Abstract
This paper presents a novel pilot protection scheme of DC cable line in voltage-source-converter (VSC) based multi-terminal DC (MTDC) grids, which utilizes a novel phase-mode transformation to decouple the bipolar DC cable current into six mode and it uses the stationary wavelet transform to extract the modulus maxima of fault initial traveling waves current (FITWC). With accurate amplitude and polarities of the FITWC being collected from the fault-detection devices located at each terminal, the proposed scheme can correctly determine the faulty segment and the faulty pole. In this paper, the ratio of amplitudes between sixth mode forward and backward travelling wave currents is used to judge the faulty segment and the polarity of fifth mode forward travelling wave current is used to identify the faulty pole. A four-terminal VSC-based MTDC grid was built in PSCAD/EMTDC to evaluate the performance of the fault-protection scheme. Simulation results for different cases demonstrate that the proposed protection scheme is robust against noise, and has been tested successfully for fault resistance of up to 400 Ω. Since the scheme merely needs the characteristics of FITWCs, the practical difficulties of detecting subsequent travelling waves are avoided. Moreover, only the state signal is needed to send to the other side in proposed scheme, so low communication speed can satisfy the requirement of relay protection and it does not need the data synchronization seriously.
Highlights
The development of power-electronic and controllable devices in power systems is rapidly expanding the field of applications for voltage source converter (VSC) based high voltage direct current (HVDC) technologies, due to its recognized advantages in comparison with traditional line commutated converter (LCC) based HVDC transmission [1,2]
In a bipolar multi-terminal DC (MTDC) grid, when a monopolar fault occurs on the DC line, the fault travelling wave (TW) signal on the faulty pole line can be coupled to the healthy pole line due to the electromagnetic coupling
This paper proposes a novel directional pilot protection for VSC-MTDC frequency-varying cable
Summary
The development of power-electronic and controllable devices in power systems is rapidly expanding the field of applications for voltage source converter (VSC) based high voltage direct current (HVDC) technologies, due to its recognized advantages in comparison with traditional line commutated converter (LCC) based HVDC transmission [1,2]. In two-level converter based VSC-HVDC system, there are large shunt capacitors in parallel at both terminals of the DC transmission lines. According to this characteristic, [13,14,15] have proposed some DC transmission line protection methods. The proposed protection method only aims at two-terminal DC transmission system, their application in MTDC grid needs to be further analyzed. According to the characteristic above, a novel pilot protection principle for VSC-MTDC cable lines is proposed, in which the amplitude difference between the six-mode initial forward and backward FITWC is utilized to judge the faulty segment and the polarity of fifth mode forward TW current is used to identify the faulty pole.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
