The electrodynamic wattmeter, shown in figureuses the reaction between the magnetic fields of two current-carrying coils or sets of coilsone fixed and the other movable.
What is Low Power Factor Wattmeter?
Fixed Coil The fixed coil is divided into two equal parts and these are connected in series with the load, therefore the load current will flow through these coils. Now the reason is very obvious of using two fixed coils instead of one, so that it can be constructed to carry considerable amount of electric current.
These coils are called the current coils of electrodynamometer type wattmeter. Earlier these fixed coils are designed to carry the current of about amperes but now the modern wattmeter are designed to carry current of about 20 amperes in order to save power.
Control System Out of two controlling systems i. Gravity control Spring control, only spring controlled systems are used in these types of wattmeter.
Gravity controlled system cannot be employed because they will be appreciable amount of errors. Damping System Air friction damping is used, as eddy current damping will distort the weak operating magnetic field and thus it may leads to error.
Scale There is uniform scale which is used in these types of instrument as moving coil moves linearly over a range of 40 degrees to 50 degrees on either side. Now let us derive the expressions for the controlling torque and deflecting torques. In order to derive these expressions let us consider the circuit diagram given below: We know that instantaneous torque in electrodynamic type instruments is directly proportional to product of instantaneous values of currents flowing through both the coils and the rate of change of flux linked with the circuit.
Let I1 and I2 be the instantaneous values of currents in pressure and current coils respectively. So the expression for the torque can be written as: Where, x is the angle. Now let the applied value of voltage across the pressure coil be Assuming the electrical resistance to the pressure coil be very high hence we can neglect reactance with respect to its resistance.
In this the impedance is equal to its electrical resistance therefore it is purely resistive. If there is phase difference between voltage and electric current, then expression for instantaneous current through current coil can be written as As current through the pressure coil is very very small compared to the current through current coil hence current through the current coil can be considered as equal to total load current.
Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by integrating the instantaneous torque from limit 0 to T, where T is the time period of the cycle.
Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeter and they are written as follows: Scale is uniform upto a certain limit.
They can be used for both to measure ac as well dc quantities as scale is calibrated for both. Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: Errors in the pressure coil inductance.
Errors may be due to pressure coil capacitance. Errors may be due to mutual inductance effects. Errors may be due connections. Errors caused by vibration of moving system. Errors due to stray magnetic field.The measurement principle of wattmeter is shown in the figure below: Applications of Wattmeter.
As other measuring instruments, watt meters are also used extensively in electrical circuit measurement and debugging.
Comment(s) to “How does a Wattmeter work? (back to basics)”. The measurement principle of wattmeter is shown in the figure below: Applications of Wattmeter As other measuring instruments, watt meters are also used extensively in .
Principle of operation of the electrodynamic wattmeter? can anyone explain the principle of operation of the electrodynamic wattmeter AND explain the principle of operation of a induction KWhr energy meter. What is Low Power Factor Wattmeter? However by doing some modification or adding some new features we can use modified electrodynamic wattmeter or low power factor to measure the low power factor accurately.
Here we are going to discuss, where we need to do modification. These are discussed one by one below:5/5(3).
Dynamometer Type Wattmeter Principle: If two coils are connected such that, current proportional to the load voltage, flows through one coil and current proportional to the load current, flows through another coil, the meter can be calibrated directly in caninariojana.commeter type wattmeter.
a measuring instrument whose operation is based on the mechanical interaction between two conductors in which an electric current is present. It consists of a measuring transducer, which converts the quantity being measured into an alternating or direct current, and a measuring mechanism of an electrodynamic system (Figure 1).