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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 choose vector group is voltag step up transformer?
A vector group table lists the 'phase shift' or 'angular displacement' for all combinations of three-phase transformer connections. In order to parallel three-phase transformers, their angular displacements (amongst other things) must be the same.
'Phase shift' or 'angular displacement', is defined as 'the angle by which the secondary line-to-line voltage lags the primary line-to-line voltage'.
Angular displacement depends on the type of transformer connection. The most common are:
- delta/delta results in an angular displacement of 0o or 180o
- wye/wye results in an angular displacement of 0o or 180o
- delta/wye results in an angular displacement of 30o or 210o
- wye/delta results in an angular displacement of 0o or 180o
In a Vector Group table, though, the angular displacement is normally expressed in multiples of 30o -e.g. '11', which means 11x 30o, or 330o.
From the above data, it would be impossible to parallel, for example, a delta/delta transformer with a delta/wye transformer.
BS 171 lists twelve main connections, arranged in four main groups according to their angular displacements. A connected designated, for example, 41 Dy 11, shows:
- 4 -the fourth main group
- 1 -the first connection within that group
- D -HV connection is connected in delta
- y -indicates LV connection is in wye
- 11 -indicates an angular displacement of (11x30o)= 330o.
What is B.H.P in 3 phase induction motor?
BHP stands for 'brake horsepower', and simply means it is describing the output, rather than the input, power of the machine. Although a motor's output power is expressed in horsepower in North America, elsewhere it is expressed in watts.
Can I use a small DC electric motor as a generator to light up several LED's in a project?
Yes you can, the power will not be stored though, the LED's will only light when the motor is turning and their brightness will depend on the velocity of the motor's revolutions. Dont forget your resistor.
What is full load current rating for 1000kva xmer?
It depends on (1) its voltage rating, and (2) whether it is single phase or three phase. And the symbol for kilovolt ampere is kV.A -not 'kva'.
There are various ways in which you can determine the reactive power (in reactive volt amperes) of a load. From the practical point of view, you can use a voltmeter and an ammeter and use the product of their readings to determine the apparent power (in volt amperes) of the load, and a wattmeter to determine the true power (in watts) of the load, then find the vectorial difference: (reactive power)2=(apparent power)2-(true power)2
What is a non auto circuit breaker?
A non-auto circuit breaker is a circuit breaker with the trip element removed. Basically, it is a modified circuit breaker that is now a disconnect switch (glorified disconnect switch).
What will happen if supply terminals of dc shunt motor interchange?
it will run in same direction because flux and armature current both will be changed wih plarity.
What digital multi meter setting should be used to measure voltage?
There are settings for AC and DC voltages. If they are not marked as such, the DC setting might be parallel lines and the AC marking may be a cycle of a sine wave (Wavy line).
What happens if you connect the neutral of your home to another transformer's neutral?
If you independently connect two different neutrals together, you violate the star concept that protects the grounded neutral. While neutrals are all grounded, their relative potential voltage could be sufficiently different that connecting them together could cause large eddy currents that might cause overheating and equipment damage. Neutrals in one system are only allowed to be tied together at the distribution panel serving that system, and inter-system cross-ties are not allowed. Violation of this rule causes violation of the principle that is embodied in Kirchoff's Current Law, i.e. that with only one path to ground, any current on ground must represent a fault - cross tying systems together prevents detection of that fault, along with introducing eddy currents.
An ampere hour (A.h) is a non-SI unit of measurement for electrical charge (the SI unit is a coulomb-which is equivalent to an 'ampere second'). So an ampere hour is equivalent to 3600 coulombs.
Cells and batteries are generally rated in terms of ampere hours, as a convenient alternative to the kilocoulomb.
How do you convert kvr into kw?
The correct symbols for reactive kilovolt amperes and kilowatts are kvar and kW, respectively.
The simple answer is that you cannot convert one to the other. A reactive volt ampere is a measure of reactive power, and a kilowatt is a measure of true power. While these are related, they are different quantities, so you cannotconvert one to the other, any more than you can convert a kilometre to a kilogram.
Which supply has polarity AC or DC?
DC has polarity, while AC is constantly reversing in polarity.
