Electrical Power System Essentials

6.1 INTRODUCTION

In the control centre, the transmission and distribution of electrical energy is monitored, coordinated and controlled. The Energy Management System (EMS) is the interface between the operator and the actual power system.

An indispensable part of the EMS is the SCADA system: the Supervisory Control and Data Acquisition system. The main functionalities of the SCADA system are to collect real-time measured data from the system and to present it to the computer screen of the operator, and to control actual components in the network from the control centre. The actual network status is stored in the ‘real-time telemetered database’, which is used as input for the other EMS functions.

The EMS is in fact an extension of the basic functionality of the SCADA system. This includes tools for the analysis and the optimal operation of the power system. In the next paragraphs some of these software tools are highlighted. The state estimator (Section 6.4 (State Estimator)) serves as a ‘filter’ of the real-time database; it determines the state of the power system that matches best with the available measurements (some of them can be erroneous). The state estimator runs at regular time intervals (typically every five minutes) because its output is the necessary input for the other analysis programs, e.g.

• loadflow (Section 6.2 (Loadflow or Power Flow Computation));
• optimal powerflow (Section 6.3 (Optimal Powerflow));
• controlled switching;
• contingency analysis;
• short circuit computations; ...