Instrument(s) required to synchronize an alternator to the grid is/are

A 3-phase, star-connected, balanced load is supplied from a 3-phase,  (rms), balanced voltage source with phase sequence R-Y-B, as shown in the figure. If the wattmeter reading is  and the line current is  (rms), then the power factor of the load per phase is

A moving coil instrument having a resistance of , gives a full-scale deflection when the current is 10 mA. What should be the value of the series resistance, so that it can be used as a voltmeter for measuring potential difference up to 100 V?

Two wattmeter method is used for measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the watt-meters reads half of the other (both positive), then the power factor of the load is  

A 0-1 Ampere moving iron ammeter has an internal resistance of and inductance of 0.1mH. A shunt coil is connected to extend its range to 0-10 Ampere for all operating frequencies. The time constant in milliseconds and resistance in of the shunt coil respectively are  

The load shown in the figure is supplied by a 400 V (line-to-line), 3-phase source (RYB sequence). The load is balanced and inductive, drawing 3464 VA. When the switch S is in position N, the three watt-meters  read 577.35 W each. If the switch is moved to position Y, the readings of the watt-meters in watts will be:

A dc voltage with ripple is given by . Measurements of this voltage v(t), made by moving-coil and moving-iron voltmeters, show reading of  and  respectively. The value of in volts, is_____________.

An energy meter, having meter constant of 1200 revolutions/kWh, makes 20 revolutions in 30 seconds for a constant load. The load, in kW, is________________.

Match the following. 

(A)        (B)        (C)        (D)

P-1        P-1          P-1          P-3

Q-2         Q-3          Q-2          Q-1

R-1         R-1          R-3          R-2

S-3         S-2         S-3          S-1

A 3-phase balanced load which has a power factor of 0.707 is connected to a balanced supply. The power consumed by the load is 5kW. The power is measured by the two-wattmeter method. The reading of the two watt meters are

The coils of a wattmeter have resistance 0.01 and 1000; their inductances may be neglected. The wattmeter is connected as shown in the figure, to measure the power consumed by a load, which draws 25 A at power factor 0.8. The voltage across the load terminals is 30 V. The percentage error on the wattmeter reading is __________.

Power consumed by a balanced 3 – phase, 3 – wire load is measured by the two wattmeter method. The first wattmeter reads twice that of the second. Then the load impedance angle in radians is

The dc current flowing in a circuit is measured by two ammeters, one PMMC and another electrodynamometer type, connected in series. The PMMC meter contains 100 turns in the coil, the flux density in the air gap is , and the area of the coil is . The electrodynamometer ammeter has a change in mutual inductance with respect to deflection of 0.5 mH/deg. The spring constants of both the meters are equal. The value of current, at which the deflections of the two meters are same, is_____________

The saw-tooth voltage waveform shown in the figure is fed to a moving iron voltmeter. Its reading would be close to_____________.

While measuring power of a three-phase balanced load by the two-wattmeter method, the readings are 100W and 250W. The power factor of the load is_____________.

Two ammeters X and Y have resistances of  respectively and they give full-scale deflection with 150 mA and 250 mA respectively. The ranges have been extended by connecting shunts so as to give full scale deflection with 15A. The ammeters along with shunts are connected in parallel and then placed in a circuit in which the total current flowing is 15A. The current in amperes indicated in ammeter X is_________.

An LPF wattmeter of power factor 0.2 is having three voltage settings 300V, 150V and 75V, and two current settings 5A and 10A. The full scale reading is 150. If the wattmeter is used with 150V voltage setting and 10A current setting, the multiplying factor of the wattmeter is______________.

A periodic waveform observed across a load is represented by

The measured value, using moving iron voltmeter connected across the load, is

A (0-50A) moving coil ammeter has a voltage drop of 0.1 V across its terminals at full scale deflection. The external shunt resistance (in milliohms) needed to extend its range to (0 – 500A) is ____________.

The input impedance of the permanent magnet moving coil (PMMC) voltmeter is infinite. Assuming that the diode shown in the figure below is ideal, the reading of the voltmeter in volts is          

Three moving iron type voltmeters are connected as shown below. Voltmeter readings are V,  and , as indicated. The correct relation among the voltmeter readings is  

A periodic voltage waveform observed on an oscilloscope across a load is shown. A permanent magnet moving coil (PMMC) meter connected across the same load reads

For the circuit shown in the figure, the voltage and current expression are  and

The average power measured by the wattmeter is

An analog voltmeter uses external multiplier settings. With a multiplier setting of, it reads 440V and with a multiplier setting of, it reads 352V. For a multiplier setting of, the voltmeter reads

Consider the following statements:

(i) The compensating coil of a low power factor wattmeter compensates the effect of the impedance of the current coil.