AnswerWhile the previous answer is quite correct in the sense of 'positive' and 'negative' charges, it's worth pointing out that 'polarity' has a second meaning in a.c. systems.In a.c., the term 'polarity' is used to describe the correct connection of the supply's line and neutral terminals. For example, with an Edison screw lamp holder, to remove the risk of shock, it's important that the line conductor is connected to the centre terminal, and the neutral conductor is connected to the outer terminal. If this has been done correctly, then we say that its 'polarity' is correct. Similarly, if the terminals of a socket outlet (receptacle) are connected the correct way around, then their 'polarity' is correct. Testing for the correct connections in an a.c. electrical system is called a 'polarity test'.
What is the cable size to take a load of 95kw?
It depends on the voltage, which was not specified. Please restate the question, giving the voltage. The reason for this is that cable size is a function of current, not power.
AnswerThe size of a cable depends on the material from which the conductor is made, the number of cores, the type of insulation, whether it is armoured or unarmoured, and how it is installed. So, even if you know the relevant voltage, the only way in which you can determine the correct cable size is the use the tables provided in your country's wiring regulations, which take these factors into account. Incidentally, the symbol for 'kilowatt' is kW, not 'kw'.
How do you disconnect ammeter from current transformer?
A CT's secondary winding must never be open circuited as it may provide a shock hazard to the user. The terminals to which an ammeter is connected to a CT is normally provided with a set of links that must be closed, short-circuiting the CT, beforethe ammeter can be removed. The ammeter must the be reinstalled before the shorting links are reopened.
What would happen if a lamp was unscrewed from a parallel circuit?
There will be no change, because it is a parallel circuit.
Why 2 holes are drilled oppositely in disc of energy meter?
To over come creeping effect on no-load, 2 holes are drilled on the opposite sides of the spindle. This causes sufficient distortion of the field to prevent rotation when one of the holes comes under one of the poles of the shunt magnet.
Courtesy - Industrial Instrumentation and Control
Is AC voltage measured from Peak to Peak or from 0 to peak?
Both. When an AC voltage is measured and a number is reported, it is necessary to state that this number is rms value or peak value or peak to peak value.
AnswerVoltages and currents are each normally expressed in root-mean-square (rms), unless otherwise stated. For example, when we talk about a '120-V service' or a '240-V service', we are expressing the voltages in rms values; it is unecessary to specify that these are rms values. For a sinusoidal waveform, Vrms = 0.707 Vpeak
What is a frequency changer substation?
These are the substations which can have the capabality to change Frequency which it gets from the generators, human interventions neccessary to accomplish this task.
How does power pass through compressor to inside motor?
. Through a terminal box with three motor terminals one for the run winding and one for the start winding and one for the common line to the run and start windings
What happens when a light bulb is connected to the output coil of the transformer?
Assuming that the voltage rating of the lamp matches the rated secondary voltage of the transformer, the lamp will operate at its rated power.
How is the resistance of a metallic conductor affected by variation in temperature?
In general, pure metal conductors increase in resistance as their temperature increases. This is not necessarily true for alloys, as some alloys are manufactured to have an approximately constant resistance over a wide range of temperatures.
How many lumens output in a 500 watt quartz Halogen bulb?
The bulb will have an efficacy of 17-20Lm per watt, so in total 500W = 8,500-10000 lumens. However, the bulbs light output is non directional, so a lot of the spilled light is in directions that you don't want it to go, so 50-70% of the figure can be used when specing up an LED variant.
Why rotor of a dc motor moves in the anticlockwise direction?
Positive and negative are reversed. It will run either direction depending on which way it is wired.
What is insulation resistance in capacitor?
ideally there will not be any resistance to the capacitor,so at this condition it should not not discharge the stored energy. but practically small resistance will be there in the capacitor so the energy stored by the capacitor will be discharged through resistance.
The kva rating includes the power factor of the connected load.
KW * Power Factor = kva.
AnswerThe above answer is incorrect, as it's actually kV.A x power factor = kW.
The answer is straightforward, the output of the UPS is the product of its rated output voltage and its rated output current, and the product of voltage and current is 'apparent power', expressed in volt amperes.
