Insulation coordination

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Introduction Methods idioms simplified statistical method statistical method applied voltage over-voltage characteristics and limitations and protective insulation insulation level Expand edit this section Introduction insulation coordination role of the voltage on the electrical equipment under normal operating conditions is operating voltage and a variety of over-voltage, the latter including temporary overvoltage, over-voltage, over-voltage lightning. For economic rational design transmission lines and electrical equipment insulation, electrical systems generally take special equipment and devices to limit overvoltage. Electrical equipment insulation level is able to withstand the test voltage: ① frequency withstand voltage value. ② lightning impulse withstand voltage value. ③ switching impulse withstand voltage value. ④ long frequency test voltage values. These test voltage waveform, numeric, application method,Adidas F50 FG, time, frequency, etc., all countries have national standards clearly defined. Edit this paragraph method idiom role in the device according to the maximum over-voltage insulation and dielectric strength equipment, the concept of minimum insulation coordination approach. Idiom simple, but can not estimate the probability of failure and a probability insulation and with the relationship between the coefficient, so this method relatively tight insulation requirements. The role of the device according to the insulation of the "maximum overvoltage" and equipment "minimum dielectric strength," the concept of the habit of insulation coordination method. First need to determine if the device may occur on the most dangerous over-voltage and minimum insulation withstand strength equipment, and then the operating experience, choose a fit factor as the ratio of these two voltages to compensate for the estimated maximum over-voltage and minimum insulation resistance by the intensity of the errors and increase the safety of more than a certain degree, to finalize the equipment insulation shall withstand voltage level. Idiom simple, but can not estimate the probability of insulation failure and this probability and with the relationship between the coefficient, so this method relatively tight insulation requirements. Because of the non-self-restoring insulation measured discharge probability high cost, it can only use the idiom. Currently, 220 kV and below electrical equipment, usually still use idioms. For example, power transformers are used lightning protection. Lightning arrester limits the ability of common arrester protection level representation. Transformer withstand lightning impulse insulation level (BIL) to be higher than the level of protection arresters, as the ratio between the two fit coefficients. China is generally used with the coefficient is 1.4. For 500 kV transformer, the International Electrotechnical Commission (IEC) regulations, with coefficients to be equal to or greater than 1.2. Statistical method according to over-voltage and insulation flashover voltage amplitude statistical properties of insulation failure rate is calculated. Sensitive to changes in the factors affecting the failure rate can be an acceptable level and reasonably determine the insulation level. Statistical method can not only quantitatively insulation coordination given the degree of safety, but also in accordance with the equipment depreciation costs, operating costs and accident damages the sum of the smallest of the three principles to optimize the design. Difficulty is that random factors, some statistical laws have yet to be understanding. Over voltage amplitude from the insulating dielectric strength facts are random variables, and insulation according to over-voltage amplitude of the statistical characteristics of flashover voltage, insulation failure rate is calculated. Sensitive to changes in the factors affecting the failure rate can be an acceptable level, the technical and economic comparison, based on the reasonable assurance level of insulation. This approach not only gives the insulation coordination quantitatively the degree of safety, but also in accordance with the equipment depreciation costs, operating costs and accident damages the sum of the smallest of the three principles to optimize the design. The present study is based on more than over-voltage amplitude probability distribution based statistical method. In EHV power systems significantly reduce the insulation level of economic efficiency. Self-restoring insulation statistical properties of the dielectric strength is relatively easy to obtain. Since the 1970s, the internationally recommended for EHV power system self-restoring insulation using a statistical method for insulation coordination. The difficulty lies in the random statistical method many factors,adidas f50 adizero, some of the statistical laws of random factors have yet to accumulate data and understanding, the low probability density part of the information more difficult to obtain. At present the calculated failure rate, usually much larger than the actual, as well as stay applications continue to improve. Simplified statistical method in order to facilitate calculations, assuming over-voltage and insulation discharge probabilities are subject to normal statistical distribution. International Electrotechnical Commission (IEC) and the China National Insulation Coordination standards, recommended a 2% probability of occurrence of an overvoltage as a statistical (maximum) over-voltage Uw, then take a 10% probability flashover voltage of statistics as insulation withstand voltage Uw, safety factor in different statistical γ = Uw / Us of the case, the calculation of the insulation failure rate R. According to the technical and economic comparison between the cost and the failure rate coordination in setting acceptable R value, according to the corresponding γ and Us, to determine the insulation level. In practical applications in order to facilitate the calculation, it is assumed over voltage and insulation discharge probability are subject to normal statistical distribution. Simplified statistical method and idioms same simple, and there are ready to be investigated curve (Figure b). Although the failure rate values ​​may not be very accurate, but easy to program in engineering for comparison, which is widely used. Power system for determining the transmission lines and electrical equipment insulation level of principles, methods and regulations. The purpose of insulation coordination studies considering the role of electrical facilities may withstand voltage (working