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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
Which is the result of using a more powerful motor to run an elevator?
The same amount of work is done in less time.
kV is kilovolts, kW is kilowatts, kVA is kilovolt amps and kVAR is kilovolt-amps reactive.
A common formula is kVA-squared = kW-squared + kVAR-squared.
What is the saturation of a permanent magnet generator?
The term, 'saturation', applies to all ferromagnetic materials including the magnetic circuits used in machines. Saturation refers to a situation where a material's magnetic field has achieved its maximum intensity.
If a length of insulated wire is wound around a ferromagnetic material, and a current passed through it, that material will become magnetised. In the case of 'soft' materials, such as iron, this is only temporary and will disappear (almost) when the current is switched off. But with 'hard' materials, such as steel, the magnetism will be retained. In this sense, the terms 'soft' and 'hard' refer to the magnetic properties of the material, and not the literal sense!
So, when current is passed through the wire, we end up with what is called a magnetic field strength (symbol: H), defined in terms of the magnetomotive force (current times the number of turns) per unit length (in metres) for the magnetic circuit, and expressed in amperes per metre (usually spoken as 'ampere-turns per metre'). If the current is increased, then the intensity of the resulting magnetic field, i.e. its magnetic flux density (symbol: B) will also increase. But it will not increase indefinitely, rather it will reach a point called 'saturation' at which point any further increase in magnetic field strength will result in absolutely no further increase in the flux density of the field. This is the point at which saturationhas been reached.
If you think of a ferromagnetic material being made up of billions of molecules which behave like tiny, individual magnets (we call these 'domains'), in the unmagnetised state these are chaotically orientated and, so, the material is unmagnetised. When magnetised, these domains align in a north-south direction and, once aligned, the material has reached its maximum flux density and we say that it is 'saturated'.
#6 copper wire has a resistance of 0.3951 ohms per 1000 ft (from wire tables). A 750 ft circuit contains 1500 ft of wire so the resistance is 0.5926 ohms. With 65 amps flowing the voltage drop is 38.5 volts.
The power lost in the cable is 2½ kW.
Why is not feasible to operate bulbs a low voltages although it amount to high efficiency?
Lamps (not 'bulbs' ; we plant bulbs!) will only produce their rated power at their rated voltage. These values are printed on the glass envelope. Reducing the voltage applied to a lamp will, therefore, reduce the power it produces. In fact, there's not a simple, linear, relationship between a lamp's voltage and its power, and this means that even small reductions in voltage will result in large reductions in power.
Operating lamps, or any devices, come to than, at lower voltages really has nothing to do with efficiency. Certainly, operating a lamp below its rated voltage will most-certainly NOT result in high efficiency. Efficiency is defined as the ratio of output power to input power and has nothing to do with voltage.
What is the difference between dynamic load and impact load?
a dynamic load is one that varies with time, sucha sproduced in road trandsportation. It could be amplified at resonance. An impact load is a dynamic load opf short duration, such as dropping a rock onto a surface, resulting in possible high acceleration depending on the stiffness.
Why the speed regulation does not apply to series motor?
Series motors have poor speed regulation because a reduced load causes the speed to rise, which causes the current to drop, which causes the speed to rise more because there is less field.
Series motors are usually used to drive massive loads such as trams, where their high starting torque is a big advantage, and the speed cannot go out of control.
Half a volt, because the energy is the charge times the potential difference.
Another AnswerYou should be asking what the 'potential difference' is between the two terminals, not the 'potential'. Note that 'voltage' is another term for potential difference.
What are the problems associated with the Y-Y three phase transformer connection?
Your third leg is called the high leg and can exceed 180 or more volts. In a 3 phase panel you will loose a third of your circuits unless they are used for motors or other equipment that uses three phase evenly through its function {meaning it doesn't use one leg exclusively for controls or 110V functions. It get a bit involved explaining the windings of a transformer and center taps but suffice it to say one leg gets more than it's share of windings in the transformer. It was used in the early years of industry when single phase 240V systems were the only game in town and they wanted to get more power from the Wye set up prior to delta. It never was popular but a necessity for industry and grew only because of slow development incorporating the 208V delta 3 phase system.
If when a relay is energized you measure 0.05 VAC across a set of normally open contacts the?
If, when a relay is energized, you measure 0.05 VAC across a set of normally open contacts, the
What are the two reasons for arcing at the commutator?
A shorted coil or shorted coils in the rotor will cause arcing at the commutator. It should also be noted that if the brushes are damaged badly enough where they make contact with the commutator, this can cause arcing. Oh, and let's not forget that a stuck brush or brush spring will prevent a brush from making proper contact with the commutator. Arcing can result from that, too.
What is the differences between a step-down transformer and a step-up transformer?
the main function of transformer is to change the magnitude of Voltage. difference between step up and step down is step up will change the input voltage into a larger magnitude of output while step down is vice versa
Same frequency as that of primary coil
What is the similarity between an AC induction motor and an AC synchronous motor?
Only Stator winding is similar in both the cases.
If rating is correct, terminal connections are correct, if safety devices are in place, if device is a standard with necessary requrement, it should not be problem to connect a transformer first time.
What is the purpose of the Merit Systems Protection Board (Whistleblower Protection and the OSC?
What is the purpose of the Merit Systems Protection Board
Portable appliance testing (PAT) is basically a method of testing (using a device and by sight) that any electrical equipment, cables, devices, machinery is safe to use.
Why do we use CT in a relay circuit?
CT is used in the relay circuits for protection purposes. As the current and voltage ratings in a power system are very high, it is not possible to measure currents and voltages of that magnitude as they are way too large for any meter of reasonable size and cost. The CT’s are generally standardized at 1 or 5 amperes secondary current. These are very moderate ratings, thus a 5 A ammeter can be used to measure 1000 amperes with the help of a 1000/5 A ratio CT. For this reason the relay circuits are connected with instrument transformers because the relay senses the input quantity before sending the trip signal to the circuit breaker, and these input quantities are measured by the use of instrument transformers.
