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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
Why neutral not conect in 3phase motor?
A 3 phase motor does not require a neutral conductor because the impedances that make up the stator coils are of equal magnitude and it is what is known as a balanced 3 phase load. If the loads of a wye connected 3 phase system were unbalanced, i.e. the load currents in each of the 3 phases are different, then the unbalanced currents would require a return path to the service transformer via a neutral conductor. The neutral conductor is the transformer centre tap and is usually earthed locally.
ANOTHER ANSWER
The impedance of each phase winding of a three phase motor is identical (we call it a 'balanced load'). For a star (wye) connected motor, the phasor sum of three identical phase currents is zero, so no current will flow through a neutral, so a neutral isn't required. For a delta-connected motor, there is no provision for a neutral.
What is the difference between a three phase induction motor and a DC motor?
There are several.
DC motors have numerous different connections, but probably the most common is the shunt-wound. In this design, two heavy leads go to the rotor windings, and two light leads go to the field windings of the stator.
In an induction motor, the only "windings" are in the stator, and there are always some multiple of three connections for those windings. The rotor has a "winding" that consists of aluminum or copper bars shorted by rings at their ends resembling an exercise wheel for a rodent cage, thus the "squirrel-cage" nomenclature. This cage is assembled around iron laminations, making a solid rotor with no electrical connections to the outside world.
DC motor are inherently variable-speed machines. By varying the voltage applied to the armature and/or to the field the motor speed and torque can be controlled. AC induction motors are not inherently variable speed. Their speed is directly dependent on the frequency of the AC power applied to the stator windings, and this is normally fixed by the utility providing the power. Then again, AC motors can be connected directly to utility power with a switch, DC motors require some type of electronic controller between them and the utility, unless the motors are small enough to be run from batteries.
DC motors require much more maintenance, as the carbon brushes and armature commutators require regular cleaning and service. Build up of carbon dust can be detrimental to the operation of a DC motor. AC motors may occasionally need to have their bearings greased or oil changed.
With the advent of high-performance variable frequency drives, DC motors are no longer the first choice for variable speed applications. The higher reliability of AC induction motors and VFDs has resulted in DC falling in popularity. There's still a lot of installed DC equipment that end users cannot justify replacing, but there are very few new installations of DC systems on modern equipment.
What are the differences between nmos and pmos transistors?
NMOS is built with n-type source and drain and a p-type substrate, while PMOS is built with p-type source and drain and a n-type substrate. In a NMOS, carriers are electrons, while in a PMOS, carriers are holes. When a high voltage is applied to the gate, NMOS will conduct, while PMOS will not. Furthermore, when a low voltage is applied in the gate, NMOS will not conduct and PMOS will conduct. NMOS are considered to be faster than PMOS, since the carriers in NMOS, which are electrons, travel twice as fast as holes, which are the carriers in PMOS. But PMOS devices are more immune to noise than NMOS devices. Furthermore, NMOS ICs would be smaller than PMOS ICs (that give the same functionality), since the NMOS can provide one-half of the impedance provided by a PMOS (which has the same geometry and operating conditions).
Definitely not it could be dangerous. AC and DC can't be interchanged in general.
What is the purpose of a neutral conductor in 3 phase?
If you want to have a 3-phase service with a neutral then one way to get it is to connect the incoming three phases of a standard 3-phase service to a transformer whose secondary windings are connected in what is called a "star" (also known as a "Y" or "wye") configuration which has a neutral point at the center of the "star" or "Y".
Then, to get a single-phase service, you can use just one phase and the neutral. This results in about half the voltage - actually it's 1 / 2./'3 (1 divided by the square root of three) - that you'd get across any two phases of the incoming 3-phase service.
Note
A three phase service on its own does not have a neutral line. The voltage difference is measured between the phases. (No voltage can be measured between any of the phase lines and a neutral because there is no neutral line.)
Any electrical equipment which uses a 3-phase service exactly as it is delivered by the power generator / utility - that is, without a neutral line - are connected in what is known as "delta" connection.
What does cause resistance in electrical wires?
electrical resistence is occur in conductor due to over flow of current,in conductor
AnswerResistance is not due to the 'flow of current'. It exists whether current is flowing or not! Resistance is determined by the type of material and its physical dimensions. Resistance depends upon the resistivity (which is also affected by temperature) of the material, and the length and cross-sectional area of that material.
Differentiate a parallel from a series connection?
DATA WILL BE SENT IN DUAL YET IN SERIES DATA WILL BE SENT IN ASINGLE LINE
How do you calculate motor wattage from its resistance?
All you can do is get in the ballpark knowing resistance of windings and the supply voltage. Current = Voltage divided by resistance.
Wattage = voltage x current x power factor. For a motor the power factor is between zero and sone number less than one, with one being just a resistive load. So if you calculate the current and use a PF = 1 you can get worse case wattage.
Maxwell's inductance capacitance bridge?
The Maxwell Bridge is known as an AC bridge. This bridge is used to find the self inductance and the whole amount of a circuit.
