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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
What is resistance on something that is shorted?
It depends on weather it is in a parallel or series circuit. In parallel the entire circuit it is in parallel with is shorted out. In series the total resistance decreases by the amount of the resistor that shorted out. Resistors usually open or change value with use.
If you mean 220 single phase as in two hots and a neutral 110V-0-110V (in the US this would be 240V 120V-0-120V), then the answer is most 3-phase meters cannot be used. A few meters can be setup for either configuration, check the manual for the specific one you want to use. If you mean 220V single phase with just one hot wire and a neutral, then a larger percentage of 3-phase meters can be used, and will meter accurately. But again, the meter has have this as one of the setup choices. Check the manual. One possibility would be if you have a meter that can be setup to use 3 CT's and tell it that it is hooked to a wye system with neutral. If it sees current on just one phase to neutral, this is a valid condition, since the system could be feeding unbalanced loads (remember the meter thinks this is a 3-phase system). This would only work if the meters wiring diagram calls for CT's on all 3 phases. Many meters call for only two CT's, calculating the 3rd leg by using the two known values. This type of setup would not meter accurately for your single phase, I believe. And this will not work on a 110V-0-110V system, because a 3-phase meter expects 120 degrees between phases, not 180. Oh, I didn't mention the case where you might have two hots and no neutral. The 3-phase meter would have to be set up for a delta connection as far as the meter was concerned, since there is no neutral. It could work, not sure on this one.
How to change the speed of a three phase motor?
A typical 2 speed three phase motor will have 6 leads on the motor windings which will require 3 contactors to incorperate both the "high" and the "low" speeps.
Inorder for the motor to run on "low" speed you need to have a contactor (c1) that pulls in for the L1, L2,L3 leads... that should achieve the "low" speed of the motor..
To achieve the "high" speed you will need a contactor (c2) to shun or short L1,L2,L3 together... and another contactor (c3) to pull in the L4,L5,L6 leads...
to recap ... Low speed will requrie c1= L1,L2,L3 powered by phase 1, phase 2, phase 3 of the primary source voltage.
High speed requires c2 to short or shun L1,L2,L3 together while c3= L4,L5,L6 to be powered by Phase 1, Phase 2, Phase 3 fo the primary source voltages.
Be sure to check for proper rotation of the motor and by reversing any 2 leads of the primary source voltage you will change the rotation for the motor.
This can also be done using two contactors by having L1,L2,L3 connected to the first contactor and also the additional contacts mounted on top of the second contactor.
L4,L5,L6 are connected to the second contactor. The important thing to remember is to use an interlock which fits into both contactors when they are clipped together. This stops both contactors operating at the same time!!! ( the additional contacts mount on top of a contactor and are mechanically connected to it so that they act together)
If the voltage in a resistive is double the power will be?
In a resistive load circuit, the power = multiplication of voltage and Current. By increasing the voltage power will not be increased. Power is defined by the load as per its design. If the voltage is higher the load current will reduce. However running a load at double the rated voltage is not good for the device. Insulation may fail.
Why capacitors are almost always connected in parallel and not in series?
to provide a discharge path for voltages.
== d. large ground faults. This is kinda tricky, but let's give it a shot. Do fuses protect against a short circuit? Yep. A short circuit creates a low resistance path in the electrical route(s) inside the unit. Lower (like almost zero in a short) resistance means more current and the fuse opens. How about overloading? An overload is, in general, a drawing of more current than is "normal" and that will burn the fuse open, regardless of the cause. Yes, the fuse provides protection. In a lightning surge, high voltage appears on the power buss and "punches through" to anywhere it feels like going. The voltage transient will easily knock the fuse open. Additional damage could result because appliances are not designed to withstand thousands of volts on the input, but the fuse has opened and made things safe. Let's look at the last one, the large ground fault. Here's a quickie review. A ground wire "grounds" an appliance to earth ground. That leaves the hot and neutral wires to provide power to an appliance in a standard 115 volt AC application. (The hot side is fused, by the way.) In an AC circuit, the current changes direction, but let's skip past that and look at the hot and neutral. Let's say the hot is the "supply side" and the neutral is the "return" and run with that. Here's another point of fact. Inside the power panel the neutral and ground have a common connection. They're at the same potential. For an appliance, power would normally "come in" on the hot side and "go out" on the neutral side, but if there is something wrong with the neutral wire, the power could "go out" on the ground leg instead of the neutral. This idea is at the heart of ground fault interruption (gfi). A 3-wire circuit (hot, neutral and ground) could operate normally if the neutral is open and there is no gfi. That means the kitchen microwave could work with a broken neutral (if there was no gfi protection). A fuse would not "protect" against the ground leg carrying the current the neutral leg would normally carry. The appliance could operate normally without anyone being the wiser. (Apologies for the long winded explanation.)
