OT: Acceptable Voltage levels at service entrance

Does anybody know off hand what the acceptable voltage levels are for a 480V 3 phase service from the power company? I have a friend with a small shop that just fried all the AC drives on a piece of equipment he hooked up. The machine was rated for 460V. His service is 480V but he got a reading of 510V on his meter. This sounds above spec to me. I felt like he should request the power company to check and adjust the tap on their equipment that is feeding him. If that is not a viable option what should he do? I assume he would need a step down transformer to adjust the voltage to an acceptable range, but what should he look for?

Thanks in advance for any advice.

480 is nominal voltage, the key word being nominal. +/- 10 volts is ok, especially where voltage drop is concerned, but I've never seen a 480 system carry 510 volts.

I've experience a lot of trouble with 6 Inverters in a plant where they would fault with the message "DC Buss Overvoltage"

Every time I was there (but for the last time ) I would read 465 to 487 Volts.

Only when in the evenning all there equipments where shutdown did this happened, and of course that's when the entrance climbed to 527 Volts.

So When they return from lunch, from there evening breack the system would not run for most Inverters had faulted.

Was it ever a pain to find. I got called a few times and all they would tell me is the fault number and what the system was doing.

The key was "Evenning" + "All Stop".

This was in Northern Ontario, Canada.

Most motor controls DC and AC are rated 460 volts +5% -10%. That is 506 volts max then you exceed the design limits. Get out the mfgr's manuals for the equipment and take a close look. I have found that any drives that have to deal with 500 volts typically loose filter caps and tend to destroy the snubber circuits which leads to thyristor and diode failures.

I always recommend that they shoot for a MAX of 490 volts.

I have never seen over 488 volts my self.

10 volts is acceptable. I have heard some say 5%, and some say 10%.

On the 120/240 that I requlary see, 128-135 is more common then 120 or under. I use 130 volt bulbs myself, they last several times longer then the "regular" 120 volt ones do.


I did have one plant that had 4 sets of busses (well, 535mcm cables) run through the plant on alternating rows of equipment.

One read 463
One read 458
One read 455
One read 435
All were fed with the same 480 volt feed from Com Ed, with a reading of 465 after the main disconnect.

None of the 600+ machines hooked up ever seemed to have a problem with the voltage, and there was little variance in readings on each line. Most machines had 2 or three small drives, or two large motors.

None of the old timers could ever figure out why the different voltages, other then, that's way it's always been.

I think the utility companies state the voltage supplied
will be +/- 10% of nominal, which in your case should be
between 432 and 528. actually, in the real world their
regulation is usually much tighter. The power company
transformer has taps to adjust the output voltage and they
shouldn't give any grief about adjusting it down.

Service in our new plant is 500-505 volts and we don't see electrical failures at all on our AB 480 components. I'd still like to see the voltage closer to 480 tho.

Usually, the power supply spec is 460V +/- 10% which figures out to 414 to 506V. I don't know where some of those other numbers came from.

Especially in areas where the supply network is soft, the utility taps up so, under normal workday heavy loads, the voltage stays around 450-460V. Unfortunately, on off-work periods like weekends, the high tap results in 500+ volts. Short of re-arranging the power supply network, you are pretty much stuck with this, especially in rural areas.

One way to reduce your headaches with respect to VFD's is to buy drives designed for the world market, rather than the North American market. The former are usually designed for 380V -10% to 500V +10%. North American drives usually are 460V +/-10%. Lots more headroom in the world drives. That doesn't mean that you have to buy imported drives. Some American made drives meet the world spec too.

The common normal electrical systems (low-voltage) for commercial
& industrial uses are 208/120, 480/277 and 240/120 for residential.
Of course, there can be others than these. The utility company
states its percent of deviation from nominal. For commercial
and residential, some utilities promise 5%. For industrial, its
can be as high as +/- 10% of 480. for a range of 480-528

Sorry, katratzi, but, at least in the US, the nominal voltage is 460V, not 480V.

Actually the US varies between 440, 460, and 480 VAC depending on where you are. I would be more worried about the voltage being too low than too high. I have seen around 505 VAC with no problems. But that extra 5 volts could make a difference I guess.

in this area, common voltage is 480V (not 460) for most industrial locations with an occasional 575V, but alot of the older textile mills still use 600V systems...not 575 mind you, but 600V.

Stasis,

You are absolutey correct..if you are talking about Power Supply Equipment. Dick DV is correct...if he is talking about Motor and Drive voltage ratings.

I will say this one more time. The proper voltage level depends on whether you are talking about a Power Using Device (460 volts) or a Power Suppling Device (480 volts). Yes, 480 IS the normal transformer-supplied voltage in the US, for the past 40 years now. (Prove it to yourself with a simple voltmeter, or read the nameplate on the nearest transformer that is newer than 1965). On the other hand , most motors, drives, starters, etc. are made to run on a nameplate voltage as low as 460 volts. You can verify this by reading the nearest motor nameplate.

The propervoltage level depends on your viewpoint, whether you are "providing" power, or "consuming" power. Remember, Provided power is higher, but Consumer devices are rated to run on lower voltage. That is only common sense, isn't it? Would anybody buy a device that would not also run at lower voltage? 480 Volts is a normal supply, 500 is High-Normal, and above 505 volts is TOO HIGH.

Glen C, the probabilities are great that:

(a)You are located in an industrial area;
(b) There are some plants on the same main power line that have power-factor correction capacitors;
(c) The power company substation probably has some capacitors also;
(d) The power company substation voltage has been adjusted to the correct level for Day Shift operations, with the motors running and the capacitors connected;
(e) At night and weekends, the voltage rises to be way above normal, becasue all the capacitors are STILL connected on-line, but the motors are mostly OFF.

Solutions:
1. Easiest and quickest fix is to change taps on your plant transformer to lower the voltage.
2. Talk to the power company about lowering the suply voltage at night, maybe by switching some of their capacitors off-line after day shift.
3. Install automatic switches on your OWN plant capacitor bank, or install a Variable Switched-Capacitor Bank.
4. Consider installing a Power Conditioner, or a Power Regulator.
5. Install some Voltage Regulator Inductors.

This shop is a friend of mine's customer. The drives that failed, the capacitors in them apparently gave out. I told him that he needed to talk to the power company supplying the shop to lower the incoming voltage to a lower level to give some protection even if it dipped a little below 460V during operations. I think this must have been the first piece of equipment that he added to the shop that had AC drives on it, so it wasn't a problem in the past.

Can he add a buck/boost transformer on the feed to the machine to lower the voltage, if the power company will not?

+/- 10% should be the minimum acceptable

Looking from a global electrical equipment manufacturer's viewpoint, we typically design for +/- 10% at 200, 230, 380, 460, 575 nominal voltages at 60 hz and derate according for 50 hz applications. We test at +/-15 % just to make sure the equipment can handle it - a safety factor to handle some of the unknowns in the real world such as phase imbalances, brownouts, overvoltage, etc. We take reliability very seriously.

Check the equipment specs and if it can not handle a 10% variation, I would conclude that it's marginally designed. Voltage control packages such as buck boosts may be used but I would first talk with the utility to get their response, why add this expense if the utility can help?

Phase monitors for under $200 could also be installed to shut down the equiment that can sense over/ under conditions to prevent damage though I'm not sure if your process can handle it.