What is the difference between single core and multicore cables?
Single core cable A single core wire is a cylindrical strand of metal. In single core wire there is only a single core of metal is present, mostly copper or aluminum.These wires are available in different thickness and gauges.Used for Domestic purpose Single core wires or cables are widely used Domestic purpose. They are mainly used in electrical appliances, these wires can take a good load that is why they are more preferred in domestic uses.Can handle high temperature Single core cables are very high ambient wires; these cables are a good conductor of electricity as well as heat. These cannot melt or burn easily.Multi core cables Multi core cables are cables, which contains more than one core in the cable. These are flexible cables which are widely used for electric purpose, these cables are professionally made with good quality.Used for industrial purpose Multi wires or cables are widely used for industrial purpose. These cables are the good conductor of electricity and can take loads and benefits in industrial sectors. It can take heavy load and can support heavy industrial machines.Use in Entertainment sector Multi core cables are widely used in the entertainment sectors like theaters, concert venues and many others. People use multi core cable and combine their power, AV and data to avoid any tangled cable.
What will happen if we use 33kv 3core 3sqmm size cable inplace of 11kv 3core 300sqmm?
In short, your replacement cable will blow like a fuse.You are replacing a cable designed to carry a lot of current. We can tell by its core gauge. While your replacement cable has insulation to withstand three times the voltage of the original one, when you close the circuit the thin core will overheat, melt and break. Given the gauge difference my bet is that it will happen instantly and spectacularly.Please keep your distance and warn others if you insist in running the system like this, for a lot of smoke and incandescent material are on script and, given the voltage rate, electric arc also would make a cameo, likely scattering molten material all over the place!
How do you calculate the size of a HT cable?
In case of LV system cable can be selected on the basis of its current carrying capacity and voltage drop but in case of MV/HV system cable short circuit capacity is an important/deciding factor. So in case of HT motor, the cable short circuit capacity alone is enough to determine the cable size as rest two parameters will automatically follow.Consider the below example:Motor KW = 350Pf = 0.8, Efficiency = 94%System Voltage, V1 = 6.6 KVCable length = 200 m (Single Run)Load Current = P/(1.732xVxPfxEff)= 350000/(1.732x6600x0.8x0.94)= 41 ASuppose Short circuit level/Fault level for H.T. system, Ish (for duration t=1sec) = 26.2 KAWith Aluminium condr, XLPE insulated cable = Ish(In KA) X t1/2 = 26.2 X11/20.094 0.094= 278.72 Sq.mmHence nearest higher size 300sqmm is required.We can see from the below table also that the short circuit capacity of 300sqmm cable is 28 KA which is more than our fault level.We can see that this will automatically satisfy other two conditions also.Let’s select 6.6 KV, 3 core, 300 http://Sq.mm, Aluminium, XLPE, Armoured cable for single runTemperature Correction Factor, K1 when cable is in the Air = 0.88 (for 50* Amb temp & XLPE cable)Cable Grouping Factor (No of Tray Factor), K2 = 0.68 (for 3 trays having 9 cable each)Total derating factor = K1 x K2 = 0.88x0.68 = 0.5984Current capacity of 300 Sq.mm XLPE Armoured aluminium cable in Air is 450 AmpTotal derating current of 300 Sq.mm Cable = 450x0.5984 = 269.28 AmpResistance = 0.130 Ω/Km andReactance = 0.0999 Ω /KmVoltage drop = 0.26 Volts/Km/Amp (as per Havell’s brochure)= 0.26x200x41/1000= 2.132 VTerminal voltage at Motor, V2 = 6600-2.132 = 6597.868 V% Drop = (V1 – V2)/(V1)= (6600 – 6597.8)x100/(6600)= 0.032%To decide 300 Sq.mm cable, cable selection condition should be checked1. Cable derating Amp (269.28 Amp) is higher than full load current of load (41 Amp) = OK2. Cable voltage Drop (0.032%) is less than defined voltage drop (5%) = OK3. Cable short circuit capacity (28.20 KA) is higher than system short circuit capacity at that point (26.2 KA) = OK300 Sq.mm cable satisfied all three condition, so it is advisable to use 3 Core 300 Sq.mm cable.You can use the Havell’s cable brochure for referencehttp://www.havells.com/content/d...
How do we calculate the size of three phase cables from kW or kVA with respect to amperes?
