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3
Notes on Rating
1070 080 058-101 (2001.04) GB
The load capability of a thyristor power unit is always predefined by the type
designation indicating the specific maximum welding transformer rating.
CAUTION
Overloading may cause damage to the thyristor power unit!
Always check the actual load applied on the thyristor power unit! Any
and all warranty excluded in case of damage caused by overload.
To check the actual load, use the load diagram. It shows the
D output currents (I
D the duty cycle (ED in %) at
D maximum ambient temperature (in °C)
that can be switched by the PST 6000 thyristor power unit.
The weld time t
and the overall weld cycle duration t
s
determine the duty cycle.
t
s
Weld time and overall weld cycle duration
The duty cycle is computed as follows:
Example:
In the graph shown above, the weld time is 2 periods
and the overall weld cycle duration is 4 periods.
This results in a duty cycle ED = 50%.
2 per.
ED =
4 per.
Note: If different weld times or overall weld cycle times occur on a
.
machine, the longest weld time and the shortest overall weld cycle
time (to be determined, if required, by adding the longest weld time to
the shortest cool time) must be used for calculating the duty cycle!
When you have calculated the duty cycle, you can use load diagrams to
verify the proper selection of the thyristor power unit.
in A) relative to
PRIM
t
sp
t
s
ED =
* 100%
t
sp
• 100% = 50%
Notes on Rating
3-1
must be known to
sp
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