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Use of DC machine
We have enough category of AC machines more relliable than DC machine then why we are using DC machines in some application yet?
rajakumar1985
- Sep 7th, 2009
Each AC and DC machine having its own characteristics.According to the reguirement, the motors will be selected. Also the availability of supply is taken into consideration. But normally AC is preffered than DC due to its low maintenance and relaiability.
shravan.rawal
- Sep 4th, 2009
Take an eg. of DC series motor, it's properties are suitable for Railway engine, at the start it has high torque and low speed and once the core gets saturated it's torque is low but the speed is higher, so for this kind of special requirement we require DC M/C
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Rated Voltage and Frequencey
Why OC test is carried out at rated voltage and frequency?
rajakumar1985
- Aug 10th, 2009
Normally the OC test is done to find out the losses. The losses depends on the voltage and frequency applied to the machine. So that while testing, the rated voltage and frequency are applied to the machine.
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Capacitor Banks
What is the best method to connect two capacitor bank?
behera.tapan
- Nov 13th, 2009
It is best to connect bank in delta because if connect in star it will required three times more?capacitance as?in case?delta for same reactive power supply and finally connect both bank parallel across load or out going feeders.
buntysurat
- Nov 13th, 2009
Capacitors should be connected in star with their star point is earthed. This arrangement reduces Phase voltage to each unit by root 3 and thus the voltage withstand capability of each unit. The star ...
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3 Phase Motors
Why do 3 phase motors rotate in the opposite direction when any two phases are interchanged?
deepanshu_jadon
- Mar 10th, 2010
By the interchange of two phases Force acted in the winding inverse.if motor rotate clockwise then by the changing the two phases it start rotate in anticlockwise direction
M.Mohanraj
- Dec 8th, 2009
Magnitude is different in 3 phases so it is possible to rotate reverse direction.
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Voltage Drop
How to can calculate voltage drop in a cable?
pveee
- Dec 29th, 2011
Voltage drop in 3 phase circuits is Vd=(1.732xI(Rcos + Xsin)L)/(1000xno.of runs)
I is full load current,
R resistance of the conductor,
x resistance of the conductor,
L length of conductor in meters.
bijumenon
- Oct 25th, 2009
According to me this is how the voltage drop in a cable is calculated.If*SQRT(Rf Cos(phi) + Xf sin(phi)) / no. of runswhere....If is the full load currentRf and Xf is the resistance and reactance of the feeder. (Rf = R *L/1000; L= length of the feeder).
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Earthing Standards
What is the standard for Cable sizing & Voltage Drop?What is the standard for earthing?
maxandrean
- Jul 5th, 2010
Standart Earthing Cable in practice is :1. For the cable size is 16 mm2 , the size is equal to the line cable.2. For cable size above 16 mm2, the size is half size of the line cable, but not less than...
salman_moazzam
- Feb 2nd, 2010
Depth to which you must dig. How much should be the amount of salt and charcole to be put. Especially in earthing we must go to the depth untill you get wet mud.
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Transformers and Varying DC Current
Will DC current that varies, for example a DC square wave, but that only sinks to neutral (0V) and not enough to cause current to flow in the opposite direction, pass through a transformer? If so, how will you be able to calculate reactance for this?
ravs42
- Aug 8th, 2010
A DC square wave will have a very high value of dv/dt as compared to the pure sine wave. When it is striked to transformer, a high value of dv/dt would not be responded by it, as a result, the waves ...
Abhijit_atrangi
- Feb 22nd, 2010
No, only change in flux will induce the emf in a ckt. and that only feasible with AC that goes in opposite direction also. But in case of DC that produce flux with no change that never cause any emf in circuit. In case of DC square wave you change the magnitude of a wave from zero to max.
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Potential Transformer
What is the function of a potential transformer?
dhands
- Jun 6th, 2010
Potential transformer is used to measure the high voltage. It is nothing but stepdown transformer. In our metring systems are dsigned only for 110 v or 220 v but we are using 11000, 22000, 33000, ect. For ex PT input is 11000 v but output is 110v.
deepanshu_jadon
- Mar 10th, 2010
Potential Transformer is used to measure VoltageIt is used in protection
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Power Lines Protection
Why the 1st zone of protection relay is 90% not 100%?
ashokumarrk
- Nov 14th, 2010
Zone-1 protection is 80% in (NTPC, POWER GRID, NPCIL, NHPC, BBMB....) bcz we have consider the errors in CT, PT and also the line length. Datas provided should be same as the actual, but it wont. In order to compensate all these Zone-1 protection is 80%
pradipsabar2009
- Jul 29th, 2010
If we consider the 100%, 100% in the sense there is another CB present there. so there is a dilemma which CB should operate first. Hence the first zone of protection is never 100%
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Main Switch
What the name given for to connect the main switch supply to the various appliances?
