On load tapchangers - US v Others

[shipmate]

The US tends to use reactors in their tap changer diverter configurations, whereas a large part of the rest of the world uses switched resistors. As a non-US electrician, what are the benefits and drawbacks of using reactors, and is this as a result of the common US practice to tap on the low voltage side of the transformer, against the neutral end of the high voltage side in other parts of the world. What is the typical maintenance program for the reactor version?

 

[DougMSOE]

The reason to go with the reactor based system is to eliminate the "change in current with respect to time (di/dt)". The resistor type is usually used to "clanp" the voltage to a definite E/R ratio. I would offer that some of these devices also use a thristor based system, typically on large inductive loads such as induction furnaces.

 

[stevenal]

I'm in the US, and only spec high speed resistive or vacuum diverter LTCs. Maintenance is the issue. Get rid of or reduce arcing, and maintenance intervals go way up. Reactive LTCs require frequent oil filtering and contact replacement.

 

[electricuwe]

I found a good explanation for the different approach in the US and elsewhere in the following book:

Laughton, M.A.; Warne, D.F.: "Electrical Engineer's Reference Book", 16th edition, Oxford, 2003

US engineers tend to specify a large number of taps with small tap steps. With the inductor approach the bridging position can be used as running tap.