Reconstruction design of intelligent high-frequency switching power supply system

　　The remote operation of relay protection, automatic devices, signal devices, emergency lighting and electrical equipment in the substation generally adopts DC power supply, so the output quality and reliability of DC power supply are directly related to the safe operation and stable power supply of the substation.

　　Purpose and necessity of DC system transformation

　　The DC system of the substation is called the "heart" of the substation, which shows how important it is in the substation. The power system of Zhongyuan Oilfield was built in the late 1970s. Due to the limitations of the technical conditions at that time, the DC system equipment of the substations built one after another was some silicon rectifier capacitor compensated DC power supply, some were KGCA-50/98~360, KGCFA-75/200~360 silicon rectifier DC power supply with lead-acid batteries, and some were BZGN-20/220 cadmium nickel battery DC screens. Some of the DC equipment of substations that were put into operation earlier and have been in operation for a long time are seriously aging, which poses a serious threat to the safe and reliable operation of the substation. For example, a 110kV substation once had a DC system failure, causing a tripping accident that caused the whole station to lose power. Although no major accidents occurred in other stations, there were always problems with the DC system, many defects, and some defects could not be handled, causing the DC system to be in a "sick" operation state for a long time, resulting in the inability to supply power to users normally.

　　With the rapid development of the electric power industry, in order to improve the power supply quality of the power grid, make the power grid safe and economical, and realize the automation of the power system, the requirements for the key equipment of the power control system - the control power supply are getting higher and higher. The original DC equipment all adopted the traditional phase-controlled power supply, which has low efficiency and large ripple coefficient, and is not satisfactory in terms of electromagnetic radiation, thermal radiation, noise, etc. In addition, the monitoring system is imperfect, and the 1+1 backup method is adopted, which is difficult to meet the technical requirements of the increasingly advanced instruments, control, and automation equipment of the secondary circuit. In addition, due to the easy fluctuation of the floating charge voltage of the phase-controlled power supply, the pulsating charge and discharge of the battery will occur, which will greatly damage the maintenance-free battery and affect the battery life. In addition, with the transformation of other equipment and the investment of new equipment, the original phase-controlled power supply can no longer meet the needs of the power system of the Zhongyuan Oilfield, and it is urgently needed to be transformed and replaced to ensure the safe operation and stable power supply of electrical equipment. The intelligent high-frequency switching power supply has been widely used in many fields due to its small size, light weight, superior technical indicators, modular design, N+1 hot backup mode, and convenience for "four remotes". Since the 1990s, all new or renovated power plants and substations in advanced industrial countries abroad have adopted high-frequency switching power supplies, and all their batteries have adopted maintenance-free batteries. In order to achieve the goal of Zhongyuan Oilfield power grid equipment reaching the advanced level of the same industry, according to the actual situation of the power grid, the DC system equipment transformation adopts the currently advanced intelligent high-frequency switching power supply system.

　　Performance characteristics of intelligent high-frequency switching power supply system

　　In order to ensure the quality of the intelligent high-frequency switching power supply system, we organized a number of technical personnel to inspect multiple manufacturers to understand the manufacturers' production processes, scales, experimental testing methods, etc. After "shopping around", the technical transformation decided to use the GZDW-200/220 operating power supply. It is a new "four-remote" high-frequency switching power supply developed specifically for power systems. It adopts high-frequency soft switching technology, modular design, and an output nominal voltage of 220V. It is equipped with a standard RS? 232 interface, which is easy to connect to the automation system and is suitable for use in various substations, power plants and hydropower stations. This equipment has the following performance characteristics:

　　1) Modular design, N+1 hot standby, and smooth capacity expansion.

　　2) The monitoring function is complete and highly intelligent, with a large-screen LCD Chinese character display and sound and light alarms.

　　3) The monitoring system is equipped with a standard RS232 interface, which is convenient for access to the automation system and the implementation of "four remote controls" and unattended operation.

　　4) Automatic management and maintenance of batteries, real-time monitoring of battery terminal voltage, charge and discharge current, automatic control of equalization and floating charge, and regular maintenance equalization charge.

　　5) With battery temperature compensation function.

　　6) The module can be plugged in and out while powered on, making replacement safe and convenient.

