~ National Lightning Safety Institute ~

Section 5.2.4

Objective

The objective of this investigation is to identify and describe research and development projects required for the advanced control of transients in electric power and telecommunication systems of the present as well as of the future, with special reference to Sweden. The concentration will be on systems with voltages up to 20 kV.

Background

The impact of information technology and micro-electronic circuits in all aspects of life at home and work place necessitates very high quality power and communication services. There is an ever increasing demand for high quality services from customers. This presents new business opportunities for utility companies, in providing customer specified quality services. The introduction of new technologies in power generation, transmission, and distribution poses new challenges and opportunities for control of transients.

To be efficient, transient control or electromagnetic compatibility (EMC) of a facility has to be incorporated at the design stage itself. It is necessary to have appropriate EMC specification of customer facilities such as residential buildings, commercial and industrial buildings, control rooms of power and communication networks, and other intelligent buildings. The purpose of EMC specification is that none of the transients outside the specified range goes into the facility or comes out of it. The research required for evolving EMC specification of customer facilities will be identified and described.

The main components of the program for the one year study from Oct. 1997 to Sept. 1998 are as follows:

Nature of transients

The present knowledge on the nature of transients in power networks and consumer facilities in Sweden caused by lightning, switching, faults, different types of loads etc. has to be gathered from the published literature and from experts. The parameters important from an EMC point of view has to be described. A research program to correct the deficiencies, if any, in our present knowledge of nature of transients in power networks has to be specified.

Response of structures and electrical system to external electromagnetic fields

Present knowledge of the theory and adequacy of analysis tools (computer simulation) has to be reviewed. Simple circuit configurations has to be tested for its response to lightning electromagnetic fields (LEMP) for understanding the coupling mechanism. Since most of the complex systems can be approximated as a combination of simple circuits, these tests can give insights into the way complex systems are interacting with the fields. A typical residential house is available near the Institute for experimental purposes. The current and voltages in the low voltage wiring system of the house due to lightning electromagnetic fields will be measured along with the electric and magnetic fields both outside and inside the house. It is to be expected that the fields inside will be different from fields outside. Special attention will be given to the radiated fields generated inside the buildings by the transients in the wiring. The character of induced transients in the wiring under different conditions, with the system connected and without connected to the normal external power will be investigated. The response of the electrical network will also be modelled using commonly used design tools commonly used by electrical engineers. It is expected that a detailed research project can be specified that can lead to the development of a practical design tool for optimal design of electrical networks against lightning induced transients.

Transient protection

The present method of transient protection in distribution networks is the isolation of the customer by switch operation or diversion of surges by shunt protective devices. Both methods adversely affect the quality of service in varying degrees. Moreover, even though the individual protector characteristics are well described, not enough research is done on the characteristics at the system level with the protectors, cables, and the loads included. A research plan has to be outlined for the optimal placing and co-ordination of protectors in a distribution network. Measurement of transients at various points in the wiring system can give information on the positions where the surge arrestors have to be placed for optimum performance. The current research at the Institute has already produced viable models of gas discharge tubes and varistors in ATP-EMTP. It was also demonstrated how the co-ordination of the above two devices in a simple protection circuit can be simulated. Similar ideas have to be developed and applied to co-ordination of protectors in typical low voltage networks. The possibility of developing an integrated design tool in ATP-EMTP or in some other program for optimal placing and co-ordination of protectors in a low voltage power installation has to be explored.

Research is required for new transient protection systems to avoid isolation and minimize bad aspects of diversion. The possibilities of transient protection system acting as a non-linear system giving constant output for variable inputs representing transients are to be explored. Intelligent protector adjust its response by anticipating the nature of transient at the very beginning of the transient.

Grounding and bonding

Grounding and bonding of electrical and mechanical systems are mainly used to control dangerous overvoltages and are very important for safety of personnel. However, the current practice of allowing the transients to spread over the grounding system produce 'dirty grounds' and this in turn cause many EMC problems. More research is required to develop the concept of ground as an absorber of transients.

Risk analysis

Risk analysis in terms of the effects of transients in typical facilities are to be performed. The risk level depend on the nature of transients, the effects of transients on the facility, and the level of tolerance in the functional deterioration of the facility. The risk analysis may even has to be carried out on sub-units of a facility such as communication room, medical ward, control room etc. Lightning is an important cause for transients in power and communication distribution network. Sweden and most countries of Western Europe are covered by lightning location systems. The archived lightning data could be used in the risk analysis of distribution systems and customer facilities at different geographical locations. The possibility of using real-time lightning data in initiating appropriate emergency control has to be explored.

Coordination of services

A facility may have many services connected to it: electricity, telephone, water, heating, TV cable, lightning protection system etc. All these services have their own installation practices which may not be the best from the point of view of transient control. More work is required to see how the design and installation of various services can be co-ordinated with the aim of efficient control of transients.

If you have any comments or contributions helpful for this project, please send it to us. For more information about the project visit our Swedish High Voltage Institute homepage at http://www.hvi.uu.se To stimulate exchange of ideas, we have started a discussion page and selected contributions will be put on the discussion page with proper acknowledgement.