Tap changer position transmitter

[calvintey]

Hi....
I have a transformer installed with an MR tap changer. The position of the tap changer is measured by resistance. I'd like to take the resistance measurement and convert to 4...20mA for input to the control system for display purpose. Any consideration I should have for selecting such a resistance transmitter? Any recommended types to use?

Rgds,
Calvin

 

[melspuds]

calvintey
I suggest using an optic encoder with a digital output on the insulated shaft before going into oil if possible.
I tried using one on a 34.5Kv voltage regulator 33 positions, feeding a 76 Mva Arc Furnace Xfmr for the furnace manual control only. The old way was a bidirectional pulse counter that was never correct. The operator had to always look at the voltage meters, when the tap changer was changing manually about 300-400 times per day. When the furnace controls were automated in 1990 with A-B PLC-5, I used the optic encoder for controlling the tap motor along with the positive mechanical locking device on the tap changer. I do not remember the name of the manufacture of the optic encoder.
Hope this helps and good luck!
Dave

 

[Marmite]

You just need a transducer that connects to the resistor ladder and outputs 4-20mA for scada. These are very common devices. Google "tap changer position transducer" and you'll get a range of devices to choose from.
Regards
Marmite

 

[ScottyUK]

PR Electronics have a few, ABB did one, as did Siemens. P&F have a couple. Plenty choice. Consider whether loss of the TPI signal will cause any problems. Finding one which works on a 110V tripping battery is a little harder.

 

[isquaredr]

http://www.fundamentalsltd.co.uk/pdfs/mA_Transducer.pdf