SECTION 2 |
General Information
7
and capacitance and causes the current vector to lead the voltage vector by Phase
Angle (
φ
) = 90°. The unit of both X
L
and X
C
is “Ohm” - also denoted as “Ω”.
The effects of inductive reactance X
L
to cause the current to lag the voltage by 90°
and that of the capacitive reactance X
C
to cause the current to lead the voltage by
90° are exactly opposite and the net effect is a tendency to cancel each other.
Hence, in a circuit containing both inductances and capacitances, the net Reactance
(X) will be equal to the difference between the values of the inductive and capacitive
reactances. The net Reactance (X) will be inductive if X
L
> X
C
and capacitive if X
C
> X
L
.
Impedance, Z: It is the vectorial sum of resistance and reactance vectors in a circuit.
Active Power (P), Watts: It is denoted as “P” and the unit is “Watt”. It is the power
that is consumed in the resistive elements of the load. A load will require additional
reactive Power for powering the inductive and capacitive elements. The effective
power required would be the Apparent Power that is a vectorial sum of the Active
and reactive Powers.
Reactive Power (Q), VAR: Is denoted as “Q” and the unit is “VAR”. over a cycle, this
power is alternatively stored and returned by the inductive and capacitive elements
of the load. It is not consumed by the inductive and capacitive elements in the load
but a certain value travels from the AC source to these elements in the (+) half cycle
of the sinusoidal voltage (Positive value) and the same value is returned back to the
AC source in the (-) half cycle of the sinusoidal voltage (Negative value). Hence, when
averaged over a span of one cycle, the net value of this power is 0. However, on an
instantaneous basis, this power has to be provided by the AC source. Hence, the
inverter, AC wiring and over current protection devices have to be sized based on the
combined effect of the Active and Reactive Powers that is called the Apparent Power.
Apparent (S) Power, VA: This power, denoted by “S”, is the vectorial sum of the
Active Power in Watts and the reactive Power in “VAR”. In magnitude, it is equal to
the RMS value of voltage “V” X the RMS value of current “A”. The Unit is VA.
Please note that Apparent Power VA is more than the Active Power in Watts. Hence,
the inverter, AC wiring and over current protection devices have to be sized based on
the Apparent Power.
Maximum continuous Running Ac Power Rating: This rating may be specified as
“Active Power” in Watts (W) or “Apparent Power” in Volt Amps (VA). It is normally
specified in “Active Power (P)” in Watts for Resistive type of loads that have Power
Factor = 1. Reactive types of loads will draw higher value of “Apparent Power” that
is the sum of “Active and Reactive Powers”. Thus, AC power source should be sized
based on the higher “Apparent Power” Rating in (VA) for all Reactive Types of AC
loads. If the AC power source is sized based on the lower “Active Power” Rating
in Watts (W), the AC power source may be subjected to overload conditions when
powering reactive Type of loads.
