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You need to also state what the load is, Fan, pump, flywheel,.....
VFD's are not a fix all they don't work in all applications, many people say just throw a VFD on it.
 

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Chief Flunky
Field Service Engineer
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I'd start by contacting both the motor and VFD manufacturers. Is the motor rated for a VFD application and is the VFD suitable for a star/delta motor?
ALL motors can run on VFDs just fine. But there are lots of retrofit pit falls.

The big things to watch out for:
1. Cable length. If it’s too long add filter (dV/dt).
2. Breaker/fuses. Does it meet the VFD requirements?
3. Cap banks. What is resonant frequency? Are we going to blow something up?
4. Harmonics. How much in terms of drives? How much will we co tribute? Need DC choke?
5. Application issues. Bearings have minimum speeds. Do you have enough “over sizing” for the application? How much speed co from? Braking? Does it regenerate?
7. Cooling. You are adding 3% of the motor rating in heat into the cabinet. Will it tolerate it?
8. Cabling. Most drives are bottom in/out. Wye delta is top to bottom. Need extra?
9. Isolation? How to LOTO? Does it change? Do you have a secondary disconnect? Does the VFD need protection?
10. Space.

An “inverter duty” motor means it has a higher surge rating, at least 1400 V vs 1200 V but most are now 1700 V. This matters if cable length is long and might let you get away with no filter. Some have better bearings and cooling for higher turn downs but it’s not automatic. You pay substantially more to have the word inverter duty on the name plate. As ABB continues to kill quality at Baldor while raising prices, you are just paying for a name.

I do retrofits all the time. It’s easy to do. But unless you need the variable speed, a soft start gives you all of the VFD benefits for a fraction of the cost and gives you better life too. I have never run into a cabinet I couldn’t retrofit from wye delta to soft start.
 

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For retrofitting, you will have all 6 leads run back from the motor to the Y-D motor starter. You will need to terminate all 6 leads into the VFD, but 99% of the time the lugs on a 100HP VFD will not accommodate two conductors, so you will need a distribution block added to the cabinet. Given that a VFD is often larger than a Y-D starter, that may be problematic.

Other than that, it’s done all the time and in fact sometimes if you read the manual of the VFD, they might provide instructions for using a Y-D motor and show how to connect it.

If the motor was not made to be used on a VFD, its life may be cut shorter, but you already have that motor so (assuming the variable speed is necessary) why not use it and if /when it dies, replace it with an inverter duty motor at that time? Just be aware of the potential costs associated with unscheduled down time though. Sometimes that can really but you in the butt.
 

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Discussion Starter · #15 ·
For retrofitting, you will have all 6 leads run back from the motor to the Y-D motor starter. You will need to terminate all 6 leads into the VFD, but 99% of the time the lugs on a 100HP VFD will not accommodate two conductors, so you will need a distribution block added to the cabinet. Given that a VFD is often larger than a Y-D starter, that may be problematic.

Other than that, it’s done all the time and in fact sometimes if you read the manual of the VFD, they might provide instructions for using a Y-D motor and show how to connect it.

If the motor was not made to be used on a VFD, its life may be cut shorter, but you already have that motor so (assuming the variable speed is necessary) why not use it and if /when it dies, replace it with an inverter duty motor at that time? Just be aware of the potential costs associated with unscheduled down time though. Sometimes that can really but you in the butt.
Thanks good information
 

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Bilge Rat
motors and controls.........
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How many wires does it have? If it's 12 then it's dual-voltage single speed.

If it has 6, you'll need to look on the nameplate and see if it'2 speed. A 2 speed motor hooks up differently than single speed one. Usually they are single voltage.

Before we can tell you how to hook it up, we need to know how many speeds and what voltage it runs at.
 

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How many wires does it have? If it's 12 then it's dual-voltage single speed.

If it has 6, you'll need to look on the nameplate and see if it'2 speed. A 2 speed motor hooks up differently than single speed one. Usually they are single voltage.

Before we can tell you how to hook it up, we need to know how many speeds and what voltage it runs at.
we need a pic of the nameplate on the motor and the connection plate if it is separate
 

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Chief Flunky
Field Service Engineer
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3,458 Posts
How many wires does it have? If it's 12 then it's dual-voltage single speed.

If it has 6, you'll need to look on the nameplate and see if it'2 speed. A 2 speed motor hooks up differently than single speed one. Usually they are single voltage.

Before we can tell you how to hook it up, we need to know how many speeds and what voltage it runs at.
There are a lot more tell tale signs than that. It might also have only 2 contactors which is another dead giveaway. But 2 contactors can also be reversing or part winding. You can tell the motor information from the name plate and you can tell a lot too by looking how the contactors are jumpered.
 

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Chief Flunky
Field Service Engineer
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2 contactors can mean Y-∆ in some cases. I see this often with packaged air compressors.
How do you do this? Leave the main leads continuously energized?

3 contactor is easy to spot. The third contactot might be smaller and often is but the dead giveaway is that the line side is dead shorted and it is numbered over to the delta contactor on the load side while that one is jumpered to the main on the line side. This is an open transition wye delta. There is also a closed transition type. It is very obvious because it requires 4 contactors and a set of resistors (that are often burned up).

The auto transformer starter can also be a 3 contactor starter arrangement but it’s pretty obvious when you see a big transformer in the bottom. A strange variation uses a goofy double throw, 6 pole contactor. I’ve seen one only once that I remember. It was an enormous “leaf” style contactor instead of a T-bar style. I recall scrapping the contents and replacing it with a Benshaw RB2 soft starter which looked TINY in there in spite of the fact that RB2s are one of the larger foot print soft starters.
 
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