Intelligent technology of metal-enclosed high-voltage switchgear

[Keywords] medium voltage switchgear intelligent measurement and control protection online monitoring by state maintenance mechanical failure abnormal temperature rise fault arc protection device.

1 Overview

The automation of distribution and transformation grids is the future development direction. In order to carry out operation monitoring and management, operation plan simulation and optimization, operation analysis and management, user load monitoring and fault alarm for the distribution and transformation grid, the main station of the distribution and transformation grid needs to obtain the on-site equipment (set of medium voltage switchgear, Circuit breakers and transformers, etc.) also require a device to not only perform remote master station commands, but also to complete commands such as closing and opening, so that medium voltage switchgear (ie, primary system) is required to increase intelligence. .

In addition, the computer technology and electromagnetic compatibility (EMC) level (ie, can resist strong electromagnetic interference), the common application and development of information sensing technology, microelectronics technology, communication and data processing technology, also promoted the complete set of medium voltage switchgear Intelligent process.

The intelligent medium voltage switchgear is mainly composed of hardware and software: (1) high-reliability switchgear with controllable operation; (2) measurement and control protection device with functions of protection, measurement, monitoring, control and communication; (3) on-line detection device Real-time monitoring of SF6 circuit breakers, oil circuit breakers, other electrical equipment and environment; (4) Advanced sensors can realize reliable conversion of various signals; (5) The medium voltage switchgear is compact and compact.

2 Intelligent measurement and control protection device

2.1 The function of intelligent measurement and control protection device

The core component of the intelligent measurement and control device is a microprocessor. The device makes full use of digital technology and software technology to integrate protection, monitoring, control, measurement and communication. In the same hardware environment, multiple functions can be realized.

(1) Basic protection functions: directional or non-directional overcurrent and ground fault protection; low cycle load shedding protection; automatic reclosing function (post acceleration); zero sequence voltage, over voltage and low voltage protection; breaker failure protection ; current quick-break, time-limited quick-break and inverse-time over-current protection.

(2) Control functions: Protection of tripping, closing, remote control, local control, display of various signal control and control objects, etc.

(3) Measuring power function: It can measure phase current, phase and relative ground voltage, zero sequence voltage and current, frequency, active power, reactive power, power factor and power.

(4) Communication function: It can complete local communication with PC or communicate with remote station through substation communication system. The device can generally support modbus protocol and standard communication protocol IEC870-5-101 (103), DNP3.0, TCP/IP, etc. Serial standard interface RS232, RS485, industrial fieldbus CANBUS, Lonworks, etc., Ethernet interface; support a variety of communication media such as twisted pair, fiber and wireless.

(5) Monitoring function: Circuit breaker status monitoring, jump, closing loop monitoring and local operation self-test.

Fault Recording and Recording Function: It can record the fault type, the occurrence time and the maximum/minimum fault amount, and also record the fault waveform.

2.2 Secondary wiring of intelligent measurement and control protection device

When an intelligent measurement and control protection device with all functions of metering, control, protection and communication is installed on the switchgear, the secondary wiring work is very simple, and the intelligent measurement and control protection device and external unit wiring are shown in Figure 1. The user only needs to connect the voltage, current signal, circuit breaker status position signal and exit control signal to the terminals of the corresponding primary component in the switch cabinet.

The intelligent measurement and control protection device completes the data processing by collecting voltage and current signals, circuit breaker status signals and other input switch signals, ground fault status, and realizes protection, control and display of fault record function, and completes information upload through communication interface. . Therefore, compared with the traditional secondary technology, the intelligent measurement and control protection device not only has more functions, higher precision, but also has a more compact secondary wiring.

