Study On Principle And Implementation Technology Of Substation-area Backup Protection In Intelligent Substation

The traditional stepped backup protection is always the weakness of power system stability because of its action delay, difficulty to setting and easy to cause a chain of accidents. Therefore the traditional backup protection has become increasingly unsuited to the requirements of smart grid. The intelligent substation adopts a number of new technologies, such as non-conventional instrument transformers, intelligent primary equipment and IEC61850communication standard. As a result, it achieves the digitized information collection, the information transmission network and unification information modeling. All the technologies provide extremely favorable conditions to study the new type of backup protection based on information sharing. So the main research contents of the dissertation are protection principle and implementation technology of substation-area backup protection for intelligent substation.This dissertation defines substation-area protection specifically, analyses the concept’s connotation and extension, and puts forward a substation-area backup protection scheme based on current differential principle (abbr. SDBP). The new scheme defines boundary differential zone, inner-station differential zone, extended differential zone and equipment differential zone. SDBP can accurately locate the fault component according whether the differential zones lie in restraining state or operating state, and implement backup trip according the act information of main protection and breaker. Several particular problems are discussed, including operation characteristic, setting principle and sensitivity. Then the author analyses the impact of TA saturation and inrush current, and gives the corresponding countermeasures. SDBP abandons the stepped setting principle of traditional backup protection, and has the following advantages: action time is fixed and is less than a At; it has absolute selectivity and high sensitivity; it is not affected by overload impact due to flow transferring and can avoid chain reaction caused by backup protection malfunction. The validity of SDBP has been verified by PSCAD simulation software under the condition of normal state and fault state with different types and locations.This dissertation presents the practical correction method to meet the data processing requirements of SDBP, which does not require interpolation, decimation or sample rate conversion. The new method applies the Fourier algorithm immediately to equal-interval sampling data, then amends the sine/cosine items according to real-time frequency, and finally acquires the signal’s virtual value and phase. Compared with the data processing scheme of interpolation and decimation in complete digital relays, the new method not only greatly reduces computation amount, but also eliminates the anti-aliasing low-pass filtering which will introduce additional quantization error and filter delay. The new method is completely suitable for the application of phasor based protective relays, especially for SDBP, verified by ATP and MATLAB.A variable data-window algorithm is put forward for phasor estimation based on narrow band-pass filter and Phaselet, abbr. NBDF-Phaselet. Firstly the approximate initial values of the Narrow Band-pass Digital Filter are get by Phaselet method with1/4cycle data-window. Then the sampled value sequence is filtered by the NBDF. Finally the accurate phasor is estimated by Phaselet method with different data-window. SDBP which employs the new algorithm can receive Phaselet of adjacent substation instead of sampled value. Therefore it can reduce the communication demand between substations and simplify the implementation of SDBP. The simulation with PSCAD and RTDS show that the NBDF-Phaselet algorithm is effective when applied to phase current differential principle.Finally the author designs the implement scheme of substation-area backup protection. The high performance hardware-software platform which suits for SDBP specially has been developed, which adopts multi-processor architecture and RTOS. The platform is mainly composed of PowerPC module and DSP module. The former realizes network communication function with Gigabit Ethernet interface and the latter acts as a data association processor. The critical software including sampled values transmission module and GOOSE transceiver module have been improved, which can enhance the real-time of information processing. The SDBP’s information model based on IEC61850and Q/GDW396standards is established. The communication solution which directly transmits sampled values is introduced into SDBP. The solution extends the process-level network from substation internal to between-substation by EoS and wide-area Ethernet technology based on IEC61850.