Transducers

[peetey]

On our system we use KYZ pulses and transducer values to an RTU to have a double check of load and capacity on our system. I am interested in learning more about transducers, how they function, formulas to convert milliamps to actual load values, etc. We on occasion work with our relay department but the transducers are theirs. With transducers how can you check the load like we do with KYZ? I don't know if this line of questioning is relevant to metering but I think they are related. Any links, e-mails or comments about this topic would be appreciated. I would also like to know how some feel about meters providing transducer values and kyz from one source? It does not allow two seperate and independent data streams about the system capacity.

--peetey

 

[rcw retired EE]

Transducers convert volt and amp signals to milliamp signals for use as inputs to SCADA, remote metering displays, control systems or other devices. Typically transducers provide information on instantaneous power, volts, amps and vars. They tell you how fast you're going, like a car’s speedometer, while the KWH meter (KYZ pulses) tell you how far you have gone (car's odometer).

Equations for the milliamp output are specific to the scaling of the specific transducer, CT & VT ratios, and type of transducer. Looking for a single equation is similar to asking for the equation for the primary mega-watt-hours represented by one kyz pulse - it depends on the meter, the VT & CT ratios, the meter constant etc.

In the US, typical outputs are 0-1mA or 4-20 mA for 0-100% of the desired scale. For voltmeters 0-100% is usually 0-150V (VT secondary, 0 mA= 0V, 1.0 mA = 150V). For amp transducers the range is usually 0-5A. Watt transducers are usually 0-600W (5A x 120V) per single phase element. Var transducers are usually custom scaled. Some transducers have bi-directional outputs from –1.0ma to 0 to +1.0 ma to indicate direction of power and var flow.

Transducers versus meters? – Meters are usually more accurate unless you pay $$$. You are depending on the same metering CT’s & VT’s, so there is only an illusion of separate systems. With modern digital meters and relays, the more accurate digital signals from the meters (the actual register readings, not kyz pulses) can be connected via fiber to the SCADA system and signals downloaded from digital relays can be used for back up and error checking.