I have a 250KVA 480 volts single phase projection spot welding job that while it is running at output of 48000 amps has a spike of 1900 amps across the single phase. This creates flicker in the lighting system of the neighboring buildings. What would be a guaranteed to work least expensive solution?

-- Mike Haller (mhaller@rolmfg.com), February 19, 2004

Answers

You can reduce the max. demand on your supply system considerably by using a 3 phase power source instead of the single phase trafo you are having. Your choices namely are (in order of increasing prices!) :

1. 3 phase frequency converter 2. 3 phase DC 3. 3 phase MFDC

You can mail me directly at prithvish.chakravarti@sondertech.com for more details and pricing. Do check out our website at www.sondertech.com.

-- Prithvish Chakravarti

-- Prithvish Chakravarti (prithvish.chakravarti@sondertech.com), February 19, 2004.

Other items to check: reduce the throat area of the welding machine (make it as small as possible; that is as closely coupled to the part as possible); to reduce the inductive loss; which will allow a reduction in primary current demand (less of a spike); if the secondary circuit weld connections are old, examine them for voltage loss across the connections; and clean or silver plate them; copper oxide is non-conductive and will deteriorate with age; silver oxide is not; a bad connection may require a higher transformer tap which results in a higher current from the plant; some people have tried power factor correction capacitors but I never heard of it working in an application as yours; it sets up ringing on the power line when the load is not present. Also examine all primary circuit connections to make sure that they are good. If it is a 220 line, look into converting to 480 if possible (sometimes power companies have those provisions close by that are cost effective -- in one case, the conversion was free). Also look at sequencing. For example, run other electrical equipment at a different time or shift if possible. Or interconnect the sequence to other high eletrical demand machines so that only one machine hits at a time. If possible, tap down the transformer and increase the weld heat. Higher tap / lower heat settings are far more demanding on the power line that low tap / high heat settings. Look for secondary circuit shorts or insulation leakage. Some of the weld current may be leaking around the part. Also look at HFDC power supplies. We plan to release a book in the near future to talk all about electrical science (such as this) around resistance welding equipment. If there is an interest, E-mail me. Thanks.

Bob Sza

-- bob szabo (bob@szabopublishing.com), April 26, 2004.