Automatic transformation and design of the seconda

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Automatic transformation and design of the secondary system of conventional substation

Abstract: combined with the experience of the completed and reconstructed unattended station, taking the typical conventional substation in Southern Hebei Province as an example, this paper discusses the automatic transformation and design of conventional substation

key words: substation; Telecontrol; Automation reconstruction

abstract:referring to the experiences of already constructed or renovated unmanned substations, this paper, taking the substations in South Hebei electric power network as examples, discussed the automation reconstruction and design of conventional substations

Keywords:substation; remote control; Automation renovation

substation is an important link in the transmission and distribution system and the main monitoring point of electricity. With the application and development of computer technology in the power system, more and more new substations adopt integrated automation design, which has become a mature finalized design for experimental analysis at the outermost edge, 1/2r and center of the end face of the forging riser in all new substations in Southern Hebei Province. However, in the power system, there are still a large number of Conventional Substations that have been in service for many years. These old substations are generally electrical hub substations with large capacity, many outgoing lines and long operation. Their primary equipment is aging, damaged and corroded seriously. The workload and cost of maintenance and renewal are increasing year by year, and the effect is not obvious. The secondary equipment in the station, from electromagnetic relay protection, transistor protection, integrated circuit protection, weak current selective control, including the materials and equipment used, to the "four in one" centralized control console, are all operating at the same time. The aging of these equipment poses a great threat to the safe, high-quality and efficient operation of the substation, and also a major hidden danger to the safe, stable and optimal operation of the electrical system. In view of the fact that a large amount of human, material and financial resources are invested in the maintenance and renovation of such substations every year, and the effect is not ideal, so it has become an urgent problem for power system engineers and technicians to make reasonable, economic, advanced and feasible transformation of these old stations to meet the requirements of unattended or few people on duty

1 transformation purpose

a. realize the real-time monitoring of all electrical equipment in the substation and improve the safety and reliability of substation operation

b. meet the requirements of unattended/few people on duty. 21. The effective experimental width of the experimental machine: 395mm. Improve the working conditions, realize the automation of CRT real-time monitoring and operation records, and improve the automation level and operation efficiency of the substation

c. meet the functional requirements of power dispatching automation and the requirements of real-time, reliability, correctness and accuracy of telecontrol data. More timely and comprehensively grasp the operation of electricity and substations, realize the "four remote" and voltage/reactive power adjustment automatic control (VQC) functions, and enhance the monitoring and control ability of the dispatching center

d. reduce electricity costs and improve economic benefits

2 transformation principle

a. make full use of the original equipment and try to reduce the transformation cost; Reasonably design the circuit to reduce the difficulty of transformation

b. enhance the "four remotes" function, use RTU to establish the station automation system and the corresponding distributed communication network, and realize the automation of the whole station. Ensure that telecontrol information is directly collected and transmitted, and telecontrol commands are directly received and controlled. The telecontrol information transmission to middle note and local dispatching adopts two ways: data serial interface communication and remote computer network interface communication

c. the relay protection device, fault recorder and system safety automatic device are set independently, and the protection signal adopts dual acquisition, that is, the main protection signal of the microcomputer protection device is connected to the central signal and the monitoring system respectively in the form of hard contact, and the digital output is connected to the monitoring system through the serial port or the protection management machine is connected to the Ethernet

d. the electric energy information is connected to the measurement and control device by the intelligent electric energy meter in the form of serial interface, and the electric energy information of the measurement gateway is connected to the measurement and control device in the form of passive pulse contact

e. the electrical analog of RTU adopts AC sampling, the system framework and capacity are considered according to the final scale of the substation, and the measurement and control part is configured according to the current scale

f. the monitoring system communicates with the industrial TV equipment of the substation through the multimedia server

3 selection of automation system mode

the key to the automation transformation of conventional substations is the selection of automation mode, which must be comprehensively and systematically considered according to the actual situation of each substation. At present, there are mainly two modes to realize the automation transformation of domestic substations

3.1 conventional telecontrol mode

conventional telecontrol mode refers to the use of telecontrol RTU of dispatching automation system to realize automation transformation. Based on the original RTU, this method adopts local Ethernet or RS485 star structure, and the monitoring system is composed of RTU with distributed functions, adding corresponding measurement and control functions and signals. The relay protection panel and central signal system in the control room remain unchanged from the original design, the original secondary system is retained, and only the original secondary circuit is modified, which is easy to operate and maintain. Making full use of the original equipment, the investment is small, the reconstruction construction is simple, and the workload is small, but the secondary circuit design after the reconstruction is more complex

in principle, this scheme should be adopted for substations that have operated for one or two decades

3.2 integrated automation mode

integrated automation mode refers to the use of a monitoring system integrating protection, measurement and control to achieve automation. This mode integrates the secondary functions of the substation, with high information sharing, simple structure and many functions. It is necessary to carry out comprehensive secondary system transformation, cancel the central signal system (signal screen, control screen), and replace the protection screen with the protection and measurement screen. The telecontrol system and computer monitoring system are considered in a unified manner, and the open system with hierarchical distributed structure is adopted to connect the signal and control circuit into the computer monitoring system. This scheme needs to replace a large number of original protection and secondary equipment, with high investment, difficult transformation, complex construction and heavy workload

it is difficult to transform the old station in this way, but the secondary circuit design after transformation is greatly simplified. It is generally applicable to new stations, and substations that have operated for more than 30 years can be considered

