Dynamic compensators cut welding disturbances

Edited by the Engineeringtalk editorial team Dec 14, 2004

Dynacomp electronic dynamic compensator systems are helping Takao Europe Manufacturing to eliminate flicker at its fully automated robotic welding facility in Gloucester.

ABB Dynacomp electronic dynamic compensator systems are helping TEM (Takao Europe Manufacturing), a world-class manufacturer of high quality metal automotive pressings and subassemblies for customers such as Honda and Toyota, to eliminate flicker at its fully automated robotic welding facility in Gloucester.

In addition to eliminating the flicker, which is a disturbance in the supply voltage created by the high currents drawn during welding processes, the eleven 800kVAr ABB Dynacomps installed at Takao to date help to reduce the inrush current - providing greater control over weld quality.

The real power load has also reduced considerably, lowering power consumption for the same production quantities with a superior quality of finished product.

Flicker occurs when a variable load such as a welding machine or crane demands a high current in a very short period of time.

Without reactive power compensation this can cause a disturbance of the supply voltage.

Flicker is simply the rate at which this voltage disturbance causes fluctuations in the voltage supplied to other equipment.

Typically, flicker is observed by dimming lights.

But it can have serious effects on a wide range of sensitive equipment, especially PLCs and computers.

As well as wanting to eliminate any potential problems with the health of its power supply, Takao also needed to ensure that it met the requirements of its local DNO (distribution network operator), Central Networks.

This called for compliance with the Electricity Networks Association Engineering Requirement P28 on limits for voltage fluctuations caused by industrial, commercial and domestic equipment.

The conventional solution for automatic reactive power compensation comprises banks of capacitors switched electromechanically by contactors.

The problem is a slow response time while the precise instant of switching is variable and not controlled.

This means that the switching of the capacitors results in a large transient.

This transient disturbs the network, is harmful for the contactors and increases the stress on the capacitors.

Electromechanically switched systems have limited lifetimes and need regular maintenance.

ABB has taken an alternative approach for applications having short rise times in designing its Dynacomp fast switching power factor correction equipment.

The use of solid state power electronics (thyristors) rather than contactors enables the Dynacomp to switch the capacitors into circuit, with no inrush current, in 10 to 20ms, which is fast enough to compensate any type of variable load.

As the switching is done at the instant when the network voltage is the same as the capacitor voltage the switching of capacitor steps do not create any switching surge, and there is no need to allow discharge time between successive switchings.

Transient free switching, with no electric arc and no moving parts, combined with the self-healing capacitors used in the Dynacomp guarantee a long system life, with no limitation in the number of switching operations.