|
The halfwave frequency converter welding transformer has three
sets of primary windings surrounding a common magnetic core. It
is similar in a way to the simple single phase AC transformer however
it has been designed to output secondary currents in the range of
70,000 to 200,000 amperes. This is done by eliminating the effects
of inductive impedance associated with large loop welding circuits.
Each weld is performed by a single pulse of current in a given polarity.
That pulse may be more than one cycle period.
Let's assume a phase rotation of A, C, B as shown below. If for
example, a weld is performed in 3 cycles, the welding control will
fire phase A+, C+, B+, A+, C+, B+, A+, C+ and finally B+ for the
first weld. On the secondary side of the welding transformer, the
inductive impedance is effectively eliminated since current is not
alternating during a weld.
The next weld will be performed by reversing the polarity by firing
A-, C-, B-, A-, C-, B-, A-, C- and finally B-. Because the core
of the transformer is seeing repetitive pulses of similar polarities,
the size of the core must be much larger than the 50/60Hz transformer
in order to ascertain that the magnetic flux will not saturate during
the performance of a weld. It is common to see a 150KVA HWFC transformer
the size of a huge desk.
|
Home 
)
)