1) the role of the transformer and distribution station relay protection: transformer and distribution station relay protection can be in the transformer and distribution station in the process of operation faults (three-phase short-circuit, two-phase short-circuit, single-phase grounding, etc.) and the emergence of abnormal phenomena (overload, over-voltage, under-voltage, low peripheral wave, gas, over-temperature, control and measurement circuit disconnection, etc.), quickly and selectively issue a trip command to remove the fault or send an alarm to reduce the scope of faults caused by outages and damage to electrical equipment to ensure the stable operation of power systems. Selectively issued trip command will be fault removal or alarm, thus reducing the scope of power outages caused by faults and the extent of damage to electrical equipment, to ensure the stable operation of the power system.
2) the basic working principle of the substation relay protection: substation relay protection is based on the substation operation process faults occurring during the current increase, voltage increase or decrease, frequency reduction, gas, temperature rise and other phenomena over the set value of the relay protection (given value) or exceed the limit value, in the set time, selective tripping orders or alarm signals.
According to the current value to selective trip for the inverse time limit, the larger the current value, the faster the trip. According to the time to selective tripping is called fixed time protection, fixed time in the fault current exceeds the set value, after the time set value of the time given by the trip command. Gas and temperature are non-electrical protection.
Reliability coefficient is an empirical data, the calculation of the relay protection action value, to multiply the results of the calculation by the reliability coefficient to ensure that the relay protection action is accurate and reliable, the range is
1.3 ~ 1.5.
The minimum value of the occurrence of a fault and the protection of the action value of the ratio of the sensitivity coefficient of the relay protection, generally 1.2 ~ 2, according to the design specifications to be selected. Design specifications to be selected.
3) substation relay protection according to the nature of the protection classification
(1) current cut-off protection: fault current exceeds the protection of the integrating value without time limit (integrating time is zero), immediately issued a trip order.
(2) current delay quick-break protection: fault current exceeds the setting value of quick-break protection, with a certain
delay issued after the trip command.
(3) overcurrent protection: fault current exceeds the fixed value of overcurrent protection, fault occurs more than the protection of the fixed time to issue a trip command.
(4) overvoltage protection: fault voltage exceeds the protection setting value, the trip command or overvoltage signal.
(5) low voltage protection: fault voltage is lower than the setting value of the protection, the trip command or low voltage signal.
(6) low frequency load shedding: when the grid frequency is lower than the set value, selectively jump off the specified unimportant load.
(7) single-phase grounding protection: when a phase is grounded for the grounding system, issued a trip command, for the neutral point is not grounded system, issued a grounding alarm signal.
(8) differential protection: when the flow through the transformer, neutral line or motor winding, the difference between the two ends of the line current changes over the set value, issued a trip command is called longitudinal differential protection, the two parallel operation of the line or the two windings between the difference in current changes over the set value, issued a trip command is called transverse differential protection.
(9) distance protection: according to the fault point to protect the installation of the distance (impedance) trip order is called distance protection.
(10) directional protection: according to the direction of the fault current, selective trip command is called directional protection.
(11) high-frequency protection: the use of weak high-frequency signals to transmit fault signals to selective trip protection is called high-frequency protection.
(12) overload: the operating current exceeds the overload setting value (generally according to the maximum load or equipment rated power to set), the overload signal.
(13) gas protection: for oil-immersed transformer, when the transformer internal turn-to-turn short-circuit electrical sparks, transformer oil is punctured by gas gas impact installed in the oil pillow channel pipe
gas relay, fault is serious, gas gas, impact force is large, heavy gas action in the trip, the fault is not serious, gas gas is less, the impact force is small, light gas action in the signal. Signal.
(14) temperature protection: transformer, motor or generator overload or internal short-circuit fault, the body temperature of the equipment rises above the set value of the trip command or alarm signal over temperature.
(15) main protection: to meet the requirements of power system stability and equipment safety, failure can be the fastest speed selective excision of the protected equipment or line protection.
(16) backup protection: the main protection or circuit breaker refuses to operate, used to remove the fault protection. The main protection refused, the power system or line of another set of protection issued by the trip command for the near backup protection. When the main protection or circuit breaker refuses to act by the neighboring (on the level of) power equipment or line protection to remove the fault of the backup protection for the far backup protection.
