ELECTRICAL RESISTANCE
In Electrical; Resistance is the opposition to the flow of Electrical current. We can understand the term resistance with an example of iron rod & fiber rod.
At normal voltage level; Current do not pass through fiber rod but it easily get conduced through the iron rod. We can say; Iron rod is having a minor or negligible resistance While a fiber rod having a very high resistance Which don’t allow current to get pass.
‘Resistance ‘ is been measured in numerical value with the units ‘ohm’ & having the symbol- Ω.
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DC POWER VS AC POWER
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Power DC is steady state stable power which remains fixed at particular magnitude with respect to time. In DC , Current flows inversely proportional to the resistance, Means Higher resistance leads to lower current & vice-versa As per According to ohm’s law Where V=IR.
DC power is simply equals to product of voltage & current such that Pdc= VI
In AC power; Things are not as simple as in DC , AC power is having a frequency. Power AC (sinusoidal) continuously moves with respect to time & periodically changes its direction. That’s why an angle exist in AC which is known as power factor.
Term power factor makes AC power; Pac=VIcosΦ(single phase)
Power DC only contains the magnitude which makes it a Scalar quantity while AC power contains both magnitude & angle; Which makes an AC power a Vector quantity.
TERM REACTANCE
“Reactance is also a type of opposition to the flow Electrical current Which is frequency dependent Which makes reactance appearance only in AC power Not in DC .”
In electrical system, there are three basic load elements which are ‘Inductor‘, ‘Resistance‘ & ‘Capacitor‘. Each load element has different behavior towards the power supply.
- AC power across resistor where power factor remains unity (cosΦ=1) Which makes Pac=VI. An ideal Resistor offers only Resistance to the flow of Electrical current.
- AC power across inductor where power factor get lower than 1 [cosΦ<1(lagging)] Which makes Pac=VIcosΦ(lagging).An ideal Inductor offers Resistance & reactance to the circuit.
- AC power across capacitor where power factor lower than 1 [cosΦ<1(leading)] Which makes Pac= VIcosΦ(leading). An ideal capacitor offers Resistance & reactance to the circuit.
Reactance across Inductor known as inductive reactance which is been represented with XL ( XL=2πfL )
Where,
f= frequency
L= inductance
Inductive reactance increases as frequency increases.
Reactance across Capacitor known as capacitive reactance which is been represented with XC ( XC=1/2πfC )
Where,
f= frequency
C= capacitance
Capacitive reactance increases as frequency decreases.
In case of DC where frequency is zero makes inductive Reactance completely zero(XL=2πfL, f=0) which results; In inductor on DC supply there is only resistance.
While on DC supply, capacitive Reactance get infinite as XC=1/2πfC, f=0 which results resistance. current don’t get pass through the capacitor.
ELECTRICAL IMPEDANCE
“In AC power, Impedance is the sum total of resistance(R)& reactance(X) Which is also been represented with the symbol Z & having the units ohm(Ω). Z=√(R²+X²).”
Impedance is a type vector quantity which contains an angle & the magnitude; the both. Impedance depend upon frequency that’s why it appears only across AC powered systems. Electrical impedance can be represented in a complex number where real part contains magnitude(resistance) While imaginary part contains an angle(reactance). (Z=R+jX)
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FORMULA, Z=√[R²+(XL-XC)²]
Inductive reactance (XL) & Capacitive reactance (XC) both are the type of reactance’s but in impedance formula; Overall reactance from these two is a subtraction of these two.
As discussed above, single phase AC power(sinusoidal); P=VIcosΦ
Where cosΦ is power factor; its valve varies from 0 to 1
Term power factor entirely depend upon the type of load.
Inductive load is basically a form of coil through which current flows. In inductive load due to magnetic field linking on the coils of the winding; back emf get generated Which opposes the changes produced by the main current. Which results current lags behind the applied voltage. That’s why power factor lags in inductive load.
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Capacitive load consists of separated conductors & dielectric material sandwiched in between them. The dielectric material is poor conductor of electricity but excellent in storing electrical charge. Capacitive load stores power in the form of Electrostatic charge. Current leads the applied voltage in capacitive load. That’s why power factor leads in capacitive load.
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“Both the Inductive & capacitive loads have entirely opposite behavior. Inductive load makes the power factor lagging while Capacitive load makes the power factor leading. That’s behavior makes the overall reactance subtracting.”
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COMBINATION OF IMPEDANCES
Combination of impedance depend upon the way of connection. In series connection, Final impedance is algebraic sum of all the connected impedances. In parallel connection, Final impedance is algebraic sum of reciprocal impedances.
Series combination
Zs= Z1+Z2+Z3 . . . ZN
Parallel combination
Zp= (1/Z1)+(1/Z2)+(1/Z3) . . .(1/ZN)
CONCLUSION
- In Electrical; Resistance is the opposition to the flow of Electrical current.
- Reactance is also a type of opposition to the flow Electrical current Which is frequency dependent Which makes reactance appearance only in AC power Not in DC.
- Impedance is the sum total of resistance(R)& reactance(X) Which is also been represented with the symbol Z & having the units ohm(Ω).
- Impedance formula; Z=√(R²+X²).
- Inductive reactance (XL) & Capacitive reactance (XC) both are the type of reactance’s but in impedance formula; Overall reactance from these two is a subtraction of these two. Z=√[R²+(XL-XC)²]
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