GB/T 47966-2026Electrical energy measurement and control - Terminology (English PDF)

3.1 Terminology related to basic circuits

3.1.1

A basic AC circuit in which a linear load is powered by a single-phase sinusoidal voltage source, and the current is also sinusoidal at the same frequency.

Note 1.A sinusoidal voltage source, see formula (1), will generate a sinusoidal current (assuming it lags behind the voltage) when supplying power to a linear load, see formula (2).

u = 2Usin(omegat) (1) i = 2Isin(omegat-theta) (2)

In the formula.

U --- RMS voltage value, in volts (V);

I --- The effective value of the current, in amperes (A);

omega --- angular frequency 2pif, unit is radians per second (rad/s);

f --- Voltage source frequency, in Hertz (Hz);

theta --- The phase angle between current and voltage, measured in radians (rad).

t --- Time, in seconds (s).

Note 2.This type of circuit is the basic unit of electrical energy transmission. Its voltage and current exhibit a sinusoidal relationship with the same frequency, and its power characteristics are determined by the phase angle. The circuit may contain...

Linear components such as resistors, inductors, and capacitors have no harmonic components; the load characteristics (such as inductance or capacitance) in a sinusoidal circuit will affect the relationship between current and voltage.

Phase relationship.

3.1.2

In a single-phase sinusoidal circuit, the product of the instantaneous voltage value and the instantaneous current value at a certain moment.

Note 1.The instantaneous power of a single-phase sinusoidal circuit changes periodically, representing the instantaneous rate of energy exchange between the power source and the load.

Note 3.The instantaneous power p of a single-phase sinusoidal circuit is given by formulas (3) and (4).

p=ui (3)

In the formula.

u --- Instantaneous voltage value, in volts (V);

i --- Instantaneous current value, in amperes (A).