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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
How do you convert ohms to mega ohms?
A Megohm is one million ohms. To convert ohms to Megohms, divide by one million.
Can we use AC capacitor in surge suppression circuit DC?
A capacitor is a capacitor, no matter what circuits you use it in. There is no difference between one used in AC and one in DC, except perhaps the size that is appropriate.
What is TAN DELTA testing of transformer?
Tan Delta is also known as the 'loss angle' or 'dissipation factor'. It is used to test the level of degradation in insulation materials of electrical machines and power cables. The winding insulation of an electrical machine, or a cable free from defects, will act as a perfect capacitor, that is, it will only store energy and not dissipate it.
In an ideal capacitor, the voltage and current are out of phase by 90 degrees and the current flowing through the insulation is purely capacitive Ic. However, dielectric losses within the insulation due to deterioration or other factors, will result in the reduction of the resistance in the insulation. This will in turn increase the resistive current Ir. The phase angle between the current and voltage is now less than 90 degrees, and the extent to which this is less than 90 degrees gives the level of degradation in the insulation. So this 'loss angle' is required to be measured.
If the angle is Delta, then the tangent of Delta can be calculated by dividing is 'opposite over adjacent', which is Ir/Ic.
There are various methods of how this is tested and industrial standards, such as the IEC provide acceptable values of Tan-delta for different types of insulation.
What is inverse time-current characteristics?
In circuit breakers this feature will provide faster or slower responses for larger or smaller overcurrents, respectively. Ie Big overcurrents will trip quickly, and small overcurrents will allow more time before tripping.
This is good as it allows overcurrents time to correct themselves (like when a refrigerator motor fires up there is a spike in current) without tripping and requiring attention; and larger overcurrents (faults) will trip quickly keeping the circuit safe from overloading, and say, catching fire.
How do you know you have constructed a perpendicular line?
You can answer that question for yourself by examining the point where the line
meets or crosses something else.
If all of the angles formed by the arrival of the new line at that point are equal,
then the new line is perpendicular to the existing plane or line at that point.
480 Volt
What were the advantages and disadvantages of ac over dc?
The most significant advantage for people who do not know much/anything about electricity is that polarity (+/-) doesn't matter with alternating current. You can read everything about the "War of Currents" at: http://en.wikipedia.org/wiki/War_of_Currents
What is the vector diagram of ynd11 transformer?
In the vector group representation for this transformer, the letter 'y' represents a wye- or star-connection, and the letter 'd' represents a delta- or mesh-connection (I have no idea what 'n' stands for -anyone?). An upper-case letter indicates the higher voltage, while a lower-case letter represents the lower voltage. The sequence of the letters indicates the primary and the secondary windings. So the transformer in question is a wye-delta connection (presumably the 'y' should have been capitalised, meaning that this is a step-down transformer: i.e. Yd11).
The number appearing after the letter group (in this case '11') is a multiplier of 30o and indicates the transformer connection's angular displacement (or phase displacement). In this case, the angular displacement is 11 x 30o = 330o.
As angular displacement is defined as 'the angle by which the secondary line voltages lag the primary line voltages', this means the secondary line voltages of this particular transformer lags its corresponding primary line voltages by 330o.
So, to draw the phasor (not 'vector') diagram for this particular transformer, you would start by drawing the phase voltages (VAN, VBN, and VCN) of the primary wye connection (using VAN as the phasor of reference), from which you would then construct the corresponding line voltages (VAB, VBC, and VCA). To finish the diagram, you will then draw the secondary delta phasor diagram, starting with Vab lagging VAB by 330o (or, if you prefer, leading by 30o), then drawing Vbc and Vca displaced by 120o.
The earliest reference to a fuse is open to question. It was suggested by W.H. Preece, during a discussion on a paper by A.C. Cockburn presented in 1887, that platinum wires had been used as fuses to protect submarine cables as early as 1864. But in 1880, T. A. Edison patented what might be regarded as the first 'modern' fuse: a semi-enclosed type consisting of a wire element surrounded by a glass envelope intended to protect the immediate environment from the effects of the wire melting.
You want know about full details of IS 13947 for electrical low voltage switchgear?
Indian Standard Specification for LT switchgear and Controlgear
IS 13947-1 General requirements of switchgear and controlgear for voltage not exceeding 1000 V ac.
IS 13947-2 LV Circuit breaker ( ACB/MCB/MCCB/RCB ) for voltage not exceeding 1000 V ac or 1200 V dc.
IS 13947-3 Air- Break switches, Air-Break disconnector and fuse combination unit for voltage not exceeding 1000 V ac or 1200 V dc.
IS 13947-4 Contractors and motor starters.
IS 13947-5 Control circuit devices and switching elements.
IS 8623-3 Specification for factory built assemblies of switchgear and controlgear for voltage uptoand including 1000 V ac and 1200 V dc.
IS 10118-4 Code for practice for selection installation and maintenance of conductors and apparatus terminals.
IS 12021 Specification of control transformers for switchgear and controlgear for voltage not exceeding 1000 V ac.
IS 11353 Guide for uniform systems of making and identification of conductors.
IS 3043 Code of practice for earthing.
IS 3072 Code of practice for installation and maintenance of switchgear.
IS 3231 Electrical Relays for power system protection.
What is the symbol for a thyristor?
It is a standard diode, with an additional line leaving the cathode (- side) for the gate. See wikipedia link.
What is GD square mentioned on the Motor?
The GD square that is mentioned in motors is also called the flywheel effect. It is usually used in most of the industrial applications and processes.