Answer
Fuses are overcurrent protection devices and, therefore, protect circuits against overload currents and short circuits (including ground faults, as they are classified as short circuits to ground). They do not, however, protect against overvoltages due to lightning strikes, etc. Whilst it is true that an overvoltage most certainly will 'punch through' insulation resistance, by the time the fuse has operated due to any resulting overcurrent, the damage has already been done (to the insulation)!
So the answer to your question is (c) lightning surges.
Why the generators are always excited using dc voltage and not ac?
Mainly there are three points,
1. If you give AC to the field coil, there is no need of rotating it, as AC itself produces alternating flux.Thus generator will give Transformer action which actually transfer the power not actually it generates or produce as per the basic law of mutual Induction.
2.In case if you rotate the field giving AC Supply by a prime mover , actually constant poles(as in physical magnet) will not be produced.For every cycle of rotation,there will be continuous change in the poles in respect to three windings of Armature.So as it results irregular waveforms of voltages,we cant tap the pure sinusoidal 3 phase supply from armature.Most probably it will get distorts & might be chances of burning of Stator(armature)coil in Alternator.
3.So to overcome come from all above disadvantages, DC excitation will be given so that constant field strength will be maintained as in case if we employ permanent magnets which produces constant flux
ratio of secondry voltage to primary voltage is called voltage transformation ratio
What is the difference between a synchronous motor and a generator?
A DC generator is Direct Current most common in industrial environments.
Limited to DC equipment such as motors, cranes, certain types of lighting etc.
A AC generator is Alternating Current can be used in virtually every environment.
These are used for virtually everything from residential dwellings to large steel manufacturing facilities.
Which steel is expensive hot rolled or cold rolled?
It takes much more energy to roll a sheet of metal in cold rolling than it does for hot rolling. Heating up a sheet of metal makes the material more malleable, so when it is rolled between two rollers, it can form into a flat sheet much easier. A cold sheet of metal that is not heated up will be put through the rollers and have a higher amount of energy needed to push it through. Though there is less heating required, this is balanced out by the fact that it must be pushed through with more energy.The cold rolling process is an expensive one, especially compared to the process of hot rolling sheet metal. For example, since cold rolling requires that workers frequently clean parts like the rollers, cold rolling has extra costs for any supplies needed to clean the parts, downtime while the parts are being cleaned and labor costs for the worker who does the cleaning. Also, the additional energy needed in the cold rolling process adds cost to the final product.
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In a circuit the voltage across all resistores is the same?
It depends upon the connection of the resistors, if the resistors are connected in parallel then the voltage is same where as in case of resistors connected in series the voltage is different across different resistors.
What is the difference between an definite purpose contactor and a lighting sontactor?
A definite purpose contactor is designed (and rated) for a specific load. So a lighting contactor is one example of a definite purpose contactor. A motor starter contactor is another example. So, a lighting contactor is a definite purpose contactor, but a definite purpose contactor is not necessarily a lighting contactor (it might be a motor starter, for instance).
Why is the rotor disc of energy meter made thin?
Aluminium is a good conductor but it is non magnetic material and therefore cannot be altered by magnetic currents and run true and hence it is preferred.
How many amps does a 2 hp 210 volt single phase motor draw?
Then you are trying to get more HP out of the motor that it can supply. Back off on the load that the motor is driving or put a bigger motor onto the load.
