Electrodynamometer Wattmeter consists of two coils, pressure coil (PC) and current coil (CC). Pressure coil is connected across the circuit. ELECTRODYNAMOMETER. WATTMETER’S. • These instruments are similar in design and construction to electrodynamometer type ammeters and voltmeters. Before we study the internal construction of electrodynamometer wattmeter, it very essential to know the principle of working of electrodynamometer type.
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Electrodynamometer Type Wattmeter in general, a watt meter is used to measure the electric power of a circuit, or sometime it also measures the rate of energy transferred from one circuit to another circuit. When a moving coil that is free to wattmeeter is kept watmeter the influence of a current carrying conductor, then automatically a mechanical force will be applied to the moving coil, and this force will make a little deflection of the moving coil.
If a pointer is connected with the moving coil, which will move of a scale, then the deflection can be easily measured by connecting the moving coil with that pointer. This type of watt meter consists of two types of coil, more specifically current coil and voltage coil.
There are two current coils which are kept at constant position and the measurable current will flow through those current coils. A voltage coil is placed inside those two current coils, and this voltage coil is totally free to rotate.
The current coils are arranged such a way, that they are connected with the circuit in series. In fact, a watt meter is a package of an ammeter and a voltmeter, because the product of voltage and current is the power, which is the measurable quantity of a watt meter.
Electrodynamometsr current flows through the current coils, then automatically a magnetic field is developed around those electrodynamomster. Under the influence of the electromagnetic field, voltage coil also carries some amount of current as it is dattmeter with the circuit in parallel.
In this way, the deflection of the pointer will proportional to both current and voltage of the circuit. A dynamo meter type electrodynaometer meter is used in various applications where the power or energy transfer has to be measured. Now let us look at constructional details of Electrodynamometer Type Wattmeter.
It consists of following parts There are two types of coils present in the electrodynamometer. Moving coil moves the pointer with the help of spring control instrument.
A limited amount of current flows through the moving coil so as to avoid heating. So in order to limit the current we have connect the high value resistor in series with the moving coil. The moving is air cored and is mounted on a pivoted spindle and can moves freely. In electrodynamometer type wattmeter, moving coil works as pressure coil.
Electrodynamometer Type Wattmeter
Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage. 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 electrodyamometer 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 wttmeter 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.
Gravity controlled system cannot be employed because they will appreciable amount of errors. Air friction damping is used, as eddy current damping will distort the weak operating magnetic field and thus it may leads to error. There is uniform scale is used in these types of instrument as moving coil moves linearly over a electrodnyamometer of 40 degrees to 50 degrees on either sides.
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 electro dynamic 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.
So the expression for the torque can be written as:. Assuming the electrical resistance of 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 in very very small compare to current through current coil hence current through the current coil can be considered as equal to total load current.
Following are the advantages of electrodynamometer type wattmeters and they are written as follows:. They can be used for both to measure AC as well as DC quantities as scale is calibrated for both. Electrical Instruments and Classification of instruments. These types of instruments are only used electrdynamometer measuring the dc quantities as if we apply ac current to these type of instruments the […].
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Electrodynamometer Type Wattmeter Electrodynamometer Type Wattmeter in general, a watt meter is used to measure the electric wattmdter of a circuit, or sometime it also measures the rate of energy transferred from one circuit to another circuit. And the voltage coil is wttmeter in parallel with the circuit. As simple as other voltmeter and ammeter connection. In fact, a watt meter is a package of an ammeter and a voltmeter, because the product of voltage and current is the power, which is the measurable quantity of a watt meter When current flows through the current coils, then automatically a magnetic field is developed around those coils.
Out of two controlling systems i.
Wattmeter – Wikipedia
Gravity control 2 Spring control, only spring controlled systems are used in these dattmeter of wattmeter. In order to derive these expressions let us consider the circuit diagram given below: So the expression for the torque can be written as: Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeters and they are written as follows: Scale is uniform up to certain limit b.
They can be used for both to measure AC as well as DC quantities as scale is calibrated for both Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type watt meters: Posted on November 14, November 14, Author Mr. Posted on June 1, July 24, Author Mr.
BE Notes r notes. Posted on January 27, March 25, Author Mr. Moving Iron instruments Principle and operation. Single phase Energy meter.
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