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Grounding of XLPE metallic screen
What size of grounding conductor should be used to ground an XLPE metallic screen?
Is there an international standard that supports it?
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Capacitive Battery
If you make a capacitor out of aluminum plates,
and electrically glue carbon or resistive plates to the aluminum ones, and use a dielectric between the sets of plates.
where the input is on the aluminum plates
where the output is on the resistive plates.
Would it charge quickly thru the aluminum plates and discharge slowly thru the resistive plates.
Making... -
3Phase rectified to single phase
If I got a 380v 3-phase supply and I want to rectify it with thyristors to single phase how much voltage will I get ?What is the relationship?thanks
SGhosh
- May 15th, 2012
The dc output of the full wave rectifier is average value the amplitude of the sine wave. In short multiply the r.m.s value of the ac input voltage by its form factor (1.11 in case of pure sine wave) ...
mahmoudp1
- May 15th, 2012
I know the output will be dc my question is how much dc voltage will be the output
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Electrical Machine Operation
In a 50hz electrical machine what happens when we use more than or less than 50hz?
mahmoudp1
- May 14th, 2012
Frequency affects on the speed and torque of the machine and thats is the principle of the drives
_punjabi_
- Aug 29th, 2010
Speed and torque of the Electrical machines can be regulated by chanigng the supply frequency. Also harmonics produced are different than normal operation
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Phase Conversion
List various methods to convert 1 phase to 3 phase.
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Distribution Tower
What types of tower & pole is used in power system distribution?
mahmoudp1
- May 14th, 2012
For lattice metal structure (High Voltage )
they can divided into (specifying the job)
suspension , angle , end , cross towersraviiisc
- Sep 8th, 2010
I think "_punjabi_" forgot about the concrete poles or towers.These towers are more practical in now a days in Power distribution sector.
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Three Phase Transformers
A 3phase wye/delta transformeris rated 225kV/24kV, 400MVA and has a series reactance of 13.3ohms as referred to its high voltage side. The transformer is supplying a load of 325MVA at 0.9 pf lagging at a voltage of 24kV(line to line)on its low voltage side. It is supplied from a feeder whose impedances are (0.15+j1.5)ohms connected to its high voltage terminals. For these conditions calculatea> The...
mahmoudp1
- May 10th, 2012
???
incorrect information
you should specify at least on of the terminals voltages -
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Transformer Signal
What is the benefit of using ac signal in a transformer?
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Editorial / Best Answer
sinhasunilk- Member Since Jul-2010 | Jul 3rd, 2010
Transformer can only operate with A.C supply. Voltage will induce in the secondary winding of transformer only when there is a change in flux. The induced voltage in the secondary winding is no. of turns in secondary x rate of change of flux. In D.C circuit the rate opf change of flux is Zero, hence induced voltage in secondary winding is Zero and no Back MMF produce in the magnetic circuit of core of transformer.?This will result in very high current drawal in the primary winding and will result in burning of primary winding of transformer. We can not think of applying D.C source in transformer.??
SURAJTHEGREAT
- May 5th, 2012
The reason why dc signal cannot applied to a transformer is that f=0,reluctance is 0,very high current flows through windings and it is burnt out!
sinhasunilk
- Jul 3rd, 2010
Transformer can only operate with A.C supply. Voltage will induce in the secondary winding of transformer only when there is a change in flux. The induced voltage in the secondary winding is no. of tu...
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Heater Effect on Bulb
If Heater of 1000W is connected in series with 60 W bulb. what is the effect on the bulb.
SURAJTHEGREAT
- May 5th, 2012
1 Thing everybody has to remember is that only current and not the voltage remains constant across the elements.Let us assume that the elements in series are connected to 220V supply source. Total po...
bittu123
- Nov 9th, 2011
@ om_zzz
You are right, bulb will glow but dimmer and heater will not heat-up(more precisely it will generate very less heat) -
OC/SC Test On Low Voltage Side
Why OC test is carried out on low voltage side of transformer?
mahmoudp1
- May 3rd, 2012
The previous answers are right + to make an accurate measurement O.C test on LV side because the current is high on the low voltage so when we repeat the experiment we will get more results with the ...
Pratyush Singh
- Jul 26th, 2011
Because during OC test, rated voltage is applied, hence the HV side is unsuitable to keep instruments, hence it is the HV side that is opened and the LV side is where instruments are placed (at their rated values)
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Induction Motor selection
Could you explain that how to select an induction motor for a specific mechanical load(inertia). is there any formula or calculation then please give me. i shell be very thankful to all of you.
mahmoudp1
- May 3rd, 2012
First know the load specifications like power needed or torque and from the catalogues choose the correct motor without any calculations.
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Making electricity
Can electricity be made by reversing. Other words can you make electricity by spinning magnets around copper wiring
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Circuit Breaker
Explain what are Single and 2 Pole circuit breaker?
mahmoudp1
- May 1st, 2012
Yes and single pole means that circuit switch two poles / two wires (eg; live and neutral)
3 poles used to switch 3 phase systems
4 poles used to switch 3 phase + neutral wire
5 poles used to switch 3 phase + neutral + ground wire
amolgaonkar
- Dec 9th, 2011
Circuit Breaker is a safety device used to safeguard electrical equipments from heavy current, it trips OFF when more than rated current passes through it.
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Induction Motor Power Factor
A 3-phase induction motor running on 500v at full load draw 40A current at 0.85 pf Lagging if 85 micro Farad capacitor connected across its terminal than what would be a New Power Factor?
mahmoudp1
- May 1st, 2012
You didn't specify the capacitors connection is delta or star
assuming (delta)
Xc = 37.462 ;
reactive power drawn by capacitor = 6684.49 VAR
active power drawn by motor = 34641 watt
old power factor = .85 lag
new power factor = .91 lag
vishnu
- Feb 18th, 2012
--> Find the reactance offered by capacitor i.e 37.46 ohm. so leading current drawn by capacitor is 9.095A @90 deg lead. --> Current drawn by the motor is 40A @ 31.788 deg lag. --> Resultant current ...
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Direction of current flow in three pole regulator
The circuit diagram is at http://avstop.com/AC/apgeneral/regulation.html
I cant completely figure out the way current is flowing through the three pole regulator that I have attached. I believe that current is coming up through the L1 coil into the positive terminal of the armature. and, I think current is flowing down through L2 coil and around back up to the positive terminal of the... -
Cable selection
Why Cable selection depends on Load current? (UG Cables & OH lines)
soumendasbiswas
- Apr 26th, 2012
Cable selection not only depends on the load current but also depends on Temperature, Length (Distance between LT Switchgear MCC/PMCC to Motor). If load is increase then current will also increase if ...
raju
- Apr 6th, 2012
Voltage is directly proportional length, current is proportional to area of cross section of the wire.
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What is the use of a VCT
What is the use of a voltage capacitor transformer?
sjw06
- Apr 15th, 2012
VCT is used to step down really high voltage to a very low voltage that can be safely fed to a measuring device or protective devices.
Harish P. Girhe
- Apr 3rd, 2012
Generally all transformers works on inductive load hence operated at lagging power factor. It is necessary to use an capacitor bank for improvement an power factor. This capacitor bank called as VCT. Generally this VCT known as RVT (Residual Voltage transformer)
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Two phase motors
Why zero sequence component not found in two phase motors?
Harish P. Girhe
- Apr 3rd, 2012
In two phase induction motors one phase & neutral is applied. For successive working of motor one phase is spitted into two equal and opposite component. These two component are having an opposite action on each other.So two phase motor works successively.
Electrical Engineering Interview Questions
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