(ii) The compensating coil of a low power factor wattmeter compensates the effect of the impedance of the voltage coil circuit.

A wattmeter is connected as shown in the figure. The wattmeter reads

An ammeter has a current range of 0 – 5 A, and this internal resistance is. In order to change the range to 0 – 25 A, we need to add a resistance of        

The pressure coil of a dynamometer type wattmeter is

The figure shows a three-phase delta connected load supplied from a 400V, 50 Hz, 3-phase balanced source. The pressure coil (PC) and current coil (CC) of a wattmeter are connected to the load as shown, with the coil polarities suitably selected to ensure a positive deflection. The wattmeter reading will be

A sampling wattmeter (that computes power from simultaneously sampled values of voltage and current) is used to measure the average power of a load. The peak to peak voltage of the square wave is 10 V and the current is a triangular wave of 5A p-p as shown in the figure. The period is 20ms.  The reading in W will be

Two wattmeters, which are connected to measure the total power on a three phase system supplying a balanced load, read 10.5 kW and -2.5 kW, respectively. The total power and the power factor, respectively, are

A PMMC voltmeter is connected across a series combination of a DC voltage source  and an AC voltage source.  The meter reads

A DC ammeter has a resistance of 0.1Ω and its current range is 0 – 100A. If the range is to be extended to 0 – 500A, the meter requires the following shunt resistance

A 1000 V DC supply has two 1-core cables as its positive and negative leads; their insulation resistances to earth are 4 MΩ and 6 MΩ, respectively, as shown in Figure. A voltmeter with resistance 50 KΩ is used to measure the insulation of the cable. When connected between the positive core and earth, the voltmeter reads

The circuit in figure is used to measure the power consumed by the load. The current coil and the voltage coil of the wattmeter have 0.02Ω and 1000Ω resistances respectively. The measured power compared to the load power will be

A galvanometer with a full scale current of 10mA has a resistance of 1000Ω. The multiplying power (the ratio of measured current to galvanometer current) of a 100Ω shunt with this galvanometer is

A moving coil of a meter has 100 turns, and a length and depth of 10 mm and 20 mm respectively. It is positioned in a uniform radial flux density of 200mT. The coil carries a current of 50mA. The torque on the coil is

A dc A-h meter is rated for 15 A, 250V. The meter constant is 14.4 A-sec/rev.  The meter constant at rated voltage may be expressed as

A moving iron ammeter produces a full-scale torque of 240 µNm with a deflection of 120° at a current of 10 A. The rate of change of self inductance (µH/radian) of the instrument at full scale is?

A single-phase load is connected between R and Y terminals of a 415 V, symmetrical, 3-phase, 4-wire system with phase sequence RYB. A wattmeter is connected in the system as shown in figure. The power factor of the load is 0.8 lagging. The wattmeter will read

A Manganin swamp resistance is connected in series with a moving coil ammeter consisting of a milli-ammeter and a suitable shunt in order to

The effect of stray magnetic fields on the actuating torque of a portable instrument is maximum when the operating field of the instrument and the stray fields are

A rectifier type ac voltmeter consists of a series resistance  an ideal full wave rectifier bridge and a PMMC instrument as shown in Figure. The internal resistance of the instrument is 100 Ω and a full-scale deflection is produced by a dc current of 1mA. The value of  required to obtain full scale deflection with an AC voltage of 100 V (RMS) applied to the input terminals is

A wattmeter reads 400 W when its current coil is connected in the R phase and its pressure coil is  connected between this phase and the neutral of asymmetrical 3-phase system supplying a balanced star connected 0.8p.f. inductive load. The phase sequence is RYB. What will be the reading of this wattmeter if its pressure coil alone is reconnected between the B and Y phases all other connections remaining as before

The inductance of a certain moving-iron ammeter is expressed as , where θ is the deflection in radians from the zero position. The control spring torque in  Nm/radian, the deflection of the pointer in radian when the meter carries a current of 5A, is

The voltage flux adjustment of a certain 1-phase 220 V induction watt hour meter is altered so that the phase angle between the applied voltage and the flux due to it is 85° (instead of 90°). The errors introduced in the reading of this meter when the current is 5A at power factors of unity and 0.5 lagging are respectively.

The line-to-line input voltage to the 3 phase, 50 Hz, ac circuit shown in figure is 100 V rms. Assuming that the phase sequence is RYB, the watt-meters would read.

If an energy meter disc makes 10 revolutions in 100 seconds when a load of 450 W is connected to it, the meter constant (in rev/kWh) is

The minimum number of wattmeter (s) required to measure 3-phase, 3-wire balanced or unbalanced power is

A 100µA ammeter has an internal resistance of 100Ω. For extending its range to measure 500µA, the shunt required is of resistance (in Ω)

The two wattmeter method is used to measure active power on a three phase, three wire system. If the phase voltage is unbalanced, then the power reading is:

A three-phase load operates with balanced voltages applied to its terminals, and draws balanced currents. The potential coil of a moving coil wattmeter is connected from R to Y terminals of the load. The current coil of the meter is connected in series with phase B. Then the quantity indicated by this wattmeter is proportional

Electrodynamic type watt-meters have large errors while measuring power in ac circuits at low power factor conditions, since the voltage across  and the current through the

A current of

 is measured with a thermocouple type, 5A full-scale, class 1 meter. The meter reading would lie in the range

Two 100μA full-scale PMMC meters are employed to construct a 10V and a 100V full scale voltmeter. These meters will have figures of merit (sensitivities) as

For the circuit shown in figure, the internal resistance of the armatures as well as that of the current coil of the wattmeter are zero and the voltmeters have a very large figure of merit.  is a 6A full scale moving iron type meter.  is a commercial full wave rectifier type meter of full scale 5A.  is a 500V meter of the peak response type.  is a 300V PMMC type meter and W is an electrodynamometer type, 5A, 230V wattmeter. Determine the readings of  and W.

A d.c. voltmeter has a sensitivity of 1000 Ω/volt. When it measures half full scale in 100V range, the current through the voltmeter is

A moving coil galvanometer is made into a d.c. ammeter by connecting

A moving coil instrument, whose resistance is 5Ω and whose working current (for full-scale deflection) is 0.015A, is to be used, with a manganin shunt, to measure 100A. calculate the error caused by a 10℃ rise in temperature, if the temperature coefficient of copper and manganin are 0.004 ohm/℃, and 0.00015 ohm/℃ respectively.

A dynamometer type wattmeter responds to the

A transfer instrument employed in the standardization of a polar type AC potentiometer is

An advantage of a permanent magnet moving coil instrument is that it is

The moving coil in a dynamometer wattmeter is connected

For a given frequency, the deflecting torque of an induction ammeter is directly proportional to

The scale of a voltmeter is uniform. Its type is

Four ammeters, M1, M2, M3 and M4 with the following specifications are available.

A current of 1A is to be measured. To obtain minimum error in the reading, one should select meter

In the circuit of figure, ammeter  reads 12A and  reads 9A. will read ________________A.  

Two 100V full scale PMMC type dc voltmeters having figure of merits (FOM) of 10kΩ/V and 20kΩ/V are connected in series. The series combination can be used to measure a maximum dc voltage of _____________________V.

A symmetrical star connected three-phase load is made of three identical coils having an internal resistance of 12 Ohm and inductance of 142mH. The power taken by this load when connected to a balanced three-phase three-wire supply of 400V, 50Hz is measured using the two wattmeter method. The watt meters used are similar and are of type of 400V, 5A, UPF, class 1 accuracy.

A 0-10mA PMMC ammeter reads 4mA in a circuit. Its bottom control spring snaps suddenly. The meter will now read nearly

The light load adjustment is carried out on a single-phase house-service energy meter under _________________ power factor conditions.

_____________ torque is not provided in an electromagnetic flux meter.         

,  and  are the balanced instantaneous line to neutral voltages and ,  and  are instantaneous line currents in a balanced three phase circuit, the computation  will yield a quantity proportional to?

An unshielded moving iron voltmeter is used to measure the voltage in an a.c. circuit. If a stray d.c. magnetic field having a component along the axis of the meter coil, the meter reading would be

Two identical watt-meters are connected to measure power in a 3-phase 3-wire balanced load. What is the load power factor if

(a)

(b) Either  is zero ____________

The current passing through a 10 Ohm resistor of figure (a) has the waveform in figure (b). The reading of the PMMC voltmeter connected across the resistor