How to calculation Hp to KW, Capacitor KVAR size  for motor

 HI ,Friends Today's topic, Motor horsepower, power factor, How to calculate KVA, KW, currrent and their relation,How to calculation Hp to KW, Capacitor KVAR size  for motor  I will give 1 example, for both  1 and 3 phase motor. 

   hp to kw conversion  hp to current   

          1st, we will calculate single phase motor, then for 3 phase motor, 

          The  single motor phase, 230 volt, PF is 0.8, PF should be known, and Hose power is 10 HP, single phase motor, may not be available for 10 HP rating, single phase motor are in small rating, but 10 HP is taken just to explain, the motor, is of 7.46 K watts, for KVA calculation, this 7.46 KW devided by PF 0.8, it comes 9.3 KVA (KVA=KW/PF). this 10 HP motor is of 9.3 KVA, 

 motor hp to current calculator for 1 phase motor

          The current flows are,

          here, we have not taken KW, we took watts 7460, if you take KW, then current answer will be in KA, it will  zero point some thing, difficult to understand, (I=P/V*PF) current comes 40.5 amps, full load current here, will be 40.5 amps, 

         

capacitor size calculator for motor  

        

          KVAR will be calculated , Here I have taken KW, such that, we get answer in KVAR, answer will come 5.6 KVAR, Means, 10 HP motor, having 0.8 power factor, at full load, will draw 40.5 amps current, and 5.6 KVAR reactive power, will flow, 

       here, this 5.6 KVAR is to be removed, we add capacitor to remove this, now if you connect a capacitor, we will connect between line and neutral, I will tell precautions also at the end, you must learn that also, I connected a capacitor here, calculated value was 5.6 KVAR, but I connected only 4.5 KVAR capacitor. because, that motor power factor will be changing, with load and RPM both, if you connect full size capacitor and if requirement comes down, then over voltage will be there, so we connect little less KVAR capacitor, Further, this calculation is done in KVAR, I did not told you capacitor micro farad, capacitor for PF correction, are defined in KVAR rating, we do not order in micro farad, for this use, buy micro farad value, is also written on the capacitor, so you need capacitor of 4.5 KVAR, 230 volt, 1 phase,

motor hp to current calculator for 3 phase motor

        Now, I will explain calculation for 3 phase motor, Here is 3 phase, 400 volts, this 400 volt, is voltage difference between 2 lines, 400 V is not between line and neutral, PF is 0.8, this motor is also of 10 HP, here also, calculation is like earlier, KVA will be 9.3 KVA, this calculation is like earlier, 

      But here, calculation for current is different, current will be equal to, power is taken in watts, to get current in amp, IF you take KW, then current will be in KA, difference between single and 3 phase is, here root 3 is used here in 3 phase(I=W / ROOT 3 *V*PF), voltage is also changed, from 230 volt to 400V, so we get 13.5 amps, so here, in all 3 wires, 13.5 amperes current will flow.

       

motor power factor correction

kvar calculation

       KVAR calculation is  done like this,(KVR= KW-root(1-pf square )/pf).  we get 5.6 KVAR, this is same as in single phase motor, because load is same, horse power is same, so KVAR also will be same, PF is same, voltage is changed, so current also changed, but power is not changed but fixed, 

how much capacitor for motor

         here what will we do?, calculated value is 5.6 KVAR, but we will not take full value, we will take less value, say, we select only 4.5 KVAR capacitor, so 3 capacitors are connected, total is 5.6 ( 4.5 selected)KVAR, sinle phase value will be 1/3 of this. because 4.5KVAR is use, so 1/3 will be 1.5 KVAR  each. so you have to use 3 capacitors, 1.5 KVAR each, 

       when you order the capacitor, if you connect capacitor yourself, then supplier will give 3 separate capacitors, or 3 assemblled in single unit, this you have to discuss with supplier, so you have to connect, 3 capacitor of 1.5 KVAR each in delta connection, delta connection will cost less, star connection will may be costly,, may be changed now, you must enquire cost for star & delta both, 

kvar calculation formula 3 phase

     what happens? 

      The capacitor will have a film inside, that is available for 400 volts, if they have to make 230 volt capacitor, then also they have to use 400 volt film, 400V capacitor will be sold as 230 V, so it becomes costly, Precautions, KVAR requirement, changes with load and RPM of motor, so PF will go on changing with fixed capacitor, to avoid this problem, we use automatic power factor controller, over correction will generate over voltage, if you connect fixed capacitor, and if load comes down, so there will be over compensation, and over voltage will be there, so solve this, either you use automatic controller, or,  always use less size of capacitor, than calculated value, so over voltage problem will be less, if PF is not know, then measure PF at full load using a PF meter, then calculate KVAR, 5th, delta connection will cost less, star arrangement may be costly, 6th is, 7th is, use automatic PF controller, Automatic PF controller, will solve many problems, and PF will be good for different load & RPM, other wise PF will go on changing, as PF will change with change in load & RPM .