1/1/2024 0 Comments Inmr tutorialIf the breaker is in the open position, it will become an end point on the circuit. However, if a properly selected arrester is not located near the transformer, it only takes one such event to cause failure of a very expensive asset in the circuit.Īnother important part of this coordination scenario is the state of the circuit breaker. In this type of coordination scenario, the probability of occurrence is quite low over the expected life of the transformer, which is probably 30-40 years. The arrester may even protect equipment on the surge side to some extent. If the only mitigation tool is an arrester at the transformer, it will protect the transformer if properly coordinated with the transformer insulation. The amplitude of these incoming surges will be equal to the flashover level of the backflashed insulator. Moreover, they are rare on systems of 500 kV or higher.įast rising surges on an incoming conductor have a high probability of flashing over insulation in the station if there are no arresters. However, owing to the high insulation withstand on systems above 245 kV, such back-flashovers are much less probable then on systems below this voltage level. In the case of air-insulated substations, if lightning strikes these lines within the span of one or two towers from the substation, a surge is likely to enter the station along the conductors.Įven well shielded transmission lines can allow a fast rising surge to enter a nearby station if there is a backflash to the conductor during a switching or lightning surge (see Fig. All stations connect to the rest of the system via incoming and outgoing overhead conductors. Even if a station is well shielded, lightning surges can enter indirectly. Substations are subject to two types of overvoltages that can stress insulation. 3Īdvertisement Substation Insulation Coordination for Lightning Surges The SIWV of external self-restoring insulation is universally tested under wet conditions because this withstand characteristic depends on an insulator’s creepage or leakage distance when wet (this being the total distance between the two terminals along the surface of all sheds). The actual direct length between the insulator terminals is the most significant factor in determining these fast impulse characteristics. 2) are universally tested and verified under dry conditions. The LIWV characteristics of external self-restoring insulation (see Fig. Insulation has two fundamental characteristics: lightning impulse withstand and switching impulse withstand, shown graphically in Fig. Because it is not possible to insulate sufficiently to withstand all lightning surges, insulators are designed and tested to determine the levels at which they will flash over. The goal is to help power system engineers decide whether or not a comprehensive study needs to be undertaken and what might be the benefits.Īll insulation has limits to its withstand capability. This edited past contribution by arrester expert, Jonathan Woodworth, offered a basic review of the fundamentals. IEEE 1313.2 are another excellent source for better understanding this engineering practice while a third highly acclaimed reference is “Insulation Coordination of Power Systems” by Andrew Hileman (1999). These standards cover 99% of what needs to be known to perform a lightning or switching surge insulation coordination study. However, as a good first approximation, system performance can be modeled using the formulas presented in IEC 60071-1, 6. This coordination task as well as the task of selecting and locating arresters can be simple while at other times complex, requiring computer simulation. The task of coordinating insulation withstand with the desired performance levels of the system can be significantly different if arresters are applied versus not applied. Insulation coordination has become a well-developed engineering practice and one where the characteristics of the system in terms of insulation and arresters cross paths. This carefully selected combination of insulators and arresters is then referred to as insulation coordination. An intermediate solution that requires some reasonable investment in insulation and protective equipment is therefore the compromise most often taken. Similarly, it seems equally unreasonable to insulate for all transient events, even if this were possible. Clearly, it would not be reasonable to insulate only for the operating voltage and thereby allow any transients to trigger insulation failure. How the insulation on any power system is protected is basically an economic issue. While arresters can be used to effectively control the most frequent type of such overvoltages, namely those caused by switching operations, transients due to lightning are more difficult to mitigate. Transient overvoltages occur on all power systems.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |