Description : How do you measure power factor?

**Answer** : P= 1.83*V*I*[email protected] where P is power V is voltage I is current COS @ is P.F [email protected]= P/(1.83*V*I) in other way cos @ = true power/apparent power

Description : What is the use of power factor correction?

Description : Can you have a power factor greater than 1?

**Answer** : We cannot have power factor greater than 1. As it is a measure of cosine of angle between voltage and current.

Description : What is the best power factor?

**Answer** : It is unity power factor but difficult to achieve in dynamic loads

Description : What is need of regulated power supply?

**Answer** : A regulated power supply is used to ensure that the output remains constant even if the input changes. But sometimes main supply voltage, load, and surrounding temperature keep changing and altering the ... power supply is needed that will accept an AC input and give a constant DC output.

Description : If we change the excitation of synchronous machine will it affect on power factor?

**Answer** : Yes, If we change the excitation of synchronous machine it will affect on power factor. If the synchronous motor is overexcited then it will have leading power factor and if the motor is underexcited then it will have lagging power factor.

Description : How can we improve power factor using synchronous motor?

**Answer** : Yes, we can make the power factor of synchronous motor leading by adjusting its excitation.

Description : Why capacitors are used to improve power factor?

**Answer** : Capacitors generate reactive power instead of that drawn from source which is required by inductive loads.so it reduce the reactive current which is drawn from source to be drawn from capacitor.This control in Electric bills cost.

Description : Why the power factor of semiconverter is better than full converter?

**Answer** : Power factor of semiconverter is better than full converter

Description : What is the value of capacitance required to improve power factor from 0.7 to 0.9. Given that: Real power = 50 W Vrms of the source = 120 Frequency = 50 Hz #powerfactor

Description : Power factor of an inductive circuit is usually improved by connecting capacitor to it in?

**Answer** : Power factor of an inductive circuit is usually improved by connecting capacitor to it in parallel.

Description : Power factor of an electrical circuit is equal to?

**Answer** : Power factor of an electrical circuit is equal to R/Z, cosine of phase angle difference between current and voltage, kW/kVA.

Description : A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

**Answer** : A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because stator supply is not required to produce magnetic field.

**Answer** : In a distribution system, in order to improve power factor, the synchronous capacitors are installed at the receiving end.

**Answer** : The primary reason for low power factor is supply system is due to installation of induction motors.

**Answer** : For high value of diversity factor, a power station of given installed capacity will be in a position to supply more number of consumers.

Description : At which power factor alternator is said to be overexcited?

**Answer** : At leading power factor alternator is said to be overexcited.

Description : In an alternator at lagging power factor the generated voltage per phase as compared to that at unity power factor?

**Answer** : In an alternator, at lagging power factor the generated voltage per phase as compared to that at unity power factor must be more than terminal voltage.

Description : State the effects of low power factor on efficiency and voltage regulation of short transmission lines.

**Answer** : i) Effect of Low power factor on efficiency:- When power factor of load reduces current drawn by transmission line increases so copper losses in transmission line increases, hence transmission ... increases, so voltage drop in transmission line increases so regulation increases. (Become Poor)

Description : Briefly explain how the power factor of an inductive circuit can be improved.

**Answer** : As we know that power factor should be corrected to ensure that the current supplied is cost friendly. Meaning the power factor should be around one but not greater than one(0.8-0.9) in a ... an inductive circuit due to the inductive reactance which oppose the change of current in the ac circuit.

Description : Discuss how power factor tariff results into energy conservation.

**Answer** : Power factor tariff results into energy conservation: i) Applying incentives and penalties according to power factor is an effective way, which enables consumer to improve power factor so that he can ... finally leads to reduction in the current drawn by the load and helps for energy conservation.

Description : Draw and explain bulk correction method for power factor & control.

**Answer** : Bulk correction method for power factor & control: i) Here individual starter controls the capacitors located at distribution panel. ii) Centralized compensation is employed in large industrial plants where many ... capacitor units in steps to maintain P.F. more than preset limit (0.95).

Description : State the incentives and penalties related with power factor tariff.

**Answer** : Incentives and penalties related with power factor tariff: In addition to basic tariff (Maximum Demand Tariff / KVA Maximum Demand Tariff / Load factor tariff) the tariff in which P.F. of ... industrial consumer/H.T/ commercial consumers with contract demand above 80 kw/ 100Kva/107 hp consumer.

Description : With a neat sketch explain working of 1 phase dynamometer type power factor meter.

