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#130331 - 03/11/06 09:50 PM Spot welders and voltage drop
Norstarr Offline
Registered: 09/25/04
Posts: 86
Loc: Wi
Anyone have experience with large capacity (nameplate 400A, 380 volt) spot welders and the best procedure to use in combating voltage drop in the building wiring system causing lighting etc to dim? These welders are only activated for very short periods but cause havoc in the rest of the building. My first suggestion to the customer would be oversized conductors but would like to hear from the rest of you should somebody have a clear and dependable way to solve this problem. Customer is building a new factory and would like to eliminate this problem at the start. Thanks in advance for any suggestions.
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#130332 - 03/11/06 10:49 PM Re: Spot welders and voltage drop
winnie Offline
Registered: 09/15/03
Posts: 649
Loc: boston, ma
I have no experience with this sort of load in this application...but the load is so large that I don't think oversized conductors will make one bit of difference as far as the rest of the building is concerned.

Oversized conductors will simply mean lower voltage drop in the supply to the machine, and probably even greater current flow through the machine, and thus even more effect on the rest of the building. What you care about in terms of the effect on the rest of the building is that portion of the supply circuit which is _shared_ between the rest of the building and the spot welders. In particular, the _supply transformer_ is probably the significant shared element.

You may need to provision a separate supply transformer for these extremely irregular loads.

#130333 - 03/12/06 06:45 AM Re: Spot welders and voltage drop
WFO Offline
Registered: 09/03/05
Posts: 202
Loc: Cat Spring, TX
I'm probably way off on this, but if memory serves, welders are notoriously inductive in nature, causing large line losses from the VA load.
Would capacitor correction help?
I realise that a capacitor large enough to go to unity PF under load would cause just as much problem when the welders weren't running, but perhaps you could fine a midway point between on and off where it would even out the voltage drop to an acceptable level.
#130334 - 03/12/06 08:52 AM Re: Spot welders and voltage drop
winnie Offline
Registered: 09/15/03
Posts: 649
Loc: boston, ma
Okay, now I am _totally_ speculating here, but perhaps this idea will trigger something that some else knows.

What about using a 'synchronous condenser'? These are synchronous motors not connected to any mechanical load, which are operated at high excitations to have a leading power factor. But in addition to providing VKARs, the machine _stores_ a certain amount of energy, and will release it if the supply voltage drops. Could a synchronous condenser be used to 'peak shave' the power consumed by the welders?

#130335 - 03/12/06 11:29 AM Re: Spot welders and voltage drop
JoeTestingEngr Offline
Registered: 11/04/05
Posts: 781
Loc: Chicago, Il.
I think Winnie's idea or just a motor generator with a huge flywheel would be able to ride through the peak demands of the welder. I'm expecting that the duty cycle is very low and that the welder isn't that picky, just hungry. It also helps for an oddball voltage , not needed elsewhere in the plant.
#130336 - 03/15/06 04:41 AM Re: Spot welders and voltage drop
Scott35 Offline

Broom Pusher and
Registered: 10/19/00
Posts: 2707
Loc: Anaheim, CA. USA

From what I remember, Spot Welders are Resistance this correct?

If yes, then the operational characteristics of a typical unit will have a very high inrush load current - which is sustained for a long period of time, with the load current becoming slightly reduced as the contacting points increase in heat.

Voltage drop - and system loading, will always be problem factors with Resistance Welding Equipment.

If possible, place them as near to the Service Equipment as possible. This may assist with the Voltage Drop problem for the Resistance Welders.

System Loading:
The extended surges of these welders will affect the remainder of equipment on your Load side of the KWh Meter - AND others on the Secondary side _ AND the Primary side (when the Primary Feeders are long, loaded and small in size).

Also, the KVA size of the Power Company's Transformer (or network) will totally affect + be affected by these welders - and overall, the system's Voltage.

Many PoCo's (Power Companies / AKA "Utility Companies") have certain demand calcs for "Welder Service" (found in their "Description of Service Manuals" or "Electrical Service Requirements Manuals").
Typically, Motor Generator type Welders & Transformer Arc type Welders are in a "Class" where ratings are taken at 100% nameplate values; whereas Resistance Welders are classed in multiple factors - depending on the exact task type and overall "Tweeks" of the Welders.

As to the existing setup - where the large capacity (nameplate 400A, 380 volt) spot welders are causing lighting etc to dim:


[*] What is the nominal load (KVA / Amperes, etc.) at the time of dimming lamps?

[*] What type of Lamps are dimming? HID, Fluorescent, Incandescent, All,

[*] What is the intensity of Lamp Dimming + time duration?

[*] What is the KVA rating of the PoCo Transformer feeding your Service?

[*] What is on the same feeder(what other equipment - if any) which the Spot Welders are connected to?

[*] Does this Lamp dimming problem occur during certain time periods, or is it something that would happen at any time - day or night - weekday or weekend?

I am thinking maybe there's a System Capacity issue.
If the Circuitry feeding the Welder has Capacity + compensated for long distance run, then the Voltage Drop at the Welder should be minor - and the entire system would react accordingly to the sudden surge + extended load.
Incandescent type Lighting will show the most drammatic effects. Fluorescent Lamps will react as well, but not as much as Incandescent Lamps.
HID Lamps may diminish in intensity, or may completely restart - all depending on the type of Ballast used and the Lamp Characteristics (+ age of Lamps too!).

Insufficient Circuit size to the Welder may result in less effects to Lighting (as would be seen with proper size circuitry), and would place the Votage Drop problems mostly on the Welder - at the Welded Work it's self.

Take a look at these items I have listed here, then apply them to the Project.
Let us know the results!

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#130337 - 03/18/06 11:34 AM Re: Spot welders and voltage drop
Larry Fine Offline
Registered: 02/18/05
Posts: 693
Loc: Richmond, VA
I agree with Jon. I'd ask the POCO for a 380v system for the welding equipment, and a 208/120 for the rest of the building. Of course, this advice is based on no knowledge of your power needs. YMMV
Larry Fine
Fine Electric Co.

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