Hence, with the load removed from the circuit, the meter will indicate zero power through the load. 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.
The moving coil is asymmetrically pivoted and is placed over a hook shaped pole piece. Therefore, a three phase wattmeter has two elements. Therefore, the R3 voltage is equal to the load voltage, and the voltage across either series resistor is proportional to the difference in the output currents of the tubes.
In order to derive these expressions let us consider the circuit diagram given below: Thus the net field is due to the current I only. The sensor element is maintained at a constant temperature by a small direct current.
This difficulty can be eliminated by incorporating two compensating windingsmounted with the primary fixed-coil current windings, as shown in figure 3- This final modified circuit so obtained is called low power factor meter. Errors caused by vibration of moving system. This type of construction provides the advantages of increased operating torquelarger angles of rotation, ruggedness, compactness, and freedom from errors caused by stray fields.
If the pressure coil has range of volts, the half of it can be used so that the range becomes volts. As the frequency increases, the stray capacitance s and inductances also increase.
These two resistors are of equal value and are made small to prevent the voltage drop across them from reducing the load voltage appreciably. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted to other equipment for further use.
In this category two cases diagrams arises and these are shown below: And from this correction factor we are going to derive an an expression for error due to inductance of pressure coil.
But the question that arises here is that how will a wattmeter measure the AC power and this power factor? Where, x is the angle. Errors may be due to pressure coil capacitance. In this the impedance is equal to its electrical resistance therefore it is purely resistive.
These opposing fields cancel. It has the disadvantage of a very narrow frequency range. These coils are called the electric current coils of electrodynamometer type wattmeter. The reason for this is that the potential coil is allowed to move whereas the current coil is kept fixed.
In practice accuracy can be improved by connecting a fixed load such as an incandescent light bulb, adding the device in standby, and using the difference in power consumption. Hence moving coil is connected across the voltage and thus the electric current flowing through this coil is always proportional to the voltage.
The supply voltage is equal to the voltage across the pressure coil. This was all about watt meters. So the wattmeter simply measures the average power in case if AC power is required. The current coils are connected in series with the circuit, while the potential coil is connected in parallel.
Gravity controlled system cannot be employed because they will be appreciable amount of errors. The average value of the difference could be measured by a dc meter connected to read the voltage potential between the grids of V1 and V2. Digital electronic instruments measure many parameters and can be used where a wattmeter is needed: The fixed coil is wound on a laminated core having pole pieces designed to give a uniform radial field throughout the air gap.
Earlier these fixed coils are designed to carry the electric current of about amperes but now the modern wattmeter are designed to carry electric current of about 20 amperes in order to save power.
Errors in the pressure coil inductance. For AC powercurrent and voltage may not be in phase, owing to the delaying effects of circuit inductance or capacitance. Control System Out of two controlling systems i.
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. This was the case of DC power. With this construction there is a tendency on the part of the pressure coil to creep move further on the hook when only the pressure coil is energized.Single and Three Phase Wattmeters and Energy Meters: Construction and principle of operation The construction and principle of operation of Single Phase Energy Meters is explained below Single And Three Phase Wattmeters And Energy Meters.
The measurement of active power is carried out by means of electrodynamic wattmeter, which is in direct connection with the consumer.
In this paper it is assumed that the results of the active power measurement by means of electrodynamic wattmeter are quite evenly spread between the highest.
The electrodynamic wattmeter, shown in figureuses the reaction between the magnetic fields of two current-carrying coils (or sets of. Dynamometer type wattmeter works on very simple principle and this principle can be stated as "when any electric current carrying conductor is placed inside a magnetic field, it experiences a mechanical force and due this mechanical force deflection of.
Before we study the internal construction of electrodynamometer type wattmeter, it is essential to know the working principle of electrodynamometer type mint-body.commeter type wattmeter works on very simple principle and this principle can be stated as when any current carrying conductor is placed inside a magnetic /5(7).
Dynamometer Type Wattmeter Working Principle | Electrodynamometer The construction of a dynamometer instrument to some extent resembles the PMMC instrument.Download