Energy Meter Describe The Principle Of Working And Constructional Features Of A House Service Meter With The Help Of A Neat Sketch. (N.C.V.T.)

ENERGY METER

Describe the principle of working and constructional features of a house service meter with the help of a neat sketch. (N.C.V.T.)

ENERGY METER

Ans. Principle of working of house service meter:

 On AC, rotation of disc in the meter is produced by the eddy currents due to the combined fluxes of two electromagnets. The fluxes of two magnets are kept at 90 degrees apart to . make rotating field.

Construction : In Fig., two magnetic fields are produced by the pressure coil and the current coil. The current coil has a few numbers of turns of thick wire and its field is in phase with current. The shunt coil is made of a large number of turns of thin wire and is connected across the line. Its field lags 90 degrees behind the supply voltage. Then the flux due to two coils produces a rotating field.

Now, field of current coil is proportional to I and field of shunt coil is proportional to V. Then the torque and so the speed of disc is proportional to the power. And if we consider the time, then the number of revolutions of the disc is proportional to the product of current, voltage and time i.e., energy.

In this meter two more devices are provided.

1 . Power factor adjustment : For adjustment of power factor and friction loss, shading rings are provided.

2. Getting exactly 90 degrees lag of two field : To get the angle of lag exactly of 90 degrees, a loop is placed on the case of electromagnet. The loop may be in the form of a short-circuited copper grup band which may be adjusted in space in the flux path or a fixed loop With it ends terminating in an adjustable resistance as shown in Fig.

I.S.I. Rules about the Energy Meters : According to IS : 4648-1968, 5 : 2, energy meters shall be installed at such a place which is readily accessible to both the owner of the building and the authorized representatives of the supply authority. These should be installed at a height where it is  convenient to note the meter reading. It should not preferably be installed below 1 m from the ground. The energy meters should either by provided with protective covering, enclosing it completely except the glass window through . which the readings are noted or should be mounted inside a completely enclosed panel provided with hinged or sliding doors With arrangement for locking it.

Accuracy of Electro chemical Meter

In an induction type meter, creep is a phenomenon that can adversely affect accuracy, that occurs when the meter disc rotates continuously with potential applied and the load terminals open circuited. A creep test is necessary when the meter is tested for the error due to creep.

Solid State Meters Some
 newer electricity meter are solid stander display the power used, on LCD.

In addition to measuring electricity used, solid state meters can also record other parameters of the load and supply such as maximum demand, power factor and reactive power used etc. They can also include electronic clock mechanisms to compute a value, rather than an amount of electricity consumed, with the pricing varying by the time of day, day of week, and seasonally.

Technology

Most solid-state meters use a current transformer to measure the current. This means that the main current carrying conductors need not pass through the meter itself and so the meter can be located remotely from the main current-carrying conductors, which is a particular advantages in large-power installations. It is also possible to use remote current transformers with electromechanical meters though this is less common. .

ENERGY METER

The AD7 755 is an accurate (to 0.1%) single-phase energy-measurement IC. It accepts a pair of voltage inputs that represent the voltage and current of a power line. Internally, these signals are converted to the digital domain with oversampling A / D converters. A fixed-function digital signal processor continuously multiplies the two signals; their product is proportional to instantaneous power. After being low-pass filtered, the digital signal is then converted to a frequency -scaled according to selectable settings to generate frequency outputs at terminals F1, F2 and CF. The signals at F1 and F2 can be used to drive an electromechanical counter (typically at full-scale rates from 0.5 to 5 Hz), while the higher-frequency CF signal is suitable for calibration. The frequency (or rate) of the pulse outputs is proportional to the instantaneous real power being monitored by the meter. Accordingly, in a given interval,


the total number

of pulses generated at these outputs is proportional to the  energy transferred to the load. Areverse-polarity logic signal indicates when the measured instantaneous power goes negative (i.e., the load is returning net power to the line). . The CF frequency output is a pulse train proportional to the F 1, F2 outputs, with full-scale output rates of 21.76 Hz, 43.52 Hz and 5.57 kHz, for ac inputs. It is will suited to interfacing to a microcontroller that performs calculations and make decisions.

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