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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
Why is graphite used to make electrical contacts in motors and generators?
Copper brushes provided poor commutation as they moved from one commutator segment to the next. The cure was the introduction of 'high resistance brushes' made from graphite (sometimes with added copper). This 'high resistance' provided a gradual shift of current from one commutator segment to the next.
Partially referenced via Wikipedia
How do you assumed power factor?
Power Factor is a maximum of one when the voltage and current in an AC waveform are in phase. Since power in watts is equal to voltage x current x power factor, you get maximum wattage with power factor = 1. This occurs with a pure resistive load. When you power an inductive load like a motor the power factor decreases and so does the delivered power. That is why motors are typically rated in VA, or volt-amperes rather than watts. So y Ou can assume power factor = 1 when you have a load measured in watts like a light bulb or space heater and perhaps in the .75 range for an inefficient motor.
What use of conservator tank in transformer?
To enable the oil in the transformer tank to expand and contract with temperature changes.
Why you use 400Hz frequency instead of 60Hz?
50 Hz has an edge over 60 Hz as it will have less skin effect and therefore line resistance will be less. Therefore, voltage drop as well as unwanted loss of energy in the line will be less. That means dip in supply voltage at user end will be less and efficiency will be more.
Answer
The difference in 'AC resistance' due to the effect of skin effect between 50/60 Hz is insignificant, just as the increase in inductive reactance, or the decrease in capacitive reactance is insignificant.
The answer to your question is that the two frequencies simply resulted from the independent development of electricity distribution networks in different parts of the world, and there is no inherent advantage of one frequency of the other.
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Transformers for 60 Hz are smaller than for 50 Hz, assuming a given power rating. That is because the iron magnetic core can be reduced in size by 20% for 60 Hz, for the same peak magnetic flux density.
How do you convert 3phase connection to 2 phase?
Any two legs of a three phase system can be classed as a single phase supply.
Alternative AnswerAs the above answer points out, connecting a load between any two line conductors of a three-phase supply will give you a single-phase load. But you must, of course, take into account the voltage rating of the load you wish to connect.
In Europe, three-phase low-voltage distribution is normally by means of a four-wire system, comprising three line conductors and a neutral conductor, operating at 400 V (line-to-line) and 230 V (line-to-neutral).
Your single-phase load's voltage rating must, of course, match either the single-phase supply's line-to-line or line-to-neutral voltages. In Europe, most single-phase loads are rated at 230 V so, for a residential three-phase, four-wire system, it is usual to obtain a single-phase supply by connecting the load between any one of the line conductors and the neutral conductor.
But, if you have a non-standard, 400-V single-phase load, then connecting that load between any two line conductors will also give you a single-phase supply.
Why watt-meter is required to measure real power delivered to a purely resistive load?
A wattmeter (not 'watt-meter') will always measure the true power of a load, regardles of whether that load is purely resistive or not. This is because a wattmeter effectively measures the in-phase component of the load current.
What are the five advantages that PLC's have over a relay logic solution?
Reduces the Hardware wiring
The System can be made compact
Contact Failure rate is very less
Speed of opeartion is very high
Easy for Trouble shooting
Reduces the Maintainance cost
Easier way of Making logics
What is Fla on motor nameplate?
FLA: Full Load Ampere.
Its the current drawn by the motor when the motor is running at full load
FLA = kW / (1.732*V*pf*efficiency*100)
What is interpole winding in DC machine?
For a D.C motor it is the field windings which must always be in series with the armature windings.
What is meant by cut off voltage in diode?
Cutoff voltage is the point at which the battery is fully discharged. This is usually the point at which the device will shut itself off.
What is resistance between primary and secondary winding of transformer?
The primary and secondary windings of a mutual transformer are electrically isolated, and should have 'infinite' resistance between them when measured appropriately (which depends on voltage ratings of the windings).
What is the relation between load and resistance?
Ohm's Law:
Voltage = Current x Resistance
Current = Voltage / Resistance
Resistance = Voltage / Current
Ohm's Law can be used to tell you what the resistance of a circuit is if you happen to know what the voltage across the circuit, and the current through the circuit, happens to be. However, it must be remembered that resistance is notaffected by either voltage or by current. Resistance is only affected by the length, cross-sectional area, and resistivity of the conductor. As resistivity is affected by temperature then a change in temperature will likely result in a change of resistance. In general, the resistance of pure metal conductors increase with temperature, whereas the resistance of most insulators decrease with resistance. So, in the case of a pure metal conductor, if the current causes its temperature to rise, then its resistance will rise too -although this has absolutely nothing to do with Ohm's Law. A practical example of this effect is an incandescent lamp which has a relatively low 'cold' resistance, but a relatively high 'hot resistance'.
Why clippers are also called limiter?
bcoz, voltage clipping limits the voltage to a device without affecting the rest of the waveform.
Because the Power Factor is over corrected.
How can you identify which one is step up or step down transformer?
A transformer has two windings, termed the 'primary winding' and the 'secondary winding'. The primary winding is the winding connected to the supply, while the secondary winding is connected to the load.
The secondary voltage of a 'step up' transformer is higher than the primary voltage; the secondary voltage of a 'step down' transformer is lower than the primary voltage.
The simplest way to determine whether a transformer is a step up or step down, is to measure the primary and secondary voltages. If you are simply looking at a transformer, then the transformer's insulated bushings will give you a clue -the higher voltage bushings are much bigger than the lower voltage bushings. If you have access to the inside of the transformer, then the higher voltage windings are thinner and have a greater number of turns than the lower-voltage winding.
What are the reasons why a current is induced in a coil?
Current is not induced into a coil. It's voltage that is induced into a coil. If the coil is connected to a load, or even short circuited, then a current will flow as a result of the induced voltage -but it's the voltage, not the resulting current, that's induced!
Voltage is induced into a coil because the the changing magnetic field, due to the change in current (0 to Imax or vice versa) applied to that coil. The process is called 'self induction'.
The rms value of sinusoidal 200v peak to peak wave is?
You can work this out yourself. For a sinusoidal waveform the rms value is 0.707 times the peak value. As you quote a peak-to-peak value, this must be halved, first. Incidentally, the symbol for volt is 'V', not 'v'.
How a Cathode Ray Oscilloscope is used to measure Alternating current?
An oscilloscope is, essentially, a voltmeter -it measures current by measuring the voltage drop caused by that current across a standard resistance.
