Active Power
The power which is really consumed or used in the power system is called active power, Real power or true power. Active power is measured in watts or Kilowatt. Active power is useful power for the electrical power system which runs the electrical circuit or load. The active power is denoted by the 'P'. Active power can be measured by the wattmeter.
Active Power = P = VI Cos Ï•
Active power is used to produce heat, light, torque in electrical appliances and electrical machines. The active power is real power that is transferred to the load such as induction motor, generators and transformer and dissipates into the circuit.
Reactive Power
The power which is moves and back from source to load and load to the source is called reactive power. The reactive power moves in both directions in the circuit. The reactive power is denoted by the character 'Q'. The reactive power is rated in Kilo volt-ampere(KVAr) or MVAr. The reactive power is also called use less power or wattless power.
Reactive power = Q = VIsinϕ
The reactive power compensation required for following purpose
1. The reactive power give better efficiency in power generation, transmission and distribution.
2. The reactive power is useful for improvement in voltage profile of power system.
2. The reactive power is useful for improvement in voltage profile of power system.
3. The reactive power useful for reducing the KVA demand.
4. The reactive power gives the higher load capability.
5. The reactive power reduces the power system losses.
6. The reactive power enhances the grid reliability.
The reactive power helps in the production of magnetic fields and electric fields in electrical circuits. The reactive power can be stored in electrical circuits and discharged by transformer and induction motors.
The power is directly consumed by resistance only. The capacitor and inductor do not directly consume any power since it's half-cycle whatever power (active or reactive) is received from the source. The power which is returned from the source and flows in both directions is called the reactive power. The reactive power does not perform any useful work in the system. Active and reactive powers do not exist in the DC system.
The sources of reactive power are
1. Synchronous generators
2. Capacitors and reactors
3. Transmission line and underground cable
4. Transformer
5. Loads
1. Synchronous generators
The synchronous generator can generate or absorb the reactive depending upon the field excitation of synchronous generator field windings.
When the field winding of synchronous generators is overexcited it generates reactive power. When the field of windings of synchronous generators is under excited it absorbs reactive power. So synchronous generator is used as a source of reactive for voltage control purposes.
2. Capacitors and reactors
The capacitive and inductive equipment are used in series and shunt compensation to control reactive power in the power system.
The capacitive compensator generates the reactive power in the power system and the inductive compensator absorbs reactive power from the power system.
The series capacitors are connected in series with the transmission line, series capacitors generate reactive power when needed. The shunt capacitors are installed in the loaded substations it generates the reactive power for keeping the system voltage in limits.
The shunt reactors are used to absorb the reactive power from the system and down the system voltage. The shunt reactors are also used to compensate for the capacitive load in the transmission line.
3. Cable and transmission line
The cable and transmission line both generate and absorbs the reactive power during lightly loaded and heavily loaded conditions.
When the transmission line is lightly loaded it generates reactive power so the system voltage increased. When the transmission line is heavily loaded it absorbs the reactive power and system voltage goes down.
4. Transformer
The reactive power is used for the production of magnetic fields and electric fields. The transformer is produced a magnetic field so the transformer is absorbed the reactive power from the power system. Reactive power consumption in a transformer depends on the ratings of the transformer.
5. Loads
Some loads in the power system consume the reactive power from the source. The reactive power-consuming loads are induction motors, induction generators, arc furnaces etc.
Apparent power
The total power means active power and reactive power flowing in the system is called apparent power. The apparent power is the root means the square product of voltage and current. The apparent power is measured or rated in Volt ampere. The apparent power is also defined as the product of the RMS value of voltage V and current I.
Apparent power S = V I Volt ampere
In the purely resistive circuit, apparent power remains the same as active power. When reactance increases, apparent power has become greater than the active power. The apparent power is denoted by character 'S'.
In resistive circuits, the voltage remains in phase with the current. In capacitive and inductive circuits current remain out of phase with the voltage. When current remains in phase with voltage it contributes the active power and when current remains out of phase with the voltage it contributes the creative power.
Important:
The resistors absorb the active power and dissipate in form of Heat.
The inductors are Absorbs reactive power and dissipate in the form of the magnetic field.
The capacitors are absorbs the reactive power and dissipate in the form of an electrostatic field.
Inductors are consumed the reactive power and capacitors are generates the reactive power.