Definition: The power factor meter measures the power factor of a transmission system. The power factor is the cosine of the angle between the voltage and current. The power factor meter determines the types of load using on the line, and it also calculates the losses occur on it.
The construction of single phase electrodynamometer Power Factor Meter is shown in figure It consists of a fixed coil which acts as the current coil.This coil is split up into two parts and carriers the current of the circuit under test.Therefore,the magnetic field produced by this coil is proportional to the main current.
The single phase electrodynamometer type power factor consists of fixed coil and pressure coil.
the fixed coil and splits into two parts and carries the currents of the circuit which is supplied to the load.The pressure coil also consists of two coils that is coil A and coil B.These two pressure coil pivoted on spindle which constitute the moving system.Pressurencoil ‘n’ is connected in series with inductance ‘L’.The current proportional to the voltage drop across the load flows through the pressure coil.The value of R & Lare so adjusted that
The angle between the plane of the coil is made equal to 90° The current Ib legs behind the voltage by 90° Current Ia is in phase with Voltage
Working/Operation:In this case to deflecting Torque produced which acts on coil a and coil b the coils are so designed that the torque acting on it are equal and opposite in direction so the pointer takes a position where the two torquess are equal .
Deflecting torque acting on coil A is:
Where, = Angular Deflection from The Plan of Reference
= Maximun Value of Mutual Inductance Between the Two Coil
Deflecting torque acting on coil B is:
Therefore the deflection of the Instrument is the measure of phase angleOf the circuit The scale of the instrument can be calibrated Indirectly in the terms of power factor
The phasor diagram is also shown For the circuit such that the cu
rrent In the coil a is approximately At an angle of 90° To the current in the coil B
The above figure shows the construction and connection of a 3 phase electrodynamometer type power factor the two moving coils of the meter are shown and so placed that the angle between their place is is 120 degrees this two calls are connected across 2 different phases of the supply circuit each of these two coils are has series resistance through which it is connected to the phase angle the voltage applied across coil a is V12 and the current flowing in it is I a the voltage applied across coil B isV13 and the current flowing through it is Ib these two moving coils are placed between segments of fixed coils
The basic working principle of power factor meter is similar to that of dynamometer type wattmeter that is when the field produced by a moving system tries to come in line with the field produced by the fixed coil deflecting torque is exerted on the moving system which deflects the pointer attached to it. Power factor meter is an indicating instrument and no controlling torque is provided in this instrument the currents are being led into the moving coil A and B by fine ligaments where exert no control.
When the instrument is connected to the load circuit current flows through the fixed coil and moving coils A and B, flux is set by the fixed coil and moving coils.
By the alignment of two fields, torque is developed that is the resultant field produced by the moving coil tries to come in line with the field produced by the fixed coil and the torque is developed still both of them come in line with each other there are three extreme conditions in which these instruments is connected in the circuit.
When power factor of the circuit is unity.
When power factor of the circuit is zero lagging
When power factor of the circuit is zero leading
Condition 1: when the power factor of the circuit is unity:
Condition 2: when the power factor of the circuit is zero lagging:
In this case current lags behind the circuit voltage by 90° therefore the current flowing through pressure coil B will be in phase with the current in the circuit coil FF both being
Lagging behind the circuit voltage by 90° .The current flowing through pressure coil A will lead the current in the current coil FF by 90° .Thus a turning moment acts on the pressure will be B and bring its plane parallel to the plane of current coil FF and the pointer indicates zero power factor lagging
Condition 3: Power factor of the circuit is zero leading:
The power factor meter is of two types they are
Single Phase Electrodynamometer
Three Phase Electrodynamometer
Moving Iron Type Meter:
Rotating Iiron magnetic field
Number of alternating field