(17) auxiliary protection: to supplement the performance of the main protection and backup protection, or when the main protection and backup protection maintenance and withdrawal of simple protection.
(18) transformer secondary line break alarm: current transformer or voltage transformer secondary line break will cause protection error, so it should be issued after the occurrence of line break signal.
(19) trip circuit breakers: circuit breaker trip circuit breakers, relay protection issued by the trip command circuit breaker can not be jumped open, so the trip circuit breakers should be issued when the alarm signal.
(20) automatic reclosing: for some transient faults (lightning, overhead line flash circuit, etc.) faults quickly removed, there will be no permanent faults, and then close the gate, you can continue to ensure that the power supply. Relay protection issued by the tripping order circuit breaker jumped open immediately after the closing command, known as reclosing.
After reclosing a reclosing is not allowed to reclosing is called a primary reclosing, allowing reclosing is called secondary reclosing (generally rarely used). With the reclosing function, in the event of a fault, the relay protection first does not take into account the protection setting time, immediately trip, trip, and then reclosing, reclosing after the fault can not be removed, and then according to the relay protection setting time for tripping, such reclosing for the former accelerated reclosing.
After the accident relay protection first according to the protection setting time for protection tripping, and then reclosing, reclosing unsuccessful without delay to quickly issue a trip order, this reclosing is called after the accelerated reclosing.
(21) standby power mutual casting: two or more power feeds into the power supply, when a power failure, the power supply load can be powered by other power supply, that is, to power switching, manual switching is called manual mutual casting. Automatic switching is called automatic mutual throw. Mutual casting has the use of bus circuit breaker for mutual casting (for multiple power supply for simultaneous operation) and into the line power mutual casting (a power supply for the main supply, the other way power for hot standby) and other forms. For the power supply is not allowed to run in parallel should also be added interlocking.
(22) Simultaneous parallelism and unlisting: for multiple power supply substation or power plant to network or Internet must meet the same period of parallel conditions before the network or Internet, network or Internet has two kinds of manual and automatic.
4) substation relay protection according to the protected object classification
(1) generator protection: generator protection stator winding phase-to-phase short-circuit, stator winding grounding, stator winding turn-to-turn short-circuit, generator short circuit external, symmetrical overload, stator winding overvoltage, excitation circuit one point and two points of grounding, demagnetization faults and so on. The exit mode for the shutdown, unplugging, reducing the scope of influence of the fault and signaling.
(2) power transformer protection: power transformer protection has a winding and its lead line phase-to-phase short circuit, neutral point directly grounded side single-phase short circuit, winding turn-to-turn short circuit, external short circuit caused by overcurrent, neutral point directly grounded in the power network caused by an external grounded short circuit overcurrent and neutral overvoltage, overload, the oil level is lowered, the temperature of the transformer, the oil tank pressure rises, or the cooling system failure.
(3) line protection: line protection according to different voltage levels, different grid neutral grounding, transmission lines and cable or overhead line length, respectively: phase-to-phase short-circuit, single-phase short-circuit, single-phase grounding, overloading and so on.
(4) bus protection: power plants and important substation bus should be equipped with special bus protection.
(5) power capacitor protection: power capacitors have capacitor internal faults and their lead line short circuit, capacitor bank and circuit breaker between the connecting line short circuit, capacitor bank in a fault capacitor removal caused by overvoltage, capacitor bank overvoltage, the bus connected to the loss of voltage.
(6) high-voltage motor protection: high-voltage motor stator winding phase-to-phase short circuit, stator winding single-phase grounding, stator winding overload, stator winding low-voltage, synchronous motor out of step, synchronous motor demagnetization, synchronous motor non-synchronous inrush current.
6. microcomputer protection devices
1) the advantages of microcomputer protection
(1) high reliability: a microcomputer protection unit can complete a variety of protection and monitoring functions. Instead of a variety of protection relays and measuring instruments, simplify the wiring of the switchgear and control panels, thereby reducing the failure of the relevant equipment, improving reliability. Microcomputer protection unit using highly integrated chips, software with automatic detection and automatic error correction, but also to improve the reliability of the protection.
