New Fast Direction Comparison Busbar Protection Principle And Implementation Technology

Busbar connects generators, transformers, rectifiers with transmission lines, busbar is one of the most important components of the power system. The tripping missing or maloperation of busbar protection results in great harm to the power system. With the development of power grid construction, busbar protection puts forward a higher requirement for the rapidity, selectivity, sensitivity and reliability. The widely used busbar protection principle which is based on current differential protection is apt to be affected by current transformer (CT) saturation and CT ratio-mismatch. Studying on new busbar protection principles is of great significance to overcoming the shortcomings of busbar differential protection principle and improving the rapidity and reliability of busbar protection. So far, most of the new busbar protection principles just propose protection schemes instead of developing actual protection devices, the performance of the proposed principles can’t be verified. Developing busbar protection device based on new busbar protection principle is of practical significance to the power system. To that end, the paper finishes the hardware development and software implementation based on the new fast direction comparison busbar protection principle and tests the busbar protection prototype. Main results of the paper are following:(1) According to the characteristics of the forward traveling wave and backward traveling wave in different fault locations, the paper puts forward a fault direction recognition principle based on direction comparison. The principle utilize amplitude relationship between the forward traveling wave and backward traveling wave in a specific period of time after the fault occurred to determine the transmission line fault direction, together the fault direction recognition results of the lines connecting to the busbar determine whether the busbar fault happens. According to the direction comparison busbar protection principle proposed, a set of protection scheme is designed. The main components are analyzed and algorithm formulas applied to engineering practice are given.(2) The busbar protection prototype based on the proposed direction comparison busbar protection principle has been developed. The hardware design diagram of busbar protection prototype is given. The main components, such as high-speed sampling unit, fast data processing unit, central processing unit and switch input and output unit are analyzed. The main components of hardware circuit diagram and workflow are explained, the working mechanism of AD7606 chip and uPP communication are analyzed. Software flow of busbar protection is designed; the synchronization of interrupts and tasks is coordinated to make sure busbar protection task can be completed priority. According to the software flow and busbar protection scheme proposed, flowchart of busbar protection is given and busbar protection algorithm is programmed.(3) Testing the busbar protection prototype by dynamic simulating system. Single-bus physical model is built in dynamic modeling laboratory, the voltage and current of the three lines connected to the busbar inset the busbar protection prototype, fault recording system is used to observe protection prototype operations under deferent failure conditions. In order to test the performance of protection prototype comprehensively, massive dynamic simulations are made to test the influences of fault location, fault type, current transformer saturation, transferring fault and switching operation. Furthermore, matlab is used to analyze the experimental data of dynamic simulation.(4) Testing the busbar protection prototype by RTDS closed-loop simulation testing system. Based on the actual 500kV substation parameters,3/2 connection bus model is set up in RTDS Lab, control logic of the simulation model is designed, input and output module of RTDS are used to make up the closed-loop simulation testing system. Protection prototype is tested fully by RTDS closed-loop simulation testing system, numerous RTDS simulations are made to test the influences of fault inception angle, fault type, and grounding resistance. Furthermore, matlab is used to analyze the experimental data of RTDS simulation.Theoretical analysis and test results show that the proposed busbar protection principle operates quickly and has high sensitivity and reliability, it can identify the switch operation correctly, and it is basically immune to fault inception angle, grounding resistance and CT saturation. The protection prototype is stable and reliable, it doesn’t operate firmly at an external fault while it operates in about 4ms when internal fault happens.