Our appliances are getting smarter by the day. Its a good thing that many companies are energy conscious and are making their appliance even more energy efficient. In India most of home appliance are now made compulsory to have 5 star energy ratings, especially cooling appliances like ACs , refrigerators.
The TV ads are now flooded with ads talking about inverter based ACs, refrigerators. This is great news for energy conservation. However there is rider to all this. These units are susceptible to damages because of power fluctuations.
A traditional circuit consisted of a step down transformer which converted 230V AC to 24V AC which was then fed to bridge rectifier. The rectifier then converted the AC to DC and then it was distributed to the internal circuits with regulator and other component. Even if the voltage increased dramatically the secondary side would experience a relatively low surge on voltage. Prolonged exposure to voltages might have caused damages to internal circuits. In short these circuits were relatively very sturdy in voltage fluctuations.
However transformer has losses. It dissipates a lot of energy in the form of heat. Even in best cases the efficiency possibly didn’t not go beyond 87%, which was problem. Transfomer is bulky. Higher powered (kVA) machines would require a bigger transformer and as result were heavy too.
What we call inverter technology today , consist of PWM inverters and SMPS based circuits, may be even more advanced. These units have done away with conventional transformer based circuit and in effect increased the efficiency. They are also light weight , very compact and dissipate less energy as heat. They also come in attractive housings
However the flip side is that these circuits are now directly exposed to raw power. This is where the new problems have come up. These circuits are having 20% tolerance to voltage fluctuations. This would mean 180V on lower side and 280V on higher side. Seems ok doesn’t it? Wrong!!!
In developing and underdeveloped countries the power conditions are not so good and voltage frequently goes beyond 350V. This is a curse for these inverter based appliances, which get damaged more frequently than their predecessors.
These circuits are not inherently designed for such conditions and since units are manufactured considering global markets which include EU and US. Many white goods brands have made their foray in a new market only to have marred their reputation by service issues. We have many brands making their disappearing act after blitzkrieg of sales and ads.
One can attribute a serious contribution of such factors on making and breaking of brand in Indian conditions. There is probably two options here, either improve the tolerance of the internal circuits or protect the units externally by use of some protection equipment.
Do let us know what you think.
Author: Amit Manjrekar
(Click the image to learn more about him.)
AVR means Automatic Voltage Regulation.
What it does is to regulate the mains voltage within a limited range. In the case of your UPS, it boost +12% when the incoming voltage is too low. Let’s say the incoming voltage is at 200 volts, the output then goes to 224Volts, +12% of 200 volts, which is still acceptable for most UPSs. When the UPS output reaches let’s say, 230V with the boost mode on, then the UPS sends a command to a component called relay so that the +12% compensation is turned off.
Basically the voltage regulation is a series of power transformers, it can either be step-up transformers or a step-down transformers They basically do the same thing a 220V to 110V step-down transformer does, or a step-up transformer does, when it gets 110V and transforms to 220V. The UPS senses the incoming voltage and commands a series of relays to select a different transformer output or “tap”, as they call it.
An automatic voltage regulator can only work within a limited range. Their “taps” are at a fixed rate lets say, +10volts. If the UPS have a 12% voltage trimming option and the incoming voltage reaches 270 Volts, it can only trim 12% of that, which will result in 237 Volts.
Voltage regulator transformer can have as many “taps” as its developer wants, but it makes the unit much heavier, it wastes more energy and generates more heat. It doesn’t matter if the AVR has four “taps” or sixteen taps, it is still slow for suppressing voltage surges
Surge suppression is basically made to protect against high energy and fast rising surges or spikes that can be caused by lightning, electric motors being turned on or turned off, etc. Surges are essentially fast rising spikes and voltage swells are slow rising and low energy in nature. Surge suppression can in some cases reduce voltage swells, but this is not its main purpose.
Surge protection is basically comprised of a component called MOV – Metal Oxide Varistor.
An MOV works at diverting surges to ground. When operating at its nominal voltage, or the mains voltage, the varistor acts like a resistor with its resistance tending to the infinite, so it does not conduct electricity to ground at this state. When there is a fast surge, it instantaneously reacts (in nanoseconds) by decreasing its internal resistance, allowing the excess energy to flow to ground.
The voltage regulator cannot act as fast as an MOV for suppressing high power and fast rising surges and would not be capable of that because of the nature of a power transformer. High energy surges must be diverted to ground and power transformers do not do that. Compared to the speed of an MOV, the voltage regulator is like a turtle.
There are some disadvantages regarding the use of MOVs for suppressing voltage swell. MOVs degrade very fast if frequent voltage swell are imposed to it, it gets too hot and it’s internal chemistry degrades. MOVs are made to react fast and come back to it’s initial state very quickly as well, which happens when a power surge occurs. That’s why manufactures of surge protective devices use an MOV that only triggers itself when the voltage is much higher than the mains voltage. If the MOV starts to conduct too early, it will degrade itself very quickly and on all power grids a relatively high number of fast duration swells, do happen
What an MOV doesn’t do…
An MOV does not provide equipment with complete power protection. In particular, a MOV device provides no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device.
An MOV provides no equipment protection from inrush current surges (during equipment start-up), from over current (created by a short circuit), or from voltage sags (also known as a brownout); it neither senses nor affects such events.
Susceptibility of electronic equipment to these other power disturbances is defined by other aspects of the system design, either inside the equipment itself or externally by means of a circuit which typically consists of a voltage-sensing circuit and a relay for disconnecting the AC input when the voltage reaches a danger threshold. See OVCD).
In nut shell…
The AVR and the surge suppression solve two different problems. They’re complimentary technologies but do not ensure total power protection.
The AVR can adjust the voltage of the line within a limited range to compensate for the voltage being too high or too low. However, the AVR does not respond quickly enough or have wide enough compensation to handle surges.
Surge protection is capable of putting huge surge voltages into ground very quickly, but won’t adjust the long-term voltage of the line as the AVR does.
Both however are ineffective against sustained high voltages. in neutral open condition , they themselves will need protection.
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