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Ohm’s Law for A-C Circuits

Geplaatst op 16 maart, 2010 21:39 door

The fundamental Ohm’s law formulas for a-c circuits are given by:

	I = E / Z		Z = E / I
	E = IZ*		P = EIcos Ø

Where:		I = current in amperes,
		Z = impedance in Ohms,
		E = volts across,
		P = power in watts,
		Ø = phase angle in degrees.

Phase Angle
The phase angle is defined as the difference
in degrees by which current leads voltage in a
capacitive circuit, or lags voltage in an inductive
circuit, and in series circuits is equal to the
angle whose tangent is given by the ratio X/R and
is expressed by:
arc tan (X/R)
Where:
	X = the inductive or capacitive reactance in ohms,
	R = the non-reactive resistance in ohms,
of the combined resistive and reactive components
of the circuit under consideration.
Therefore:
in a purely resistive circuit, Ø = 0°
in a purely reactive circuit, Ø = 90°
and in a resonant. circuit, Ø = 0°
also when:
Ø = 0°, cos Ø = l and P = EI,*
Ø = 90°, cos Ø = 0 and P = 0.
————–
Degrees x 0.0175 = radians. 1 radian = 57.3°

Power Factor
The power-factor of any a-c circuit is equal to the true power in watts divided by the apparent power in volt-amperes which is equal to the cosine of the phase angle, and is expressed by
EIcos Ø p . f . = —————- = cos Ø E*I
Where:
	p.f. = the circuit load power factor,
	EIcos Ø = the true power in watts,
	EI = the apparent power in voltamperes,
	E = the applied potential in volts
	I = load current in amperes.

Therefore:
in a purely resistive circuit.
Ø = 0° and p.f. = 1
and in a reactive circuit,
Ø = 90° and p.f. = 0
and in a resonant circuit,
Ø = 0° and p.f. = 1

Ohm’s Law for D-C Circuits
The fundamental Ohm’s law formulas for
d-c circuits are given by,
	E I = --- , R	E R = --- , I
	E = IR*	P = IE*
where:
	I = current in Amperes,
	R = resistance in ohms,
	E = potential across R in volts,
	P = power in watts.