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Electrical Engineering

~33500 answered questions
Parent Category: Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.

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what is most commonly caused bt current flowing through high resistance due to faulty wiring igniting insulation and other materials
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Copper is more usual for wires because it is the best conductor, except silver which is slightly better. Aluminium can also be used.  It does not conduct so well but it is a much lighter metal so it is popular for overhead power lines which use stranded cables with aluminium strands on the…
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loss of free current carriers as temperature drops.
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if the total resistance r_total and the resistance of the parallel elements is r_1, r_2 etcThen the total resistance is 1/r_total = 1/r_1 + 1/r_2 ....If the parallel elements have capacitance or inductance, the resistances above can be replaced by impedances z_1, z_2 ....
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we can measure the resistance if we know the voltage and current passing through a line (V=IR)AnswerYou can measure its approximate resistance using an ohmmeter, but ohmmeters aren't particularly accurate.  A better way would be to use a Wheatstone Bridge, which is highly accurate.
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All high-voltage distribution systems are three-phase.  Single-phase 'spurs' off the main line, supplying, for example, farm houses, are simply two lines of a three-phase system.
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A squirrel-cage rotor consists of uninsulated copper or alumnium bars, short-circuited by rings located at opposite ends, and semi-enclosed within a laminated iron rotor, and there is no provision for any form of external connection.  So it would be quite impractical to do what you suggest.
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A two-phase system is an archaic 'polyphase' system, in which two phase voltages are displaced by 90 electrical degrees, enabling the use of self-starting induction motors.  It's unlikely you'll come across a two-phase system these days.
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yes SF6 gas is used in modern ckt. breaker.
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a voltage source with zero internal impedance.
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Yes, it will spin a bit faster on 60 Hertz.
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It really depends on what units you use to measure time:  seconds, minutes, or hours! It also depends on the value of current flowing, which you don't specify.  So your question cannot be answered.
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Ohm's law defines the relationship between current and voltage across a conductor.It states that the voltage across two points on the conductor is proportional to the current flowing through the conductor. Mathemetically :- Voltage / Current = Resistance (constant). or V / I = R. …
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Basically it takes a higher current to start a fluorescent lamp that it does to sustain the arc. (It's higher current, not voltage. The voltage is constant.) The ballast regulates the current flow through the lamp. Removing the voltage from devices requiring power will turn any device off.
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No.  A volt-ohmmeter will not check insulation.  To check cable insulation you need a special device (called a megger) made for the purpose that imposes a high voltage and measures current leaks. 
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In the case of a capacitor-start/run single-phase induction motor, the main field is provided by the main (running) winding, and the capacitive branch is the auxiliary winding.  In the case of a capacitor-start motor, the main winding is the running winding and the auxiliary winding is the star…
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If the lamps are connected in parallel, the higher wattage lamp has the lower resistance and draws the greater current.
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To operate this type of low voltage wrench, a power supply will have to be used. When looking for this type of power supply the output has to be 12 volts DC with a capacity of 15 amps or W = A x V = 180 watts.
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Conductivity is a measure of how easily electrons can flow through a conductor.This is dependent on how much the atoms in the conductor are moving around relative to one another. At low temperatures the atoms in the conductor are arranged in a regular pattern and they hardly move around relativ…
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rectifier. not unique to laptops.
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ac transmits the voltage over long distances. so v use ac in trains
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Various ways. In transformers with ferrous cores current is induced in the cores which is dissipated as heat. Not all of the magnetic energy need be converted back to electrical energy in the secondary.
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In simple terms:  generation, transmission, and distribution.
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Standard residenetila and some smaller industrial type breaker don;t use any oil in them,,,they use a silicon grease as a lubricant and contact protectant.
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Because a fuse is more reliable in the case of an auto mobile but not anywhere with extricable high voltage.
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It floats, thus no physical contact ... except with air.
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Electricity does not flow in an open circut
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A three phase 4-wire supply that is correctly balanced has zero current in the neutral wire, which means that no power is lost in it.  A three-phase 3-wire supply that is unbalanced has unnecessarily high currents in one or more wires, so again power is lost.  
