Power in AC circuits
– Instantaneous power is the time rate of flow of energy in an electric circuit.
– Energy storage elements like inductors and capacitors can cause periodic reversals of energy flow.
– Instantaneous active power results in net transfer of energy in one direction.
– Instantaneous reactive power oscillates between the source and load without net transfer of energy.
– Apparent power is the product of RMS values of voltage and current.
– Complex power (S) in phasor form is the product of voltage (V) and current (I).
– Real power (P) is derived from complex power by taking the cosine of the phase angle.
– Reactive power (Q) is derived from complex power by taking the sine of the phase angle.
– Real power can be simplified for purely resistive loads.
– Reactive power can be simplified for purely reactive loads.
Power factor
– Power factor is the ratio of active power to apparent power in a circuit.
– A lower power factor results in higher circulating currents and higher losses.
– Circulating currents are caused by energy returning to the source from energy storage in the load.
– Higher losses reduce overall transmission efficiency.
– Power factor is an important factor in electrical grids and can lead to network collapse if not properly managed.
Importance of reactive power
– Reactive power does not do any work but serves an important function in electrical grids.
– Reactive power must be supplied by the power source and is necessary for the operation of power systems.
– Failure to provide sufficient reactive power can lead to lowered voltage levels and blackouts.
– Capacitors are treated as generators of reactive power, while inductors are treated as consumers.
– Capacitive and inductive circuit elements tend to cancel each other out.
Units and representations
– Power is measured in watts (W).
– Apparent power is often expressed in volt-amperes (VA).
– Reactive power is measured in volt-ampere reactive (var).
– The relationship among active, reactive, and complex power can be represented using vectors or complex numbers.
– The power triangle is a diagram that represents active power, reactive power, complex power, and apparent power.
Power factor and reactive power control
– Power factor is 1.0 when voltage and current are in phase and zero when current leads or lags voltage by 90 degrees.
– Power factor is negative one when voltage and current are 180 degrees out of phase.
– Power factor is usually stated as leading or lagging to show the sign of the phase angle of current with respect to voltage.
– Reactive power occurs due to the AC nature of elements like inductors and capacitors and is measured in volt-amperes reactive (var).
– Reactive power flow influences voltage levels across the network.
– Reactive compensation is used to reduce apparent power flow to a load by providing reactive power locally.
– Transmission connected generators are required to support reactive power flow.
– The system operator performs switching actions to maintain a secure and economical voltage profile.
– Other sources of reactive power include shunt reactors, static VAR compensators, and voltage control circuits. Source: https://en.wikipedia.org/wiki/AC_power
In an electric circuit, instantaneous power is the time rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductors and capacitors may result in periodic reversals of the direction of energy flow. Its SI unit is the watt.
The portion of instantaneous power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as instantaneous active power, and its time average is known as active power or real power. The portion of instantaneous power that results in no net transfer of energy but instead oscillates between the source and load in each cycle due to stored energy, is known as instantaneous reactive power, and its amplitude is the absolute value of reactive power.