(2) high precision, fast speed, multi-function. The digitization of the measurement part greatly improves its accuracy, the CPU speed can be improved so that all kinds of events can be timed by m s, and the improvement of the software function can be accomplished through a variety of complex algorithms to complete a variety of protection functions.
(3) flexibility, through the software can easily change the protection and control characteristics, the use of logic judgment to achieve a variety of interlocks, a type of hardware using different software, can constitute a different type of protection.
(4) maintenance and debugging is convenient, fewer types of hardware, line unity, external wiring is simple, greatly reducing the maintenance workload, protection, debugging and adjustment of the use of input buttons or above the computer downlink, debugging is simple and convenient.
(5) good economy, high performance-price ratio, due to the multifunctionality of the microcomputer protection, so that the measurement, control and protection of the substation station to reduce the overall cost of the part. High reliability and high speed, you can reduce the outage time, save manpower, and improve economic efficiency.
2) the characteristics of microcomputer protection devices: microcomputer protection devices in addition to the above advantages of microcomputer protection, compared with similar products have the following characteristics:
(1) complete varieties: microcomputer protection devices, the varieties are particularly complete to meet the various types of substation power distribution station of various equipment for various types of protection requirements, which gives the design of the substation power distribution station and the computer networking provides a great deal of Convenience.
(2) hardware using the latest chips to improve the technical sophistication, the CPU uses 80C196KB, measurement for 14-bit A/D conversion, analog input loop up to 24, the data collected with the DSP signal processing chip for processing, the use of high-speed Fourier transforms, to get the fundamental wave to the 8th harmonic, the special software auto-correction, to ensure that the measurement of high precision. Utilizing dual-port RAM and CPU to transform the data, it constitutes a multi-CPU system, and the communication adopts CAN bus. With high communication rate (up to 100MHZ, generally running at 80 or 60MHZ) and strong anti-interference ability and other characteristics. Through the keyboard and LCD display unit can be convenient for on-site observation and a variety of protection methods and protection parameters set.
(3) Hardware design in the power supply, analog input, switch input and output, communication interfaces, etc., using special isolation and anti-interference measures, anti-interference ability, in addition to centralized screen, can be installed directly on the switchgear.
(4) The software is rich in functions, in addition to completing various measurement and protection functions, through the cooperation with the upper processing computer, it can complete the fault recording (1-second high-speed fault recording and 9-second fault dynamic recording), harmonic analysis and small-current grounding selection and other functions.
(5) RS232 and CAN communication mode can be selected to support a variety of remote transmission protocols, convenient to network with a variety of computer management systems.
(6) using a wide temperature band background 240 × 128 large screen LCD liquid crystal display, easy to operate, beautiful display.
(7) high degree of integration, small size, light weight, easy to centralized screen installation and decentralized installation in the switchgear.
3) The use of microcomputer protection devices
(1) Small and medium-sized power plants and their step-up substations.
(2) 110 kV / 35 kV / 10 kV regional substations.
(3) Urban 10 kV grid 10 kV switching station
(4) User 110 kV /10 kV or 35 kV /10 kV main step-down station.
(5) user 10 kV substation
4) Types of microcomputer protection devices
(1) microcomputer protection devices **** there are four major categories.
(2) line protection devices: microcomputer line protection devices; microcomputer capacitor protection devices; microcomputer directional line protection devices; microcomputer zero-sequence distance line protection devices; microcomputer transverse differential current directional line protection devices
(3) the main equipment protection devices: microcomputer double-winding transformer differential protection devices; microcomputer three-winding transformer differential protection devices; microcomputer transformer back-up (3) main equipment protection devices: microcomputer double winding transformer differential protection device; microcomputer three winding transformer differential protection device; microcomputer transformer backup protection device; microcomputer generator differential protection device; microcomputer generator backup protection device; microcomputer generator backup protection device; microcomputer motor differential protection device; microcomputer electric motor protection device; microcomputer plant (station) transformer protection device
(4) Measurement and control devices: microcomputer telemetry telecontrol device; microcomputer telemessaging telecontrol device; microcomputer telecontrol device; microcomputer telemetering telecontrol device; microcomputer remote control devices; microcomputer automatic synchronization device; microcomputer standby self-injection device; microcomputer PT switching device device; microcomputer PT switching device; microcomputer pulse power measurement device; microcomputer multi-function transmission measurement device; microcomputer unlisting device
(5) management device unit: communication unit management unit dual-computer management unit
(5) microcomputer protection device function: microcomputer protection device of the general technical requirements and indicators (working environment, power supply, technical parameters, the structure of the device) and the main functions (protection performance indicators, the main functions). Functions (protection performance indicators, the main protection function, protection principle, fixed value and parameter setting, as well as external terminals and secondary diagram) see the relevant product manual.
