Defining Creepage Distances

Feb 27 / Hasti Jahangiri
In late February, Hasti (R&D Manager) and Ian (Technical Director) visited Toulouse for discussions on surface discharges. Any electrical system contains creepage distances where solid insulation is used to separate two electrodes operating at different voltages.

Whether it’s the terminal block used in an electrical machine or the top of a power electronic module, we need to ensure that safe creepage distances are defined.

The workshop we attended involved presentations by a range of industrialists and academics. All were clear that defining safe creepage distances is a major challenge that the aerospace sector is yet to overcome. 
EC 60664-1 is the usual go to reference for creepage distances. It provides definitions of safe distance as a function of voltage for both clean/ dry and polluted surfaces. However, it is difficult to translate this standard directly into the aerospace environment for a number of reasons.

  • The standard was originally produced using pollution data gathered in ground level tests – there is no reason to expect this data to be transferrable to the aerospace environment
  • The standard does not specify the pollution type or a quantifiable degree of pollution.
  • The standard has no altitude correction factor for creepage distances – even though test work that we have carried out has shown this is essential
  • It’s not clear how the RMS voltage stated in the creepage distance table should be translated to DC / PWM systems

How Can we Help you specify safe creepage distances?

At aHV we’ve been working on methods to support companies who face these challenges. The test of clean/ dry surfaces is straightforward, and we can measure the partial discharge inception voltage values/ flashover voltages in a range of environmental conditions.

Testing of wet surfaces is more complex but we can both deposit pollution on test objects and then test in high humidity conditions (both with condensing and non-condensing humidity).

If you would like to discuss how we can help you specify safe creepage distances in your products, please get in touch. Measuring the pollution level seen in the actual application is a great first step if we can support you in that. If that’s not possible, we have access to a range of other data that can help you design a safe system.
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