A lot of power saver brand-makers are brutally advertising their brands now-a-days. Their claim is that by simply plugging in a small device into any socket in you home will effectively reduce their electricity bill by 35 to 40%. I have searched about this issue over the internet to know what people are saying about power savers. By searching I came across a website which completly denies the fact, that any power savers can save power to reduce electricity cost. But by doing this they simply kept their eye closed on a one simple fact.
They have proved with a simple case by using a formula. We know that Power Factor PF is simply cosine of an angle between Current and Voltage across any device. And power factor of 1 is considered ideal.
There are two types of loads, one type is resistive and other is reactive i.e., capacitive and inductive ones. The example of resistive loads is light bulb, while of inductive load is an electric motor. When voltage is applied to any resistive load then it does not splits voltage and the current produced, by any angle. In reactive devices with the application of voltage, current is produced which is not in phase with the applied voltage rather it leads or lags behind by some angle, and cosine of that angle is known as power factor. Having power factor 1 is cosidered as ideal. Power factor cannot exceed 1, because no input to cosine gives us value more than one.
And also,
PF = Real Power (Watts) /Apparent Power (VA)
Now Real power is the power for which we pay in our electricity bills.
Real Power (Watts) = Apparent Power × PF = Voltage × Ampere × PF
Now, real power of any device is fixed. Apparent power can however vary. This is because it is the vectoral sum of real and reactive power. Considering real power and voltage costant now if we vary the power factor it comes out that decrease in PF increases the current demand of the device. Please keep a note that it is the demand, and not the consumption.
The decrese in power factor increases the current demand of any device. For example consider a motor, now as it is an inductive load its power factor will be less than 1. Now if we increase the coiling to increase the inductance, or by any other method, the current demand will increase. As a result more current will pass through the windings. Windings have resistive element too, when relatively large current flows in the later case due to increased inductance and decreased power factor, more power is lost by the resistive element of the device. This additional power loss will be real power because it has been consumed by the resistive element of the device, i.e, Resistance of windings. Moreover power loss also increases in the cables providing current to the device. Since cables also have resistance no matter small, but when this increased amount of current passes through the cables it causes considerable power loss. And this power loss is again real power, for which we pay.
What most people think is that correction in a power factor only reduces the apparent power. But as we only pay for real power the decrease in apparent power has nothing to do with our electricity bill. But what they do not keep into account is the effect of increased current on the resistive factors of any device.
Let us demonstrate this with the help of an example:
CASE 1
Consider load having power factor 0.6.
Real power consumption is 300 Watt.
Resistive value of transmission cables is 20 Ohm.
Voltage applied is 220 Volts.
Then putting in the above formula
300 Watts = 220 V x Current x 0.6 PF
Current = 2.2 Amperes.
Loss of power in cables is = 2.2 x 2.2 x 20 = 96.8 Watts
CASE 2
Power factor of load is 0.8.
Real power consumption is 300 Watts.
Resistive value of transmission cables is 20 Ohm.
Voltage applied is 220 Volts.
Then putting in the above formula
300 Watts = 220 V x Current x 0.8 PF
Current = 1.7 Amperes.
Loss of power in cables is = 1.7 x 1.7 x 20 = 57.9 Watts
DIFFERENCE = 38.84 Watts
So you have now seen that small changes in power factor can greatly reduce your power losses and iturn your electricity bills.
These additional losses considerably increase the consumer bills. Now what power savers do is that they correct the Power factor of the circuit. And it is possible to change the power factor of any electric device. For example to increase the power factor of a simple motor, we simply put a calculated amount of capacitance in parallel to it. As capacitance and inductance have effect opposite to each other, it cancels the effect of increased inductance. This is what, which is done in factories having large motors installed in them. This method is known as power factor correction method and it reduces the electricity bill.
Power savers operate on the same principle. They contain in them a pre-calculated amount of capacitance which is rather dynamic instead of static. It tracks the power trends of any our homes and then adjusts the capacitance accordingly, to correct the power factor.
This is why we are often told to buy cables made of pure copper as it reduces the resistance of cables; moreover the wire with which the motor is wound should also be of high quality to reduce the power losses.
Summarizing the above discussion we come to know that Power savers considerably reduce the electricity bills. But not to the extent which is heavily advertised. If you have lots of inductive loads like motors, air conditioners and other such type of loads then you can benefit from them.
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