Wattmeter and Energy Meter Construction
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Questions and Answers

What is the primary function of the copper band in the driving system?

  • To align the flux produced by the shunt magnet perpendicular to the supplied voltage (correct)
  • To measure the power consumption in kilowatt hours
  • To increase the rotation of the aluminium disc
  • To reduce the eddy current in the aluminium disc

    • What is the purpose of the permanent magnet in the braking system?

  • To increase the rotation of the aluminium disc
  • To reduce the rotation of the aluminium disc (correct)
  • To measure the power consumption in kilowatt hours
  • To generate a magnetic field around the conductor

    • What is the relationship between the number of rotations of the aluminium disc and the power consumption?

  • The number of rotations is directly proportional to the power consumption (correct)
  • The number of rotations is independent of the power consumption
  • The number of rotations is inversely proportional to the power consumption
  • The number of rotations is equal to the power consumption

    • What is the principle behind the working of an electric energy meter?

    <p>Faraday's law of electromagnetic induction</p> Signup and view all the answers

    What is the function of the registration or counting mechanism?

    <p>To record the number of rotations of the aluminium disc</p> Signup and view all the answers

    What is the primary function of a wattmeter in an electrical circuit?

    <p>To measure and develop electric power in an electrical circuit</p> Signup and view all the answers

    Which type of wattmeter is used for measuring both DC and AC power?

    <p>Electrodynamometer wattmeter</p> Signup and view all the answers

    What is the function of the coil connected in series with the circuit in a wattmeter?

    <p>To measure current</p> Signup and view all the answers

    What is the primary function of an energy meter?

    <p>To measure the energy utilised by the electric load</p> Signup and view all the answers

    How many main parts does an energy meter have?

    <p>Four</p> Signup and view all the answers

    What is the primary purpose of an electric energy meter?

    <p>To accurately quantify the electricity usage for billing purposes</p> Signup and view all the answers

    What is the function of a voltage coil in an electric energy meter?

    <p>To produce a magnetic field proportional to the voltage</p> Signup and view all the answers

    How is the power consumed by the load calculated in an electric energy meter?

    <p>By multiplying the instantaneous voltage and current values</p> Signup and view all the answers

    What is the unit of measurement for electrical energy consumption in an electric energy meter?

    <p>Kilowatt-hours (kWh)</p> Signup and view all the answers

    What is the purpose of periodic calibration of an electric energy meter?

    <p>To ensure the meter's accuracy within certain tolerances</p> Signup and view all the answers

    What is the minimum number of CT's required to accurately meter a three-phase, four-wire wye service?

    <p>Three</p> Signup and view all the answers

    What is the unit of reactive power typically measured in?

    <p>Volt-amperes reactive (VAR)</p> Signup and view all the answers

    Why is a single-phase varmeter not suitable for measuring reactive power in high-voltage circuits?

    <p>It is not designed to handle high voltage levels</p> Signup and view all the answers

    How many wattmeters are required to measure the reactive power in a three-phase balanced load?

    <p>One</p> Signup and view all the answers

    What is the phase angle between voltage and current in a single-phase varmeter?

    <p>90°</p> Signup and view all the answers

    What is the main reason a 3-phase meter is needed in Indian households?

    <p>When the load is higher than 5KW or 7 KW</p> Signup and view all the answers

    What is the total number of slots in a three-phase energy meter?

    <p>8</p> Signup and view all the answers

    What is the main reason why the three-phase system has a higher efficiency compared to the single-phase system?

    <p>It requires fewer conductors</p> Signup and view all the answers

    What is the significance of the 120º phase difference in the three-phase system?

    <p>It is necessary for the proper working of the system</p> Signup and view all the answers

    How are the phase wires connected to the meter in a 3-phase metering system?

    <p>The 1st phase wire is connected to the 1st slot, the 2nd phase wire is connected to the 3rd slot, and the 3rd phase wire is connected to the 5th slot</p> Signup and view all the answers

    What is the function of the two remaining slots in a three-phase energy meter?

    <p>To patch the incoming phase wires to the switchboard and for the neutral wire</p> Signup and view all the answers

    What is the main difference between the star connection and the delta connection in the three-phase system?

    <p>The presence of a neutral point</p> Signup and view all the answers

    What is the main difference between a three-phase, three-wire meter and a three-phase, four-wire meter?

    <p>The number of wires used in the meter</p> Signup and view all the answers

    What is the condition for a three-phase load to be considered balanced?

    <p>All phases have the same angle</p> Signup and view all the answers

    What is the purpose of Blondel's Theorem in relation to metering a three-phase service?

    <p>To determine the type of metering installation needed</p> Signup and view all the answers

    What is the primary benefit of using a 3-phase energy meter in industrial and commercial applications?

    <p>To distribute the load and provide real-time power consumption data</p> Signup and view all the answers

    What is the recommended load requirement for using a 3-phase energy meter?

    <p>More than 5 KW to 7 KW</p> Signup and view all the answers

    What is the main difference between a 3-phase power system and a single-phase power system?

    <p>The number of phase conductors</p> Signup and view all the answers

    Why is it important to analyze a 3-phase balanced load on the basis of each phase?

    <p>To ensure accurate energy measurement</p> Signup and view all the answers

    What is the main advantage of using a 3-phase energy meter in areas with a heavy electric load?

    <p>It provides accurate real-time power consumption data</p> Signup and view all the answers

    What is the relationship between the reactive power and the cosine of the angle between voltage and current?

