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For power factor correction, synchronous motors operate at no-load and greatly over-excited fields.

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Answer : The standard full-load power factor ratings for synchronous motors are unity or 0.8 leading.

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 : Capacitors for power factor correction are rated in?

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

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 : What is the use of power factor correction?

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.

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 : If the load of the normally excited synchronous motor is increased the power factor will?

Answer : If the load of the normally excited synchronous motor is increased the power factor will become lagging.

Description : The synchronous motor which works on leading power factor and does not drive any mechanical load is called?

Answer : The synchronous motor which works on leading power factor and does not drive any mechanical load is called synchronous condenser.

Description : If the field of synchronous motor is under excited, power factor will be?

Answer : If the field of synchronous motor is under excited, power factor will be lagging.

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 : 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

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

Description : Can a synchronous condenser improve power factor?

Answer : Yes, synchronous condenser can improve 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.

Answer : Synchronous motors are generally not self-starting because the direction of instantaneous torque reverses after half cycle.

Answer : Air blast circuit breakers for 400 kV power system are designed to operate in 50 millisecond.

Description : Damper winding is provided in 3 phase synchronous motors to :

Answer : Damper winding is provided in 3 phase synchronous motors to : provide starting torque and prevent hunting

Description : What is the difference between synchronous and asynchronous motors?

Answer : The motor which rotates at constant speed is called synchronous motor. And that constant speed is called as synchronous speed.  And the motor which does not rotates at constant speed are called asynchronous motor. Asynchronous motor is also called as Induction motor.

Answer : Synchronsizing power of a synchronous machine is inversely proportional to the synchronous reactance.

Description : The synchronous motor will develop maximum power when the load angle is?

Answer : The synchronous motor will develop maximum power when the load angle is 900.

Description : The efficiencies of transformers compared with that of electric motors of the same power are?

Answer : Transformers have high efficiency than the same ratted motors

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.

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

Answer : An induction motor has relatively high power factor at near full load.

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 : At which time power factor of the induction motor is low?

Answer : The power factor of the inducction motor is low at the time of starting as compare to while the induction motor is running.

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

Answer : For a consumer the most economical power factor is generally 0.95 lagging .

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.

Answer : The power loss is an important factor for the design of transmission line.

Description : The maximum reluctance power of a salient-pole synchronous motor having direct-axis reactance, 1.0 pu and quadrature-axis reactance, 0.5 pu, and input voltage, 1.0 pu is (A) 0.25 pu (B) 0.5 pu (C) 1.0 pu (D) 1.5 pu

Answer : The maximum reluctance power of a salient-pole synchronous motor having direct-axis reactance, 1.0 pu and quadrature-axis reactance, 0.5 pu, and input voltage, 1.0 pu is 0.5 pu

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 : 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 : 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 : 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 : 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 : The power factor of a D.C. circuit is always?

Answer : The power factor of a D.C. circuit is always unity.

Description : The ratio of active power to apparent power is known as____ factor.

Answer : The ratio of active power to apparent power is known as power factor.

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 : Power factor of electric bulb is?

Answer : Power factor of electric bulb is unity.

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