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Motorized Potentiometer
2

Motorized Potentiometer

Motorized Potentiometer

(OP)
Our SR 745 relays (transformer differential relay) has an auto CT mismatch compensation wherein it requires resistive analog input to its terminals A3-A4 for OLTC tap position indication. This means, the relay powers the input and measures the resistance and relates it to the relay's tap changer range settings as part of it's algorithm

Unfortuntatley our power transformer tap changer control only have tap position output in 4-20mA signal.

Is there any motorized potentiometer powered and controlled by a 4-20mA input signal. The resistive output will then be wired to the relay.

Did anyone purchased this kind of device?

  

RE: Motorized Potentiometer

Basler makes a microprocessor based reference pot called a RA70 converts a 4-20 mA to a adjustable resistor. David

RE: Motorized Potentiometer

Something on your tapchanger produces a signal which is converted to 4-20mA. It doesn't emerge as 4-20mA direct from the tapchanger mechanism on any design I've seen (although there's always a first time...) so it is probably worth taking a much closer look at the tapchanger and finding out what the primary transducer is. My guess is that it is a stepped series of resistors, and a resistance-current converter is fitted at the marshalling kiosk. It is probably easier to eliminate the existing converter rather than add a second one unless your relay is a long distance away from the transformer.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Motorized Potentiometer

(OP)
Thank you scottyuk for your reminders, I'll double check that.

Pwrengrds, thanks for the supplier tip.

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