Voltage issues with plc

Hello all. We are an OEM and one of our plc controlled machines has a mixture of 3ph and 1ph motors on it. The 3ph motors are for drilling wood and the 1ph motors are standard wood routers for routing hinge pockets.

In the past we have hung a large transformer on the machine to get the 120VAC for the routers. We only required the customer to run 3ph 3 wire (+ ground)to the machine. When the routers start they pull a lot of current so we had to oversize the transformer.

I want to eliminate the costly transformer and require the customer to run 3ph 4wire to the machine to get my 120VAC. This will not cause such a strain on the transformer and the system in general.

We recently ran into a customer who did not have 3ph 4wire. He had a separate service for the 3ph and another service for his 120VAC power.

I am curious as to whether some of you guys have ran into this issue and what approach you might have taken. It seems to me that most modern machines with the same power requirements would require the customer to supply 3ph 4wire to the machine. Thanks.

Greetings!

I have run into this problem several times on a variety of applications. Before I answer your specific question, here is a more general answer that should benefit you and others in this forum in the future...

First, I always make sure before a motor is "spec-ed" out on a new project what the available electrical service is. This is extremely important if you are an OEM serving a global market. For example, let's say you have a machine or process that requires a large amount of small motors. A special voltage might cost 20% more than what you are buying as "standard". Furthermore, your vendor may give you special pricing on the one(s) you use most. Sometimes the engineer isn't even aware of this.

Unless you are protected in the purchase order or thought of this in advance, this 20% upcharge comes from your bottom line (profit).

Second, sometimes the available electrical service can make a design quite challenging. For example, let's say only 220VAC 50 Hz is available. You may need to get special components to fit your needs or de-rate a larger model. This also can be pricey.

Third, there is extra design time involved. And time is money. Even if you have a standard design, you must modify at least three drawings to show the differences. This could be substantial, because a simple transformer change (size or type) affects the schematic, the panel layout, and the bill of materials, not to mention wire sizing...

In summary, if you as an engineer along with your company's sales force don't understand the cost ramifications of a different electrical service up-front (at the quote stage), it's either going to cost you or start a fight over money with the customer, who is "always right".

Now back to your specifics. On large machines, I have had the customer check with his electric utility to see if they could accommodate the service my machine required by adding a new incoming line. This may be cheaper in the long run than having a special transformer to heat up and service...

I guess I will have to rework our electrical worksheet that the salesmen use with the customer. In the past the salesmen really did not push the customer to get a qualified electrician to fill out the worksheet because of the fact that there was a transformer on the machine to get the proper voltages.

My biggest fear is that someone wires up the high leg on a center grounded delta to our 120vac routers and burns them up.

I know there are alot of configurations out there, but so far I have put the following on the worksheet checklist.

#1. 3ph 208/120 wye.
#2. 3ph 240/120 center grounded delta.
#3. 3ph 240 corner grounded delta.
#4. 3ph 240 ungrounded delta.

Thanks.

zmanvortex said:

I know there are alot of configurations out there, but so far I have put the following on the worksheet checklist.

#1. 3ph 208/120 wye.
#2. 3ph 240/120 center grounded delta.
#3. 3ph 240 corner grounded delta.
#4. 3ph 240 ungrounded delta.

Click to expand...

Just be sure to add a "#5 Other (please specify)" so they don't just pick the one in your list that's 'closest'. Also provide an entry for Hz... :nodi:



-Eric

What? No 480VAC?

In this case, I would spec 208/120.

I have been in many plants where power varied from area to area, addition to addition. Generally, there was always 3 phase of some kind, and single phase 120/240 available.

Unfortunately, even in some modern plants, the 120 volt house source was undersized originally, and has to have a transformer.

Many large plants are 480 3 phase only, and each cell or small area has its own step down xfmr. Maybe the NEC should have addresses this long ago, like in the 30's.

Good Luck!

regards.....casey

CaseyK said:

Many large plants are 480 3 phase only, and each cell or small area has its own step down xfmr. Maybe the NEC should have addresses this long ago, like in the 30's.

Click to expand...

I think this issue applies both in the US and, to a much greater scale, the rest of the world. This is especially due to the addition of "hurts" in the equation... (ouch)

Now that I think about it, I do not think that 480 volts was available in the 30's. Many places I worked at in the 70's were just getting 480. Where I live now, the whole downtown business and industrial district is 208/120 for 3 phase, or standard 120/240 single.

Ahhhhh, the simple life out in the cornfields.

My first industrial job was in a 240 3 phase open delta plant. I learned about the wild leg after several months. 150 watt flood bulbs were really bright on it. When I figured it out, I wired them correctly, but was told to hook them back up the way they were. Seems the R+D crew liked the "WHITE" light, no matter how long the bulbs lasted. Since the had a Peterbuilt" pick up truck, it was obvious that money was not a problem. Maybe that is why your pumpkin pie mix was so expensive. The plant canned over 90% of the worlds pumkin each summer, and would sit idle the other 9+ months each year, with a few dozen maintenance people wandering around inside.

When I moved to a "Modern" plant, I appreciated the fact that I could run smaller wire.

regards.....casey

Ok, I have revised my Electrical Worksheet Checklist. I have also commented as to whether we would have to install a transformer on the machine next to each item on the list.

#1. 440-480 VAC 3PH Wye or Delta (transformer required)

#2. 208/120 VAC 3PH Wye 4 wire. (transformer not required)

#3. 240/120 VAC 3PH Center Grounded Delta. (transformer not required, caution wild leg)

#4. 240 VAC 3PH Ungrounded Or Corner Grounded Delta. (transformer required)

#5. Other (Please Specify Below)


Well I think that should do it. Thanks guys.

I am curious if changing the 1PH motors to 3PH was considered. I am assuming since they are routers that its an item you buy pre-made so it is not an option (at this time). If that is the case then it may be possible to obtain them (at some time) utilizing 3PH motors which would make it easier to offer the system with one power source.

If you are designing your own routers then it may be cost effective in the long run to consider using all 3PH even if the production cost increases slightly.

Do you ever ship machines to Canada? There are quite a few places there with 575 VAC 3-phase, eh?

I mention that because of a Murphy's Law case study I endured several years ago. On this particular machine, we subcontracted the main DC drive to a drives vendor. The first machine went to Canada where the plant voltage was 575 volts. The next two machines went to the same customer in the US where the plant voltage was also 575 volts. By the time we got an order for the fourth machine which was to go to a plant in the US where the voltage was 480 volts, the drives vendor had forgotten that the isolation transformer with a primary voltage of 575 was a non-standard thing, and went ahead and ordered their "standard" bill of materials.

When we got to start-up at the customer's plant, it took awhile to figure out why the 3-phase supply to the drive was too low no matter which taps we used. As the OEM, my rear end was covered because I had specified the correct voltage on the PO to the drives vendor, but that didn't alter the fact that startup was delayed while we waited for the correct isolation transformer.

rsdoran,

These are your everyday Porter-Cable routers and we use them on quite a few of our machines so we get special pricing. This just happens to be the only machine which mixes 3phase motors and the single phase router motors. All other machines that use these routers are single phase machines. Thanks for the feedback.

Steve,

We do ship quite a few machines to Canada, so hopefully they will fill in the Other option and we can go from there.