# Voltage above nameplate on 3 phase motors



## MikeFL (Apr 16, 2016)

I believe 460 in that application is pronounced "four hundred eighty" in which case you're 9 over or a healthy 2% over.

But let's see what some of our motor men say about it.


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## SpaceMonkey (Sep 19, 2018)

Thanks for the response. Also to clarify I'm just interested in general what would happen if the voltage was far over nameplate, say around 600v for a 460v motor.


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## Bird dog (Oct 27, 2015)

SpaceMonkey said:


> Thanks for the response. Also to clarify I'm just interested in general what would happen if the voltage was far over nameplate, say around 600v for a 460v motor.


Get the right motor for the system voltage.  You don't put a 480v motor on a 600v system. IIRC motors are designed to run on nameplate voltage -5%, +10%. So, your 460v motor is fine up to 506v.


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## MikeFL (Apr 16, 2016)

Hooking up a 460 motor to 600 lets the magic smoke out.

Get a motor which matches supply voltage or make the supply voltage match the motor. You can buck or boost the supply voltage or you can use a VFD to make voltage match a motor requirement. 

You haven't filled out your profile. You were supposed to do that (by forum rules) before we're allowed to advise you. In particular you need to list your electrical industry occupation and location. Please do that before a moderator comes along and locks the thread. If you are not an electrical industry professional you are invited to visit this site's sister site over at www.DIYChatroom.com where there are plenty of capable people eager to help you with your project.


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## SpaceMonkey (Sep 19, 2018)

Holy smokes guys, I think there's a misunderstanding. If I thought it was okay to hook up a 460v motor to 600v I don't think I wouldn't known about the 10% variance, which I mentioned in the first post.

This is completely hypothetical, literally just curious. Obviously the motor would fail quickly. I mean what actually would happen inside the motor.


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## micromind (Aug 11, 2007)

If the motor is 230/460 12 lead ∆, it can be connected to operate on 600 volts but it won't produce its full HP rating. It can operate at reduced HP continuously though. 

I can't remember the connection offhand, I'd need to draw it out but I'll do it if anyone is interested. 

As for the original question, as voltage is increased, generally speaking power factor decreases and therefore amps will increase with the load being constant. 

If the voltage is increased far enough, the core will saturate, the current will go way up and the excess current will appear as heat.


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## 460 Delta (May 9, 2018)

High voltage causes high starting torque which isn't always a good thing, poor power factor and excessive heat due to magnetic saturation. 460 motor on a 575 system will run for a short while and run HOT.


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## gpop (May 14, 2018)

I was always taught that there is a voltage to hertz relationship which is why at reduced hertz say when using a vfd you also reduce the voltage to prevent heat. 

May be totally wrong.


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## splatz (May 23, 2015)

489 is 106.3% of 460 

I have a book with a chart that lists the "Characteristics of T-Frame Motors Voltage Variations" with a column for 110% voltage 

Starting / max running torque 
ΔV^2 increase
+21% 
at 106% that would be +13%

Percent slip 
1/ΔV^2 decrease 
15-20% 
at 106% that would be 10-15%

Efficiency 
full load - 0-3% decrease (0-2% at 106%?) 
3/4 load - no change / slight decrease 
1/2 load - 0-5% decrease (0-3% at 106%) 

Power Factor 
full load - decrease 5-15% (3-9% 106%?)
3/4 load - decrease 5-15% (3-9% 106%?) 
1/2 load - decrease 10-20% (6-12% at 106%?) 

Full Load Current 
5-10% decrease (3-6% at 106%?) 
note: high efficiency motors will experience a current rise 

Starting Current 
ΔV increase 
10% increase (6% increase at 106%) 

Temperature rise - full load 
2-15% increase (1%-10% increase at 106%?) 

Maximum Overload Capacity
ΔV^2 increase 
increase 110% 
that would be 13% increase at 106%

Magnetic Noise 
Slight increase


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## Dennis Alwon (May 9, 2009)

Splatz has a good post. Not sure where space monkey got over 10% because it is only 6.3 percent higher. Generally speaking that is not an issue however it does change a few things, as mentioned above, but not drastically.


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## paulengr (Oct 8, 2017)

The big thing is the temperature rise which reduces full load capacity. This happens because the core is overfluxed.

IEEE states +10/-10% on voltage variation. UL requires ÷10/-15.

The idea is you set the transformer for some standard, multiples of 120, so 120, 240, 480, 600, 2400, 4160. Then accounting for 3-5% drop from line losses gets you to utilization equipment which is 110, 220, 460, 2300, 4000. Less losses at medium voltage, more at low voltage. That's the starting point. THEN apply your +10/-15. In reality a lot of industrial busses are soft so totally unloaded they tend to be around 500-520 but after the first transformer powers up they drop right down to around 480 which is typically where they were first set up at (tapped).

In general few plants size motors cirrectly...most are grossly oversized. Too high of voltage is generally beneficial (more torque) but power electronics has less room to handle for instance braking/regeneration. For drive nerds, your modulation index suffers. VFDs actually work better at lower than nominal voltages for this reason. Since the DC bus voltage is 145% of RMS they can handle it easily except at 100% of rated frequency and at rated full load. At all other conditions lower voltage is a benefit. Particularly with European drives that are designed for 440 but will barely do 480 and can't handle 500+ at all without bus overvoltages.

APC UPSes also suck...they do stupid crap if the voltage is outside about +/-5%. Don't buy APC for that reason. Buy another brand. APC is extremely over rated with the IT guts anyways along with the absolute worst Ethernet switch brand for industrial networks (Cisco) which also freaks out at low voltage.

Most PLCs crash or fault at around 90 V. Most contactors open at 85 V. There are some low voltage designs but not common at all. High voltage just overheats the contactors. Use the electronic coils if they're larger size.

I have lots of experience with this. Mining excavators fluctuate to +/-20% during normal operation every dig cycle (every 30-60 seconds).

I've successfully started sync motors down to -60% but you have to have a UPS on the controls including the contactors so they don't open and disable undervoltage protection and not be starting under load and disable any timeout type of protection.


Sent from my SM-T350 using Tapatalk


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## JRaef (Mar 23, 2009)

Here’s a decent graphic that illustrates the issue. 









Meh, fricken Google and Apple are messing with image links now from an iPhone... I’ll do it again from my PC later.


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## JRaef (Mar 23, 2009)

Here it is...


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