3 online monitoring device

3.1 Maintenance by state technology

Due to the importance of high-voltage electrical equipment in the power grid, in the event of an accident, power outages in local or large areas will cause huge economic losses and social impacts. Therefore, after running these equipment for a period of time or during operation, necessary Inspection and maintenance. So far, the power sector has been using the traditional maintenance method: regular maintenance technology. The so-called regular maintenance is the maintenance of the specified items for a specified period of time (such as 5 years). These items are equipment inspection, replacement parts, and disassembly. Check and so on. It should be said that this kind of regular maintenance technology plays a good role in reducing and preventing the failure of equipment. However, there are many defects in this type of regular maintenance. For example, when the equipment is dismantled, a part of the circuit breaker and electrical equipment needs to be carried out. Disintegration, not only requires power outages during operation, but also requires considerable cost depending on the project. In addition, the state of the equipment (such as temperature, operating voltage, etc.) and the state of operation of the equipment after power failure are inconsistent, which may affect some data determination.

Due to the shortcomings of regular maintenance technology, on the other hand, with the development of science and technology, the development of electronic technology, optical sensing technology, computer technology, and signal processing technology has enabled traditional periodic maintenance technologies to be maintained in a predictive manner, that is, by state maintenance. Way to transition.

Compared to traditional scheduled maintenance techniques, stateful maintenance technology has the following advantages:

(1) The basic point of maintenance technology according to the state is to monitor and judge the equipment in real time in real time, so it can avoid the waste caused by fixed maintenance and other shortcomings;

(2) Maintenance technology by state is based on information technology and adopts automatic management technology to achieve reasonable extension of equipment life, thus reducing the total cost of equipment operation.

Figure 2 shows the online detection system for high-voltage SF6 circuit breakers at the Dorsey test station near Winnipeg Manitoba, Canada. Various types of sensors are installed on the test circuit breakers to realize on-line monitoring of electrical energy, machinery, and SF6 gas, and many valuable results have been obtained. 3.2 Online monitoring project

(1) Monitoring of mechanical and electrical performance of circuit breakers. Such as closing, opening coil current, operating mechanism characteristics, contact stroke and speed, vibration signal monitoring.

(2) Temperature rise detection of the busbar junction in the medium voltage switchgear.

3.3 Monitoring of mechanical failure of circuit breaker

3.3.1 Monitoring of circuit breaker closing and opening coil current

If the operating mechanism of the high-voltage circuit breaker is an electromagnetic operating mechanism, the closing and opening coils are generally powered by a DC power source, as shown in FIG. Experience has shown that the current of the closing and opening coils can be used as information for diagnosing mechanical faults. The current signals of the closing and opening coils can be given by the compensation type Hall current sensor, and the current signals of the closing and opening coils are also shown. image 3.

In the figure, it is the starting time, which is the starting point of the combining and dividing process. t1 is the current in the coil, the magnetic flux rises to the movement of the driving core, that is, the moment when the iron core starts to move; t2 is the load that the iron core has touched (started) the operating mechanism, This is also the moment when the switch contact starts to move; t3 is the time when the switch auxiliary contact cuts off the power supply, that is, the electromagnetic coil circuit is disconnected. The degree of failure of the operating mechanism can be diagnosed by using changes or differences in the comparison current waveform. 3.3.2 Monitoring of stroke and speed

The speed of the circuit breaker contacts has a great influence on the arc-extinguishing performance. Appropriately increasing the speed of the branching is very effective in reducing the arc energy and reducing the burning of the components. However, excessively increasing the speed of the segmentation does not necessarily improve the arc-extinguishing performance. On the contrary, it will increase the burden on the operating mechanism; also the closing speed of the circuit breaker contacts has a great influence on the arc extinguishing performance. Therefore, it is important to measure the stroke and speed characteristics of the circuit breaker contacts and to monitor them online. In order to complete the correct measurement, a suitable displacement sensor must be selected.

You can choose to rotate the optical encoder sensor. The rotation angle and direction can be measured by the incremental rotary optical code sensor. Generally, the rotary optical code sensor is mounted on the rotating shaft of the circuit breaker operating mechanism. The structure principle of this sensor is shown in Fig. 4.

