Intelligent distribution network is an important part of smart grid. Automatic reclosure provides line status acquisition, fault location and fault isolation for the realization of smart distribution network. It includes circuit breaker body and recloser controller, in which the controller is the core part of automatic recloser.
Firstly, this paper describes the hardware function modules of the recloser controller from the hardware framework; secondly, in the software design, it fully considers the software engineering and modular design ideas, and explains the software structure of the controller from the software module division and the relationship between the modules; finally, in the electromagnetic compatibility design, according to the relevant. According to the test standard, the designed recloser controller is tested at the highest level, and there are no abnormal phenomena such as device damage and controller restart during the test. Smart grid covers five links: generation, transmission, substation, distribution and power consumption. Intelligent distribution network is one of the key links of smart grid. Its goal is to improve the reliability of power supply, improve power quality and improve the efficiency of operation and management of distribution network, and realize the optimization and economic operation of distribution network. In order to improve the reliability of power supply, the system is required to achieve fast fault location, automatic fault isolation, network architecture reconstruction, shorten the system outage time and narrow the scope of fault outage.
Recloser controller is one of the important links to realize fault location and automatic fault isolation. It integrates the functions of remote communication, remote measurement and remote control. It judges line fault by monitoring the operation status and parameters of feeder circuit, carries out delay and overlap according to the predetermined settings, and can locate and isolate distribution line faults quickly. Load condition realizes network reconfiguration, so as to improve the reliability of power supply. The recloser controller is composed of power supply module, main processor module, coprocessor module, switch driver module, Ethernet module, standby battery and various communication modules. The schematic diagram is shown in Fig. 1.
Intelligent protection and control functions: three-stage multi-time-limit inter-phase over-current protection with arbitrary setting value and time period; multi-curve anti-time over-current protection with 60 common curves (including standard curve, non-standard curve, fixed-time curve, etc.) and anti-time curve editable; grounding protection with fixed/reverse-time over-current protection with arbitrary fixed value and time period Setting; triple comprehensive reclosure, reclosure times and intervals can be arbitrarily set, the type of overcurrent protection curve after reclosure can be arbitrarily set, according to the specific situation of the site, the sequence of action and curve type can be arbitrarily set, such as one fast three slow, two fast two slow, one fast two slow and so on. Hand-closing logic, fault locking reclosure; cold load start-up; sequential coordination function, grounding switch-off, reclosure retry function, high current lock-up and other protection logic.
Full power measurement function: realizing three-phase voltage, three-phase line voltage, three-phase current, three-phase active power, total active power, three-phase reactive power, total reactive power, total reactive power, three-phase power factor, total power factor, three-phase positive active power, total active power, total active power, three-phase positive reactive power, three-phase positive reactive power, total reactive power, 2-14 harmonics Wave (optional). Load statistics function: Calculate the average current of sampling interval (default value 15 minutes), can save 4500 points, and according to FIFO save, generate the nearest current load curve. The average daily current of peak and valley value is saved and loaded according to the daily load time scale. Panel design: 160 * 160 LCD display, support telemetry query, remote message viewing, parameter query / setting, control output. Parameter setting and control output with permission management, intuitive operation status indication. Load statistics and daily load statistics can be queried through LCD interface. Using communication trigger, local manual operation trigger and protection trigger control logic, IGBT switching control and high current permanent magnet control drive can complete most of the international mainstream permanent magnet switches. By debugging serial communication, the functions of data viewing, parameter setting and waveform browsing of the controller can be easily realized, and the function of GPS signal timing can be supported. Serial communication, support 101 protocol, support event reporting; support DNP 3.0 protocol; Ethernet communication, support 104 protocol. It has the functions of large capacity event sequence record (256 items), operation message storage and fault data, and permanent magnet drive process record (512 items). It meets the requirements of the highest level of surge (shock) immunity test of GB/T 17626.5-2008 and completes the simulation