The flux paths through the disk are from 2 to 1, from 2 to 3, from 3 to 4 and from 5 to 4. The flux paths through the disks are from left to right. This causes eddy currents to be set up in the disk. The reaction between the eddy currents and the field tends to move the disk in the direction of the field. While on load, the disk revolves continuously.
This induces the emf electromagnetic force in it dynamically, as it cuts through the flux between the poles, in addition to the statically induced emfs due to the alternating flux in these poles. Torque is produced due to dynamically induced eddy currents in the disk. This torque is negligible as compared to the operating torque produced by the statically induced currents. Tr is the retarding torque due to eddy currents in proportional to the speed of revolution, N, of the disk, i.
This means that the speed of revolution of the disk is proportional to the power. The total number of revolutions, N T , over a time interval T is given as:. This equation shows that the total number of revolutions is proportional to the total energy supplied.
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Polyphase energy can be measure by several single phase circuits that make up the polyphase circuit. The energy delivered over a polyphase circuit is the total energy delivered over each equivalent single-phase circuit.
Polyphase energy can be measured by connecting a single-phase watt-hour meter in each phase and then adding up readings of individual meters. This is not commercially practicable because:. The polyphase watt-hour meter is a combination of single-phase watt-hour meter stators that drive a rotor at a speed proportional to the total power in the circuit.
The meter consists of a multi-stator motor, means for balancing the torques of all stators, a magnetic retarding system, a register, and compensating devices. These components are assembled on a frame and mounted on a base. The operating principle of polyphase watt-hour meters, having any number of stators, is the same as single-phase watt-hour meters.
Torque on each stator results from current in one set of electromagnetic coils and eddy currents induced in a disk, or disks, by current in the other set of coils. The torques of the several stators combines to give a resultant torque proportional to total power. Because the same rules apply to measurement of both polyphase energy and polyphase power, principal parts of single-phase watt-hour meters can be combined for polyphase energy measurement, much as components of single-phase watt-meters are combined for polyphase power measurement.
Blondel's theorem applies to measurement of energy exactly as it does to measurement of power. A polyphase watt-hour meter is built with the number of elements necessary to satisfy Blondel's theorem. Hill-Schotter kVArh meter. This meter is essentially an induction type ampere hour meter with the registration mechanism designed for a particular system voltage. The system undergoes some voltage variation, to compensate for which a voltage compensating device is added to the system. Principle of operation. This is an integrator type of meter because it essentially consists of both kWh and kVArh meters together with a mechanical device called spherical integrator.
The spherical integrator functions to receive speeds proportional to kWh and kVArh and to transmit the resultant speed to the resistor mechanism. Thus the registration is proportional to kVArh. The spherical integrator consists of a sphere driven by friction from two equal discs mechanically coupled to kWh and kVArh meter respectively. The distance between the two discs are so adjusted that their points of contact with the sphere are separated by one quarter of the circumference of the sphere. The third friction disc C is driven by the sphere at a speed equal to the square root of the sum of squares of speeds of kWh and kVArh meters.
Let us assume that N W and N R be the speeds in r. But, in general, the two speeds are not same and the two diameters a and b are not equal. Let N be the speed in r. If the radius of the disc V is also r then angle of rotation of V in time T is:. This mechanism of transmitting the resultant of speeds of kWh and kVArh meters consists of five gear system, each of them driving a final drive at a particular power factor. Thus the combination of speeds is not exact at all power factors except at five power factors 1, 0. But the errors are small.
Also the drive is appositive at all points. The final drive from each of the five gear system is taken to a ratchet-coupling linked to the kVArh register shaft. The ratchet-coupling is used so that the kVArh register is always driven by that gear system which has the maximum speed, while all other four gear systems remain ideal on the ratchet. The gear system which correspond to unity and zero power factors are direct drives from kWh or kVArh meter, while the other gear systems are driven through differential gears. The planet wheels of the differential gears drive the final shaft linked through ratchet coupling.
When the power factor changes by an appreciable amount, the drive shift to a different ratchet as a new shaft takes up the fastest running speed. If you have a multiplier other than 1, it will be indicated on the face of your meter. In some cases, the energy meter does not have sufficient capacity to register the customer's consumption. For this reason, some 4 dial meters are designed to record only a fraction of the actual kWh passing through the meter.
These meter readings have to be multiplied by a specific factor, known as the multiplier, to determine your actual energy consumption. In three phase and four wire system, supply voltage is about volts and amps. The voltage and current must be reduced or stepped down by potential transformer PT and current transformer CT respectively before entering the meter. This is because maximum capacity of the meter is volts and 5 amps used.
The factor by which they are reduced is known as multiplier factor.
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Apparent power — Apparent power is the power made available to us by electricity authority for which we pay tariff. Reactive power — Reactive power is a nuisance power generated by the connected load in the system itself. For AC systems voltage and current pulsate at the system frequency.
Although AC voltage and current pulsate at same frequency, they peak at different time power is the algebraic product of voltage and current.
Real power is the average of power over cycle and measured by volt-amperes or watt. The portion of power with zero average value called reactive power measured in volt-amperes reactive or vars.
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The total power is called the apparent power symbolized by the capital letter S and measured by volt-amperes or VA. The motion from trampoline always perpendicular to the direction the person is walking. So that the direction between P and Q 90 degree Out of phase. A convention is also adopted stating that the reactive energy should be positive when the current is leading the voltage inductive load.
In an electrical system containing purely sinusoidal voltage and current waveforms at a fixed frequency, the measurement of reactive power is easy and can be accomplished using several methods without errors. However, in the presence of non-sinusoidal waveforms, the energy contained in the harmonics causes measurement errors.
According to the Fourier theorem any periodic waveform can be written as a sum of sin and cosine waves. As energy meters deal with periodic signals at the line frequency both current and voltage inputs of a single phase meter can be described by:. The implementation of the active power measurement is relatively easy and is done accurately in most energy meters in the field. Apparent power The apparent power is the maximum real power that can be delivered to a load.
As Vrms and Irms are the effective voltage and current delivered to the load,.