Advanced Welding Processes: Technologies and Process Control

Mains
input
Power
regulation
Control
Welding power source technology 27
from each line. In addition, the power source design must meet the following
requirements:
∑ conformity with prescribed codes and standards;
∑ safe installation and operation;
∑ provide satisfactory operator interface/controls;
∑ provide automation system interfaces, where necessary.
3.3 Conventional power source designs
Conventional power sources have for many years used electro-magnetic control
systems to enable the output power to be adjusted; some of the more common
designs employ the following control techniques:
∑ tapped transformers;
∑ moving-iron control;
∑ variable inductor;
∑ magnetic amplifier.
3.3.1 Tapped transformers
By incorporating tappings in the primary coil of the welding transformer, the
turns ratio of the transformer may be varied and the output regulated. It is
normal to provide tappings that allow adjustment to suit a range of mains
input voltages in most transformer-based designs, but when this technique is
the principal method of control, additional tappings that are selected by a
switch, as shown in Fig. 3.2, are provided. This type of control is simple,
robust and low in cost, but it will only provide a stepped output and, unless
a large number of switch settings or dual-range switching are provided, the
output voltage steps tend to be coarse. Remote control or continuous regulation
Arc
3.1 Functional requirements of welding power sources.