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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 earth fault current is less than short circuit current?
A short circuit occurs when the current pass through earth directly or the current returns to its source without passing the load. It is caused by a very low or zero impedance wire that may be connected line to line or line to ground.
A fault current can be a short circuit but the wire have an impedance that may still give current to the load. the protective device operates when the current exceeds the rating of circuit breaker, by load current + fault current.
Why is dielectric constant for metals is infinity?
It is not infinite. At some extreme values electron-positron pairs will start forming rapidly what will result current flow.
However from practical standpoint vacuum dielectric strength is limited by field emission from electrodes. Best results are about 40MV/m , what is far worse than some good dielectrics can provide.
The amperage rating of a copper wire is related to its resistance and to the type of insulation used (i.e., what temperature the insulation can handle) and the ambient temperature. The fatter the copper wire, the more amps it can handle, everything else being equal. A mineral-insulated wire, buried underground, would handle more amps than a similarly sized copper wire in thermoplastic insulation in air.
There are electrician charts available to determine the MINIMUM size of copper (or aluminum) wire necessary for a particular load.
Consider also that longer the wire, the more resistance there is, so a very long wire would need to be larger to handle the same load safely.
What happens if resistance decreased in earthing?
It will work properly! The resistance and impedance of the earth lead must be low, though the corollary is that it must be capable of passing any likely fault current safely.
A UV air purifier along with a HEPA and carbon filter will help clean the air, not only from airborne particles and smoke, but also from germs.
The UV light is normally added to combat/kill floating fungus and bacteria. If you live in a damp place (near swamp, leaking pipe etc) you'll probably be inhaling spores from molds. This is where a UV light air purifier would be useful.
One of the best known UV air purifier is the Alen A375UV
How would you measure voltage passing through a light bulb using a digital multimeter?
Simply set the multi meter on DC voltage, which is denoted by a line with dotted lines under it. Then place the red lead on the positive side of the bulb and the black lead on the negative side. If you do this incorrectly it will be a negative number but the same number if the leads are reversed.
If you have a bad bulb the meter will show all zero´s. Otherwise you´ll get something like 0.01 which is a good indicator for a working bulb.
The voltage across the light bulb will be the same voltage as the supply. Regardless of whether the bulb is good or bad the voltage potential will still be there. You are measuring voltage not amperage.
How much can you power on a 2.5kva generator?
It can supply 2.5 kW to a load with a power factor of 1. Otherwise the power available must be multiplied by the power factor which is always less than 1. If uncertain assume 0.8 which makes it 2 kW.
Some electric motors have windings enabling them to run at different speeds.
How do you calculate actual power factor?
The power factor of a circuit is defined as the cosine of the phase angle -which is the angle by which the supply current lags or leads the supply voltage in AC circuits.
Power factor is always expressed as either a 'lagging power factor' or as a 'leading power factor'.
The terms 'lagging' or 'leading' describe the relationship of the supply current to the supply voltage. Since current lags voltage in an inductive circuit, 'lagging power factors' describe inductive circuits; since current leads voltage in capacitive circuits, 'leading power factors' describe capacitive circuits. In practice, lagging power factors are more common than leading power factors, because most practical loads are inductive (e.g. motors, etc.).
Power factors are normally expressed as a decimal (e.g. '0.8 lagging') although, in the past they were often expressed as a percentage (e.g. '80% lagging'). 'High' power factors tend towards unity, whereas 'low' power factors tend towards zero.
In terms of power, the cosine of a circuit's phase angle and, therefore, its power factor is the ratio of that circuit's true power (expressed in watts) and its apparent power (expressed in volt amperes).
Power factor has no effect whatsoever upon the energy consumed by a load, but it does effect the amount of current drawn from the supply. 'Low' power factors result in unnecessarily-large load currents for any given load, which mean that the supply utilities need to use larger than necessary conductor sizes (expensive!). For industrial or commercial (but not residential) loads, therefore, it is often desirable to 'improve' the load's power factor towards unity, which acts to reduce the load current. This is most-usually done by installing capacitors close to the load, and is termed 'power-factor correction' or 'power-factor improvement'. Capacitors used in this way are rated in reactive volt amperes, rather than in microfarads.