    <p>The reactive power is directly proportional to the cosine of the angle between voltage and current</p> Signup and view all the answers

    What is the condition for a single phase power circuit to be fully resistive in nature?

    <p>The phase angle between voltage and current is 0 degrees</p> Signup and view all the answers

    What is the direction of energy flow in a circuit with active power?

    <p>From source to load</p> Signup and view all the answers

    What is the significance of the value of cos2ωt in a single phase power circuit?

    <p>It cannot be greater than 1</p> Signup and view all the answers

    What is the name given to the power consumed due to the resistive effect of an electrical circuit?

    <p>Resistive Power</p> Signup and view all the answers

    Study Notes

    Wattmeter and Energy Meter

    • A wattmeter is an instrument used to measure electric power given to or developed by an electrical circuit.
    • There are two types of wattmeters:
      • Electrodynamometer wattmeter (for both DC and AC power measurement)
      • Induction wattmeter (for AC power measurement only)
    • A wattmeter consists of two coils:
      • One coil is connected in series with the circuit (current coil)
      • One coil is connected in parallel with the circuit (voltage coil)

    Energy Meter

    • An energy meter is a device used to measure and record the consumption of electrical energy.
    • It is widely used in residential, commercial, and industrial settings to ensure accurate metering of electricity usage.
    • An energy meter has four main parts:
      • Driving System (electromagnet and copper band)
      • Moving System (aluminium disc)
      • Braking System (permanent magnet)
      • Registering System (counting mechanism)
    • The working principle of an energy meter is based on Faraday's law of electromagnetic induction.
    • The energy meter measures the power consumption of a load by interacting the magnetic fields of a current coil and a voltage coil.

    How an Energy Meter Works

    • Current Measurement: The energy meter measures the current flowing through it using a current coil.
    • Voltage Measurement: The energy meter measures the voltage using a voltage coil.
    • Electric Energy Calculation: The energy meter calculates the power consumption by multiplying the instantaneous voltage and current values.
    • Power Calculation: The power consumed by the load is calculated by multiplying the voltage and current values.
    • Energy Integration: The energy meter integrates the power over time to calculate the total energy consumption.
    • Display and Communication: Modern energy meters have digital displays and communication capabilities to transmit data remotely.

    Application of Energy Meters

    • Single-phase energy meters are used in residential and small commercial settings.
    • Three-phase energy meters are used in industrial and commercial settings with high electrical loads.
    • Three-phase energy meters are suitable for measuring energy consumption in factories, power requirements in commercial buildings, and consumption of large machinery and equipment.

    Types of 3-Phase Energy Meters

    • There are two types of 3-phase energy meters:
      • Three phases, three-wire meters (permanent horseshoe magnet)
      • Three phases, four-wire meter (three coils and three aluminum discs)

    Benefits of Using a 3-Phase Meter

    • The ability to use different phases for different rooms.
    • The ability to distribute the load.
    • Real-time and recorded power consumption data.
    • Protection of valuable equipment from high voltage damages.

    Analysis of Three-Phase Systems

    • A three-phase system consists of three phase conductors and a neutral conductor.
    • The sum of the line currents in a 3-phase system is equal to zero.
    • The three-phase system has several advantages, including:
      • Fewer conductors required compared to single-phase systems.
      • Continuous supply to the load.
      • Higher efficiency and minimum losses.
    • The three-phase system can be connected in two ways:
      • Star connection (four wires, including a neutral conductor)
      • Delta connection (three wires, no neutral point)### Three-Phase Loads
    • A three-phase load can be balanced or unbalanced.
    • A balanced load has equal magnitude and phase angle between the three phases.
    • In a balanced load, all phase voltages and line voltages are equal in magnitude.

    Three-Phase AC Generator

    • A three-phase AC generator has three windings, each with two terminals (start and finish).
    • Connecting a separate load across each phase winding would require six wires, making the system complicated and costly.

    Blondel's Theorem

    • Blondel's Theorem is used to determine the type of metering installation needed for a particular service.
    • The theorem states that one less element (or CT) is required in a watthour meter than the number of wires in the service to accurately meter the service.
    • For a single-phase two-wire service, a watthour meter with one stator (1s meter) is required.
    • For a three-phase, three-wire service (delta service), a form 5s meter with two elements is required.

    Reactive Power Measurement

    • Reactive power (Q) is caused by the phase shift between voltage and current due to inductance and capacitance.
    • Reactive power is denoted by Q and expressed in volt-amperes reactive (VAR).
    • The formula for reactive power is Q = VI sin Φ.
    • Reactive power measurement is essential to determine the nature of the load and measure power factor.

    Measurement of Reactive Power in Single-Phase Circuits

    • A single-phase varmeter (volt-ampere reactive meter) is used to measure reactive power in single-phase circuits.
    • The varmeter has an inductive voltage coil, which causes the current to lag 90° behind the voltage.
    • The meter indication is Q = VI sin Φ.

    Measurement of Reactive Power in Three-Phase Circuits

    • For a three-phase balanced load, the reactive power measured is the same in all phases.
    • Only a single wattmeter is required to measure the reactive power.
    • The current coil is inserted in one phase, and the voltage coil is connected across the remaining two phases.

    Active Power

    • Active power is consumed due to the resistive effect of an electrical circuit.
    • It is also known as resistive power.
    • The active power is always positive, regardless of the instantaneous direction of voltage and current.
    • It is the rate of energy consumption by the load.

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    Description

    Learn about the construction and theory of operation of wattmeters, including types such as electrodynamometer and induction wattmeters. Understand how they measure electric power in electrical circuits.

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