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As an electrician I can give you a vague answer with the information given.  You need more specifics to do the calculations for the load amps and the supply voltage.The particular motor I looked at is a .6hp fan motor - 4.0 Amps @ 230V(2650 x Full load amps ) divided by supply Voltage = MF…
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A battery is charged by having a DC current flow through it.
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Large electricity users like factories have to watch the power factor of the load they place on the supply. For most pieces of equipment the power factor is a lagging one and the problem therefore is to improve the power factor of the whole factory by placing a load on the supply with a leading powe…
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You could not do that with an induction motor because the rotor is made like a squirrel-cage with solid copper bars. Synchronous motors use a rotor with a DC supply current, which enables them to run at the synchronous speed, 3000 or 1500 rpm on a 50 Hz supply, while induction motors necessarily r…
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Many types of capacitor can work with either ac or dc.  An exception is electrolytic capacitors which must be connected to a dc circuit with positive and negative the right way round.  
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In case of parallel circuit the effective resistance is given byReff = R1*R2*R3 /(R1R2 +R2R3 +R3R1)As short circuit takes place then any one R1,R2,R3 becomes zero. Hence Reff becomes zero.
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Just divide 75,000 volt-amps by 240 and you will find the amps.
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It's the current flowing in a wire that causes it to overheat. 
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The half-wave rectifier gives one pulse every cycle, while a full-wave rectifier gives two pulses per cycle.  With two pulses per cycle instead of one, the peak current is less so that the resistance of the transformer is less important and the output from the reservoir capacitor is better regu…
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Two wattmeter method is used in a three phase sysstem to measure the true power without regard to the balance ie. It can be used to measure both balanced loads and unbalanced loads.The three phase power could be measured using single phase wattmeters in each loads of the system. But using three watt…
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The input is a Gate that is essentially infinite impedance, so no current. The output is essentially the resistance between Source and Drain, which controls the current flowing through it.
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Apparent power is the product of voltage and current in an a.c. system, and is expressed in volt amperes.  The rated apparent power of a transformer is the product of  its rated secondary current and rated secondary voltage.
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The metaphor of stepping down is that you are going to a lower level of voltage.  So no, a step down transformer does not increase voltage, it decreases it.
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Yes, 1 k-ohm means 1 kilohm or 1000 ohms.
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You step down 460 3 phase to 240 3 phase using a three phase 460 volt to 240 volt step down transformer.
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Using Fourier Analysis -which is too difficult to explain in this forum.
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Nothing.  Resistivity, expressed in ohm metres, is a constant for any particular conductor although it is affected by temperature.
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Not enough information the voltage is needed also.
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If you want a five-phase supply you need to start with a three-phase supply and a transformer that has 15 symmetrical cores.  But why would one need a five-phase supply . . three is enough.
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Multiply its rated secondary voltage by its rated secondary current. This applies whether the transformer is a step-up or a step-down.
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yes, i think dc transmission is best, coz in dc losses is low, no iductance between conduct, less corona loss.AnswerNeither is 'better'; they each have advantages and disadvantages. For example, although there might be less losses with d.c. transmission, the equipment required to raise and reduce th…
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There is no such a thing as a thermocouple volt meter. A analogue or digital millivolt meter or volt meter is connected across a shunt or parallel with the shunt to measure the current through the resistor. Say the resistor value = 1 Ohm, then by using the Ohm law formula to calculate the current, s…
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For an electrical load, such as a lamp, heater or motor, to operate at its rated power, it must be subject to its rated voltage which always corresponds to the supply voltage.  For this to happen, individual loads must be connected in parallel with the supply and with each other.  So all t…
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If you are referring to a pole-mounted distribution transformer, it's in order to maintain a safe clearance between its high-voltage connections and ground level.
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motor whose speed can be controlled is called a variable-speed motor; dc motors are variable-speed motors. The speed of a dc motor is changed by changing the current in the field or by changing the current in the armature. When the field current is decreased, the field flux is reduced, and the count…
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The question is misstated.  Resistors are measured in ohms, not in centimeters.  Please restate the question.
