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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
dc motor- a basic dc motor has a stator and a rotor..
stator may consist of either permanent magnet or electromagnet. this s to produce the required magnetic field.
rotor consists of the armature conductors which carry current. when supply is given to the rotor it experiences a force and hence it rotates.
Compare and contrast a circuit breaker and a fuse?
A circuit breaker is something you can reset. When the switch "trips", the position of the switch goes to the middle. To reset it, move to Off, then On.
When a fuse blows, its two external contacts are no longer connected by the internal piece of fuse wire and an electrical current can no longer flow.
More technical details about fuses
In all types of disposable fuse, two contacts which are on the body of the fuse are connected to a piece of fuse wire inside. The material used to make the fuse wire, and its thickness, designed to melt - and thus break the circuit - if the current flowing through it exceeds a certain amperage, which is known as the fuse's "maximum rated current".
There are many different types of disposable fuse: some are screwed into what looks like a light bulb socket.
Other types are small tubes - made of glass or ceramic - with a metal contact at each end. They are held in a fuse holder that has contacts, clips or springs which make contact with each of the fuse's end contacts.
Some commonly used automotive fuses are made of plastic and have two flat metal "pins" which plug into a pair of contacts in the fuse box.
Difference between back EMF and induced EMF?
An induced electromotive force (emf) is an induced voltage. Voltage (emf) causes current flow, and this induced voltage will cause a current that is called the induced current.
We might also add that the induced current will cause a magnetic field to expand about the current path, and this field will "sweep" the conductor. The sweeping of the conductor by that expanding magnetic field will set up an emf that will oppose the emf that was creating it.
CommentTechnically, there is no such thing as an 'induced current'. It is voltage that is induced. Any current flows as a result of that induced voltage being applied to a load. But that current is certainly NOT induced!
How reactive power contributes to additional losses?
Reactive power is well known as that component which is shunted back and forth from the source to the load over the AC cycle. However, this does not mean the system has no reactive power losses. In fact they would be quite high. Loss is always measured with respect to load and not the source. When we term it reactive power loss, it is not the amount of power taken away from the source and not returned. That way, there would absolutely be no reactive loss at all because all the energy stored in the reactive elements are anyway returned. The idea is after all to provide the power to the load. So, the loss represents the amount of power unable to reach the load. The power lines are not purely resistive. They comprise considerable level of reactive elements especially line inductance.
Now, the active power which actually runs the load is never a separate entity. It co-exists with reactive power because the reactive (more so inductive) components of the load need to be energized in order to power the load. Reactive power loss is thus that amount of power which is deficient or 'not supplied' to the storage (reactive) elements of the load because of the reactive elements on the line. Thus the loss is always to be visualized in terms of load. That is why the complete return of reactive power to the source in the negative cycle has got nothing to do with loss understanding actually.
Hope this helps!
Why -48 Volts used in telecom equipments?
(i) Positive voltages cause comparatively more corrosion in metal than negative voltages. (ii) Negative voltages are safer for human body while doing Telecom activities. (iii) Lightning may cause positive voltages in the equipment circuitry. In that case, negative voltages (lack of electrons) neutralize positive charges and prevent excessive heat. (iv) Negative voltage is safer for long telephone line for transmitting power trough it. The reson for electing -48V in reference to ground is to avoid the nasty galvanic effects in telephone cabling. +48V would have nastier effect on wet cabling.
Does graphite conduct electricity?
It in-fact does conduct electricity, molten graphite is a key element in which terrorists use for I.E.D'S it causes a large heat blast when heated with electricity and mixed with different compounds.
What is the cable size for 55kw motor on 3 phase?
Without knowing the nominal voltage rating, who can tell?
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The sizing of cables or conductors is based on the amperage that the conductor can safely carry. The formula for amperage is I = W/E. Amps = 12000/Volts. With out a voltage stated an answer to this question can not be answered. When you calculate the amperage, re-ask your question for a conductor size for a given amperage.
Its a servo.
Why you use constant current source?
What follows below is not a full description. Full descriptions are in chapters of books about electronic power supplies.
A constant current source is an electronic device which acts as a source of power whereby, however the load resistance changes - within a certain fixed range - the device is designed to monitor the output current drawn from it and will change its output voltage to keep the output current constant within a certain fixed range.
Another answer
A constant current source will provide constant current with a load if the load changes the volts will change to compensate for the constant current flowing. Which is just opposite to a constant voltage source whereby a load change will change the current but not the voltage. And that how it works.
How does a two-phase system differ from a three phase system?
A two-phase system is archaic and you are unlikely to find it in use anywhere these days, so it is mainly of historical interest. A two-phase, three-wire system, consists of two phase voltages, displaced from each other by 90 electrical degrees, and a phase voltage which is 1.414 x phase voltage.
A three-phase system consists of three phase voltages which are displaced from each other by 120 electrical degrees. In the case of a three-phase, three-wire, system, the line voltages are numerically equal to the phase voltages; in the case of a three-phase, four-wire, system, the line voltages are 1.732 x phase voltage.
-- The current in each individual resistor is
(voltage across the whole circuit) divided by (the resistance of the individual resistor).
-- The current in any individual resistor is less than the total current in the circuit.
-- The total current in the circuit is the sum of the currents through each individual resistor.