Drawing of speed-torque curve for synchronous machine?
Theoritical torque speed curve for a synchronous machine will be a vertical line located vertical to the synchrounous speed at x axis, from starting torque to stalling torque value. This is because theoritically synchronous motors are not self starting. Practically however they start as induction motors and at near synchrounous speed the excitation is switched on. Anand Sekhar
computer-based system(it contains both hard ware and software) that can process data that are incomplete or only partially correct
Fuzzy logic was introduced as an artificial intelligence technique, when it was realized that normal boolean logic would not suffice. When we make intelligent decisions, we cannot limit ourselves to "true" or "false" possibilities (boolean). We have decisions like "maybe" and other shades of gray. This is what is introduced with fuzzy logic: the ability to describe degrees of truth.
Example:
in fuel station if you stop a fuel injecting motor at 1.55897ltrs.it can be done with the help of fuzzy logic.fuzzy has a meaning like accurate.
132kV substation is part of transmission and distribution of power in which the transmission voltage is 132kV. The substation is for stepping down or stepping up of the voltages to the required voltage. the substation also serves as a place where the transmission lines can be isolated, controlled and monitored. The substation consists of different equipment that is used to regulate, monitor and distribute the required power.
Another Answer
In the UK, 132 kV voltages are considered to be the lowest transmission voltages. Other transmission voltages are 275 kV and 400 kV. A '132-kV substation' is normally one in which this voltage is stepped down to a primary distribution voltage, usually 33 kV but, sometimes, 66 kV. As the previous answer points out, substations contain transformers, switchgear, busbars, and protection equipment.
What is the different between ac dc motors?
DC Motor works on DC source and AC motor works on AC source
What value of resistance is used to convert galvanometer into voltmeter?
It depends on the resistance of the galvanometer and its full scale current. A 100 ohm meter reading 1 milliampere would require 0.1 volts to reach full scale, so it would require about 0.1 ohms in parallel to become a 1 ampere ammeter.
Why does a phase in secondary side in distribution transformer give low voltage?
transformer is busted; if input voltage is normal you have short circuit or open circuit somewhere
Can current flow both ways through a lamp?
Yes, we use AC (alternating current) in our homes, the current changes direction 120 times a second.
The normal phase of aluminum at room temperature is a solid.
You can, however, heat to really high temperatures until it becomes a liquid or even a gas.
Can you run AC and DC cables in the same conduit?
In California and I believe the NEC states " no low voltage can share conduit with high voltage". Also it's not recommend to even run "with" or alongside conduit w/ AC in it. The interference will kill you transmission speed.
Answer:
The above answer is very true. While Cat5 can intersect with AC wire at 90 degrees to the AC wiring, it should not be run parallel with it, unless it's at least a foot or so away.
If we change the polarity of capacitor in ceiling fan why it starts rotating reverse direction?
by changing the polarity of capacitor of single phase ceiling fan can we change the direction of rotation from anticlockwise to clockwise
How does identify the capacitor capacity for 1.5 kw single phase motor?
If the power factor is 0.7 the reactive power equals the real power, so the capacitor should be 1.5 kVAr. That is a reasonable estimate for a small induction motor.
What is the disadvantages of using auto transformers?
there can be a lot of leakage flux in auto transformer. because primary and secondary winding in auto transformer is not separated.
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There is no primary to secondary isolation.
Current rating is limited to the size of the conductor used for the entire winding.
And also With an autotransformer, there is a absolute electrical affiliation from primary to secondary. It is generally the case that the anterior coupling that exists with accustomed two-winding transformers is a big advantage that would not be had with an autotransformer. For example, an autotransformer added readily couples voltage transients from one voltage to the other; with two-winding transformers, voltage transients are accompanying by the capacitive voltage affiliate aftereffect and may be suppressed.
A transformer is an apparatus that is used for reducing or increasing the voltage of an alternative current.
How do you calculate the of turn and the secondary voltage of the 15kw transformer?
First of all, transformers are rated in volt amperes, not watts. Secondly, in order to determine a transformer's turns-ration, you need to know its primary and secondary voltage ratings.