　　7) The voltage reduction method adopts a new high-frequency soft switch stepless bidirectional voltage regulation, abandoning the traditional silicon stack voltage reduction method, with high output voltage accuracy and fast dynamic response speed.

　　8) Adopt the latest soft switching power supply technology and imported components.

　　The composition and functions of each part of the intelligent high-frequency switching power supply system

　　The intelligent high-frequency switching power supply system consists of AC power distribution, insulation detection, monitoring module, rectifier module, voltage regulation module, DC feeder, etc.

　　The AC power distribution provides the system with three-phase AC power, monitors the three-phase voltage, current and contactor status, determines whether the AC input meets the system requirements, and automatically cuts off the faulty line when the AC input is overvoltage, undervoltage or unbalanced, and switches to another power supply, and the system issues an audible and visual alarm. A three-phase lightning arrester with a flow rate of 40kA per phase and a response speed of 25μs is installed, which can effectively prevent damage to the equipment caused by lightning strikes.

　　Insulation monitoring uses imported non-contact DC micro-current sensors, and uses the leakage current generated by the grounding resistance of the positive and negative busbars to the ground to measure the grounding resistance of the busbar to the ground, thereby determining the grounding fault of the busbar. This technology does not require any signal to be superimposed on the busbar, and will not have any adverse effects on the DC busbar power supply. It completely eliminates the misjudgment and missed judgment caused by the DC busbar-to-ground capacitance, and is an important breakthrough in microcomputer grounding monitoring technology.

　　The monitoring module is the control and management core of the entire DC system. Its main task is to conduct long-term automatic monitoring of each functional unit and battery in the system, obtain various operating parameters and status in the system, process in real time according to the measured data and operating status, and control the system based on this, so as to achieve fully automatic and accurate management of the power supply system, thereby improving the reliability of the power supply system and ensuring its continuity, safety and reliability. It has four remote functions of "telemetry, remote communication, remote control and remote adjustment", and is equipped with a standard RS? 232 interface, which is convenient for inclusion in the power station automation system

　　The rectifier module provides normal load current for the closing bus and the control bus. It has an LCD Chinese character display and an operation keyboard. The working status and working parameters of the module are clear at a glance. It can be plugged in and out under power and has accurate software, autonomous current sharing, and ZVS soft switching technology.

　　Regardless of how the closing bus voltage changes, the output voltage of the voltage regulating module is stably controlled at 220 (1±0.5%) V. It has live plug-in technology, soft switching technology and bidirectional voltage regulation characteristics.

　　The DC feeder is equipped with control output, closing output, battery input, flashing, emergency lighting, 48V power output, etc. The control bus has three ways to supply power to ensure safe and reliable power supply of the control bus. It is equipped with an intelligent DC monitoring unit that can measure the bus voltage, current and switch status.

　　The battery inspection instrument monitors the battery voltage in real time and feeds the information back to the monitoring module in a timely manner.

　　The battery is fully enclosed, maintenance-free, pollution-free, and corrosion-free. It can be placed in any direction and has a wide operating temperature range (-40℃～60℃). It can be discharged to zero volts and can be restored by charging within 24 hours. It can discharge with a large current, has a large starting current, and has an extremely low self-discharge rate. It has a safe explosion-proof exhaust system and is an ideal uninterruptible power supply for operation and control.

　　Problems to be improved in the transformation of DC system equipment

　　1) Improved the unreasonable layout of the DC feeder line of the new equipment. In order to save investment, we used the outgoing lines of the control, signal and closing circuits of the original DC system, but they were not suitable for the position and size of the feeder lines of the new equipment. Therefore, we modified the DC feeder line of the new equipment according to the actual situation on site, making the installation easier, the wiring more reasonable, and the operation more reliable.

　　2) Added a battery discharge circuit.

　　3) Based on the actual situation of the Zhongyuan Oilfield power grid, changes were made to the inappropriate parameter settings of the equipment when it left the factory to ensure that the equipment is more reliable after operation.

　　4) The installation positions of electrical components such as flash relays were adjusted. The original installation positions of the components were not reasonable, and it was inconvenient to maintain and replace them after they were damaged. The modified positions are easy to maintain, saving time and effort.

