How to transform volt-amperes to watts

How to transform volt-amperes to watts

Active power, and in volt-amperes - full is measured in watts. On some devices only the second size and also power factor is specified. Knowing them, active power can be calculated.


1. If only the full capacity, and power factor is specified (cos φ) - no, the last size needs to be measured. For this purpose use the so-called phasemeter. Carry out assembly and dismantling of the chain consisting of the device and loading only in the absence of supply voltage. The scheme of this chain is specified in the instruction to concrete model of the phasemeter. Consider that it shows not the angle of shift of phases (φ), and at once its cosine therefore in addition it will not be required to calculate this trigonometrical function. The measured size, as well as value of any other cosine, will be dimensionless and less than unit.

2. To determine active power in watts (it is measured by the household electric meter), calculate it on the following formula: P=S*cos φ where P is the active power (W), S is the full capacity (VA), cos φ - the power factor, dimensionless size.

3. The power factor is closer to unit, the full and active capacity is closer to each other. The reactive power (Q) which is the difference of full and active capacities is allocated on the bringing wires and therefore it is spent it is useless. Therefore at cos φ less than 0.7 it is expedient to apply proofreaders of power factor. Almost without raising active, they sharply reduce reactive and by that raise cos φ almost to 0.9.

4. In the absence of the automatic proofreader it is possible to increase cos φ reactive loading by means of the unpolar condenser. It has to be calculated on connection parallel to the power supply network and maintain amplitude value of its tension. To learn amplitude value, increase acting on 1.41. Parallel to the condenser surely install the resistor with a resistance about 1 megohm and with power not less than 0.5 W. Turn on the safety lock so that in case of breakdown of the condenser it opened a chain. Capacity of the condenser has to be such that it together with inductance of loading formed an oscillatory contour which resonant frequency is as it is possible closer to the frequency of network.

Author: «MirrorInfo» Dream Team