What are the differences of Long shunt vs short shunt generator?
In long shunt the shunt field winding is in parallel to both generator and series field. In short shunt the shunt field is in parallel to generator only.
What is the full load amperage of a 500 HP motor at 4160 volts?
20.833 amps at 240volts equals 5000 watts. Wattage is volts times amps.
What you the current in an ac circuit with 120 volts and a 60 watt light bulb?
Questions seem to be two! First is the direct current in a circuit with 12 V battery and 3 ohm resistor in it. The answer is 4 ampere if there is negligible internal resistance in the battery.
By ohm's law V = R I So, I = V/R
Second one is the alternating current with 120V given to 60 W bulb. The answer is 0.5 ampere. This 0.5 is the rms value of alternating current.
Power P = V I So, I = P/V
What is the difference between line to line voltage to line to ground voltage?
A three-phase, four-wire, system consists of three 'hot' conductors which are called line conductors, and a neutral conductor, sourced from a wye (or 'star') connected alternator or transformer. For this type of system, line voltages exist between line conductors, and phase voltages exist between any line conductor and the neutral conductor.
A three-phase, three-wire, system consists of three 'hot' conductors which are called line conductors, sourced from a delta (or 'mesh') connected alternator or transformer. For this type of system, the phases are connected between lines. Line voltages exist between line conductors, and these are numerically equal to the phase voltages.
Who proved ohms law to be true?
Its not so much the proof of the law, as it is the acceptance of the terminology created by the law.
Ohm's law states that the current through a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of that conductor. In mathematical terms this is ...
I = V/R
... where I is current in amperes, V is voltage in volts, and R is resistance in ohms.
This is not Georg Ohm's original equation, but rather a modern interpretation of the wording of the law.
The impact of Ohm's law is in the definition of the ohm. Rewrite the above equation as R = V/I, and you see immediately that the ohm is simply volts per ampere. Take it deeper, realizing that the volt is joules per coulomb and that the ampere is coulombs per second, and you discover that the ohm is joules-seconds per coulomb squared. How would you like to use that term, instead of the elegantly more simple term ohm?
In summary, then, ohm's law sets the relationship between what we call the volt, the ampere, and the ohm.
Can you calculate power by multiplying voltage and current?
Not enough information. Power = current x voltage. Since voltage can be anything, there is no way to calculate power. Time is irrelevant; though once you have the power, it can help you calculate energy (energy = power x time).
How do you calculate the number of turns that are required for the coils of three phase AC motor?
There is software that can be downloaded to help calculate the number of turns for a three phase motor. There are also diagrams which can be found for the most frequently used calculations.
What amp do you need for 230 volt?
Watts is a unit power and it is found muliplying Volts x Amperes, so how many amps to 230 watts depends on the voltage. If it is line voltage 120 V then 230 divided by 120 the result is a little less than 2 Amps RomeoTango
What will happen to the resistance if the length of the conductor increase?
ERMM THE RESISTANCE INCREASES ) when longer
What is the advantage of leaving some slack when installing electrical cables?
Number of reasons:
* Provides room for expansion when the building heats up. * Allows slack to move wires when remodeling. * Allows slack to reconnect wires when redoing terminations.
What is windage loss in a dc machine?
Friction losses due to air
CommentIt's worth pointing out that the windage is pronounced 'wind-age' (i.e. 'wind' as in breeze, not 'wind' as in coil!), and not 'winde-age'.
How does voltage drop effect the amps?
Yes. When the voltage drops and the power requirement (watts) stays the same, the amperage goes up.
Why are electric meters connected in series with the rest of the circuits in the house?
Electric meters are connected in series with the rest of the circuits in the house because, that way, the meter can measure the current used by all of the circuits in the house. The meter integrates and records the current as power in kilowatt-hours.
Another Answer
Actually, energy meters are not simply 'connected in series' with the rest of the circuits in a house.
In simple terms, an analogue energy meters contain twocoils: a current coil and a voltage coil. The current coil is, indeed, connected in series with the rest of the household circuits, but the voltage coil is connected in parallelbetween the line and neutral conductors. This means that the energy meter is monitoring the (in-phase) load current and the supply voltage, and the torque produced by the resulting magnetic fields is proportional to the power of the load.
Power is a measure of the rate of energy consumption and, so, to determine the energy consumed by the load, the meter's combined magnetic fields drive a disc which, as it rotates, drives dials that record the amount of energy consumed over a given period (between meter readings). Energy (notpower!) is expressed in kilowatt hours (kWh).
Does a starting winding has more or less turns than a running winding?
Starting winding has more resistance and less induction than main winding, this means has smaller diameter and less turns.
How do transformers reduce electrical voltage?
This type of transformer is called a Step-Down transformer.
All transformers have an input to output ratio. The transformers that increase voltage are called Step-up, and the transformers that protect against surges are called unity gain. The Unity gain transformer has a 1:1 ratio and provide a mechanical way to isolate a source of voltage from a load.