lightning operation test. This module uses STM32 series CPU of Italian Semiconductor Company as the core processor to complete AD sampling of AC/DC signals, large capacity DataFlash storage load recording and recording curve, EERPOM parameter storage, real-time clock and other functions. Full-power measurement provides three-phase current, three-phase voltage, zero-sequence current and zero-sequence voltage acquisition. It provides the voltage monitoring of lithium battery with 10 channels of switch input and acquisition, 7 channels of relay output, three-stage current protection function, reverse time protection function, reclosure function, cold load protection logic, load statistics, daily extremum statistics function, Ethernet communication, serial port, wireless radio frequency, GPRS and so on. The multi-protocol parallel communication of this kind of communication interface can flexibly expand the distributed intelligent control logic and the full power measurement function according to the need. This module supports PT power supply. The power module converts the PT power supply provided by the outside into about 28V DC power supply for charging the external 24V batteries. When the external power supply is insufficient, the equipment can be supplied uninterruptedly through the batteries immediately. The 28V DC power supply is isolated and converted into 5V, 15V, -10V and 220VDC needed by the controller through the switching power module. The module completes the intelligent drive control of permanent magnet switch. It can analyze the coil current in the process of permanent magnet drive in real time and optimize the process of permanent magnet drive. It has the function of recording large capacity storage of permanent magnet operation waveform, and can monitor capacitor voltage and aging status online. Large capacitor banks provide two sets of 22000uF/250V capacitors to ensure the energy supply required for the switching operation of permanent magnet switches in four times of switching and three times of reclosing. The spare battery is 24V/7AH maintenance-free lead-acid battery, which ensures reliable switching/closing operation under the condition of circuit power loss. The function of communication module is to complete the support of 101, 104, DNP 3.
0 protocol. The communication module contains a 232/485 interface, so that the recloser controller can be operated by debugging software. According to the priority of tasks and the characteristics of non-operating system MCU program, the main program architecture is divided into foreground main operation cycle and background interruption tasks. Among them, the priority of 1ms interrupt and communication data sending and receiving interrupt is lower, while the priority of sampling interrupt is the highest. The main task flow chart of the software is shown in Figure 2. Module Division will divide source files according to the concept of software engineering, and pay attention to the module division of driver and application software. Drivers related to specific CPU are put into corresponding driver modules, which are divided into the following modules: as shown in Table 1. According to GB-T 17626.2-2006 standard, air discharge and contact discharge of recloser controller are tested. The test levels are 4 levels, i.e., test voltage is ( 15KV) and ( 8KV), respectively. No abnormality occurs. According to GB-T 17626.8-2006 standard, the test of power frequency magnetic field immunity of recloser controller is carried out. The test grades of stable magnetic field (continuous) and short-time magnetic field (1-3s) are all 5 grades, that is, the magnetic field intensity is 100A/m and 1000A/m, respectively. No abnormality occurs.
The immunity test of damped oscillating magnetic field for recloser controller is carried out according to GB-T 17626.10-1998 standard. The test grade is 5, that is, the intensity of damped oscillating magnetic field is 100A/m (peak value), and no abnormality occurs. Differential mode and common mode tests were carried out according to GB-T 17626.4-2008 standard for fast transient impulse group immunity test of recloser controller. The test levels were all 4 levels, thermostatic element i.e. voltage peak values were ( 2KV) and ( 4KV), respectively. No abnormalities were found. The surge (impact) immunity test of recloser controller is carried out according to GB-T 17626.5-2008 standard. The test grade is 4, i.e.
the peak value of open-circuit voltage is ( 2KV) and ( 4KV), and the peak value of short-circuit current is 1000A and 2000A, respectively. No abnormality occurs. Through the hardware design, software design, EMC design and test of the recloser controller, the system achieves the expected function and performance.
In the process of designing the recloser controller, modular design is adopted in both software and hardware, which helps to reduce the development cost, shorten the development cycle and later product maintenance costs. The recloser controller has a short-distance wireless communication module. It can read event sequential record (SOE) and operate the recloser through the handheld terminal. At present, the recloser controller has completed the hanging test with the permanent magnet switch produced by our company. From the monitoring results, the operation is stable.