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The Single and Three phase refer to Alternating Current electrical power supply outlet system and the corresponding equipment requirements. The single phase system is generally used the power requirements are low or moderate as for household applications , while the Three phase supply syst…
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Wire sizing is based on the amperage. The formula you need to find amperage from HP for single phase is, I = HP x 746/E x %eff x pf. For three phase I = HP x 746/1.73 x E x %eff x pf. A standard motor's efficiency between 5 to 100 HP is .84 to .91. A standard motor's power factor between 10 to…
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Could it be.... 20 ohms(?)
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The term, 'bus', is derived from the word, 'omnibus', meaning to 'serve all', and that's exactly what a busbar does.A busbar is a length of conductor which offers a common point of connection for several circuits.  For three-phase systems, one busbar is required for each of the three lines and …
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because dc voltage flows only in one direction and ac voltage oscillates ,and is more efficientAnswerBecause, for d.c., after an initial 'charging current', the voltage across a capacitor is equal and opposite that of the d.c. applied voltage.  This means the net voltage in the circuit is zero …
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An 'instrument transformer' is a category of transformer used to supply measuring instruments or protective relays.  There are two types of instrument transformer:  a 'voltage transformer' (known as 'potential transformer' in North America), and a 'current transformer'.  They are used…
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If you really do mean the number of 'turns', then you cannot really determine this, as it is determined as a part of its design process and can vary considerably from machine to machine.If, on the other hand, you actually mean 'windings' ('coils') then, typically, there are two:  the 'main wind…
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Yes this size motor can be operated by bringing a 600 volt three phase supply to it.
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The term, 'overcurrent', describes either an 'overload current' or a 'short-circuit current'.An 'overload current' is a current that is higher than a circuit's 'rated current'.  For example, if you have too many loads plugged into the same circuit, then the resulting current is an 'overload cur…
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In three-phase systems, we have to measure the current in each of the three line conductors individually.  There is no 'overall' current for a three-phase system.  So if you know the current in each phase, then that's it!  There's nothing else to calculate.
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10 hp is its output power.  To determine its input power, you need to know its efficiency, then use the following equation:efficiency =  (output power)/(input power) You will first have to convert 10 hp into watts.  There are 746 W in one horsepower.
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A reactor is an inductor, so has only one winding.  A transformer, on the other hand, has two windings:  a primary and a secondary.
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There is no SI symbol, as such, for power factor.  As power factor is the cosine of the phase angle (the angle by which the load current leads or lags the supply voltage), power factor is normally written as 'cos' followed by the lower-case Greek letter we pronounce 'phi' (I've no idea how to t…
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cannot determine without other information not given.using a voltage regulator would be the better way to go
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Air-blast circuit breakers are used to disconnect high-voltage transmission or distribution circuits in the event of a fault.  One circuit breaker is required for each of the three line conductors;  there is not normally a neutral conductor in high-voltage three-phase transmission/distribu…
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I don't know if you are trying to ask if you can run a 240V panel off a GFCI or run a 120 V sub panel off of a GFCI. Can you clarify please,,,Thanks
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An 'air-blast' circuit breaker is just one of several designs of high-voltage circuit breaker.   It uses a blast of air to stretch and snap the arc created when the main contacts part.  Air-blast breakers are normally outdoor breakers and, in the UK at least, are used in circuits of 33 kV …
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87 amps three phase means 87 amps on each phase. Additional Answer It's only 87 A per phase for a wye (star) connected load; for a delta connected load, the current per phase will be 50 A, while each line current will be 87 A. That's assuming a balanced load, of course. Line currents pass through th…
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A 7 HP motor running at its maximum mechanical power output would produce 5.21 kilowatt-hours of mechanical energy each hour, and it would consume about 6.1 units of electrical energy per hour assuming an 85% conversion efficiency.
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For the same reason that the majority of all electrical wiring is done with copper wire. It is a good conductor of electricity and the mineral is readily available at a lower cost of production than other conductive materials.
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The ratio of voltage to current is resistance.
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No, it may power the device on, but only for a limited time. You are trying to draw five times more amps out of the power supply than what it was designed to operate at. If left connected to the five amp device smoke will soon appear and the power supply will probably burn open never to work again.
