Electrical Measurements and Instruments (EX-303) - Important Questions

Explain the construction and working principle/operation of the D'Arsonval galvanometer

Explain the static and dynamic characteristics of measuring instruments / measurement systems

Describe the construction and working of a ballistic galvanometer and explain the constructional differences from a D'Arsonval galvanometer

Explain the concept of errors in measurement, their classification, sources, and methods for reduction.

Discuss classification of instruments, explaining deflection type and null type instruments with examples and applications.

Prove that in a ballistic galvanometer the charge is proportional to the first swing of the moving coil

Compare flux meter and ballistic galvanometer

Explain selection criteria for measuring instruments including reliability, cost, loading effect and environmental factors.

What are the different types of errors in measurement?

Numerical on damped ballistic galvanometer oscillations to find damping ratio, logarithmic decrement and damped/undamped periods

Derive the equation of motion for a ballistic galvanometer

Determine relative error in power measurement from errors in current and resistance.

Explain how the range of a PMMC / galvanometer instrument is extended to act as ammeter and voltmeter, deriving shunt and multiplier expressions

Explain the construction of current transformer and potential transformer

Explain PMMC, MI, and electrodynamometer type instruments and compare their construction, working principles, advantages, and disadvantages.

Explain the construction and working of digital multimeters and wattmeters, including their applications and limitations.

Explain the construction, principle and applications of instrument transformers including CT and PT in detail

Explain the necessity of instrument transformers in high voltage and high current measurements with advantages and limitations

Explain design modifications / steps taken for minimizing / reduction of errors in potential transformer

Explain the effect of secondary burden on ratio and phase errors of a current transformer

Determine the angular deflection of an electrodynamic ammeter at full scale given rate of change of inductance and spring constant.

Explain how an electrodynamometer type instrument measures the true r.m.s. value of voltage or current irrespective of waveform.

Explain the working operation of moving iron instruments and derive its torque equation.

Explain construction of multi-range voltmeter and range extension of DC voltmeter

Errors in electrodynamometer type wattmeter including stray magnetic field error and remedial measures.

Explain the construction and working of two-element (double-element) dynamometer type wattmeter for three-phase systems, including three-element type.

Constructional details of electrodynamometer type wattmeter with neat sketch.

Derive the torque equation for electrodynamometer type wattmeter.

Explain power measurement in three-phase circuits using two-wattmeter and three-wattmeter methods with advantages and limitations.

What is a low power factor wattmeter? Explain its construction, working and special features for low power factor applications.

Numerical on two-wattmeter readings for a given three-phase load power and power factor.

Constructional details of electrodynamometer type wattmeter along with derivation of torque expression on A.C.

Explain the construction and working principle of an electrodynamometer type single-phase wattmeter.

Prove with circuit diagram and phasor/vector diagram that total three-phase power equals the algebraic sum of the two wattmeter readings.

Numerically determine the percentage error / error limits of a single-phase energy meter from test revolutions, time, meter constant and reference wattmeter readings.

Discuss the errors of a single-phase energy meter.

Calculate the electrical energy consumed from voltage, current, power factor and time.

Explain measurement of power factor using single-phase and three-phase electrodynamometer type and moving iron type instruments.

Explain the working of electronic energy meters and compare them with electromechanical energy meters.

Explain the construction and working of a three-phase AC energy meter with circuit and phasor diagram.

Describe the construction and working of a 3-phase electrodynamometer / alternating-field power factor meter.

Write short notes on frequency meter, ratio meter, digital voltmeter, Lloyd Fischer square for power loss measurement

Explain the construction and working of a digital / electronic energy meter.

Explain the construction and working of a maximum demand meter.

Explain the details and limitations of an energy meter.

Describe the circuit for testing a single-phase induction-type energy meter at different loads and power factors.

Describe the experimental method for determination of B-H curve / hysteresis loop of a magnetic specimen, e.g. method of reversals, six-point / step-by-step method for bar form.

Explain principle, theory and derivation of Kelvin's double bridge for low resistance measurement and how contact and lead resistances are eliminated.

Explain the methods for measurement of earth resistance

Describe the Lloyd-Fisher square method for measurement of iron / power loss in ferromagnetic (transformer steel strip) material using the wattmeter method.

Write short notes on Wheatstone bridge balance, eddy current damping, ammeter range extension and use of megger.

Explain Wheatstone bridge and Kelvin's double bridge with circuit diagrams and their applications.

Explain magnetic measurements including B-H curve determination, hysteresis loop, and measurement of power loss in sheet metal using Lloyd-Fisher square.

Explain factors affecting precision measurement of medium resistance with Wheatstone bridge and how they are minimized.

Explain working of Wheatstone bridge and the type of resistance for which it is used.

Explain the loss of charge method for measurement of high/insulation resistance of cables.

Calculate unknown low resistance from balanced Kelvin bridge constants.

Explain inductance and capacitance measurement using bridge methods. Discuss sources of errors and precautions.