What is the meaning of excitation in an alternator?

What is the meaning of excitation in an alternator?
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1 Answer

Answer :

An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation.
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Related questions

What are the excitation methods used in an alternator?*

Description : What are the excitation methods used in an alternator?*

Last Answer : Rotary : Using rotating diode rectifiers, primary exciter and main exciter. Static : Excitation given by brushes and slip rings.

How is the excitation achieved in this?

Description : How is the excitation achieved in this?

Last Answer : Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, ... this is that a small DC exciter current indirectly controls the output of the main alternator.

Is the alternator connected star or delta

Description : Is the alternator connected star or delta

Last Answer : Look up in Dennis T Hall. Also in your ship ask E/O. Normally star.

Even though the main engine runs at varying speeds, how does the alternator maintain constant frequency?

Description : Even though the main engine runs at varying speeds, how does the alternator maintain constant frequency?

Last Answer : By use of thyristor controlled frequency (rpm) converters.

What is a brush less alternator?

Description : What is a brush less alternator?

Last Answer : A brushless alternator is composed of two sections: main alternator and the smaller exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator ... has a rotating field as described above and a stationary armature (power generation windings).

Why is it necessary that incoming alternator frequency is more than bus bar?

Description : Why is it necessary that incoming alternator frequency is more than bus bar?

Last Answer : Prior to paralleling alternators together, the frequency of the incoming alternator is made slightly higher. This is to ensure that the incoming generator will take some of the bus load. If the incoming ... onto the bus. If this happens it is possible to cause other generators to trip off line.

Is the ship's alternator Star wound or Delta wound?

Description : Is the ship's alternator Star wound or Delta wound?

Last Answer : Refer Dennis T Hall

Why are motor ratings given in KW and that of alternator and transformer given in KVA?

Description : Why are motor ratings given in KW and that of alternator and transformer given in KVA?

Last Answer : kW is the output mechanical power of a motor and is expressed in kW. kVA is the net (apparent) power input to the transformer. This input power is the output + losses. kW = kVA x system power factor

Size of V belts used for 25KW Alternator a. C121 c. C122 b. C123 d. C124

Description : Size of V belts used for 25KW Alternator a. C121 c. C122 b. C123 d. C124

Last Answer : c. C122

State working principle of alternator. State the meaning self and separate excitation.

Description : State working principle of alternator. State the meaning self and separate excitation. 

Last Answer : Working principle of alternator: When a conductor is moved in magnetic field or a magnetic field moved with respect to conductor, according to Faraday's law of electromagnetic induction, the conductor ... like battery or shaft-mounted exciter, then the excitation is said to be separate excitation.

If the excitation of an alternator operating in parallel is decreased below normal, its _____________. A. power factor will change in the lagging direction B. power factor will change in the leading direction C. ampere load will be greatly increased D. kilowatt load will be greatly decreased

Description : If the excitation of an alternator operating in parallel is decreased below normal, its _____________. A. power factor will change in the lagging direction B. power factor will change in the leading direction C. ampere load will be greatly increased D. kilowatt load will be greatly decreased

Last Answer : Answer: B

If field excitation is suddenly lost to an alternator operating in parallel, that alternator will _____________. A. supply excessive current to the bus B. operate at the same load, but with reduced voltage C. lose its load and tend to overspeed D. become overloaded and slow down

Description : If field excitation is suddenly lost to an alternator operating in parallel, that alternator will _____________. A. supply excessive current to the bus B. operate at the same load, but with reduced voltage C. lose its load and tend to overspeed D. become overloaded and slow down

Last Answer : Answer: C

A change in field excitation of an alternator operating in parallel will cause a change in its _____________. A. alternator frequency B. kilowatt load C. voltage output D. all of the above

Description : A change in field excitation of an alternator operating in parallel will cause a change in its _____________. A. alternator frequency B. kilowatt load C. voltage output D. all of the above

Last Answer : Answer: C

Routine maintenance of a ship's service alternator should include ______________. A. changing the pedestal bearing insulation yearly B. megger testing of all rectifying diodes C. lubricating excitation slip rings D. periodic cleaning of the air filters or screens

Description : Routine maintenance of a ship's service alternator should include ______________. A. changing the pedestal bearing insulation yearly B. megger testing of all rectifying diodes C. lubricating excitation slip rings D. periodic cleaning of the air filters or screens

Last Answer : Answer: D

The standard method of controlling the output voltage of a 440 volt, 60 Hz, AC generator is accomplished by adjusting the ____________. A. prime mover speed droop B. number of poles C. alternator field excitation D. load on the alternator

Description : The standard method of controlling the output voltage of a 440 volt, 60 Hz, AC generator is accomplished by adjusting the ____________. A. prime mover speed droop B. number of poles C. alternator field excitation D. load on the alternator

