State estimation of voltage and phase-shift transformer tap settings

Traditionally, state estimation algorithms have treated each transformer tap setting (voltage transformer turns ratio or phase-shift transformer angle) as a fixed parameter of the network, even though the real-time measurement may be in error or nonexistent. Such a strategy can lead to misdirecting residuals in adjacent valid measurements when the modeled transformer setting is incorrect. Ultimately, a network solution is derived which does not match actual real-time conditions. A new transformer tap estimation technique is presented which incorporates the function directly into the state estimation algorithm. The procedure provides for turns ratio and phase angle measurements and treats each transformer tap setting as an independent state variable. Test results for an actual 300-bus network demonstrate the tap estimation capability