7. 220/380V low-voltage power distribution system microcomputer monitoring system
1) 220/380V low-voltage power distribution system features
(1) a wide range of applications, now industrial and civil power except for mines, medical care, hazardous materials storehouse, etc., are 220/380V, so the scope of application is very broad.
(2) low-voltage distribution systems are generally TN -S, or TN -C -S system. TN -C system for the three phase (A, B, C) and a neutral (N), N line in the transformer neutral grounding or in the building into the house. The N line is grounded at the neutral point of the transformer or repeatedly grounded at the building entry point. Transmission lines for four lines, cable for four cores, no protective earth (PE), less a line. Equipment shell, metal conductive part of the protective grounding connected to the neutral (N), known as the zero system, zero system security is poor, interference with electronic equipment, design specifications have been stipulated no longer used.
TN -S system for three-phase, a neutral (N) and a protective earth (PE). N line and PE line in the transformer neutral centralized grounding or repeated grounding in the building into the house line. The transmission line is five, the cable is five cores. Neutral (N) and protective earth (PE) are connected together at the grounding point and can no longer be connected, so the neutral (N) must also be insulated. Neutral line (N) lead out if you do not use insulation to the ground insulation, or lead out and protective ground connection, although the use of five wires, but also for the TN -C system, which should be especially noted. TN -S or TN -C -S system security is good, the interference with electronic equipment can be **. TN -S or TN -C -S system security is good, the interference of electronic equipment is small, can *** with the ground wire (CPE), the use of equipotential connection security is better, less interference. Therefore, the design specifications, except for special places, are used TN -S or TN -C -S system.
(3) 220/380V low-voltage distribution system protection is still using low-voltage circuit breakers or fuses. So 220/380V only monitoring without protection. Monitoring includes current, voltage, degree, frequency, power, power factor, temperature and other measurements (telemetry), switch operating status, accident trip, alarm and accident preview (overload, over-temperature, etc.) Alarm (telemetry) and motorized switching remote closing and closing operations (remote control) and other three contents (referred to as the three remotes), and there is no protection.
(4) 220/380V low-voltage distribution system circuit are generally single bus or single bus segmentation,
more than two transformers are single bus segmentation, there are a few transformers will be divided into a few segments, this is because of the user substation transformers are generally not used in parallel operation, which is designed to reduce the short-circuit current, reduce the short-circuit capacity, or else, low-voltage circuit breaker disconnecting capacity should be Increase.
(5) 220/380V low-voltage distribution system into the line, bus, large load line and low-voltage contact line due to large capacity, generally all the way (1 circuit breaker) occupies a low-voltage cabinet. According to the different size of the power supply load current, a low-voltage switchgear with two outlets (install two circuit breakers), four outlets (install four circuit breakers), as well as five, six, eight and ten outlets, unlike the high-voltage distribution system, a circuit breaker occupies a switchgear. Therefore, low-voltage monitoring unit should be used for all the way, two or more points, the design should be based on the number of outgoing circuits of each low-voltage switch and low-voltage monitoring unit specifications to design.
(6) low voltage circuit breaker in addition to manual operation, but also can choose electric operation. Large-capacity low-voltage circuit breakers generally have manual and electric operation, the design should be selected with remote control of the low-voltage monitoring unit, small-capacity low-voltage circuit breakers, design, most of the selection of only manually operated circuit breakers, so that the low-voltage monitoring unit of the remote exit can not be wired, or the selection of low-voltage monitoring unit without remote control.
2) 220/380V low-voltage distribution system microcomputer monitoring system design
(1) 220/380V low-voltage distribution system microcomputer monitoring system, first of all, according to the primary system and the user's requirements for telemetry, telemetry and remote control design.