How many windings in single phase motor?
A three phase motor needs 4 connections made to it from the power supply: Phase A, Phase B, Phase C, and Ground. However, many times the motor has 12 labeled leads inside the connection compartment. Refer to the motor's nameplate to connect the right wires to each other, before connecting them to the power supply. Many times the connections will be made differently for different source voltages.
If you do not understand the work well enough to accomplish it yourself properly and safely, don't try it. Consult a professional electrician, as they are proficient enough to do it properly and safely.When working on electrical circuits and equipment, make sure to de-energize the circuit you will be working on. Then test the circuit with a definitive means to make sure it is off (multimeter with metal tipped leads, voltage tester with metal tipped leads, etc., not a non-contact tester, which is non-definitive.)
What component is used to change alternating current to direct current?
Youd need at least a rectifier and to flatten the ripples you need a capacitor.
Can electrical tester be used for testing both dc and ac?
AC, when you're going to test a product which cannot tolerated the power source in your home. ex. in testing a 15A bulb, you cannot test it directy to the wall plug in your home instead you use AC tester(alternate current) to convert the supply to its limit or else it will fry your bulb. DC(direct current), when you're testing a high voltage product and it can tolerated the power source from your wall plug.
What is the difference between potential difference and current?
think of potential as pressure and current as flow. you can have pressure in a water hose with out flow. open the valve and current happens.
The difference in potential divided by the impedance is equal the current.
If the two resistors are in series, then the larger one is 2 ohms.
(The smaller one is 1 ohm. Their combined series total is 3 ohms. 9/3 = 3 amps.)
If the two resistors are in parallel, then the larger one is 9 ohms.
(The smaller one is 4.5 ohms. The combined parallel total is 3 ohms. 9/3 = 3 amps.)
What conservation laws governs kirchhoff's loop rule?
Kirchoff's first rule is a demonstration of law of conservation of charge and his
second rule is a demonstration of law of conservation of energy.
What is the gradient on a load voltage graph?
The gradient on a load voltage graph represents the rate of change of voltage with respect to load current. It is indicative of the internal resistance of a power source; a steeper gradient suggests a higher internal resistance. In practical terms, it helps to assess how voltage drops as load increases, reflecting the efficiency and performance of the power supply under varying loads.
What would happen if a fuse wasnt in a circuit?
Any overload might result in a fire since there isn't a standard method of limiting current without the circuit breakers.
Circuit breakers cannot and do not protect a person from being electrocuted (a ground fault interrupter GFI breaker can, but that is a different device that is only required on outlets near water like sinks and showers). The ONLY reason they are there is to prevent a short circuit from causing the wiring to melt and catch the house on fire!!! They are thus a requirement of both the electrical code and the fire code. What is likely to happen is if that circuit was connected by a licensed electrician he would lose his license and probably be criminally prosecuted and you could also sue him for damages in civil court. If not installed by a licensed electrician when (not if) your house eventuallyburned down and the fire investigation was done, your insurance would refuse to pay any claims for fire damage as the building failed to meet code and that failure was the direct cause of the fire.
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The electrical code calls for an over current device every time there is a conductor size change. On a 100 amp service, the conductor size is a #3, with an insulation factor of 90 degrees C it is rated for 115 amps. This is the same ampacity rating of the distribution panel. You can see that by installing a household circuit with a #14 conductor which is only rated at 15 amps, the only overload protection for that wire will be the 100 amp main breaker ahead of it. Drawing 100 amps on a #14 wire will heat the wire up to a point where the insulation will melt off the wire. If the wire grounds out sparks will fly and this action could ignite surrounding combustible material. To answer the question, if you are not standing physically close to the panel nothing will happen to you but you might not have a house left to live in.
How do you change rotation on a Century AC motor?
There are two alternate methods depending on whether the motor is single phase or three phase. On a single phase motor, reverse either the start winding coil lead or the run winding coil lead but not both. This action will reverse the motor's rotation. On a three phase motor, interchanging any two of the three coil leads will reverse the motor's rotation.