Last Answer : Answer: C

The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation of the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. type of alternator

Description : The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation of the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. type of alternator

Last Answer : Answer: B

The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation to the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. number of field poles per alternator

Description : The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation to the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. number of field poles per alternator

Last Answer : Answer: B

RC time constant characteristics, as shown in the illustration, are important in _____________. EL-0086 A. bridge rectifiers for alternator excitation B. timing and pulse shaping circuits C. transistor power amplifier biasing D. motor controller overload protection

Description : RC time constant characteristics, as shown in the illustration, are important in _____________. EL-0086 A. bridge rectifiers for alternator excitation B. timing and pulse shaping circuits C. transistor power amplifier biasing D. motor controller overload protection

Last Answer : Answer: B

How does increase in excitation of the Alternator connected to infinite bus-bars affect this operation?

Description : How does increase in excitation of the Alternator connected to infinite bus-bars affect this operation?

Last Answer : Increase in excitation level of the synchronous generator will effectively increase the reactive power supplied by the generator keeping steam input constant.

What happens if speed of prime mover is changed keeping excitation of alternator constant?

Description : What happens if speed of prime mover is changed keeping excitation of alternator constant?

Last Answer : If speed of prime mover is changed, the speed of alternator also changes hence frequency also changes. The frequency increase with increase in steam input and hence speed and vise versa.

What happens if excitation of alternator is changed keeping speed of prime mover constant?

Description : What happens if excitation of alternator is changed keeping speed of prime mover constant?

Last Answer : The emf induced will be changed and hence terminal voltage will also change. The terminal voltage will increase with increase in excitation and vise versa.

When Alternator excitation increases and machine is operating at lagging power factor then a) I increase b) I decreases c) No effect on current d) None

Description : When Alternator excitation increases and machine is operating at lagging power factor then a) I increase b) I decreases c) No effect on current d) None

Last Answer : Ans: I increase

An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be (A) less. (B) more. (C) more or less. (D) the same.

Description : An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be (A) less. (B) more. (C) more or less. (D) the same.

Last Answer : Ans: B Over excitation gives leading power factor and under excitation gives lagging p.f .

If the excitation of an alternator operating in parallel with other alternators decreased, its:

Description : If the excitation of an alternator operating in parallel with other alternators decreased, its: (1) Power factor becomes more leading (2) Output Kw will change (3) Power factor becomes more lagging (4) Power factor becomes unity

Last Answer : If the excitation of an alternator operating in parallel with other alternators decreased, its: Power factor becomes more leading

A field excitation of 20 A in a certain alternator results in an armature current of 400 A in short circuit and a

Description : A field excitation of 20 A in a certain alternator results in an armature current of 400 A in short circuit and a terminal voltage of 2000 V on open circuit. The magnitude of the internal voltage drop within the machine at a load current of 200 A is  (A) 1 V (B) 10 V (C) 100 V (D) 1000 V

Last Answer : 800

While keeping the excitation constant, if the steam supply of an alternator running in parallel with another

Description : While keeping the excitation constant, if the steam supply of an alternator running in parallel with another identical alternator is increased, then (A) It would over-run the other alternator (B) Its rotor ... (C) Its portion of share in load will increase (D) Its power factor would be decreased.

Last Answer : While keeping the excitation constant, if the steam supply of an alternator running in parallel with another identical alternator is increased, then Its portion of share in load will increase

What is the meaning of a normally open contact?

Description : What is the meaning of a normally open contact?

Last Answer : The contact is open in the normal (de-energised condition).

What is the meaning of residual magnetism?

Description : What is the meaning of residual magnetism?

Last Answer : Residual magnetism is a property in which certain amount of excitation remains back in the conductor even after the removal of the magnets.

What is meaning of short circuit?

Description : What is meaning of short circuit?

Last Answer : A short circuit occurs when conductors are connected (shorted) together by a fault. This is normally phase to phase fault due to failure of insulation by something cutting the wires, fires, etc.

What is the meaning of overload?

Description : What is the meaning of overload?

Last Answer : An overload is a current over and above the normal load current (over the load). In other words greater than the original design current. This can be a momentary overload such as the starting ... such as plugging in too many appliances at once or a motor that has faulty bearings or gets jammed

What is the meaning of ACB, MCCB, NFB?

Description : What is the meaning of ACB, MCCB, NFB?

Last Answer : Air circuit breaker for 400V higher current ratings. Moulded case circuit breaker for 400V medium current ratings. No Fuse Breaker – 75 A capacity

What is the meaning of Star winding/ Delta winding?

Description : What is the meaning of Star winding/ Delta winding?

Last Answer : Refer Dennis T Hall

What is the meaning of earthing in a ship?

Description : What is the meaning of earthing in a ship?