Why does star connected motor run at less amps?
In star, a motor is connected with 415V across 2 phases, which means Line voltage is 240V (415 / 1.7ish) In delta theres 415 across each phase, therefore I = much higher according to Ohms law (I = V/R) Hypothetically; load of 24ohms connected on the motor In star; I = 240 / 24 = 10A In delta I = 415 / 24 = 17.2A Hope this helps a little
What do you call a moving walkway that goes up or down hill but does not have steps?
Another word for a moving staircase is 'escalator'?
In the unknown of measuring the voltage what should be the setting of VOM selector?
Use the highest available voltage setting. One should know the system voltage before attempting to measure, other wise it may lead to accidents.
What happens when an ammeter is connected in parallel?
It would be equivalent to adding a high value resistor (>10M ohms) in series in the circuit. Voltmeters typically present a high internal impedance so as to not change the current flow in the circuit you are tying to measure.
the circuit wont work the voltmeter only takes a voltage reading power does not actually pass through the meter
sometimes it can be used to measure very low leakage current using the hi impedance of the meter. EXAMPLE leakage offset from an amplifier. it could be into the nanoamps.
If the resistance in a circuit is doubled while the voltage remains the constant the current is?
It is halved. coz voltage=current * resistance
What is the formula for finding resistance for a parallel series?
There is no such thing as a "parallel series".
The total effective resistance of many resistors in series is the sum of the
individual resistances. It's more than the greatest individual.
The total effective resistance of many resistors in parallel is the reciprocal of the
sum of the individual resistances' reciprocals. It's less than the smallest individual.
What is stronger concrete or cement?
Concrete is stronger than cement.It is composed of aggregates (sand and gravel) and cement; and may be cast with reinforcing bar within it (reinforced concrete). Cement is only a part of concrete. Cement has no tensile strength while concrete has compressive and tensile strength.
Which principle is used in a DC motor?
Current carrying conductor kept in a magnetic field gets deflected. This is the basic principle. In short Lorentz force causes the rotation
What is the heat generated with a 40Watt bulb when its for 2 hours?
Let's assume that this is an incandescent bulb with a light efficiency of 35 percent ... i.e. 35 percent of the electric power it consumes is converted to light, and the other 65 percent becomes heat, which the bulb then dissipates into the room. So the bulb is dissipating heat at the rate of (0.65 x 40) = 26 watts = 26 Joules per second. 2 hours = (2 x 3,600) = 7,200 seconds 26 joules per second x 7,200 seconds = 187,200 Joules of heat
Difference between electrical and mechanical energy?
Light travels exclusively through space or along optical fibres by the mechanism of electromagnetic propagation. Electrical energy can also do that, in which case it is called microwave radiation or radio waves, but it can also be carried on wires.
How do you calculate or choose capacitor bank?
Normal power is the multiplication of current to combination of resistive and reactive or capacitive load. From the vector sum of Apparent power minus real power we can get reactive power(KVAr), which is basically lagging power due to reactive load. This will be the exact rating of capacitor bank. You can find it by cos $ of apparent power.
What is the reason for overheating in transformer?
The main reason that a transformer overheats is too much current for the transformer design. So my guess is that you have more load than the transformer was designed for. So my answer would be not powerful enough.
You are not actually worried about the "power" of the device. You could use a 15 amp power supply on a device that needed a .015 amp load.
What you are REALLY waning to make sure of is that the desired voltage is matched. A 12 volt D.C. supply should only be used with systems that need 12 volts D.C. To use anything else causes issues. Too low of a voltage gives you brown out issues and too high of a voltage could cause you to draw so much current you burn the device up.
Power (P) is the rate of doing work (W), so its fundamental formula is:
P=W/t
That is:
Power = Work divided by time.
Clear explanation: Power is equal to:
How much work is done (in joules) divided by the time (in seconds) it took to do that work.
For example:
Problem: If a construction worker pushes the wheelbarrow, expending 50 J of work in 2s, how much power does he use?
Answer: 50 J divided by 2 s is 25 W so, the power is equal to 25 watts.
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For electrical engineering and electronics, power is calculated as:
P = I2R, or
P= V2/R, or
P= VI
where P is power, I is current, R is resistance, and V is voltage.
The big power formulas are:
Formula 1 - Electrical (electric) power equation:
Power P = I × V = R × I2 = V2 ⁄ R
where power P is in watts, voltage V is in volts and current I is in amperes (DC).
If there is AC, look also at the power factor PF = cos φ and φ = power factor angle (phase angle) between voltage and amperage.
Formula 2 - Mechanical (mechanic) power equation:
Power P = E ⁄ t = W
where power P is in watts, energy E is in joules, and time t is in seconds. 1 W = 1 J/s
There is much potential for confusion between the value for Work (measured in joules but often written in formulas as W) and Power (measured in watts and often written in formulas as W). However, symbols for quantities (work) are italicised, W,whereas symbols for units are upright.
In these formulas, W always refers to watts, although units should never be written in equations.
Scroll down to related links and look at "Calculation: electrical voltage, current, resistance, and power". Look at the written italic letters and normal letters. The SI unit of "work or energy" is the same. One joule is the amount of work done when an applied force of 1 newton moves through a distance of 1 metre in the direction of the force. That is energy.
