Chapter 4�Measurement of Electric Energy (11M)
Energy Meter
Definition: The meter which is used for measuring the energy utilises by the electric load is known as the energy meter. The energy is the total power consumed and utilised by the load at a particular interval of time. It is used in domestic and industrial AC circuit for measuring the power consumption. The meter is less expensive and accurate.
Working of Single phase energy meter
Construction And Working of Single-phase Induction meter
Construction �The entire parts of single phase induction type energy meter can be divided into four different systems.�1) Driving System�2) Moving System�3) Braking System�4)Registering mechanism�
Block Diagram of Single Phase Electronic Energy Meter
Working of electronic energy meter:-
1. CT reduces current to reasonable value for current scaling network.
2. Voltage & current scaling networks reduce proportionally the voltage & current to
values suitable for the analog multiplier.
3. Analog multiplier gives a dc voltage proportional to the product of the voltage and
current drawn from supply that is the power drawn.
4. The voltage controlled oscillator gives a frequency proportional to its input (which is
proportional to the power).
5. The ADC converts the square wave frequency analog output to display the energy in
watt-hour.
Advantages of Electronic Energy Meter:
1) Low cost.
2) High accuracy.
3) More flexibility.
4) High sensitivity
5) No frictional losses.
6) Less loading effect.
7) High frequency range.
8) Power consumption is less.
9) High resolution.
10) No requirement for external adjustment.
11) Low load, full load, power factor and creeping adjustments are not required
.
Block Diagram of Three Phase Electronic Energy Meter
Construction:
As shown in above diagram, the three phase supply terminals with neutral point (R,
Y, B & N) are connected from supply side. CT1, CT2, CT3, are connected in R, Y, B
phase respectively. They steps down the current to a suitable value and give it to a
signal processing unit. PT or potential divider unit is used to step down the line
voltage to a suitable value and give it to a signal processing unit. CT4 is connected in
neutral to check balance load condition.
Working:
1) The signal processing unit computes the active, reactive power & energy in kWh.
2) The control processor does the necessary data processing work and memory
management to monitor and evaluate different parameters.
3) Real time clock (RTC) is provided for synchronization of all data processing
works. The display unit is interfaced with control processor.
4) Different electric parameters can be displayed on LCD display and SMPS is
provided to give constant DC supply.
5) The Data in energy meter can be transferred to an external device like AMR
through RS232 port.
Errors and their Compensation(Correction)
Calibration of Electronic Energy Meter by Direct Loading Method
The following figure shows the arrangement of calibration for single phase electronic
energy meter. A phase shifter is connected for changing power factor of circuit.
The energy readings are taken for different values of current at different power factors.
Let D = Registration of meter under calibration in kWh &
Ds = Registration of standard meter in kWh
Then % error = [(D – DS)/DS] x 100
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