Research On Integrated Protection For Digital Substations

With the rapid development of photoelectric technology and computer technology, digital substation has become the main development trend of substation automation. Digital substation is a system that can use the Optic-electric Transformers and Intelligent Switches to convert analog signals into digital signals completely during the Acquisition, Transmission, Treatment and Output Process. There are also corresponding protection control units and communication network in it, achieving in data and information acquisition, digital transmission and sharing. Digital substation has the feature of intelligence with the first device, second device network and operation management automation, which has higher requirements on relay protection.This paper summarizes two schemes of relay protection configuration: the conventional configuration and the integrated protection configuration. An integrated protection scheme for digital substations on the basis of sequence components is presented according to the principle of integrated protection configuration. The method, which is based on sequence components occurred in fault, combined with sequence voltage , sequence power direction and sequence current differential principle to determine the faults, includes three stages: the fault bus determination, selection of fault line and fault zone. This method is able to respond to various faults occurred in the full phase and non-phase operating conditions.By analyzing zero sequence voltage occurred when the end of line in bilateral power network falls to the grounds, the system operating condition that can protect the installation place of the lowest zero sequence voltage is deduced in this paper. It provided the theoretical basis to make the zero sequence protection play a big role in the spot.Combined with second-order low pass digital filter and difference half-wave Fourier algorithm, the protection configuration can complete judgment of the criterion within a short time, and then carry out the rapid action.By modeling and simulating with MATLAB under the various fault conditions, a large amount of data is achieved. It shows that the proposed integrated protection theory based on sequence components can not only quickly identify a variety of asymmetric faults, but also reflect the three-phase short circuit fault with a few short moments. Simple principle and clear logic characterize the protection configuration, which positively exploring the relay protection of digital substations.