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
How does a washing machine know when the water level is full?
If I understand you correctly ..yes. This is why most manufacturers suggest you wait till the tub is full before you add your clothing. You should add your clothing so that it freely agitates. The way the machine knows is that it has a full level it also knows to empty water if it get higher then the safe ( overflow) point.
What is the CT ratio adopted for 1000 KVA transformer in neutral circuit?
Your question is not 100% clear to me.A 1000 kVA transformer puts out approximate 1400 Amps per Phase at 230 Volts.A CT ratio used at the bushings would be 1600/5 or 2000/5 Amps for metering.A Neutral CT maybe used for buszone protection or tripping the TX when excess unbalancing occurs. Depending upon how you want to set the protection level it could be a 800/5 Amps CT.For 115 Volts systems double the CT ratio’s 3200/5 or 4kA/5 Amps.
What is the transformer HT/LT current calculation formula?
Transformers are rated in volt amps, VA. For an ideal single phase transformer (no losses)-VA is HT volts multiplied by HT amps. VA is LT volts multiplied by LT amps.HT volts X HT amps = LT volts X LT amps = VATo find LT amps-LT amps = VA/LT voltsTo find HT amps-HT amps = VA/HT voltsLet us take a 1200 VA transformer where the primary voltage is 120 Volts and the secondary is 12 Volts. Then-HT amps = 1200/120= 10 AmpsLT amps = 1200/12= 100 AmpsAnother way of doing this is to look at the voltage ratio, 120 to 12 volts in this case. That is a ration of 10:1.The current will be the same ratio but reversed, 1:10. 10 amps at the primary and 100 amps at the secondary.Hope this answers your question.RegardsNorman
Why should I use a 16 A 'C' characteristic MCB against a 32 A 'B' characteristic MCB for my air conditioner?
Type "B" Curve MCB's are meant for resistive type of Loads like Heaters, Geysers, Microwave Ovens etc, Type "C" Curve for Inductive type loads like Motors, AC's, Fridges,Booster Pumps.For a Normal 1.5 Tr AC 2000 watts a Type "C" 20 or 16 Amps Single Pole MCB is sufficient in the AC Socket Box near the AC if Meter and AC located in the same level.If Meter is in Ground Level & AC in Higher Floor Level then put 40 Amps DP "C" type MCB or 40/63 Amps DP Isolator in Ground Level and SP "C" type 16 Amps MCB in AC Socket plus AC PIN Box in which the AC Wire is put !If a 32 A Single pole MCB is put in the AC Box in case of short circuit it will not trip & will be a safety hazard.There is also “D” Curve MCB's which are used for CT Scan, X Ray, MRI Machine loads which are super inductive in type & in industrial applications like precision welding + large winding machines !Updated:-20-Jan-2019In my Uncle's Mansion in Rishikesh Uttarakhand the Electrician's had put wrong MCB Type & Ratings like “B” Type Curve 6/32 Amps in AC Box ! In September 2018 I removed all the Six & put L/T 16 Amps SP “C” Curve MCB in the AC Metal Box ! I wanted Indo Asian or Havells but L/T was equally good but as a brand it is more suited towards Industries than homes !As all AC's 'll be of 1 TR Split Type due to Room Size 16 Amps was sufficient !Swami Aniruddha !
Why the secondary winding of current transformer is always shorted?
We know that, in a CT the primary current is dependent on the load current or line current as CT is connected in series with the line. So, primary current of CT (assuming constant line current) is constant irrespective of whether the secondary of CT is connected with burden or not.During normal operation of CT, the primary and secondary winding produces mmf which by lenze’s law opposes each other. As the secondary mmf is slightly less than the primary mmf, the net mmf is small. This net mmf is the working/magnetizing mmf of the core of CT.Now, in case secondary winding is kept open, then secondary current will be zero while the primary current of CT will remain same. Therefore the opposing mmf of secondary will no longer exist. Hence the net mmf is due to primary current only i.e. N1I1 (N1 = No. of Turns in Primary,I1 = Primary Current) which is very large. This large mmf will produce large flux in the core and will saturate the core.Again, due to large flux in the core, the flux linkage of secondary winding will be large which in turn will produce a large voltage across the secondary terminals of the CT. This large voltage across the secondary terminals will be very dangerous and will lead to the insulation failure and will lead to failure of CT.The failure of CT will lead to outages of transmission elements causing loss of power and consequently loss of revenue.Thus, the secondary of CT must always be shorted when primary is energized.
How to pass a Labcorp drug test?
I have a test in a few days and the other day (wednesday) my back was hurting so my sister gave me one of her pain pills I've done the research and it will show up in a drug test as an opiate ...I also smoked weed that same day... According to labcorp their cut off levels for opiates is 2000ng/ml and for pot it's 50ng/ml they also test the creatine levels which means I cant just drink a **** load of water....which sucks!!!! I've had a friend use sure jell in the past and he passed his but i dont know where he went to get it done so i dont know if the cut off levels are the same .... any ideas on how to pass it?? and dont bother to answer if your just going to write...that i shouldnt do drugs....piss off i dont tell you what to do in your life so why should you mine??? exactly....anybody out there PLEASE help I really need this job....I've also thought about buying one of the flushing systems at my local headshop but i dont know which ones will work...
What is the difference between 0.2 and 0.2S class CT?
A2A.0.2 and 0.2S refers to the accuracy of the Current Transformer. A 0.2S CT has a much higher accuracy than 0.2.Since, accuracy depends on the load of the system, IEC/AS[1] have developed different standards to define accuracy under different load conditions, known as “Accuracy Class”For Accuracy Class 0.2, the declared accuracy is guaranteed from 5% loading. However the accuracy deteriorates under lower load conditions and below this load, the error is not guaranteed.Example:[2] In large industrial projects, where the project is commissioned in steps only, initially the loading will be very low. If the tariff metering CT errors are haphazard, it may not be acceptable either to the supplier (in case of negative error) or to the consumer (in the case of positive error). And the magnitude can be quite large, say, with a sanctioned demand of 10MVA, even 1% error means 100kVA.To cater such situations, Standards have introduced 0.2S, for tariff metering purposes. These special CTs guarantee the declared accuracy, even at much lower load currents. And some definite error can be defined even with a load as low as 1%. Thus they are suitable for industries where loads are commissioned in steps or stages.Footnotes[1] ETSNZ What does the s on the Accuracy class 0.2s & 0.5s mean?[2] CT Class Differences
Why is an open circuit test, in the case of transformers, done with the high voltage side open and the low voltage side connected to the source?
The circuit diagram for an open circuit test can be represented as follows:The high-voltage side is generally kept open because the current in high-voltage winding is less compared to that on low-voltage winding.We can further refer the knowledge of the equivalent circuit and phasor diagram that the current drawn by shunt parameters is a no-load current a very small current. Therefore the current that will flow in the circuit in the open circuit test is very low so the measurement of quantities voltage, current and power must be in the low voltage side so that the corresponding value will be readable in the instruments. And, therefore the open circuit test must be performed in the low voltage side.Source: Electrical Engineering