Thursday, November 24, 2016
transformer instalation VIDEOS
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Electrical ohms law
Ohm law
States that the current through a conductor between two points is directly proportional to the voltage across the two points.
I= V/R
States that the current through a conductor between two points is directly proportional to the voltage across the two points.
I= V/R
Monday, November 21, 2016
Sunday, November 20, 2016
power factor
What is Power
Factor?
Power factor is
defined as the cosine angle between voltage and current in an alternating
current (AC) circuit. Unlike in DC circuits, a phase angle difference, ϕ exists between voltage and currents in an AC circuit. The
cosine of ϕ (or Cos ϕ) is termed as the power factor.
1.REACTIVE CIRCUIT
(UNITY POWERFACTOR)
2.INDUCTIVE CIRCUIT
(LOGGING POWERFACTOR)
3.CAPACITIVE CIRCUIT (LEADING
POWER FACTOR)
If the circuit
consists of inductive elements or it behaves like an inductive circuit (where
current lag behind the voltage), then the power factor in that circuit is
referred as a lagging power factor.
On the other hand, if
the circuit is capacitive in nature where current leads the voltage, then the
power factor is referred as the leading power factor. If there is no phase
angle difference between the voltage and current then it is unity power factor.
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Consider above waveforms and phasor diagram of an inductive circuit where current lags the voltage by an angle ϕ. Here, the total current is resolved into two components.
The I cos ϕ component is called wattful or active component and it is in phase with
the source voltage. The I sin ϕ component is called
wattless or reactive component and it is 900 out of phase with the
source voltage.
From the figure we can
say that the angle from these two components decides the power factor, and it
implies that if the reactive component is small, the phase angle ϕ is small resulting high power factor (In every electric
circuit, power factor should be maintained high for a better utilization of
power). Thus, a small reactive current in the circuit results a high power
factor and vice-versa.
It is to be noted that
the power factor can never be more than unity. The most efficient loading of
the supply results a power factor of 1. Suppose, if the power factor of the
load is 0.8 means there are much higher losses in the supply system.
Generally power factor
is indicated with words lagging and leading, in addition to the value. This is
to represent whether current leads or lags by the voltage. For example, 0.8
lagging implies that the circuit has a power factor of 0.8 where current lags
the voltage. Sometimes, it is also indicated as a percentage such as 80%
lagging.
Power factor can also
be expressed in terms of power consumed by electrical equipment or a complete
electrical installation. In such case power factor is defined as the ratio
between the true power (KW) to the total apparent power (KVA).
Consider the above
power triangle which gives the relation between various powers. The VI cos ϕ, component is called true or active power which is
measured in watts (W) or Kilowatts (KW). It causes useful work in the circuit.
he VI sin ϕ, component is called wattles or reactive power and it is
measured in volt-amperes-reactive (VAr) or kilo-volt-amperes-reactive (kVAr).
It is caused by inductance or capacitance in the circuit and it does two main
functions; to provide magnetic field and to charge capacitors.
The resultant
component of true and reactive or simply a VI component is called apparent
power and it is measured in volt-amperes (VA) or kilo-volt-amperes (kVA).
From the figure, power
factor, cos ϕ = active power/
apparent power = VI cos ϕ/ VI
cos ϕ = KW/KVA
The above expression
of power factor measures how efficiently electric power is converted into
useful work output. And also, from the power triangle, reactive power component
measures the power factor. If the reactive power component is small, the power
factor will be high and vice-versa.
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