powerfactor correction in primerily welding transformer loads

A possibility would be an overexcited synchronous motor whose excitation was tied to the pf of the welding transformer. When load came on the transformer and pf decreased, the excitation of the synchronous motor could be increased to bring pf back to 85% or so.

Don't let it get too close to 100% as this will cause resonance problems.

An active harmonics filter of a fast capacitor switch and controller would do it but it won't come cheap. Your installation is probably too small for this type of technology.

The problem with capacitor in welding application are usually caused by resonances since the welder produce a large frequency spectrum that excites all the LCs.

The only cheap solution I can see is to use power resistors in series with your capacitor bank(s) to reduce the bandwidth and damp the resonance. You will probably need about 10% of the bank capacity and use a fan to cool the resistors. This is not energy efficient but should protect the capacitors and the other equipment.

N.B. Don't oversize the capacitor KVAR but use a higher voltage rating. This give you more robust capacitors.

Dear Sir,

Static Var Compensator(SVC) would have been ideal solution for this problem. But I agree with Mr.Marcot reply , the applcation of dynamic filter like SVC will not be an economic solution in this case.

However as the welding machine produces spectrum of harmonics during operation, and to economise the solution , we may use HP(High Pass )Filter designed for 5 th harmonic.The HP resistor shall be connected in parallel with the reactor.All the frequencies above 5th Harmonics will be filtered ,although not 100% , but sufficient enough without producing any risk parallel resonance with system impedence.

V.Ambarani

Good, but do not tune at the 5th as the filter could be overwhelmed if a strong source of 5th is in the vicinity. De-tune at 4,3h to 4,5h.

The inductor should conduct most of the 50-60Hz current for power factor correction which is usually the major component. This will reduce the power dissipation in the resistors. This might be a good compromise.

Most transformer style welders if required usually have a fixed bank of PF correction capacitors installed. As the machines are on intermittent use they will have a capacitive load when not in use but this generally is more than compensated for by the factory general inductive load. Also when the work is finished they can be switched off altogether.