Question 1

Q.1. (a) A set of voltmeter reading was taken by five observers as 99.7, 99.8…

Accepted Answer

For the given voltmeter readings (99.7, 99.8, 100.0, 100.2, 100.3V), the arithmetic mean is 100.0V, average deviation is 0.2V, standard deviation is approximately 0.255V, and variance is approximately 0.065 V-squared; systematic errors are repeatable errors from known causes (instrumental, environmental, observational), random errors are unpredictable small variations from uncontrollable factors, normal (Gaussian) error follows the bell-shaped normal distribution, and gross errors are large human/procedural mistakes.

Question 2

Q.1. (a) The standard deviation of 100 readings is 1.380 degrees C. Determine…

Accepted Answer

For a standard deviation of 1.380 degrees C over 100 readings, the probable error of a single reading is approximately 0.931 degrees C, the standard deviation of the mean is approximately 0.138 degrees C, the probable error of the mean is approximately 0.093 degrees C, and the standard deviation of the standard deviation is approximately 0.098 degrees C; accuracy indicates closeness to the true value, precision indicates repeatability/consistency among readings, hysteresis is a lag in instrument response depending on the direction of change, and probable error defines the interval within which 50% of readings are expected to fall.

Question 3

Q.2. (a) Explain the construction and working principle of LVDT. [8]

Accepted Answer

The LVDT (Linear Variable Differential Transformer) is a displacement transducer consisting of a primary winding and two secondary windings wound on a hollow cylindrical former, with a movable ferromagnetic core whose position determines the differential output voltage between the two secondaries, giving a linear, contact-free measurement of small linear displacements; a thermistor is a temperature-sensitive semiconductor resistor with a large negative (or, less commonly, positive) temperature coefficient of resistance, manufactured in bead, disc, rod, or washer forms, and widely used in temperature measurement, compensation, and control applications.

Question 4

Q.2. (a) Explain the strain gauge transducer and derive its gauge factor. [8]

Accepted Answer

A strain gauge transducer converts mechanical strain into a proportional change in electrical resistance, characterized by its gauge factor (the ratio of fractional resistance change to applied strain, typically around 2 for common metallic foil gauges); active transducers generate their own output signal energy directly from the measured quantity, while passive transducers require an external power source and merely modulate a circuit parameter, and primary transducers directly sense the physical quantity while secondary transducers convert an intermediate mechanical output into a further, more convenient electrical signal.

Question 5

Q.3. (a) Explain the working principle of function generator with block diagr…

Accepted Answer

A function generator produces multiple standard waveform shapes (sine, square, triangular) at variable frequency, typically built around a core integrator-comparator (relaxation oscillator) circuit generating a triangular wave, which is further shaped into a square wave (via comparison) and a sine wave (via a non-linear shaping/diode network), with output amplitude and frequency control stages; an instrumentation amplifier built from three op-amps provides a high-input-impedance, high-common-mode-rejection differential amplifier specifically suited to amplifying small differential signals (such as from a strain-gauge bridge) in the presence of common-mode noise.

Question 6

Q.3. (a) Explain the working of frequency to voltage converter. [8]

Accepted Answer

A frequency-to-voltage converter produces a DC output voltage proportional to the frequency of an applied AC/pulse input signal, typically implemented using a charge-pump (pulse-triggered constant-charge-injection) circuit followed by a low-pass smoothing filter; a temperature-to-current converter produces a standard current-loop output (commonly 4-20mA) proportional to sensed temperature, typically combining a temperature sensor (RTD or thermocouple) with a signal-conditioning amplifier and a voltage-to-current converter output stage.

Question 7

Q.4. (a) Discuss about the active and reactive power in the different plants.…

Accepted Answer

Active power represents the true, useful energy converted to work/heat and is generated/consumed similarly by all plant types subject to their prime-mover characteristics, while reactive power is required to establish magnetic/electric fields in inductive/capacitive equipment and is supplied differently by different plant types (thermal/hydro generators via excitation control, synchronous condensers, and static compensators); a single-phase induction-type energy meter measures cumulative active energy consumption using two electromagnets acting on a rotating aluminium disc, whose rotation speed is proportional to instantaneous power and whose total revolutions register cumulative energy via a geared counter mechanism.

Question 8

Q.4. (a) What are the different methods of measurement of frequency in power …

Accepted Answer

Frequency in the power-frequency range is measured using electrical resonance type, vibrating reed type, and electronic digital counting type frequency meters, with the response type (moving-iron ratiometer) frequency meter using two coils with different inductive/capacitive series impedances driving a common moving-iron pointer mechanism to indicate frequency directly on a calibrated scale; LT (Low Tension) panels distribute low-voltage (typically below 1kV) power to end-use loads, while HT (High Tension) panels handle higher-voltage (above 1kV) incoming supply, metering, and protection equipment feeding step-down transformers.

Question 9

Q.5. Write short note on - (a) Capacitive voltage transformers [8] (b) Protec…

Accepted Answer

A Capacitive Voltage Transformer (CVT) uses a capacitor divider to step down a high transmission voltage to an intermediate level before a conventional voltage transformer further reduces it to standard secondary voltage, providing an economical alternative to conventional electromagnetic VTs at extra-high voltage levels; the protection circuit of a current transformer must always short-circuit the CT secondary terminals whenever the primary circuit is energized and connected instrumentation/relay burden is disconnected, since an open-circuited CT secondary under load current conditions produces dangerously high induced secondary voltages.

Question 10

Q.5. (a) Explain the effect of following on the performance of CT - (i) Chang…

Accepted Answer

A change in system frequency alters a CT's core magnetizing reactance and hence its ratio and phase-angle errors, generally requiring re-verification of CT accuracy if operated substantially away from its rated frequency, while a change in primary winding current (loading) shifts the CT's operating point along its excitation characteristic, with errors generally being larger at very low primary current (a smaller fraction of the exciting current being negligible relative to total primary ampere-turns) and again increasing at very high overcurrent due to core saturation; the Wilson compensation method reduces CT ratio and phase-angle errors by injecting a small additional compensating current, derived from an auxiliary winding/transformer arrangement, to offset the CT's inherent exciting-current-related error.

Power System Instrumentation