　　5) The module monitoring unit, DC monitoring unit, and AC monitoring unit have been improved, and protective covers have been added to prevent short circuits, dust intrusion, etc.

　　Application of intelligent high-frequency switching power supply system

　　After two years of operation, the transformed DC system equipment has reasonable technical indicators, correct display of various parameters, convenient and intuitive operation, high degree of automation, greatly reduced maintenance workload, complete equipment protection functions, and reliable operation. Faults are reported promptly and accurately, and the battery can be automatically managed without the need for special maintenance. The equipment operates stably and reliably, and has never affected the normal power supply.

　　Compared with the original DC system, the transformed DC system has stable performance, high precision, safety and reliability, ensuring the oil and gas production of the oil field, the electricity consumption of residents, hospitals and roads, reducing noise, improving the working environment of the on-duty personnel, ensuring the safe and reliable operation of the substation equipment, and generating significant economic and social benefits, which are mainly reflected in the following aspects:

　　1) The original phase-controlled power supply has a large ripple coefficient, and its output contains a large AC component. This is especially obvious in the Zhaocun substation, where the AC component content is higher, which has the greatest impact on secondary equipment, causing secondary equipment to malfunction, damage, or even some equipment cannot work properly. The modified intelligent high-frequency switching power supply has a very small ripple coefficient and a particularly stable output.

　　2) The original phase-controlled power supply uses silicon stack voltage regulation, and the silicon voltage reduction response speed is slow, with a reaction time of tens of milliseconds. When the input voltage suddenly changes, it will produce a large impact on the output, which is easy to burn out the secondary equipment due to the unstable impact. The modified high-frequency switching power supply adopts stepless voltage regulation, which has a fast response speed. When the input voltage suddenly changes, the module completes the adjustment within 200μs, and the overshoot is less than 5%.

　　3) The original phase-controlled power chargers and floating chargers were noisy and had no cooling measures. Some substation floating chargers had serious heat generation. The modified intelligent high-frequency switching power supply has low noise, and the module uses high-quality fans for cooling, which ensures the normal operation of the module components and greatly improves the working environment of the on-duty personnel.

　　4) The original lead-acid battery or nickel-cadmium battery required special battery workers for maintenance and upkeep, as well as related containers, instruments, raw materials, distillation pots, distilled water, etc. for battery maintenance. After the transformation, the American "Leoch" maintenance-free battery was used, which did not require a series of maintenance work at ordinary times, reducing manpower and material resources.

　　5) The original phase-controlled power supply has a low power factor, generally below 0.7, and an efficiency of about 60%, while the power factor of the modified intelligent high-frequency switching power supply reaches above 0.9 and the efficiency is as high as over 94%.

　　6) The original phase-controlled power supply often fails, and sometimes the inability to operate power transmission causes crude oil production losses. For example, on September 23, 1997, a 110kV substation tripped due to a DC system failure, causing the entire station to lose power and burning 3 kilometers of 35kV lines. The economic loss was as high as more than 4 million yuan. In recent years, various DC systems have often experienced various failures, causing great losses to oil and gas production, and also brought inconvenience to the lives of residential users and huge economic losses to industrial users. After the transformation to an intelligent high-frequency switching power supply, the DC system has not had any accidents so far, and the power supply is more reliable

　　7) The modified intelligent high-frequency switching power supply has a 48V power outlet, which provides power for the communication network of the substation, etc., without the need to purchase a special 48V power supply, reducing equipment investment and space occupation.

　　8) The modified control bus has the following three power supply channels, ensuring the safe and reliable power supply of the control bus, making it foolproof.

　　—When the AC power is normal, the control bus can be powered directly by the rectifier module;

　　——When AC power is lost, the step-down module supplies power;

　　——Supply power from 90% of the battery voltage to the control bus through a diode.

　　The transformed intelligent high-frequency switching power supply system has stable performance, high precision, greater safety and reliability, and many innovative points. It has achieved good results and significant social and economic benefits, providing reliable power guarantee for the oil and gas production and other loads of the Zhongyuan Oilfield. At the same time, it also laid the foundation for the automation of substations.