Power and energy measurement in RLC circuits.

The current in a serial RLC circuit amounts to:

I = I0sin(ωt)

Voltage at the terminals of the source:

U = U0sin(ωt + φ)

Power constant current

The power of direct current could be measured using a voltmeter and an ammeter joined according to the schemes shown in the picture.

In both systems , the power is equal to: P=U*I

The alternating current power is described in the following patterns:

Active power P=U*I*cosφ Reactive power Q=U*I*sinφ Apparent power S=U*I

To measure the active power of alternating current wattmeters are used. In the electrodynamic wattmeter stationary coil the current is connected in series with the receiver of electricity, and the moving coil voltage parallel to the receiver.

Active power

Reactive power

To measure the reactive power a specialized power meter is used . The reactive power meter is different from a regular wattmeter.

Apparent powerApparent power is the power that appears because of the circuit

impedance. Apparent power is the combination of true power and reactive power.

To calculate apparent power, you may use either of the following

formulas: 

The project is realized with the finance support of the European Commission within the "Longlife learning program".

The presentation was made as a result of the Leonardo da Vinci project titled "Your future

career prospects" carried out in "Zespół Szkół Zawodowych" no 3 in Katowice

between 2011 and 2013.

The publication reflects the standpoint of the authors only and neither the European

Commission nor the National Agency bear responsibility for the essential contents included in the presentation and for the way of using the

enclosed information.

The end

Authors:

Michał Bijak

Daniel Skupnik

February 2012