|
The fault characteristics of UHV transmission line are of obvious transient process with a great deal of transient components, as a result of long distance, large distributed capacitance and small distributed inductance and resistance. Compared to the high voltage system, the UHV system has the features of slower DC component time constan and larger harmonic components and distributed capacitance current. This featrues may lead to the failure of traditional protection. More over, because of the large transmission power of UHV system, it is becoming quite important to clear the fault quickly, in order to maintain the security steady of UHV system. all of this have premoted the proposal of ultra-high speed protect principle. At the same time, this kind of protection proposed higher request to their auxiliary elements, such as starting elements of fault and faulty phase selector.At first, the UHV transmission line model is built based on lumped parameter.Using this model author gives some theoretic analysis about the dynamic process under some kinds of faults. Proceed from the Generation Mechanism of transient current compoment, the transient current’s character is analyzed qualitatively. After that, Prony’s method is applied to the fault signal’s analysis and processing. Additionally, the transient process of UHV system and 220kv system is compared.Secondly, A wavelet transform modulus maximum based fault starting algorithm suitable for ultra-high speed protect of UHV transmission lines is introduced. According to the different characteristics between fault signals and noises under different scale after transformed by wavelate, the fault starting is realized. Simulation results based on PSCAD/EMTDC show that this method is fast and reliable. Moreover, this method is almost not affected by sampling frequency, fault inception, fault resistance, fault location, etc. And it has high sensitivity.Finally, The basic characteristics of the current modular fault components are analyzed. According to energy differences of current modular fault components under different fault types, this paper proposes a new fast faulted phase selection method. Taking energy of each modular fault current as character quantity and utilizing their minimum, faulted phase selection is achieved. The principle of this method is easy to understand, reliable and easy to implement. Simulation results based on PSCAD/EMTDC show that this method can rapidly and accurately identify various fault types on UHV transmission line. Moreover, this method is almost not affected by sampling frequency, fault inception, fault resistance, fault location, etc. So it has a good adaptability.
|