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| Distance Relay Based on Rogowski Coil Current Transformer by Using Instantaneous Value after Equal Transfer Processes |
| Li Baowei1,2, Shi Xin2, Wang Zhiwei2, Wen Minghao1, Zhang Xu2 |
1. State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Wuhan 430074 China;
2. XJ Electric Co. Ltd Xuchang 461000 China |
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Abstract Since the output voltage of the coil is proportional to the rate of change of the primary current, it is required to be integrated to recover the measured current, which is usually realized by electronic integrator circuits. High-frequency transient signals tend to be generated during power system operation or short-circuit faults. After being processed by the integrator, the output signal of electronic transformer may be seriously distorted, resulting in mal-operation of the relay. Many researchers have proposed a variety of detection methods for abnormal output of the Rogowski coil, but the impact of additional components caused by integrators on protection cannot be avoided. An improved method of line relay directly using the differential output of Rogowski coil is put forward. Besides, a distance relay based on Rogowski coil current transformer by using instantaneous value after equal transfer processes is proposed. In the novel scheme, the current differential signal output by Rogowski coil is directly used to eliminate the influence of transient transmission error introduced by integrator.
Firstly, according to the equal transfer process of transmission lines(ETPTL) theory, the virtual Rogowski coil digital transmission link is constructed to process the voltage signal with the same transmission characteristics as the Rogowski coil digital transmission link, so that the voltage and current signals used for distance protection pass through the same transmission link. Secondly, the R-L equations are solved by least square method to calculate the fault location, so as to improve the stability of the calculation results. Thirdly, the voltage at the fault point is reconstructed and passed through the digital transmission link of virtual Rogowski coil to make it have the same transient transmission process as the voltage at the protection installation, so as to reduce the initial calculation error of fault and accelerate the convergence of fault calculation to stability. Finally, a method of model error discrimination is proposed. According to the R-L model, the voltage of the protection installation can be calculated from the calculation results of the fault location. It is compared with the actual voltage at the protection installation site to verify the calculation results of fault location, so as to prevent the distance protection from misoperation under working conditions such as abnormal data interference.
Simulation results demonstrate that the performance of the proposed distance relay method is not affected by the system operation mode, line length, fault location and fault type. In the case of metal fault, it can accurately calculate the fault location within 8.75 ms, and has a certain ability to withstand transition resistance. Compared with the traditional algorithm, the new algorithm has faster calculation speed, smaller fluctuation range and better stability under fault conditions and it is less affected by abnormal current signal transfer. To verify the performance of the improved distance relay algorithm proposed in this paper in practical applications, an actual Rogowski coil and relay device are used to build a test environment to test different fault conditions. The experiment results show that when different faults occur at different points, the time required for the measurement error of the improved distance relay to stabilize within 5% does not exceed 10ms, which is consistent with the simulation test results.
The study comes to the following conclusions: (1) According to the ETPTL theory, the current signal directly adopts the differential output of Rogowski coil, the voltage signal adopts the output of a virtual Rogowski coil with the same transfer features, so the relationship between them still satisfy the distributed parameter model of the original transmission line. (2) The current signal of the improved distance relay is directly from the Rogowski coil transducer without the integrator. It can radically eliminate the impacts of the Rogowski coil transducer integrator on the relay. (3) Various PSCAD simulation and experiment results show that it takes no more than 10ms for the measurement error of the improved distance relay to be stabilized within 5%, which is signed prior to the present method. The novel proposal immunes to system operation mode and can be applied to different length lines.
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Received: 20 October 2021
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2023, Vol. 38 
