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Tan Delta Figures

Since the opening of our coil shop in 1988, our expert engineers have been able to combine over a century of coil making experience to create unique HI products that have been unsurpassed in the market by any of our competitors.

In 1989 we had the honour of being the first UK coil shop to be awarded the old BS 5750 British Standard, since amended to BS EN ISO 9002. A fluid manufacturing process coupled with the constant development of our materials means we are now able to produce coils with what are arguably the best tan-delta figures in the world.

What is Tan Delta testing?

The insulation of the stator coil can be considered as a capacitance in parallel with a resistance (see figs 1 - 2, click to enlarge). Current flows through both the capacitance - Ic and the resistance - Ir, producing a total current - It.

Fig.3 to the right depicts the vector diagram for such a system, and the loss angle is shown. It can be seen that the greater the current flowing through the resistance, then the greater the loss and hence the greater the loss angle.

All materials have a loss that can be measured and at Houghton International we use a Schering Bridge to do this. By applying a low voltage to the specimen under test, the loss angle is easily determined, this loss being termed as the material loss.

As the voltage is increased up to phase voltage, any void present in the insulation will discharge repetitively, causing breakdown and ionisation and contribute to the total loss. This further loss is known as the gaseous loss and adds to the material loss causing the loss tangent curve to tip up.

The main cause of void content in coils is down to the shape of the wire. Voids normally occur where the rounded edges of two stacked conductors meet and during consolidation, the resin fails to fill all the gaps.


Houghton Coil Figures

The graph below shows our improvement against the standard. It also clearly shows us approaching the manufacturers figure for insulated solid bar.