Coordinación de aislamiento

ON THE INSULATION CO-ORDINATION STUDIES USING (EMTP) M. Aburaida (AMIEE) Sceco-east, Secti, Dammam, P. O. Box 5190 Dammam 31422, Saudi Arabia
ABSTRACT:
The reliability of supply provided by an electric power system, as judged by the frequency and duration of supply interruptions to its customers, depends to a great extent on the surge performance of the system. Although there are many othercauses of interruptions, breakdown of insulation is one of the most frequent. In reality, the insulation has to withstand a variety of overvoltages with a large range of shapes, magnitudes and duration. These various parameters of overvoltages affect the ability of insulation to withstand them. So proper insulation levels are required for equipment as well as proper overvoltage protection. Theobjective of this paper is to explain the different methodologies of insulation co-ordination studies and show how the EMTP can give an easy and reliable approach to insulation co-ordination problem. This will include modeling of the different elements of the power system and simulating their behavior under different types of surges (lightning, switching, fault clearing, …etc..). The insulation level ofeach equipment will be examined with reference to BIL as well as the selection, specification and location of arresters. Practical cases will be explained. hand, will usually fail by arcing around the string. 1. INTRODUCTION Once the initial arc is extinguished, the insulation Insulation co-ordination refers to the art of selecting capability is restored. Statistical specification of aappropriate insulation levels for equipment (e.g. BIL is not appropriate to a non-self-restoring transmission lines, transformers, generators..etc..) insulation, but is quite appropriate to a self-restoring and the corresponding overvoltage protection system insulation. (arresters). For transmission lines, this means the It is important to understand the meaning of design of the conductor-to-conductor andtower BIL and BSL specifications. These specifications are clearances, the selection and specification of intended to measure the ability of equipment to insulator strings, the placement of ground (and in withstand representative overvoltages, intended to some cases shield and counterpoise) conductors and capture the general ability of the device with respect the specification of towers and towerfooting to a general kind of overvoltage condition. The BIL resistance. For equipment such as transformers this is specified with reference to a specific waveform: means the specification of BIL (basic lightning 1.2 microseconds rise time, 50 microseconds time to impulse insulation level) and. Both conventional and decay to half value. The BSL waveform has a 250 statistical ways of specifying theseinsulation levels microseconds to peak, 2500 microseconds to decay are recognized in the standards. For equipment such to half value. The implication (not necessarily as breakers, additional specification parameters correct) is that typical lightning and switching include the TRV (transient recovery voltage) waveforms have the same general characteristics and characteristics [1]. shape. While theexpected characteristics of the Selection of insulation levels for equipment overvoltage resulting from switching can usually be and selection and location of overvoltage protection determined with good accuracy using the EMTP equipment are interrelated: the insulation level of a type programs (and consequently the designer can piece of equipment or line depends on the type of verify to whatextent the standard test waveform is overvoltage protective equipment installed. Recent applicable), actual lightning waveforms can differ practice has been to attempt to reduce insulation considerably from the assumed ones [2]. levels by more liberal use of arresters, particularly Insulation coordination also means the zinc oxide arresters, and also the limiting of selection, specification and...