Testing Transformer: What is the Top Metal Thing?

AI Thread Summary
The metal component on top of the testing transformer is identified as a corona ring, commonly made of hollow aluminum. Its primary function is to mitigate corona discharge, which occurs at high voltages starting around 1000V and becomes significant above 100KV due to voltage gradients at sharp edges. The rounded shape of the corona ring helps reduce ionization of air, preventing electrical discharge. The discussion also contrasts the corona ring's design with that of a lightning rod, which serves a different purpose. Understanding the role of the corona ring is essential for effective high-voltage equipment design.
eric336
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Hi everyone.

What is the metal thing on the top of the testing transformer (figure below)? It looks like electrode, but what is the use? I find it ubiquitous in many HV equipments.

Ac_Test_System_Hctt_Test_Transformer.gif
 
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Corona Ring.
Usually a hollow aluminum spinning.
 
At high voltages ( Starting around 1000V and becoming very pronounced > 100KV) the voltage gradient around sharp corners will cause the air to ionize, causing Corona. The rounded shapes help to reduce the effect. And to clarify CP's post, the aluminum is not spinning, that is the manufacturing process often used to make the ring. Google (as usual ) has some good info. - Also note how a lightning rod is physically the opposite.
 

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