This paper reports on the implementation of Voltage Security Assessment tools in the energy management system of RTE, the French transmission system operator. In particular, secure operation limits are determined in voltage sensitive regions. This involves a load increase in the region of concern, covered by a power transfer from various locations throughout the system. The limit is the maximum load power increase such that the system can withstand every contingency of a list. A salient feature of the tool is the use of a simplified, fast time simulation based on the quasi steady-state approximation. This is justified by the presence of controls reacting to the load power increase and the contingency, which makes standard power flow computations inappropriate. The paper also describes the implementation of the tools in the energy management platform of RTE and shows some typical results.

This paper reports on prospective tests of a system protection scheme against long-term voltage instability relying on a set of distributed controllers, each monitoring a transmission voltage, blocking tap changers and shedding loads in a zone. The emergency actions adjust in magnitude and location to the disturbance. Each controller acts in closed-loop, which guarantees robustness. The method is illustrated on a real-life model of the Western region of the RTE system. The choice of the controller settings is discussed in some detail and examples of performance are given, combining the above remedial action with capacitor switching and secondary voltage control.

A background of increasing uncertainties in all time horizons of power system planning and operation has prompted the development by RTE and NGT of a comprehensive methodology for assessing both the static and dynamic security of a real network facing a large number of uncertainties. The proposed paper briefly describes this methodology and then focuses on one application: study of the collapse modes of an area of the French network

This papers deals with the emergency control of load tap changers (LTCs) to face low transmission voltages or voltage instability situations. The proposed simple control logic consists in reverting the tap movements once the voltage at a monitored transmission bus falls below some threshold. A deadband on this voltage allows the system to settle down in between the normal and reverse logic modes. In order to control a large number of LTCs, the latter are divided into clusters, each with its own monitored voltage. The paper also considers the control of two levels of LTCs in cascade, where proper coordination is required between the two levels. The proposed scheme has been tested on a detailed EHV-HV-MV planning model of the Western region of the French transmission system operated by RTE. Long-term time responses to major disturbances are shown to illustrate the performance of the proposed scheme.

Optimal operation of an electrical power system requires complete control of the economic impact of security and raises the question of the accurate estimation of the risks. Therefore, the ability of an electric utility to achieve these goals in the context of more and more complex power systems will be a major factor of competitiveness. With this in mind, EDF has decided to develop a voltage security assessment tool. This software is based on a fast time domain simulation engine, which has been embedded in the EDF grid security analysis framework. Its main features are the simulation of voltage stability phenomena and slow dynamics, the computation of different kinds of security margins, the suggestion and the validation of corrective actions. It is being experimented upon in the French national control center, where it should be used to prepare the system operation, specially the day before, as well as in an online environment.

This paper reports on prospective tests of a system protection scheme against longterm voltage instability relying on a set of distributed controllers, each monitoring a transmission voltage, blocking tap changers and shedding loads in a zone. The emergency actions adjust in magnitude and location to the disturbance. Each controller acts in closedloop, which guarantees robustness. The method is illustrated on a real-life model of the Western region of the RTE system. The choice of the controller settings is discussed in some detail and examples of performance are given, combining the above remedial action with capacitor switching and secondary voltage control.