Electrical Apparatus and Safety: Measuring Voltage and Current

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Why does waveform error occur in MI instruments?

The current coil is designed to carry less than 20 amperes

Deflection torque is directly proportional to the square of the current (correct)

The fixed coil is not air-cored

The pointer mounts on the fixed coil

What provides the controlling torque to the electrodynamometer wattmeter?

Moving coil

Eddy current

Fixed coil

Spring control system (correct)

What causes serious errors in dynamometer type wattmeters at low power factors?

Movement of the pointer

Enclosure in an iron case

Inductance of the potential coil (correct)

Use of linear scale

What is the function of the fixed coil in the electrodynamometer wattmeter?

Produce uniform electric field Signup and view all the answers

Why is magnetic shielding provided in dynamometer type wattmeters?

To prevent stray fields affecting the reading Signup and view all the answers

What symbol is used to represent current?

I Signup and view all the answers

In which way should an ammeter be connected in a circuit to measure current?

In series Signup and view all the answers

What is the main reason why an ammeter should never be connected in parallel with any circuit component?

To prevent short-circuit current Signup and view all the answers

Which instrument should be used to measure potential difference or voltage?

Voltmeter Signup and view all the answers

Why are ammeters manufactured with very low values of internal resistance?

To minimize the effect on the circuit's resistance Signup and view all the answers

Why must a voltmeter be connected in parallel in a circuit?

To avoid the loading effect on the circuit Signup and view all the answers

What is the purpose of manufacturing voltmeters with a very high internal resistance?

To improve accuracy by minimizing the loading effect Signup and view all the answers

In a moving iron instrument, what type of force allows the iron plate to deflect from low magnetic field to high magnetic field?

Repulsive force Signup and view all the answers

What feature allows moving iron instruments to be used for both AC and DC?

High torque weight ratio Signup and view all the answers

What is a disadvantage of moving iron instruments that hinders accurate readings?

Hysteresis Signup and view all the answers

What is the main component of the driving system in a single-phase energy meter?

Electromagnet Signup and view all the answers

In the moving system of an energy meter, what induces the eddy current in the aluminium disc?

Current coil Signup and view all the answers

What material is the coil former typically made of in a PMMC instrument?

Aluminum Signup and view all the answers

How does the braking system in an energy meter reduce the rotation of the aluminium disc?

By cutting the magnetic flux of the permanent magnet Signup and view all the answers

What is the main function of the registration or counting mechanism in an energy meter?

Recording the number of rotations of the aluminium disc Signup and view all the answers

What component is responsible for producing the damping torque in a PMMC instrument?

Eddy currents due to movement in the magnetic field Signup and view all the answers

What does PMMC stand for in the context of energy meter instrumentation?

Permanent Magnet Moving Coil Signup and view all the answers

What are the permanent magnets in a PMMC instrument typically made of?

Alnico and Alcomax Signup and view all the answers

Which material is typically used to make the control springs in a PMMC instrument?

Phosphorus bronze Signup and view all the answers

What generates the mechanical torque that acts on the coil in a PMMC instrument?

Current-carrying coil in the magnetic field Signup and view all the answers

What is a key advantage of using a PMMC Instrument for measurements?

It has no occurrence of hysteresis losses Signup and view all the answers

Why is the linear scale of a PMMC Instrument divided uniformly?

To measure the quantities easily and accurately Signup and view all the answers

Why does a PMMC Instrument use eddy current damping?

To effectively dampen vibrations and oscillations Signup and view all the answers

Which is a common disadvantage of the PMMC Instrument?

Errors can occur in readings due to ageing of control spring Signup and view all the answers

Why is earthing important in electrical systems?

To protect equipment and personnel from lightning surges Signup and view all the answers

What is the depth at which the copper plate is placed for plate earthing?

3m Signup and view all the answers

What material is used to keep the earth electrode resistance value below 5 ohms in plate earthing?

Water Signup and view all the answers

What is the diameter of the galvanized iron pipe used for pipe earthing?

38mm Signup and view all the answers

How deep is the GI iron pipe placed for pipe earthing?

4.75m Signup and view all the answers

What mixture is used to fill the area surrounding the GI iron pipe in pipe earthing?

Salt and coal Signup and view all the answers

According to the provided text, what should be done if there is any accidental contact of a person with a live wire?

Immediately switch off the main switch Signup and view all the answers

What types of tools are recommended to be used while working with electricity?

Insulated tools Signup and view all the answers

What should be avoided when working with electricity according to the text?

Touching electrical equipment with wet hands Signup and view all the answers

In case of any short-circuiting or accidental contact with a live wire, what should be done before anything else?