Incremental rotary optical coding generally has 3 code channels (A channel, B channel, Z channel), and A channel and B channel are 90° out of each other. The number of chips per week can be selected according to the measurement resolution. Used to determine the number of rotations. When the shaft rotates, the encoder outputs the orthogonal pulses with the angles of 90° between the two channels A and B, and inputs the signal processing circuit. The relative position of the two signals from the A and B channels can determine the rotation direction of the rotating shaft. Before the B channel, it is a positive rotation, and the B channel is preceded by the A road, which is a reverse rotation. Then, by counting and counting the signals of the A and B channels by adding and subtracting the counter, the magnitude and direction of the rotation angle can be obtained, so that the movement and rebound of the moving part of the circuit breaker can be measured, and the moving contact stroke can be calculated; Average speed; overtravel; speed (mainly average speed, maximum speed) after 10 minutes or just before the start.

3.4 Medium voltage switchgear busbar junction temperature rise online detection

3.4.1 Causes of abnormal temperature rise at the bus junction

Temperature is a basic physical quantity, and many equipment failures are caused by abnormal temperature rise. During normal operation, the energy generated by the high-voltage electrical circuit's conductive circuit for a long time through the working current is converted into thermal energy, so that the temperature of the electrical material rises, generally does not exceed the specified range; but when the conductive circuit is unreliable, the temperature of the electrical material rises. The height is outside the specified range, and the mechanical strength and physical properties of the electrical materials are degraded. Therefore, the national standard "GB 3906-91 3~35kV advanced metal-enclosed switchgear" and "GB/T 11022-1999 high-voltage switchgear and control equipment The long-term operating temperatures allowed for different electrical materials are specified in the Standard Common Technical Requirements.

There is a contact resistance at the junction of the two busbars. When the current flows, the heat is generated at the place due to the contact resistance. If the temperature exceeds the specified value, the contact will be oxidized, and the oxidation result will cause the contact resistance. Rise, which in turn promotes increased heat and temperature, causing malfunctions. Therefore, the national standards "GB 3906-91" and "GB/T 11022-1999" stipulate electrical appliances that have long-term operation for rated voltages of 3kV and above and frequencies of 50Hz. For example, circuit breakers, disconnectors, enclosed combination appliances, metal-enclosed switchgear, load switches, etc., must be tested for temperature rise to ensure that the temperature of the electrical connection does not exceed the allowable value of the standard when the equipment has passed the rated operating current for a long time.

3.4.2 Real-time monitoring of the temperature rise of the temperature rise part buried in the busbar with a quartz temperature sensor

The quartz temperature sensor is a natural quartz crystal that has been cut in a specific direction. It can be found that the oscillation frequency has a certain relationship with the temperature. Special cutting can enhance this change, so the f-T characteristic can be used for temperature measurement.

The quartz crystal has three crystal axes of X, Y and Z. If the slice plane is written by X and Y, the angle between the X-axis and the Z-axis is Φ, and the angle between the X-axis and the X-axis is φ.

F1=f01+A(t-t0)+B(t-t0)2+C(t-t0)3

In the formula, A, B, and C are constants related to the cutting angle, respectively, and are related to Φ, φ. F0 is the oscillation frequency at the temperature t0. If Φ=9.4° and φ=11.6° are satisfied, then in the range of -80 to 250 °C: A=35×10-6/degree, B=C=0.

So the above formula becomes: f1=f01+A(t-t0), and f1 is proportional to t.

When t0=0°c, f0=28.2MHz, substituting A value, the frequency sensitivity is 987.3Hz/°C, that is, the temperature changes by 1°C, the frequency changes by nearly 1000Hz, the resolution is 0.001°C, and the quartz crystal temperature sensor is at -80. The basic error in the range of ~250 °C is ±(0.04~0.075) °C, the stability is about ±0.007 °C / month, so it has quite superior precision and stability ratio, because the measured value is frequency, it is easy and computer Cooperate.

The temperature rise online detection device of the busbar junction developed by ABB is shown in Figure 5. Its characteristics are as follows:

(1) When the bus passes current, its alternating electromagnetic field provides the working power required by the temperature sensor probe. When the current through the bus is 40A (50Hz), the sensing probe can work normally, and the short-circuit current generated by the short-circuit fault will not damage the sensor.

(2) Since there is a strong electromagnetic field at the measurement point and it is at a high potential, an infrared modulation emission technique is employed. The infrared light emitting diode sends the temperature value (pulse value) at a high potential to the infrared receiver at a low potential. The measured values ​​of several sensors can be sent to the same receiver.