**Answer** : Working of 1 phase dynamometer type power factor meter : The current coil is connected in series with load. Two pressure coils marked as A and B are connected across the supply terminals ... becomes stationary and the pointer shows steady deflection corresponding to the power factor of the load.

Description : State the significance of power factor.

**Answer** : Significance of power factor:- 1. Cosine of angle between voltage & current in a circuit is called power factor. 2. It is a measure of the real power in a circuit. 3. Inductive & ... KVA rating equipment 5. Greater conductor size 6. CosØ = R/Z CosØ= Active Power/ Apparent Power

Description : A transformer has negative voltage regulation when its load power factor is (1) Zero (2) Unity (3) Leading (4) Lagging

**Answer** : Leading

Description : The power factor of dielectric : (A) is a function of temperature of the dielectric only (B) depends only on voltage stress to which the dielectric is stressed (C) always constant (D) both (A) and (B)

**Answer** : The power factor of dielectric : (A) is a function of temperature of the dielectric only (B) depends only on voltage stress to which the dielectric is stressed (C) always constant (D) both (A) and (B)

Description : Power station having Load factor = 70%, capacity factor = 50%, used factor = 60%, maximum demand = 20MW then annual energy production is (1) 122.8 GWh (2) 198.55 GWh (3) 128.2 GWh (4) 188.82 GWh

**Answer** : Power station having Load factor = 70%, capacity factor = 50%, used factor = 60%, maximum demand = 20MW then annual energy production is 122.8 GWh

Description : In a synchronous generator delivering lagging power factor load (1) the excitation emf leads terminal voltage by the power angle (2) the excitation emf lags terminal voltage by the power angle (3) ... by the power factor angle (4) excitation emf lags the terminal voltage by the power factor angle

**Answer** : In a synchronous generator delivering lagging power factor load the excitation emf leads terminal voltage by the power angle

Description : What is the power factor when a single phase watt meter operating on 200 V and 5 A for 5 hours makes 2016 revolutions and the meter constant in revolution is 420? A) 0.04 B) 1.04 C) 0.96 D) None of these

**Answer** : What is the power factor when a single phase watt meter operating on 200 V and 5 A for 5 hours makes 2016 revolutions and the meter constant in revolution is 420? A) 0.04 B) 1.04 C) 0.96 D) None of these

Description : The benefit of power factor correction in a power system is (A) lower power consumption (B) increased demand charge (C) reduced load carrying capabilities in existing lines (D) reduced voltage profile

**Answer** : The benefit of power factor correction in a power system is lower power consumption

Description : The power factor angle and torque angle of a salient pole synchronous generator drawing a current of 1.0 pu from a lagging load are 45o and 15o, respectively. The direct axis and quadrature axis currents, respectively, are (A) 0.5 pu ... pu, 0.5 pu (C) 0.707 pu, 0.707 pu (D) 0.5 pu, 0.5 pu

**Answer** : The power factor angle and torque angle of a salient pole synchronous generator drawing a current of 1.0 pu from a lagging load are 45o and 15o, respectively. The direct axis and quadrature axis currents, respectively, are 0.866 pu, 0.5 pu

Description : The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA The power drawn by the circuit is?

**Answer** : The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA The power drawn by the circuit is 32 kW.

Description : The power factor at resonance in R-L- C parallel circuit is?

**Answer** : since a rlc circuit at resonance behaves like a pure resistive circuit, i.e there is no phase difference between current and voltage, hence the power factor is unity.

Description : Power factor of the system is kept high?

**Answer** : Power factor of the system is kept high to reduce line losses, to maximise the utilization of the capacities of generators, lines and transformers, to reduce voltage regulation of the line.

Description : Capacitors for power factor correction are rated in?

**Answer** : Capacitors for power factor correction are rated in kVAR.

Description : Poor power factor?

**Answer** : Poor power factor reduces load handling capability of electrical system, results in more power losses in the electrical system, overloads alternators, transformers and distribution lines, results in more voltage drop in the line.

**Answer** : The power factor of a single phase load can be calculated if the instruments available are three ammeters or three voltmeters.

**Answer** : In a dynamometer 3-phase power factor meter, the planes of the two moving coils are at 120°.

**Answer** : In a single phase power factor meter the phase difference between the currents in the two pressure coils is exactly 90°.

**Answer** : A power factor meter has one current circuit and two pressure circuits.

**Answer** : In a low power factor wattmeter the compensating coil is connected in series with pressure coil.

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