bring down the main generator or even disrupt the power to your neighbor (ok, that is a bit of an overstatement).
Eventually, a huge debate started as to the use of power electronic devices. On one side, you couldn’t deny the fact that they are useful. A world without electronics is hard to imagine. No laptops, computers as big as rooms, no TVs or mobile phones. In fact, the world as we know it wouldn’t exist without them. But then again, the problem they were causing was too severe, the advantages of semiconductors wouldn’t count for anything if there is to grid to power them in the first place. Eventually, their pros outweighed their cons and people started looking at other ways to prevent harmonics.
So what changes were brought about?
First off, there was control brought in to limit large creators of harmonics. Heavy fines were imposed on such industries. Different control techniques for power electronics were introduced that could reduce the dreaded triplen harmonics (3rd, 9th, 15th etc.), which cause more harmonics. Various filters were put in place to reduce and stop the mitigation of harmonics. Devices to measure harmonics, like harmonic analyzers were introduced, and they were used to analyze harmonics present in the distribution side and also find sources of harmonics.
Despite all these preventive measures, harmonics still exist in power systems and they still continue to harm consumer goods. As a consumer, there is very little you can do to stop creating harmonics, but you should be aware of the quality of power you receive and check how much your devices are being affected by harmonics. Spectrum analyzers are available that you can use to check the quality of power being delivered to your home. Research is still going on as to the reduction of harmonics and their long-term effects on various equipment. Various new methods are being investigated to stop their creation and prevent their mitigation.
Soham Chatterjee 