(2) Measurement circuit design
A: Measurement part of the secondary wiring and high-voltage, the same as the current circuit is connected in series with the voltage transformer secondary circuit, the voltage circuit is connected in parallel with the voltage measurement circuit. As 220/380V low-voltage distribution system without voltage transformer, voltage measurement can be directly connected to the 220/380V bus, and the meter voltage circuit can generally not add fuse protection, but the cabinet wiring should be as short as possible, when possible, it is best to add fuse protection to facilitate maintenance.
B: power measurement can be used to bring their own power with pulse output pulse meter, for the calculation of
Calculate the power and power function of the low-voltage monitoring unit, only as an internal billing, you can no longer use the pulse meter.
C: the selection of low-voltage monitoring unit with a display function, you can no longer design the current and voltmeter, the selection of low-voltage monitoring unit without display function should also be designed for the current or voltmeter, should not be designed for both.
(3) signaling circuit design: design, low-voltage circuit breaker to increase a pair of normally open contacts to the low-voltage monitoring unit switching status input terminals. There is an accident trip alarm output contact, and then connect it to the low-voltage monitoring unit accident preview terminal.
(4) remote control circuit design: the remote control design of the low-voltage monitoring system is relatively simple, electric operation of low-voltage circuit breakers have a pair of closing and splitting buttons, as long as the low-voltage monitoring unit closing and splitting output terminals and closing and splitting buttons on the button can be necessary, if necessary, can be designed to design an on-site and remote control operation switch to prevent local maintenance switch, remote control operation caused by the accident.
(5) power supply and communication cable design: low-voltage monitoring unit power supply for AC 220V power supply, power consumption is generally only a few watts, the design of the power supply from the terminal to a 220V/5A two-pole low-voltage circuit breaker, and then lead to the switchgear terminal, and then unified with the KVV-3 × 1.0 cable centralized to the low-voltage cabinets all the way to a small The capacity of the outlet line. When needed, a UPS power supply can be added.
Communication cable general distance does not exceed 200 meters can choose KVV -3 × 1.0 ordinary shielded control cable, more than 200 meters should be shielded twisted-pair cable (preferably with a sheath type) or computer communication cable.
8. Transformer and distribution station automation system
1) system components: high-voltage microcomputer protection, low-voltage monitoring unit, and then the communication cable will be networked with the computer can be composed of a modernized transformer and distribution station management system - transformer and distribution station automation system.
2) substation automation system design
A: high-voltage microcomputer protection unit (group screen or installed in the switchgear) selection and design of the second map.
B: low-voltage microcomputer monitoring unit (installed in the switchgear) selection and design of the second map. C: management computer (placed in the duty room, unmanned can be placed in the power dispatching room) selection. D: analog disk (placed in the duty room or dispatching room) design.
E: upper computer (with the plant computer or power department scheduling networking) networking program design. F communication cable design (including management computer and the host computer).
3) management computer: management computer can be configured according to system requirements.
4) analog disk: the user requires an analog disk, you can design the analog disk, small systems can be wall-mounted, large systems with floor-to-ceiling, the analog disk size according to the power supply system once the map and the area of the duty room to decide. Analog disk using a dedicated control unit, its communication cable to the management computer. Analog disk also needs a 220V AC power supply, the capacity of only a few tens of watts, the design should be considered together with the management computer power supply.
5) substation automation system main functions: substation automation system management computer through the communication cable and installed in the field of all microcomputer protection and monitoring unit for information exchange. Management computer can be sent down to the remote control operation orders and related parameters to modify, at any time to accept the microcomputer protection and monitoring unit up to the telemetry, telemetry and accident information. Management computer can be processed through the information, storage and preservation, through the record printing and screen display, but also on the system's operation analysis, through the remote letter can be found at any time to deal with accidents, reduce accidents and blackout time, through the remote control can be reasonable allocation of the load, to achieve optimal operation, so as to achieve the modernization of the management of the conditions must be provided.
The management computer software should be standardized, the operation should be simple and convenient, the human-machine interface is good, the configuration is convenient, the user is simple to use and secondary development, easy to master.