Line Voltage too High

[Batterybrianone]

I am wondering if anyone else has the same issue as I do with excessively high line voltage.
I don't have three phase coming into my house so I run a rotary phase converter. My problem started
a few years ago when the power company upgraded their feeder lines, and my incoming power
increased . I now get at least 125V per phase, some times a volt or two more, giving me over 250V
on my three phase. Several of my motors don't like this and vibrate loudly on startup till they start turning,
just like they were saturating. I have corrected the situation by using a 230-208 stepdown transformer, which
when powered by 250V gives 230V out, which my machines are happy with .
Does anyone else have this issue?

 

[e30ryan]

I have single phase "240 V" going into my shop, but my actual line voltage is 250-255 V. I also have an RPC, but it does not seem to mind this higher voltage. I use a transformer AFTER the RPC to drop the output 3 phase to <220 V for my machine.

 

[eKretz]

I don't, but it sounds like you are solving the problem correctly. For a 240VAC utility the acceptable range of voltage according to ANSI standard should be 228V-252V from what I could find, so they aren't outside that, but getting awfully close. If they go above that I would document it and get after them to see if there is anything they can do about it.

 

[FredC]

I have a similar situation at this shop. Line voltage is about the same on all 3 phases. On my Hardinge GT several boards popped. I called Hardinge and they told me change the transformer tap for the control. Have not blown anything else since on that machine.
My Omniturn with the variable speed drive the braking resistor would overheat when the voltage got over 248. I put 2 buck boost transformers on it and solved the problem. Buck boost setups are lower priced than regular transformers when purchased new. And with single phase input to your RPC you would only need one. Get some technical help to verify this and get the proper size.

 

[JST]

The machines are the problem, not the voltage..... but changing the voltage will solve the issue.

UL requires that products accept up to 264VAC on a nominal 240VAC line. The catch is that they do not require the machine to ever work again, it just cannot produce a "hazardous condition".

A prudent and competent designer would design for no damage up to 264VAC. Apparently few do.

 

[GregSY]

I find it very hard to believe 250V. will cause a motor to be unhappy and the same motor is happy at 230V.

 

[rons]

The power company ups the voltage to insure that a high load from a district will remain above a certain voltage.

When I have a circuit that is at some specified voltage and the current draw ramps up. The voltage drops.

So open circuit voltage measurements are nice, but put it under load and then measure.

When I measure residential 230, it's 248.

 

[FredC]

I find it very hard to believe 250V. will cause a motor to be unhappy and the same motor is happy at 230V.

Regular motors will probably be happier with the higher voltage. They will draw less amps in service. The electronics in a CNC can be a very different story. Plus 10% in many CNC controls is the limit. With the wild leg in a PPC who knows what the voltage will be till it is fully loaded. An idling CNC control could be easily damaged.

 

[FredC]

The power company ups the voltage to insure that a high load from a district will remain above a certain voltage.

When I have a circuit that is at some specified voltage and the current draw ramps up. The voltage drops.

So open circuit voltage measurements are nice, but put it under load and then measure.

When I measure residential 230, it's 248.

Years ago, I called the power company about the 248 and they came out checked it then went to a substation and adjusted a tap to lower it. Now there are many oil wells out here running big motors and they would not lower it again. That is when I bought the buck boost set up. I think the power company likes to keep it high to keep their amp load lighter and run the voltage high, so it is still normal at the ends of the service lines.

 

[GregSY]

I can't say exactly why power companies run the voltage high, but one does have to wonder if it is because it's a sneaky way of selling more power. Although the motor will pull fewer amps, in theory, due to the higher voltage it will also run higher on the saturation curve and the net effect is....more $$$ on your bill. It might be $2 per month, but multiply that times 4 billion customers....

 

[FredC]

I can't say exactly why power companies run the voltage high, but one does have to wonder if it is because it's a sneaky way of selling more power. Although the motor will pull fewer amps, in theory, due to the higher voltage it will also run higher on the saturation curve and the net effect is....more $$$ on your bill. It might be $2 per month, but multiply that times 4 billion customers....

