Transformer Tap Position Estimation

The estimation of voltage transformer tap position is a desirable feature that can be appended to most state estimation algorithms. The primary requirement to estimate transformer tap position is the availability of a three-phase reactive-power measurement through either the fixed or tap side of the transformer. These ``measured´´ flows can also be calculated, depending on the availability of reactive injection and reactive transmission line flow measurements around the fixed or tap side buses. The gain matrix of the state estimator is not modified so only the tables used to calculate real and reactive residual mismatch need to be updated during the state estimator solution. The computational cost of including transformer tap position estimation is extra iterations of the state estimator. A number of tests were conducted using the IEEE 118 bus system as a model. The results of one of these tests are presented along with the algorithm to modify the tap positions while the State Estimator solution proceeds. A practical stopping criterion for the algorithm is also presented. The extension of the algorithm to line parameter estimation is also discussed in the Appendix.