Some applications require DC/DC-converters with a very high galvanic isolation between primary and secondary or between primary/secondary and earth. The high isolation requirements are necessary because of the high voltage potentials that are present on the primary or secondary side:
DC/DC Converters, which are supplied directly by the traction line, like flat battery start units. The supply voltages for traction lines are specified in the standard EN 50163. Most traction lines use a nominal supply voltage of 750 VDC or 1500 VDC.
DC/DC-converters, which supply a secondary circuit with a high voltage potential between output and earth, like modern gate drive units. The high voltage potential between output and earth can reach up to a couple of kilo-volts. IGBT drivers for 3.3 kV to 6.5 kV IGBT applications are an example.
For railway applications, the requirements for the isolation coordination, e.g. clearance and creepage distances, are specified in the standard EN 50124-1. The calculation for the isolation distances is based on the rated insulation voltage Unm.
Unm is the maximum permanent voltage (> 5 min) between a live part of equipment and earth or another live part. For above application examples:
After Unm has been determined, other factors can increase the requirement for the isolation distances considerably:
The higher the rated insulation voltage Unm, the overvoltage category, the pollution degree and the altitude, the higher the required clearance distances.
Furthermore, to assess the quality and the lifespan of the insolation system, partial discharge requirements have to be fulfilled. Partial discharge are localized electrical discharges within the isolation barrier, caused by a high electrical field.
For above reasons, the isolation distances become very high and the isolation barrier between primary and secondary cannot be crossed with conventional methods, like “normal” transformers for the power-path and “normal” optocouplers for the regulation-path.
Special techniques must be used to overcome the big isolation distances.
intreXis AG has overcome this challenge and has designed DC/DC-converters with impressive isolation data:
If you have an application with high voltage and high isolation requirement, contact intreXis AG and take advantage of our experience!
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