Cable Selection For 150A AC Drive to Motor

→ British Standard 7671.

The cable is over heating due to harmonics.

Generally it suggested to provide an Output Reactor, if the distance between the VFD and the motor is above 30 metres.

What country are you in.....? Different countries have different wiring codes, but generally speaking, the method in which the cable is run, and the type of cable employed, have a direct bearing on the current carrying capacity and indeed the volt drop.

In America we use HP (horse powers) for motors, not kWs. However, 90 kWts is about 120 HPs. The ampere rating of conductor depends on both power and voltage for any particular type of motor. For three phase motor we find FLC (Full Load Current) from the table in NEC (National Electrical Code). For 125 HP, 230V, 3-phase motor we have 312 Amperes of FLC. Your motor is working on different voltage, so whatever it is, multiply 312A by 230V and divide it by your voltage, and you will find your FLC. You should multiply your FLC by 125%; the result is the ampere rating of your wires. If you still have problems or questions, just let me know (my user name is my e-mail as well). It would be easier to determine wire current if I new the voltage and all about your motor. Good luck, Andrey.

Hello Dear

Selecting 95 mm2 Al cable for 90 Kw motor is basically wrong. It is clear that you have not considered the derating factors that must be used to size the cable. The derating factors are: a) Ambient air temp b) Ground temp c) whether cable is laid on open racks in air or buried under ground d) whether cable is laid along with other cables in touched or speced configuration e) thermal resistivity of soil (for u/g laying) and f) depth of laying. Since you have not mentioned any of these factors in your query, I presume you have not used any of them in your cable sizing calculations. Assuming you have laid the cable under ground in touching configuration with other existing cables, my calculations tell me that you should have gone for 185 mm2 Al cable. Voltage drop is not the deciding factor here as the is distance is small. Please refer any cable manufacturer's catalogue for cable sizing.

Raina

Aluminium Cable of 95 mm2 will not take 150A and stay cool!

If the Cable was copper, then 190A should be maximum ( without derating for temperature etc) BUt for Aluminium, you must divide by 2 as a rule of thumb (or look in the cable rating table of the maker...). Therefore, 95A will be the max you can load the Al 95 mm2.

You are having 134A going thru ! Your Cable will Overheat whether harmonics or not!

Harmonics and wave shape: After the VFD, the shape of the voltage wave will not be sinusoidal like the mains voltage. Therefore, harmonics will appear. The length of the cable normally warants that you screen it so that it will not broadcast some high frequency voltage and interfere with other electrical cables nearby. The harmonics will contribute to the heating of the cable but if properly dimentioned, (and a choke... check with maker of VFD first if it should be recommended between the motor and the VFD...), it will not overheat the cable that much: Cable Size and being Al....