Electrolysis protection in water-cooled converters
Most of the converters currently in operation for inductive applications are equipped with water-cooled thyristors. The thyristor heat sinks are on power potential, the water manifolds are connected to earth potential.
Between the components of the converter with DC voltage (e.g. positive and negative rectifier output, DC link chokes, water-cooled busbars, positive and negative inverter feed) and the water distribution and collecting pipes, there is inevitably an electrolysis process, since these are at earth potential.
As a result of this electrolysis, the hose connection nozzles of the components involved are either damaged by material deposits
added or weakened by material removal, depending on the installation location.
There are two ways to reduce the effects of electrolysis:
- Use of so-called sacrificial electrodes (also known as sacrificial anodes):
These are inserted into the cooling water hose in front of the cooling water connection concerned and are also electrically connected. They take over the effects of the electrolysis and thus protect the downstream cooling water connection.
Disadvantage: The sacrificial electrodes inserted in the hoses are added or reduced just as quickly as the hose nozzle of the corresponding component to be protected. Changing the sacrificial electrodes is time-consuming and involves relatively high material costs.
- Use of a water treatment:
With this method, the cooling water of the converter is supplied via a deionization cartridge and then neutralized by adding a chemical, as it is initially quite aggressive.
In a further variant, a small amount of the converter cooling water is constantly fed over the cartridge.
Disadvantage: Increased service effort, since the contents of the cartridge will be regularly exhausted and must be changed. Water treatment does not prevent electrolysis, it only reduces it. Experience shows that even with properly maintained systems, the first electrolysis damage occurs after a few years, which is then quite costly.
To solve this problem, we developed very long-lasting sacrificial electrodes that are suitable for use in both variants:
- Instead of the original electrodes
- For retrofitting in systems with treated water
Our sacrificial electrodes have significant advantages over the original equipment:
- Connection sleeves made of temperature-resistant plastic that do not get any effects from electrolysis
- Much larger surfaces that can absorb deposits over many years
- Much greater wall thicknesses, which can suffer wear over many years
- Much larger inner diameters in the metallic area, e.g. 24mm with a version for a 10mm
- Inner tube diameter and 30mm for a version for a 13mm inner tube diameter
- Easily recyclable if ever necessary
- Less expensive
The sacrificial electrodes are available for installation in the cooling water hose and for installation on the water manifold pipe.