4 specific methods

4.1 the measurement parameters of the telemetry part

that need to enter the computer monitoring system are determined according to the relevant regulations and the actual needs of users. The main problem is how to ensure that the old RTU does not shut down during the replacement of the system

the measurement and metering of the original old substation share one TA volume, and the RTU is used as the terminal of the measurement circuit of the whole station, which is connected in series behind the watt hour meter screen

according to dl/t technical specification for design of electric measurement and electric energy metering devices, Ta should be replaced in combination with expansion and technical transformation projects, and special metering TA should be set. The telemetry signal is connected in series behind the instrument, and the cable is from the control panel to the RTU acquisition panel; The electric energy meter is connected to the special TA, and the circuit and cable wiring from the original control panel to the electric energy meter panel and from the electric energy meter panel to the RTU acquisition panel remain unchanged. After putting into operation, the old RTU can be removed directly

if the TA cannot be replaced, the telemetry signal is connected in series after the instrument, and a four core cable is used from the control panel to the RTU acquisition panel (IA, IC, IA ', IC'). The circuit and cable wiring from the original control panel to the watt hour meter panel, and from the watt hour meter panel to the RTU acquisition panel remain unchanged, and the old RTU can be removed directly after operation

4.2 remote signaling part

4.2.1 total accident signal

a. the collection of total accident signal is cumbersome and there are many schemes. The general method is to transform the secondary circuit and collect it from the central signal circuit. Abandoning the local sound function, or manually switching between "local" and "remote" by adding a pressing plate or relay, this method has the problem of signal mistransmission, and does not meet the operating conditions of "dual track system", which is not conducive to long-term operation; At the same time, whenever the station carries out an accident audio inspection, the dispatcher will receive the accident signal, resulting in the misoperation of remote signaling

b. adopt multi contact static signal relay to realize multiple acquisition of total accident signal. The relay can provide three or more pairs of contacts, one of which is active contact to light up the light plate and ensure local functions; The other two pairs are passive contacts, one of which supplies the protection action signal of RTU, and the other pair is connected in parallel with the signal relay contact of other sets of protection and sent to RTU to generate the total accident signal. When any set of protection in the station starts and trips, the total accident signal and the protection action signal are sent out at the same time. This method makes the total accident signal operate independently between local and remote places, and solves the above problems

c. processed and generated by RTU software, or processed and generated by the master station software at the dispatching end. Start all protection signal software that starts tripping to generate total accident signal. This method is basically unchanged in the field signal circuit and wiring, safe, reliable, simple and easy to operate, and the construction workload is small

4.2.2 control circuit disconnection signal

control circuit disconnection is a signal to monitor whether the opening and closing circuit of the circuit breaker is intact. If the position relay is installed in the original control circuit, it can be achieved by connecting the standby normally closed contact of the opening and closing position relay to the RTU. In fact, the installation of position relay is not considered in the design of most old substations. If the position relay is reinstalled, the investment will be increased, which will not only make the construction difficult, but also destroy the overall sense of the screen

a. generally, the signal is transferred to RTU by using photoelectric isolation from the optical plate

b. use red and green indicator lights with driven contacts, which have a normally open and a normally closed contact. Connect the normally closed contacts of red and green indicator lights in the same control circuit in series to RTU to obtain the control circuit disconnection signal. During construction, it is only necessary to replace the indicator light and connect two signal wires. Using this method, the same screen control circuit can share cables, reducing capital investment and construction difficulty

4.2.3 position signal of circuit breaker and isolating knife switch

the position signal of circuit breaker and isolating knife switch is a signal reflecting its operation state, which is generally collected from the spare auxiliary contact of circuit breaker and isolating knife switch, but the cable laying workload is large

based on the above experience, the normally open contact of the driven relay of the red and green indicator lights in the control circuit is used to output the switch position signal, and the cable is shared with the control circuit disconnection signal, further reducing the cost investment and construction workload

4.2.4 other remote signaling quantities

other remote signaling quantities include: temperature out of limit of main transformer, light gas, abnormal oil level, abnormal pressure of SF6 circuit breaker, pressure locking, spring energy not stored, abnormal mechanism, DC grounding, fusing of accident signal fuse, fusing of prediction signal fuse, etc. The above-mentioned many signals can only provide a pair of active contacts at a time, which can be used to light up the optical plate after action

a. if the extinction plate is taken, change it into a passive contact or directly provide it to RTU

b. if the optical plate is retained, the DC power supply that triggers the optical plate in the station when the protection action or equipment is abnormal can be used, and an intermediate relay with above regulation level is added or an optical plate with driven relay is used. When the device acts, the on-site optical plate is lit; At the same time, start the relay and use the normally open contact of the relay to send a telecontrol signal

c. adopt optical terminal and use photoelectric isolation method to connect from optical plate to RTU. When the protection action or equipment is abnormal, start the on-site light plate at the same time; Drive photoelectric isolation, and use the switching characteristics of the switch tube to form a loop with the DC 24 v/48 V power supply of the telecontrol RTU to send the telecontrol signal

d. the main problem of keeping the optical plate and the telecontrol signal coexist at the same time is that the telecontrol signal will be sent by mistake during the transmission test of the optical plate. resolvent

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