Validation of performance of Joint Excitation and Reactive Power Controllers using commercially available power system analysis software packages

This paper presents the comparative analysis of two different approaches of reactive power allocation among synchronous generators within a steam power plant (SPP). The analysis is performed in or­der to validate by comparison of simulation results obtained with the two most widely used power system analysis software packages, PSSE®PTI Siemens and DlgSILENT Power Factory, with the case study measurement results. The measurements are obtained at the point of common coupling (PCC) of two adjacent Steam Power Plants (SPP) following the action of Joint Excitation and Reactive Power Con­trollers (JEQC). The accuracy of simulation results is essential for the Transmission System Operator (TSO) who is using these software packages to calculate power losses in the network due to reacti­ve power flows. The allocation of reactive power (Q) among the generators involved is performed by JEQC according to criterion of maximum Q reserve at plants PCC, while the algorithms built in PSSE®PTI Siemens and DlgSILENT Power Factory calculate Q allocation in order to minimize tran­smission losses by activating the OPF option. The aim of JEQC testing initiated by the Transmission System Operator (TSO), was to check the compatibility of results obtained by the JEQC algorithm ac­tion and that obtained by optimal power flow algorithm based on minimization of transmission criterion. The compatibility of the results, if confirmed, should enable the use of JEQC as an efficient tool for secondary voltage control in the power system.

The analysis was performed for a case study of parallel operation of two excitation and reactive controllers (JEQC) installed in two largest steam power plants in Serbia, SPP "Nikola Tesla A" SPP "Nikola Tesla B", which are electrically close to each other. The main purpose of the JEQC is to perform a slow voltage control at PCC of the plants by automatically adjusting the levels of generated reactive power of the SPP's generators while i) ensuring the uniform and synchronized response of all participating generators in case of power system disturbances, ii) preventing generators from operating in forbidden areas of the capability chart where overheating of stator core can occur, iii) restoring operating point of the generator after a major disturbance to the pre-fault value. The case study considered the Q-V controller outputs at the high voltage side of the SPP's step-up transformer.

The parameters used are given in the official technical documentation provided by the owner of the SPP. This was done due, to high voltage side location of the measuring points in the transmission network which TSO uses for gathering relevant data for safe and reliable operation of the transmission system. The performed simulations confirmed that all calculations results are in compliance with the national Grid Code (official version released on June 2014),