Samlexpower Evolution EVO-1212F, Руководство пользователя

Страница: 9 / 112

8 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 9
vector leads or lags the voltage vector in a sinusoidal voltage. In a purely inductive load, the
current vector lags the voltage vector by Phase Angle (
φ
) = 90°. In a purely capacitive load, the
current vector leads the voltage vector by Phase Angle, (
φ
) = 90°. In a purely resistive load, the
current vector is in phase with the voltage vector and hence, the Phase Angle, (
φ
) = 0°. In a load
consisting of a combination of resistances, inductances and capacitances, the Phase Angle (
φ
) of
the net current vector will be > 0° < 90° and may lag or lead the voltage vector.
Resistance (R), Ohm, Ω:
It is the property of a conductor that opposes the flow of current
when a voltage is applied across it. In a resistance, the current is in phase with the voltage. It is
denoted by “R” and its unit is “Ohm” - also denoted as “Ω”.
Inductive Reactance (X
L
), Capacitive Reactance (X
C
) and Reactance (X):
Reactance is the
opposition of a circuit element to a change of electric current or voltage due to that element’s
inductance or capacitance. Inductive Reactance (
X
L
) is the property of a coil of wire in resisting
any change of electric current through the coil. It is proportional to frequency and inductance
and causes the current vector to lag the voltage vector by Phase Angle (
φ
) = 90°. Capacitive re-
actance ( X
C
) is the property of capacitive elements to oppose changes in voltage. X
C
is inversely
proportional to the frequency 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 oppo-
site 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 Power (S), 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.
SECTION 1 | Safety Instructions & General Information