DickDV
Member
Kid, to answer your questions in your reply,
First, yes conduit is a pretty good noise suppressor. Not as good as shielded cable but still pretty good.
The motor lead cable is made mostly to provide grounding and shielding to reduce radiated EMI/RFI. I've never heard the corona discharge claims. They might be true, however.
Just why you can get away with longer leads on higher hp motors has to do with the lower impedances of the larger motors and lower distributed inductance of the larger cables. The rules for length I gave you are only for the protection of the motor insulation. You may need to shield the wiring sooner for EMI/RFI problems.
The MG1P31 is a reference to special testing that NEMA mandates in their specification MG1 Part 31. This testing involves higher voltages and pulse power rather than sine wave power to adequately test insulation integrity on motors intended for inverter power. Inverter power stresses motor insulation more than ordinary sine wave power so suitable testing was put into place for motors claiming to be "inverter duty". Without that spec endorsement, you don't know what you are buying.
A six, twelve, or eighteen pulse drive refers to the number of input power phases and the resulting number of diode rectifiers that are used to convert the AC to DC. For example, a drive with only single phase input AC could be said to be a two pulse drive, if three phase then six pulse, if six phase then 12 pulse, and if nine phase then 18 pulse.
If a drive is designed for ordinary three phase input power and has a diode rectifier input design, then it is a six pulse drive. Most commodity drives are like that.
The extra phases and extra diode rectifiers are done primarily to reduce input current and voltage distortion. Six pulse drives so not use input power smoothly and the resulting disturbances cause all kinds of trouble with transformers and other sensitive electronic devices that are using the same power. Today, there is new technology around that reduces input distortion and harmonics without all the extra phases and the special transformer that is needed to create them.
Your selection of a k rated isolation transformer is good as it tends to block the passage of distortion and harmonics backward into the power network. It also provides a nice close grounded wye source for power to the drive. Be sure to ground the center of the wye secondary to the drive. Doing that will help avoid other problems if your plant grounding system is anything less than excellent.
Hang in there and keep learning! The risks are great but, with care and due diligence, you can pull this off. If there is help available, be sure to take it. It makes the learning experience somewhat more "comfortable".
First, yes conduit is a pretty good noise suppressor. Not as good as shielded cable but still pretty good.
The motor lead cable is made mostly to provide grounding and shielding to reduce radiated EMI/RFI. I've never heard the corona discharge claims. They might be true, however.
Just why you can get away with longer leads on higher hp motors has to do with the lower impedances of the larger motors and lower distributed inductance of the larger cables. The rules for length I gave you are only for the protection of the motor insulation. You may need to shield the wiring sooner for EMI/RFI problems.
The MG1P31 is a reference to special testing that NEMA mandates in their specification MG1 Part 31. This testing involves higher voltages and pulse power rather than sine wave power to adequately test insulation integrity on motors intended for inverter power. Inverter power stresses motor insulation more than ordinary sine wave power so suitable testing was put into place for motors claiming to be "inverter duty". Without that spec endorsement, you don't know what you are buying.
A six, twelve, or eighteen pulse drive refers to the number of input power phases and the resulting number of diode rectifiers that are used to convert the AC to DC. For example, a drive with only single phase input AC could be said to be a two pulse drive, if three phase then six pulse, if six phase then 12 pulse, and if nine phase then 18 pulse.
If a drive is designed for ordinary three phase input power and has a diode rectifier input design, then it is a six pulse drive. Most commodity drives are like that.
The extra phases and extra diode rectifiers are done primarily to reduce input current and voltage distortion. Six pulse drives so not use input power smoothly and the resulting disturbances cause all kinds of trouble with transformers and other sensitive electronic devices that are using the same power. Today, there is new technology around that reduces input distortion and harmonics without all the extra phases and the special transformer that is needed to create them.
Your selection of a k rated isolation transformer is good as it tends to block the passage of distortion and harmonics backward into the power network. It also provides a nice close grounded wye source for power to the drive. Be sure to ground the center of the wye secondary to the drive. Doing that will help avoid other problems if your plant grounding system is anything less than excellent.
Hang in there and keep learning! The risks are great but, with care and due diligence, you can pull this off. If there is help available, be sure to take it. It makes the learning experience somewhat more "comfortable".