voltage and over-voltage), the effectiveness of over-voltage protection devices, as well as equipment for insulation materials and structures for a variety of roles withstand voltage characteristics and other factors, and considering economic rationality to determine the transmission lines and electrical equipment, insulation levels. Electrical equipment often run under the operating voltage power system, but also by a variety of over-voltage function. Electrical equipment insulation for various applied voltages have a certain tolerance limits. When the insulation is damaged, it will result in equipment damage or even system outages. To avoid these losses must ensure electrical insulation device having a predetermined strength, which is the level of insulation. Determine the insulation level required to handle technically applied voltage, over-voltage limitation measures, insulation tolerance among mutually supportive relationship, but also requires coordination of economic investment costs, maintenance costs and accident costs between losses relations, in order to achieve better overall economic efficiency. Edit this paragraph the applied voltage applied to the electrical voltage on the device is the normal operating conditions of the operating voltage and a variety of over-voltage. Power system during normal operation, each point frequency voltage is different. Transmission line voltage on the sending end of the device is higher than the voltage on the receiving end device. Thus, for each rated voltage of the power system, but also provides a maximum operating voltage of the system. Maximum operating voltage to be based on energy distribution, transmission distance, the grid structure, system flow distribution, stability characteristics, reactive power compensation, the economy, as well as equipment insulation design and other comprehensive factors to determine. China for 220 kV and below power system, the maximum operating voltage is specified at 15% higher than the rated voltage; For 330 ~ 500 kV EHV power systems, the maximum operating voltage of 10% above the nominal voltage. Including temporary overvoltage overvoltage, over-voltage, over-voltage lightning. Because of its different causes, have certain features. The insulating performance perspective, in addition to attention over-voltage amplitude, the need to distinguish between them and the voltage waveform of the time course of action. This is because the insulating strength of a volt-second characteristic, the ability to withstand voltage due to the voltage waveform and a duration of action differ. According to the applied voltage waveform can be divided into the following five kinds. ① Under normal operating conditions, the power frequency voltage. ② temporary overvoltage: typically a few hundred Hz Hz or does not decay or weak oscillation attenuation, the maximum duration of about one second. ③ slow front overvoltages: Wave head duration of tens to thousands of microseconds or asymmetric double exponential decay oscillation. Gaps, insulators and electrical equipment external insulation standard operating shock wave head test waveforms generally 250 microseconds / wavetail 2500 microseconds. ④ fast wave front overvoltage: the first wave duration is a few tenths to tens of microseconds unipolar double exponential wave. Standard lightning impulse test waveforms for the first wave of 1.2 microseconds / wavetail 50 microseconds. ⑤ steep wave front overvoltage: the first wave duration of only tens of nanoseconds, followed by a few megabytes to 100 MHz frequency oscillation superimposed. Standard steep wave front impact test waveforms in developing among the wave front time of 15 nanoseconds. Edit this paragraph voltage limiting and protection for economic rational design of transmission lines and electrical equipment insulation, electrical systems generally take special equipment and devices to limit the over-voltage, referred to as over-voltage protection. Usually high voltage shunt reactors, static var compensator elevated frequency voltage limit value; rapid protection with reduced frequency voltage increases its duration; using good conductor transmission line overhead ground wire, and in some circumstances can reduce ground fault caused by frequency voltage increases. In EHV power systems, load line when closing and reclosing can produce a relatively high over-voltage, but there is frequent,nike mercurial vapor 2013, the power system insulation level generally play a decisive role. Improve the performance of the circuit breaker, using closing parallel resistance, narrow-phase closed and others have very different effects on; through-flow capacity of larger metal oxide surge arresters, can also be used as an over-voltage protection devices. Substation equipment from the lightning overvoltage arrester for protection. Device overvoltage arrester performance lines to wave conditions, substation wiring layout and so on. Power system insulation coordination to include protective measures against over-voltage and integrated request formulated. Edit this paragraph electrical insulating properties and insulation level set

insulation coordination

prepare insulation can be divided into self-restoring insulation and non-self-restoring insulation two categories. Self-restoring insulation insulation can restore itself after the destruction, generally refers to the air in contact with air gap and external insulation. Non-self-restoring insulation after discharge its insulating properties can not recover on its own, usually by solid medium, liquid medium consisting of equipment insulation. Equipment insulation strength and shape of the electrode, an insulating material, the distance between the electrodes, the waveform of the voltage, among other factors, with the dispersion. Therefore, great importance in practical engineering Electrical Equipment true type insulation test. Electrical equipment insulation level means that the device can withstand (flashover does not occur, discharge or other damage) test voltage values. According to electrical equipment in the system may be exposed to a variety of applied voltage, the characteristics of protective devices and equipment insulation withstand voltage for various effects features, formulated some basic insulation level indicates that the device test voltage values. They are: ① frequency withstand voltage value; ② lightning impulse withstand voltage value; ③ switching impulse withstand voltage value; ④ long frequency test voltage values. The test voltage waveforms, numeric values, the test voltage is applied to the method, time, frequency, etc., in the country's national standards are clearly defined.