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100kV lab transformer

Posted by tiziano on
100kV lab transformer


This transformer, capable of generating 120 kV AC, comes from a real high voltage laboratory! Unlike potential transformers or NSTs, it allows a variety of very particular wirings, like cascade or anti-parallel. Being a test transformer it is short circuit proof. It has a high enough Vcc% making the short circuit current not too big. It is also free from partial discharges.

With a weight of 190 kg (!!) and over 50 years of age, it can supply 50 mA at 100 kV for 15min followed by a 15min break. Being insulated in resin (Araldite) it does not have excellent thermal characteristics. But such insulator makes it perfect for a domestic environment;).
Each “arm” can generate 50 kV and, depending on the primary fed, the voltage to earth can be chosen (0 – 50 kV – 100 kV or 50 kV – 0 – 50 kV).

Feeding the primary “U” you can get at the “V” terminal 100 kV, and also 220 V insulated from earth can be taken. At this point, you can connect another transformer primary to the insulated low voltage winding. It is the cascade connection, and obviously, you can increase the output voltage.
Powering the primary “X”, the “U” and “V” secondaries will be at 50 kV from earth, with opposite phases. This connection has the lowest Vcc% making the short-circuit current of 1.8 A at 100 kV! (and over 800 A on the 220 V winding). Also with this setup and two diodes you can make a 70 kV DC dual wave rectifier circuit.

As can be seen from the graph, when the core is far from saturation, the transformer absorbs a capacitive no-load current! Exceeded 175V the inductive component (the magnetization current) exceeds the capacitive one.

Some discharges

90kV 100mA

In addition to the transformer, I managed to save the rest of the kit from being scrapped: resistors, capacitors, diodes, insulators, etc. In the tests, I assemble them in a modular way. I admit they are very comfortable!

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