Electrical Engineering

Different material welds differently depending on polarity. There are also different types of welding rods, so polarity must be tested.

Input offset voltage is the equivalent voltage at the input of an operational amplifier. If an amplifier has a voltage gain of ten and an input offset voltage of 10 microvolts, a level of 100 microvolts will appear at the output with no input. Manufacturers try to design an op amp so the input offset voltage is as small as possible to minimize this error voltage at the output of the amplifier, especially for applications where small voltages are being amplified.

No. A megger's output voltage is not high enough to test the insulation of a high-voltage transformer if, by 'high-voltage transformer ', you mean a distribution transformer or power transformer. Instead, a high-voltage test set or 'pressure tester' (e.g. a 'HiPot' tester) must be used, as these produce far higher voltages.

two contecter

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There are three contactors used in a Star Delta configuration.

It is called electromagnetic energy! But the range of frequencies goes from the lowest which are long wave radio waves, up to the shortest which are gamma rays. On the way it includes infra-red, visible, ultra-violet, microwaves, and X-rays.

A twisted cable is two conductors of a single circuit that are twisted together. They are twisted together to cancel out electromagnetic interference.

Series. An ammeter is used to measure current, and is connected in series!

There are also clamp on ammeters that use a small current transformer that is placed around a wire in the current loop in question. A small amount of current will be induced on this wire which can be read by the meter. This is not exactly in series or in parallel, but it "steals" some power from the circuit to induce in the meter, and at the same time keeps the circuit intact.

You can't. You need to find the information about current -- a homework question normally gives you a hint.

Cooling will impact load losses (Since the resistance of copper will increase as it's temperature increases); Core losses are a characteristic of the transformer, so there is nothing you can do about them after it has been made. Insuring you aren't overexciting the transformer (overvoltaging) may help if you periodically have high voltages.

Overloads for motors are sized from the full load amperage that is taken from the motors nameplate. Depending on who the manufacturer of the motor contactor is will govern the sizing of the relay. Some contactors use bolt in heaters and others use a separate unit that connects to the contactor. No matter what method is used make sure to use the manufactures recommended overloads that are based in the motors FLA.

BHP = Flow(GPM) X TDH(FT) x SG /3960xEFFICIENCY(%)Example: BHP = (100 GPM) x (95 Ft) x (1.0) / 3960 x .6BHP = 4.0

Inductance is the field created when sending a charge through a coil of wire. It's used for shunts in systems to prevent damage from shorts. So I guess if you could neutralize the charge between two coils with large capacitors ,bouncing the current back and forth like a doubler, it may be possible.

becoz of high starting torqe to move train

To measure resistance, you could use an ohmmeter. But ohmmeters are not particularly accurate, so other methods are preferable. These include the use of Wheatstone's Bridge (which compares the unknown resistance with known values) or a Ducter (for very low resistances).

...It is due to the fact that at higher temperatures, the energy in the semiconductor is greater than Eg by a considerable amount, meaning that the conduction band is more full. At these high temperatures, the dopants' role on electron-hole pairs is negligible.

The current varies but a rule of thumb is to allow 7 amps per horse power on 240 v, that means 7.64 amps on 220v, which 1.68 kVA.

1 horse-power is 746 watts, and with a conversion efficiency of 0.85 the power drawn is 880 watts on full load.

The main source of direct current is the conversion of alternating current. Typically, AC is a sinusoidal waveform. Using what is called a full-wave rectifier, one can make all of the negative halves of the waveform positive. This means the waveform will have a series of humps in the positive region. This, however, is not usable DC yet; one must use a filter, or a series of filters, to smooth out the waveform until it is roughly linear and constant. The resultant signal is direct current. This is roughly what is contained within power adapters that you plug into your electronics from the AC wall outlet; they convert the AC signals to DC so the electronics can use the electricity.

There are many reasons for doing it this way. Mainly, though, AC power is easier to produce and more efficient to transmit over long distance. DC, however, is often more usable, so the AC is converted after transmission.

Another example of a DC source are solar panels, or photovoltaic cells, which produce electricity when hit by light.

Not usually, but it may depend on the context. For instance, surge current might be used for a generator that is going to start a motor. Motors draw high current as they start, then the current drops to a normal level, called RLA, or running load amps. Generators have a watt rating for continuous operation called running watts, but they also have a 'surge' rating. You might see a generator listed as a '6000/5200 watt. The 6000 watts is the 'surge' rating. This means the generator can supply 6000 watts for a few seconds, such as might be needed to start a motor, but cannot supply more than 5200 watts continuously. Short circuit current on the other hand simply means how many amps will flow instantaneously if you drop a wrench across the two wires! For a normal utility power service, the short circuit current, also called fault current, can be several tens of thousands of amps, even though the main breaker is only a couple hundred amps.

It is the one type of coil in the electrical motor starters. It is used to release the switch, i.e. turns off the motor, when heavy load is connected to the motor. It is used for the protection purpose.

The formula you are looking for is, R = Volts (squared)/Watts.

There are two kinds of transformers, autotransformers and isolation transformers. An autotransformer has one coil, an isolation transformer has at least two. To find the output voltage of a transformer, you need to know three things. First is the input voltage. Next are the number of turns on the primary coil, and last is the number of turns on the secondary coil. So! Our input voltage is going to be 120 in all three of the cases I'll give, and the number of turns on the primary coil will be 120--this makes the math easy, although you aren't restricted to putting 120 turns of wire in a 120v primary. You can put a million turns on if you want, and I've seen it. If our secondary has 12 turns, the output voltage will be 12--there is a 10:1 primary:secondary ratio. Normally this is called a "stepdown" transformer. It's used when the device requires less than line voltage to operate. A secondary with 120 turns will give a 120v output voltage. This is an "isolation" transformer. You use this as a safety device. Secondaries with 2500 turns give a 2500v output voltage--perfect for radio frequency amplifying tubes like the 4CX250A. For extra entertainment let's talk about the autotransformer for a minute. As I said above, this has one coil. It's tapped. If you've got 220v coming into a 220-turn coil and there's a tap at 110 turns, you're getting 110v out of it. Every soldier stationed in a country that uses 220v power buys one of these from the local post exchange so he can use the TV set he brought from home.