ABSTRACT
This chapter presents the first source of errors, imperfect measurements due to signal noise, metering accuracy, and analog-to-digital conversion. The network topology and parameters are assumed as known until they are fitted to the data in parameter estimation. The power system is assumed to be operating in a steady-state condition with fixed voltages, currents, and power flow. The remote terminal units (RTUs) that sample network analog variables and convert the signals to digital form are periodically interrogated for the values of the signals. The data collected by the RTUs are often redundant. There may be voltage sensing by step-down transformers on each phase of the transmission line, whereas only one is needed for balanced operation. Another purpose of a state estimator is to detect changes in network configuration. If a transmission line has one phase abruptly open circuited, the average power flow on the intact phases is far less than a value given by the last state estimate.
