Hello Everyone,
I am currently studying Electrical Engineering (Completed my first year) and these days working as in internee with an HVAC organization. My supervisor has given me an assignment to work on involving VFD. I will list all the details I have.
1. Vertical Discharge VFD operated Condenser Pump for Hot Water Absorption Chiller
2. Actual Flow Rate = 825 USGPM
3. Actual Developed Head = 90 ft
4. Pump Efficiency = 0.75
5. He said the motor they will use is a 18.5KW IP55 Class F Insulation.
6. He said the VFD will be a 22KW
7. Supply = 380V, 3Phase, 50Hz
He has asked me to calculate the MCCB and wire size. Now this is what I have done,
1. In order to calculate the Hp we will use the following method;
Hp= (USGPM * Head * Specific Gravity)/(3960 * Efficiency of pump)
Hp= (825*90*1)/(3960*0.75)
Hp= (74250)/(2970)
Hp= 25
1Hp = 746W , Therefore 25Hp = 18.5KW motor. Is this right??? Is this how he sized the motor to be 18.5KW?? And for the VFD, they used the next size up ? Am I right?
As for the VFD, I had no information which model to select, so I did some research and found a danfoss VLT HVAC Drive. As per the technical information the rated amps are 44A.
As for the MCCB, What I have learned is this that for VFD operated motor we use the maximum rated amps of the VFD and not the motor. What ever the maximum rated amps of the VFD are we multiply it by 125% or 150%. ( I am confused here, as some articles say it should be 125% and other say it should be 150%) Any how if I multiply by 125% than I get a value of 55A so I guess we can use a 60A MCCB and if I multiply 150% than I get a value of 66A so I guess we can use a 80A MCCB.
Now when I asked my supervisor, he said I am wrong. He said they used a 100A MCCB. Now I am confused what to do. I know I am wrong and I am missing something very important.
I would appreciate, if anyone can help me with this. And also how to calculate the wire size, the info over the internet is way too cloudy.
Kind regards;
I am currently studying Electrical Engineering (Completed my first year) and these days working as in internee with an HVAC organization. My supervisor has given me an assignment to work on involving VFD. I will list all the details I have.
1. Vertical Discharge VFD operated Condenser Pump for Hot Water Absorption Chiller
2. Actual Flow Rate = 825 USGPM
3. Actual Developed Head = 90 ft
4. Pump Efficiency = 0.75
5. He said the motor they will use is a 18.5KW IP55 Class F Insulation.
6. He said the VFD will be a 22KW
7. Supply = 380V, 3Phase, 50Hz
He has asked me to calculate the MCCB and wire size. Now this is what I have done,
1. In order to calculate the Hp we will use the following method;
Hp= (USGPM * Head * Specific Gravity)/(3960 * Efficiency of pump)
Hp= (825*90*1)/(3960*0.75)
Hp= (74250)/(2970)
Hp= 25
1Hp = 746W , Therefore 25Hp = 18.5KW motor. Is this right??? Is this how he sized the motor to be 18.5KW?? And for the VFD, they used the next size up ? Am I right?
As for the VFD, I had no information which model to select, so I did some research and found a danfoss VLT HVAC Drive. As per the technical information the rated amps are 44A.
As for the MCCB, What I have learned is this that for VFD operated motor we use the maximum rated amps of the VFD and not the motor. What ever the maximum rated amps of the VFD are we multiply it by 125% or 150%. ( I am confused here, as some articles say it should be 125% and other say it should be 150%) Any how if I multiply by 125% than I get a value of 55A so I guess we can use a 60A MCCB and if I multiply 150% than I get a value of 66A so I guess we can use a 80A MCCB.
Now when I asked my supervisor, he said I am wrong. He said they used a 100A MCCB. Now I am confused what to do. I know I am wrong and I am missing something very important.
I would appreciate, if anyone can help me with this. And also how to calculate the wire size, the info over the internet is way too cloudy.
Kind regards;