Last Answer : Ask E/O

What is the meaning of saying I and V are in phase?

Description : What is the meaning of saying I and V are in phase?

Last Answer : The angle between the I and V waveforms is zero which means the load is purely resistive.

What is the meaning of power factor?

Description : What is the meaning of power factor?

Last Answer : Power factor is the cosine of the angle between voltage and current waveform.

What is the meaning of preferential trip? Why is it provided

Description : What is the meaning of preferential trip? Why is it provided

Last Answer : Preferential trip is a kind of electrical arrangement on ship which is designed to disconnect the non-essential circuit i.e. non-essential load from the main bus bar in case of partial failure or overload ... gear) and trips the non essential loads (like AC and galley) and is a safety feature.

5) An iron ring of mean circumference of 80 cm is uniformly wound with 500 turns of wire. Calculate the value of flux density that a current of 1 A would produce in the ring. Assume relative permeability 1400.

Description : Please ripley me due to emergency

Last Answer : To calculate the flux density in the ring, you need to use the following formula: B = (μ * I * N) / (2 * π * r) where: B is the flux density in the ring (in teslas) μ is the relative permeability ... 2 * π * 0.127 m) = 0.53 T So the flux density in the ring would be approximately 0.53 teslas.

Can you help me solve my electrical mystery?

Description : Can you help me solve my electrical mystery?

Last Answer : Any signs of animal life? They can get in the walls and chew on the wires. Or is it the entire area served by that breaker? The breaker could be bad. It happens with anything mechanical.

How to tell if a power strip is burned out?

Description : How to tell if a power strip is burned out?

Last Answer : answer:Personally, I would either toss it, or down grade it to outdoor use only. I wouldn’t take a chance with it in the house. Yes, you can let it cool down, then test it again. But a failure is a failure. Does it have a reset button? What price range did you pay?

I accidently soaked an extension cord. Is it safe to use it again after letting it dry out for awhile?

Description : I accidently soaked an extension cord. Is it safe to use it again after letting it dry out for awhile?

Last Answer : The plug end is easier to dry out than the socket end get out your blow-dryer and set it to high and blow the end that got wet for a while. That will get most of the water off/out of ... up or sputter. Most modern extension cords are pretty watertight so there shouldn't be any water down the wire.

How can a solar array power source be bypassed when the batteries run low?

Description : How can a solar array power source be bypassed when the batteries run low?

Last Answer : Ah got it. If anyone else is interested, you need an “automatic transfer switch” – or get a manual one for that mad scientist charm.

How to stop a signal going through a wire?

Description : How to stop a signal going through a wire?

Last Answer : Use a switch or a variable resistor

Air conditioning will not turn on, is it electrical?

Description : Air conditioning will not turn on, is it electrical?

Last Answer : Pull the Thermostat off the wall and see if it is connected correctly to the AC switch. There should be no dangling wires, and the post labeled for the AC should have an attached wire.

What is the speaker driving voltage of an amplifier?

Description : What is the speaker driving voltage of an amplifier?

Last Answer : I have to ask WHY? That said, Speakers and a light bulb are two different types of load, and the the lights will probably fry the output transistor.

Why is my Garbage disposal leaking water from the bottom?

Description : Why is my Garbage disposal leaking water from the bottom?

Last Answer : Replace it. The seal is leaking, and most cases it is just not worth the cost and work, quicker and cheaper to replace it .

Have you ever taken a shower or bath during an electrical storm?

Description : Have you ever taken a shower or bath during an electrical storm?

Last Answer : I’ve heard this rumor, and I too question it’s validity. I mean, if electricity can’t travel up a stream of urine (See mythbusters) I’m pretty sure it couldn’t travel through a shower stream. Perhaps through the drain? In either case, I’ve taken a shower in a storm before, and.. well, you see?

Electrical breaker box is buzzing-why??

Description : Electrical breaker box is buzzing-why??

Last Answer : No! Do not upgrade the breaker. The wire must also be upgraded if you do. Try plugging it in a different room. Is the problem still there?

Laptop What ?

Last Answer : Laptop Yes A Portable Computer.

circuit I mean What ?

Last Answer : electricity Source , conductor , control Instruments , Usage Machines , Protection Machines In combination Such A Path Whose The middle With Current Flowing To be Can Him Circuit Or Circuit Says.

House Wiring How much? Type, What? What ?

Last Answer : House Wiring Mainly Two Type. A ) Surface Wiring B ) Concealed Wiring Surface Wiring 5 Type : 1 ) Batten Wiring 2 ) Conduit Wiring 3 ) Clit Wiring 4 ) Casing Wiring 5 ) M. S. Wiring Concealed Wiring Again Two Type , 1 ) Concealed Conduit 2 ) Concealed Wire Wiring