Quadrature flash testing for intelligent circuits

John Barnett describes how the introduction of intelligent electronic circuits has created a new concept in flash (hipot) testing.

The advent of new smart domestic electrical products has seen the introduction of more complex electronics within products such as showers, washing machines, and kitchen appliances.

These products typically employ a small electronic brain that is responsible for the control of the internal motors, valves and heating elements.

The purpose of the electrical safety test in essence is to check the protective ground (earth) to the product and the quality of the insulation of any internal component within the product.

The recommended approach is to apply a high voltage (flash or hipot) test between any internal component/wiring that carries the supply voltage and the outer case (chassis ground).

With the advances in smart electronic circuitry, manufacturers now face a new challenge when trying to ensure that their products are 100% electrically safety tested.

The electronic brains that are finding their way into these smart domestic products are effectively switching the supply to some of the internal electrical components.

However, without the supply being present to this "electronic brain", the supply will not be connected through to the internal electrical components/wiring.

As a result, during the application of a typical high voltage (flash or hipot) test, this component will not be supplied with power and therefore the test will only be applied to the supply connection wiring up to the "electronic brain".

All reputable and good quality manufacturers must design and manufacture their products in accordance with the international standard for that particular type of product.

These standards stipulate that all internal electrical components/wiring must have their insulation fully tested at the time of manufacture, or after a major service/rework.

The only way to achieve this is by testing the insulation whilst the product is therefore powered from the supply, thus effectively connecting all the internal electrical components to the supply connections, enabling them to be tested by the high voltage test.

The only way this can be readily achieved is by a new test technique developed by Clare and referred to as quadrature flash (hipot) testing.

This technique effective applies the flash (hipot) test whilst the product under test is energised from the supply in the normal operating mode.

The technique for doing this has been patented by Clare and so cannot be described fully, but the operation for testing a typical product in this way is as follows.

First, apply a ground bond test to ensure that the product has a suitable protective earth connection.

Secondly, apply a flash (hipot) test between the phase and neutral (linked), to earth (ground) connection to ensure that the primary insulation is sufficient.

Thirdly, energise the product from a protected supply and ensure that the current consumed is within specification for the product, and that all internal circuits are energised.

Fourthly, apply a high voltage (flash or hipot) test onto the phase and neutral connections with the product energised - this is the quadrature flash test.

All internal circuits are now subjected to the high voltage test, as the electronic control circuitry is energised.

This technique cannot be employed using standard test equipment.

Clare offers a range of products that can be configured to perform this type of specialist test.

Clare is currently the only manufacturer of electrical safety test equipment to offer this type of specialist test method for testing products that incorporate intelligent control circuits.

This method was developed through Clare's relationship with BSI.

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