Difference between voltage and emf?
'Voltage' is simply another term for 'potential difference', and an electromotive force is the open-circuit, or no-load, potential difference of a source such as a battery or generator.
Example component use integrated circuit?
(I am assuming you are asking "What are some examples of devices that use Integrated Circuits?") Note that an Integrated Circuit (IC) is normally regarded as a "component" itself. ICs are used in virtually every electronic device found today including, but by no means limited to: MP3 players, Computers, Computer Peripherals, TVs, DVRs, Radios, Cars, Microwave Ovens, and on and on ... hopefully you get the idea.
What is knee point voltage of current transformer?
10 % increase in voltage gives you 50 % increase in excitation current is called knee point voltage. To measure this first demagnetise the CT and apply voltage gradually from secondary keeping primary winding open circuited. while doing this above phenomeneo will be obsesrved.
What is Power systems protection?
Primary and back-up protectionThe reliability of a power system has been discussed in earlier sections. Many factors may cause protection failure and there is always some possibility of a circuit breaker failure. For this reason, it is usual to supplement primary protection with other systems to 'back-up' the operation of the main system and ensure that nothing can prevent the clearance of a fault from the system.
Back-up protection may be obtained automatically as an inherent feature of the main protection scheme, or separately by means of additional equipment.
Time graded schemes such as over current or distance protection schemes are examples of those providing inherent back-up protection; the faulty section is normally isolated discriminatively by the time grading, but if the appropriate relay fails or the circuit breaker fails to trip, the next relay in the grading sequence will complete its operation and trip the associated circuit breaker, thereby interrupting the fault circuit one section further back. In this way complete back-up cover is obtained; one more section is isolated than is desirable but this is inevitable in the event of the failure of a circuit breaker.
Where the system interconnection is more complex, the above operation will be repeated so that all parallel infeeds are tripped.
If the power system is protected mainly by unit schemes, automatic back-up protection is not obtained, and it is then normal to supplement the main protection with time graded over current protection, which will provide local back-up cover if the main protective relays have failed, and will trip further back in the event of circuit breaker failure.
Such back-up protection is inherently slower than the main protection and, depending on the power system configuration, may be less discriminative. For the most important circuits the performance may not be good enough, even as a back-up protection, or, in some cases, not even possible, owing to the effect of multiple infeeds. In these cases duplicate high speed protective systems may be installed. These provide excellent mutual back-up cover against failure of the protective equipment, but either no remote back-up protection against circuit breaker failure or, at best, time delayed cover.
Breaker fail protection can be obtained by checking that fault current ceases within a brief time interval from the operation of the main protection. If this does not occur, all other connections to the bus bar section are interrupted, the condition being necessarily treated as a bus bar fault. This provides the required back-up protection with the minimum of time delay, and confines the tripping operation to the one station, as compared with the alternative of tripping the remote ends of all the relevant circuits.
The extent and type of back-up protection which is applied will naturally be related to the failure risks and relative economic importance of the system. For distribution systems where fault clearance
Times are not critical, time delayed remote back-up protection is adequate but for EHV systems, where system stability is at risk unless a fault is cleared quickly, local back-up, as described above, should be chosen.
Ideal back-up protection would be completely independent of the main protection. Current trans-formers, voltage transformers, auxiliary tripping relays, trip coils and D.C. supplies would be duplicated. This ideal is rarely attained in practice. The following compromises are typical:
a. Separate current transformers (cores and secondary windings only) are used for each protective system, as this involves little extra cost or accommodation compared with the use of common current transformers which would have to be larger because of the combined burden.
b. Common voltage transformers are used because duplication would involve a considerable increase in cost, because of the voltage transformers them-selves, and also because of the increased accommodation which would have to be provided. Since security of the VT output is vital, it is desirable that the supply to each protection should be separately fused and also continuously supervised by a relay which will give an alarm on failure of the supply and, where appropriate, prevent an unwanted operation of the protection.
c. Trip supplies to the two protections should be separately fused. Duplication of tripping batteries and of tripping coils on circuit breakers is sometimes provided. Trip circuits should be continuously supervised.
d. It is desirable that the main and back-up protections (or duplicate main protections) should operate on different principles, so that unusual events that may cause failure of the one will be less likely to affect the other.
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What is advantages and disadvantages of SCR?
Advantages: simple turn On Latcing device, turn ON gain is very hih, low cost,Hih voltage and high current device. Disadvantages: Low switching speed, most suited for line commutated applications betwee 50 and 60 Hz can not be turn off with gate controlled. From: N.G.PATEL(UPS)B.TECH.(ELECT)
How do you calculate percent modulation of an AM wave form?
%m = Ei/Ec *100 or % m= V max -V min/Vmax+Vmin * 100
What are the different earthing schemes?
According to IEC terminology, there are 3 typesof earthing schemes. they are
TN, TT and IT.
Fuse coordination is the process of carefully selecting fuses in a system so that faults in branch circuits do not cause 'upstream' fuses to operate. This is done by comparison of fuses' operating characteristics: in particular pre-arcing energy let-through and total energy let-through.
When does the new transformers come out?
when does the new transformes come out when does the new transformes come out
What voltage is applied to a 4 ohm resistor if the current is 1.5 amps?
Ohm's law: Volts = amps times ohms
In the case of a 4 ohm resistor with 1.5 amps of current, the voltage is 6 volts.
Determine the fundamental period of the signal xt2cos 10t 1sin4t1?
- Fundemental Period of building moving forward and backward