You hire a licensed Electrical Engineer. Seriously, depending on the application this could be very dangerous. This task is not as easy as you may think.This is not a straightforward question to answer. There are a lot of factors that need to be taken into consideration. For most cases however, you need to do two things:Convert from KVA or KW to Amps. The two formulas you need are:KW = KVA x “Power Factor”For motors, use a “Power Factor” of 0.8For electronics, use 1.0Then, KVA = 1000 x VA = 1000 x Volts (Phase to Phase) x Amps x 1.732You can browse around here for more.After you have determined the Amps we can get into the real part of your question, how do we calculate the size of the cables. For this, we turn to the National Electrical Code here in the US. It is published by the National Fire Protection Agency and is intended to help you size wires without burning buildings down.The table you probably want is 310.15(B)(17) which is pictured below. The numbers in the table are amps. You need to choose a cable type and an insulation type from the top. The most common building cable type is THHN copper wire at 90 degrees C. You may need to look into what your specific cable is first.Finally, you use that column, go down to the next highest ampacity, and find the correct AWG size on the left. For example, if you are using 90C copper THHN and need an ampacity of 100A (83kw at 480V 3Ph), then you need 6AWG wire which is rated for 105A.Remember, this is seriously oversimplified. An engineer will calculate the size of the wire based on:How many wires are in the conduit?What is the conduit made of?What is the ambient temp of the ground?Is this run along a roof?Is this run under a heat source?What are the heat dissipation characteristics of the soil if this is in the ground?Do I need to oversize the wire based on dirty power characteristics like harmonic distortion?What size should the neutral wire be? 50%? 100%? 200%?Can I use the 90C column? Usually I cant since I can’t be sure the terminals are rated for that temp.Do I need to oversize for voltage drop if this is a long distance?The list goes on. If this is for a public building in the US, you are legally required to get a licensed engineer to do this for you. I expect in many other countries this is the same.
Why do we use kVA instead of kW to rate alternators and transformers?
Let us begin with the difference between kVA and kW.The k just means 1000 times whatever the units are.VA is Volts multiplied by Amps. V x A.W is Watts which is Volts multiplied by Amps multiplied by Power Factor. V x A x PF.Now the transformer is a power conditioner. It is there to pass on power at a specific voltage for something that someone (or lots of ones) wants this power to do.Boil kettles, wash clothes, cook food, light lights, run conveyors, fire furnaces, saw wood and everything imaginable, both domestically and industrially. These collectively are loads.Loads are what creates reactance, and this is what determines the Power Factor. Motors are inductive, and precipitators are capacitive.In most cases the engineer providing a power transformer does not know what the applied loads are going to be. That engineer then states that s/he is providing a certain number of Amps at this specific Voltage. The engineering shorthand for this is VA, kVA (x 1000), MVA (x 1 000 000). Other engineers who are doing the load appropriations will then know how much they can load that particular transformer.A full transformer specification will look like this – Volts in/Volts out at this VA.Example – 11/3.3kV 500kVAExplanation – 11000 volts in, 3300 volts out, at 500000VA or 500000/3300=151.5 AmpsUsage – For an induction motor/s PF 0.8 - 3300x151.5x0.8=400000W or 400kW maximum loadPower Transformer-Efficient-Expensive-Long Lasting-Deserving of RespectHope this answers your question.Regards
What is the difference between an AC cable and a DC cable?
No difference. both are same there is no ac and dc cable i mean there is no specific cable to be used for both individually. Any conductor works for AC will work for DC too.
How many amps are there in a 30 KVA generator?
More information is needed to answer your question, but some assumptions could be made to give a reasonably accurate answer. We start with the basic calculation which is fairly simple:For three phase current, VA = Voltage x Amps x P.F x √phases = V x I x P.F x 1.73WhereI = amperesV = voltagePF = power factor (usually either 1.0 or 0.8)kVA = VA x 1000(Note that the square root of three is only used for 3 phase current. In single phase calculations, the square root of one is used, which equal one and therefore won’t change the result)To find amperes (current) for three-phase current we just rearrange the formula.I = (kVA x 1000) / (V x √3)For single phase current you can just leave out the √3I = (kVA x 1000) / VWith that knowledge, we can calculate some real numbers just for fun. Naturally, you should plug in your own voltages and phases. 30kVA = 30,000VA240V Single Phase → 30,000VA / 240V = 125 amperes240V Three Phase → 30,000VA / (240 x 1.73) = 72.25 amperes208V Three Phase → 30,000VA / (208 x 1.73) = 83.37 amperes480V Three Phase → 30,000VA / (480 x 1.73) = 36.13 amperesYou can find out more about single- or three-phase generators and how they are different here → Single-Phase versus Three-Phase Generators.MJ
What is the current carrying capacity of ACSR conductors?
Current carrying capacity of ACSR conductor depends upon following;Cross-sectional area of the conductorConductor MaterialSurrounding temperature (Ambient temp.) of conductor used in transmission lineAge of the conductorBelow table will show you the current carrying capacity of various types of ACSR conductor;Image Source: Aluminium Conductors Steel Reinforced (ACSR ) ManufacturerPlease read my answer on Vijay Belekar's answer to What is power handling capacity of ehv transmission line?Please read my other answers related to transformer core, diff. b/w power & distribution TX, EHV lines, Lightning & airplanes, transformer testing, AC vs DC, Buchholz relay, 3ph vs 1 ph, grounding, reason for power trip, MCB vs MCCB, DC motors, electrocution of birds by power lines etc on Vijay Belekar.
If 3mw of power is to be transmitted over a distance of 30km, what will the desirable transmission voltage be?
For 3mw power needed voltage is 110 kv.From P=√3 VIcos∅.HERE Distance does not affect the selection of transmission voltage.