Actually, I think it is the other way around. A motor will pull less amps with the higher voltage. Line loss on your side of the meter will be less with lower amps. Lower voltage does the exact opposite with the risk that motors would stall and burn up. Same is true on the other side of the meter, line losses will be lower with less amps pulled. In these rurals there are miles of line between customers maintaining adequate voltage on the ends of the lines means running it high elsewhere. When your neighbors have 500 horsepower well pumps you better hope the voltage is high when they start those motors!

 

[Sargunes1903]

too much

 

[Laverda]

The single phase coming in to my property averages 249 volts. Connected to four VFD's to run the machines and never have any problems.

On occasion I have seen 260 volts coming in and it causes no problems either.

My shop, main house, guest house and barn all see this voltage.Lots of things on my property run on 240V and no issues.

 

[rons]

Does anyone else have this issue?

Your issue is not apparent with equipment relay coils that have a wide working range.
It's not going to do so much with equipment that is using a transformer to step down the voltage, like for a voltage regulator.
A motor is seeing the bare potential, so I believe you.

 

[GregSY]

Actually, I think it is the other way around.

Read again what I wrote re: saturation

 

[JST]

Regular motors will probably be happier with the higher voltage. They will draw less amps in service. The electronics in a CNC can be a very different story. Plus 10% in many CNC controls is the limit. With the wild leg in a PPC who knows what the voltage will be till it is fully loaded. An idling CNC control could be easily damaged.

It seems that the designers of CNC equipment have never heard of a voltage regulator..... It is absolutely possible to design a high efficiency switchmode regulator that will hold a percent or so on the output while accepting a 2:1 variation on the input side. A matter of +- 15 % or more ought not to be an issue

Putting the responsibility for voltage on the power customer, who has about as much control of power quality as the fish have over the tides, just seems wrong. Add the fact that these machines are intended to exist in an industrial environment, which is known for noisy power and variable loads, and it really seems that someone has dropped the ball.

 

[rons]

Several of my motors don't like this and vibrate loudly on startup till they start turning,
just like they were saturating. I have corrected the situation by using a 230-208 stepdown transformer, which
when powered by 250V gives 230V out, which my machines are happy with .

I would look at the values of any start/run capacitors.

 

[johansen]

High line voltage let's them drop it when they need to, to reduce the load. Good part of the grid is still resistive heat.

Motors only use less power at high line voltage if they are loaded over 75% nominal load. I am curious what the average load is.

At one point in various areas especially, 90% of the utilities load, is motors above 100hp. I haven't read a report lately on this but the last one I recall reading was around 10 years ago

 

[FredC]

Read again what I wrote re: saturation

You are right I missed the saturation part. No clue what it means to the discussion. I was under the impression a moderately loaded motor used less power with more voltage, maybe I am wrong.
Getting the proper voltage out to the end of the line is a thing out in the rurals for the utilities. I found a way to slow the crock pot down when cooking a large roast. Line the inside of the pot with thickly sliced onions to prevent the meat from contacting the sides. Cheap crock pots do not have a thermostat and run hotter with the higher voltage. Hope that tip makes up for the misunderstanding.

 

[Garwood]

My power used to be 250+ volts. Lost several Fanuc spindle drives before I put machines on transformers. The main IGBT's would fail in the drives.

I have never had a motor fail.

My power co dropped the line voltage down to 245 volts. Most of my CNC's run fine on that, but I have two that don't like it and trip off during regen from overvoltage. I have those on transformers. My target voltage for machines made in the 90's and newer is 230-235V. My target voltage for Fanuc CNC's made before 1990 is 200-220V.

240-208 transformers are desirable. They can be hard to find/expensive. I've been collecting for 15 years and have enough big universal transformers on my mezzanine to power every machine at the voltage it likes if I ever pony up for the big 480 service I want.