What is the general difference between DC and AC machine?

What is the general difference between DC and AC machine?
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1 Answer

Answer :

1. In DC machine armature rotates and the field is stationary, In AC machine armature is stationary and the field is rotating. 2. DC machine contains commutator and brush, AC machine contains slip ring and brush.
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Last Answer : Answer: D

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What are the minimum recommended PI values for AC and DC rotating machines?

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Description : Why AC is more dangerous than DC? 

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State DC/AC equivalent factor (K).

Description : State DC/AC equivalent factor (K).

Last Answer : Ratio of direct current (DC) to its equivalent rms value of alternating current (AC) having the same probability of inducting ventricular fibrillation. K = I DC fibrillation / I AC ... in the extremities during the flow of current. Above 300 mA unconsciousness frequently occurs.

What are the importances of conversion of AC into DC?

Description : What are the importances of conversion of AC into DC?

Last Answer : a. For traction purpose a DC series motor is most important. Examples in railways, in electrical lifts etc. b. For electrolytic and electro chemical processes such as electro plating, electrolysis, ... arc welding. d. It is required for operating relays, timer, telephone, circuit breakers etc.

What are the advantages of AC over DC?

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Last Answer : a. For the same capacity alternators are cheaper than DC generators, because alternator is not having commutator arrangement and there by small in size. b. Alternating current produces pulsating magnetic field and ... motor requires very less maintenance. g. Charge per unit for AC is less than DC.

How can we start-up the 40w tube light with 230v AC/DC without using any choke/Coil?

Description : How can we start-up the 40w tube light with 230v AC/DC without using any choke/Coil?

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Why AC systems are preferred over DC systems?

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Description : A stepper motor is (A) a dc motor. (B) a single-phase ac motor. (C) a multi-phase motor. (D) a two phase motor.

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If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of wood C. inject small amounts of CO2 into the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents

Description : If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of ... the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents

Last Answer : Answer: A

When using a megohmmeter to determine which shunt field coil is grounded in a DC machine, you must ____________. A. insulate the field frame from the ship's hull B. disconnect each shunt field coil before testing C. use a motor driven high capacity megohmmeter D. remove all main line lead connections before testing

Description : When using a megohmmeter to determine which shunt field coil is grounded in a DC machine, you must ____________. A. insulate the field frame from the ship's hull B. disconnect each shunt ... C. use a motor driven high capacity megohmmeter D. remove all main line lead connections before testing

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Description : A flickering ground detection lamp on a DC system would indicate a _____________. A. multiple-ground condition in the distribution system B. ground in an armature coil of an operating machine C. ground in a motor accompanied with a short D. short between two adjacent bars of the generator commutator

Last Answer : Answer: B

The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step

Description : The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step

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Description : Explain the process of commutation in a dc machine. Explain what are inter-poles and why they are required in a dc machine.

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Which one of the following statements for a dc machine which is provided with inter pole winding (IW) as well as compensating winding (CW) is correct a) Both IW and CW are connected in series with Armature winding b) Both IW and CW are connected in parallel with Armature winding c) IW connected in series but CW is connected in parallel with Armature winding d) CW connected in series but IW is connected in parallel with Armature winding

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Last Answer : Ans: Both IW and CW are connected in series with Armature winding

The armature of a dc machine is laminated to reduce: (A) Eddy current loss (B) Hysteresis loss (C) copper losses (D) friction and windage losses

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Last Answer : Ans: A Thinner the laminations, greater is the resistance offered to the induced e.m.f., smaller the current and hence lesser the I2R loss in the core.

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Last Answer : (C) less than 800 rpm.