Measurement of Frequency and Power Factor MCQ Quiz in मल्याळम - Objective Question with Answer for Measurement of Frequency and Power Factor - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

• Single-phase power factor meter is designed based on the principle of electrostatics. In electrostatics, the controlling torque is provided by the electrostatic forces between two plates.
• A power factor meter is a type of electrodynamometer movement when it is made with two movable coils set at right angles to each other.
• Single phase power factor meter measures the power factor of a transmission system by measuring the phase angle between current and voltage.
• It can also determine the types of loads on the line and calculate losses.

Vibrating reed type frequency meter:

• A vibrating-reed frequency meter is a measuring instrument that is used to measure the frequency of various electric circuits. 
• Vibrating Reed Frequency meters indicate the supply frequency by means of individual reeds when rated voltage ± 20% is applied across the terminals of the meter.
• It consists of 7 vibrating reeds and each vibrating reed has a specific value. 
• These reeds vibrate when this frequency meter is connected to the supply for the measurement of frequency.
• The reed which will vibrate the most is the one whose natural frequency is equal to twice the frequency of the supply.

​Features of vibrating reed meter:

1. No aging effect
2. Faster response
3. Lighter in weight
4. Low power consumption
5. Rugged construction
6. High reliability

Multiplying factor

\(\begin{array}{l} = \frac{{VIcos\ \phi }}{{fullscalepower}}\\ = \frac{{150 \times 10 \times 0.2}}{{150}} = 2 \end{array}\)

The correct answer is  100Hz to 100 kHz.
Concept:

Wein bridge:

At balanced bridge condition

Frequency \({\bf{f}} = \frac{1}{{2{\bf{π }}\sqrt {{{\bf{R}}_1}{{\bf{R}}_3}{{\bf{C}}_1}{{\bf{C}}_3}} }}\)

And, \(\frac{{{{\bf{R}}_1}}}{{{{\bf{R}}_3}}} + \frac{{{{\bf{C}}_3}}}{{{{\bf{C}}_1}}} = \frac{{{{\bf{R}}_2}}}{{{{\bf{R}}_4}}}\)

Note:

If C1 = C3 and R1 = R3

Then

R2 / R4 = 2  and f = 1 / 2π R1C1

Applications:

• It is used for the measurement of frequency from 100Hz to 100 kHz.
• Used in distortion analyzer.
• This bridge is not suitable for the measurement of the frequency of signals having harmonics, because bridge balance is difficult.

Wien's Bridge An AC bridge circuit known as a Wien's bridge is used to determine the frequency of an unknown signal.
German physicist Max Wien created it in the latter half of the 1800s. An adjustable frequency oscillator, resistors, and capacitors make up the bridge circuit.

Operation of Wien's Bridge Circuit The Wien's bridge establishes a balanced situation at a particular frequency by combining resistors and capacitors.
The bridge's output voltage drops to zero when it is balanced. The oscillator's frequency can be changed to balance the bridge at various frequencies.
 

Determining the Frequency Range The values of the resistors and capacitors employed in the circuit determine the frequency range that the Wien's bridge can monitor with accuracy. The relationship between the resistors and capacitors in the Wien's bridge determines the frequency range.

The equation for Wien's Bridge The formula for the Wien's bridge's balance condition is f = 1 / (2 * π * R * C). Where: The frequency of the balanced state is denoted by f. The bridge circuit's resistance is denoted by R, and its capacitance is shown by C. This equation shows that the frequency and the product of the resistance and capacitance are inversely related. Therefore, one must increase the capacitance or resistance in order to extend the frequency range.

Concept:

IEC 61000-4-15:

• IEC 61000-4-15 gives a functional and design specification for flicker measuring apparatus intended to indicate the correct flicker perception level for all practical voltage fluctuation waveforms. Information is presented to enable such an instrument to be constructed. 
• A method is given for the evaluation of flicker severity on the basis of the output of flicker meters complying with this standard.
• The flicker meter specifications in this part of IEC 61000 relate only to measurements of 120 V and 230 V, 50 Hz and 60 Hz inputs.

Calculation:

The given configuration corresponds to wien bridge

Under the condition of tridge balance,

\(f = \frac{1}{{2\pi \sqrt {{R_1}{R_2}{C_1}{C_2}} }}\)      ----(I)

\(\frac{{{R_1}}}{{{R_2}}} + \frac{{{C_2}}}{{{C_1}}} = \frac{{{R_3}}}{{{R_4}}}\)      ----(II)

Put the relevant Values in equation

\(\frac{{{R_1}}}{{{R_2}}} = \frac{{{R_3}}}{{{R_4}}} - \frac{{{C_2}}}{{{C_1}}}\)

\( ⇒ \frac{{{R_1}}}{{200}} = \frac{{1000}}{{400}} - \frac{{1MF}}{{2MF}}\)

⇒ \(\frac{{{R_1}}}{{200}}\) = 2.5 - 0.5

⇒ R1 = 200 × 2 = 40052

Put the relevant Values in equation

\(f = \frac{1}{{2\pi \sqrt {440 \times 200 \times 1 \times {{10}^{ - 6}} \times 2 \times {{10}^{ - 6}}} }}\)

\( = \frac{{{{10}^{ - 6}}}}{{2\pi \times \sqrt {16 \times {{10}^4}} }}\)

= 398 HZ

Therefore, correct Answer is option (b).

In an Anderson bridge, the unknown inductance is measured in terms of known capacitance and resistance.

The circuit diagram of Anderson Bridge is shown in the figure.

L1 = self-inductance to be measured

R1 = resistance of the self-inductor

r1 = resistance connected in series with self-inductor

r, R2, R3, R4 = known non-inductive resistances

C = fixed standard capacitor

Under the Balance condition,

I₁ (r₁ + R₁ + jωL₁) = I₂R₂ + IC_r

and, \(I_C(r+\frac{1}{jωC})=(I_2-I_C)R_4\)

After Solving it,

R₁ = \(\frac{R_2R_3}{R_4}-r_1\)

and, L₁ = \(C\frac{R_3}{R_4}(r(R_4+R_2)+R_2R_4)\)

Concept:

Electrodynamic Power Factor Meter:

• It is also known as Dynamometer phase angle meter and Dynamometer power factor meter.
• It measures the power factor or cosine of the phase angle between voltage and current.
• There are 2 stationary coils (SC) also called as current coil, that are connected in series to the load.
• The current coil produces a magnetic field proportional to the current.
• There are 2 moving coil (MC) also called as voltage or pressure coil, that are connected parallel to load.
• One moving coil is connected with a high resistor while another with a high inductor. These 2 coils make separation of 90° electrical.
• The pointer is connected to the moving coil.
• During the phase angle or power factor measurement, the values of R and L are so adjusted that R = ωL, so that both coil carry equal current.
• The coils are arranged in such a way that 2 equal and opposite torques are produced and the pointer shows desired result.
• Therefore, there is no requirement of a controlling system.