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There is no such thing as a DC 3-phase motor.AnswerOn the contrary, there IS such a thing as a three-phase d.c. motor, and they are widely-used, for example, for driving water pumps (e.g. for swimming pools) supplied from solar panels.  The supply to the (Hall-effect) d.c. motor is via a solid-…
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You cannot use an isolator as a circuit breaker, as they are designed to do two different jobs.  A circuit breaker is a protective device designed to interrupt an overcurrent, which can be substantially larger than a circuit's rated current. An isolator, on the other hand, is designed (as its n…
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You will not be able to use the line voltage to operate the photocell directly as the photo cell is usually rated for 120 volts or in some instances 240 volts. You will need a step down transformer 480 to 120 volts. The starter will also need to have a 120 volt coil. The black and white wire of the …
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reciprocal of the square root of 2, converts from peak voltage to rms voltageAnother AnswerThis figure results when you work out how much work is done by one complete cycle of a.c. current. Since work is proportional to the square of a current, if you  divide one complete cycle of a sine wave c…
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Because with more field, the armature produces the same voltage at less speed.  The voltage generated by the motor must always be less than the supply voltage. A motor that is driven faster than it wants to go becomes a generator.
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No, a three phase motor will not start if one leg of the motor feeder is open. The motor will stay running once the motor looses a leg but not for long if the proper motor protection is provided. The motor protection will sense the line failure and disconnect the motor from the voltage sou…
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You need to know the rated voltage of the generator to determine its rated current.  Divide the number of volt amperes by the rated voltage.
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A transformer is the device used to increase or decrease the voltage of alternating current (AC) This is done through a process referred to as inducing.It's operation is based on the fact that electricity produces a magnetic field around itself. By placing 2 coils of cable beside each other, the mag…
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In an alternating current (AC) circuit, the electric charge periodically reverses direction at a certain frequency.  This is in contrast to a direct current (DC) circuit, in which charge flows in one direction only.  
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For a three-phase, three-wire, system there are three conductors called 'line conductors', and there is a voltage between any pair of line conductors, so there are three voltages.For a three-phase, four-wire, system there are four conductors:  three 'line conductors' and a 'neutral' conductor. …
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A timer can be of two types. An off-delay timer is used when the circuit needs to be energized for a specific amount of time after the off-delay's timers coil becomes de-energized. An example of this is when a cutoff saw becomes de-energized but the conveyor, to move the wood along, needs to be oper…
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Most practical circuits are parallel circuits.  A parallel circuit has two advantages: (1) the voltage appearing across each branch is the same as the supply voltage and, (2) on one branch becomes disconnected, then the other branches continue to work.  The reason that (1) is important is …
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No, three phase motor overloads just monitor the motor's lines for an overload. Once detected the circuit holding the magnetic starter in will drop out and take the motor off line.
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It's not 'necessary';  rather, it's a consequence of three-phase a.c. generation.  When three potentials rise, in sequence, then the order in which they rise is the 'phase sequence' of those potentials.
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Theoretically, yes.  But, in practise, probably not! The main thing to understand about a current transformer is that its primary winding is always connected in series with a circuit's load, rather than in parallel with its supply and, so, must be capable of handling the circuit's load current …
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Generally lower earth resistance is preferable but for certain applications following earth resistance are satisfactory Large Power Station s– 0.5 Ohm Major Power Stations - 1.0 Ohm Small Substation – 2.0 Ohm In all Other Cases – 8.0 Ohm
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A delta connected appliance can be connected to a 3-phase system by leaving the neutral unconnected.  The appliance must be properly earthed.  
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No-one created circuit symbols;  they evolved over time. And, in fact, different countries use different standards for their symbols so US standard symbols, for example, are different from European standards.
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As well as providing a cooling medium, transformer oil is also used to insulate a transformer.  As its dielectric strength (how well it insulates) is much higher than air, it means that components within a transformer that are at different potentials can be placed much closer together if they a…
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All induction motors require a rotating magnetic field in order to drive their rotors. Unlike a three-phase motor, a single-phase induction motor does not have a naturally-rotating magnetic field set up in the air gap between the stator and rotor and, so, this rotating magnetic field must be artific…
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That's true. This is because when there are several resistors in parallel, the electrons have additional paths to choose from - it becomes "easier" for them to get through. This is what the resistance expresses. You can also play around with the formula for parallel resistance:1 / R(total) = 1 / R1 …
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