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Voltage Levels
Why all voltage level are multiples of 11, like 220V, 440V, 1100V instead of 200V, 400V, 1000V?
pradipsabar2009
- Jul 30th, 2010
The value of form factor is 1.1 which is calculated for the sine wave. At this value of form factor, leakage flux is minimum and efficiency is maximum for any electrical machines. These machines are operated at sine waves.
dhrumil041189
- Jun 11th, 2010
Because number of disc of insulators are rated in order of 11 kV so all these are transmitted in the multiple of 11.
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Fault Detection in Underground Cables
If there are three underground cables if a fault takes place in one of them, How will you detect it?
pradipsabar2009
- Jul 28th, 2010
Measure the resistance of each cable between farther ends, if there is a considerable variation in any one of the cable, that is the faulty one. This method is also used in industries called as "Insulation Resistance Test".
dhands
- Jun 6th, 2010
1. Check phase to pase insulation resistance value and phase to earth insulation resistance value.
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Power Factor
A powerplant has 8 gensets operating in grid parallel mode. In one genset sometimes there is pf variation and kvar variation. The plant operates in pf mode. When this variation is onbserved the load is stable, voltage is also stable, freq and genset speed is also stable. How will you check the functioning of pf card. What shall be the ideal output vdc of the pfc, from there it is input to avr.
mani777
- Jun 23rd, 2010
1. pf...........cos #=watt/voltage*current2. pf is cos thita between v & i3. pf is apperent power/realor reactive power.
saginala13
- Jun 19th, 2010
here the variation in the power is is the pf factor of load, in generating station all alternators are connected to a busbar, and load is connected to bus bar so the load will be shared by all generators
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3 Phase Motor
How can we test a 3 phase motor on single phase supply?How can we run a 3 Phase Motor on Single Phase supply for testing?How can we verify of a 3 phase motors' 6 wire & name them a1/a2/a3..b1/b2/b3 and c1/c2/c3 for connecting star delta starter?
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Power Factor Panel
What will happen if 400 KVar Capacitor banks are on in manual mode and there is no load on mains?
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Water Level Sensor
What sensor is used to measure the level of water in a tank?
thakur.rajesh.ranjan
- Sep 25th, 2010
A small rubber ball, we generally use in our dewatering sump for water level sensor. This gives command mechanically to level switch.
ravs42
- Aug 6th, 2010
A simple mechanical model for water level indicator includes a float(rubber ball) providing? a mechanical link to the indicator i.e. d output. When the water level rises the float due to it's light weight raises up and via the link the pointer will move to display the required output.
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Reactive Power
How much reactive power does a generator of rating 3.5MW generate?
Raman Jain
- Jan 3rd, 2011
The reactive power , Generator can supply, can be determined by the Capabilty Curve of the Generator , supplied by the manufracturer.This is a design criterion.
raviiisc
- Sep 8th, 2010
Generally the Alternator or Generator is rated in MVA format rather than MW format.The reactive power supplied by the generator is then decided.I think the questioner thinking about the ratings provid...
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Apparent Power and Reactive Power
What is apparent power and reactive power?
Steeve Cantave
- Mar 15th, 2011
Apparent power is the power that is needed for the circuit to perform. In an AC circuit with resistive, capacitive, and inductive components, not all power is converted from electrical to non-el...
zaheerdahri
- Dec 23rd, 2010
Apparent PowerApparent power (S) is the power delivered to an electrical circuit. The measurement of apparent power is in voltamperes (VA).Reactive PowerReactive power (Q) is the power consumed in an ...
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Tubelight Stator and Choke
What is the use of stator and choke in tubelight?
G.Harish
- Nov 19th, 2016
It gives initial current to bulb
rohansharma
- Mar 26th, 2011
Choke Coil : for producing a very high voltage across the terminals of Tube Light.Starter : It applies that high voltage suddenly to the tube light filaments, which makes ionisation of the gases in the light.
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