(3) The temperature sensing unit is composed of a quartz crystal, an auxiliary power supply and a signal output circuit. It can be easily installed at the busbar junction. Quartz crystal temperature sensor is characterized by small size, high accuracy and good aging resistance.

In May 1992, ABB provided a new temperature monitoring system with a very small temperature sensing unit mounted on the exposed portion of the 12-contact (busbar contact) of a medium voltage switchgear. Three sensing units were installed. At the busbar junction, three cables at the upper end of the circuit breaker, and three at the cable end. In general, only nine sensors are used because the lower end of the circuit breaker is close to the cable termination.

4 fault arc protection device

4.1 Internal fault arc

In the metal-enclosed high-voltage switchgear, due to accidental factors such as small animals, overvoltage, humidity, etc., internal arcing occurs, and of course, there are artificially caused arcings such as accidental charging intervals and misoperation of the isolating switch. At about 15000~20000 °C, the arc will directly heat the surrounding insulating gas, and the heat can be quickly transmitted through convection and conduction, causing over-pressure in the switch cabinet compartment. When the pressure exceeds the allowable pressure limit, hot gas will rush out of the pressure relief device that closes the cabinet. Hot gases and transient pressure waves can damage workers in the power distribution room (such as injury to the respiratory system); Equipment and buildings.

The degree of damage to the fault arc depends on the magnitude of the arc current and the time of the cut. For example, in 1985, when the Tianjin Substation closed the power transmission, the switch cabinet had an arc fault, and finally burned 8 switch cabinets. In April 2004, a 35kV armored open switch cabinet in a company's power distribution system produced an arc explosion, resulting in an arc explosion. The cable compartment of the switchgear exploded and deformed, and the rear door, side panels and side reinforcing ribs were blown and twisted, and the wooden door of the power distribution room was opened by the shock wave, and a glass window was blown up.

Therefore, for metal-enclosed switchgear used in important occasions, internal fault arcing test and fault arc protection device should be carried out. The fault arc test provisions can be seen in GB3906-2005 and IEC62271-200 standards.

4.2 Fault arc protection device

Fault arc protection devices developed by ABB have long been used in AX1 switchgear; Germany's Moeller has already developed Arcon fault arc protection devices.

The general arc protection device consists of three parts: the protection main unit; the overcurrent and arc detection auxiliary unit; and the arc light sensor.

4.2.1 Arc light sensor

As a light-sensing element, it is installed at several positions in the busbar room of the switchgear to detect the sudden increase in light intensity when a fault occurs.

4.2.2 Overcurrent and arc detection auxiliary unit

The arc detection auxiliary unit collects the light information from the arc light sensor and transmits it to the main unit. The overcurrent detection auxiliary unit provides overcurrent action information, which is one of the action criteria, and can further ensure the accuracy and reliability of the arc light protection system.

4.2.3 Protecting the main unit

It is the heart of the arc protection system and is used to manage and control the entire arc protection system. It receives the detection of the short-circuit current and the information from the arc light sensor, processes and judges the collected data, and if it is confirmed that it is an arc fault, issues a trip command to trip the incoming circuit breaker, that is, cuts the incoming power. If the incoming circuit breaker cannot trip (resume), the breaker failure protection logic is activated, and a trip command is issued to the upper circuit breaker to cut off the power. In addition, according to the information sent by the overcurrent and arc detection auxiliary unit, an arc fault point and an alarm signal are provided.

There is also a method here: if it is confirmed that the arc is faulty, the quick short-circuit switch is activated to make it quickly close, and the arc fault is converted into a three-phase short-circuit current, and the upstream circuit breaker is opened to achieve the purpose of quickly extinguishing the arc.

The block diagram of the fault arc protection system is shown in Figure 6.

5 Conclusion

(1) Intelligent switchgear is a new generation of electrical products, which integrates computer, information, control, sensor and neutrino technology. The communication interface of each intelligent unit is connected with the duty room computer to form a substation synthesis. The automation system can realize protection on the spot and in the distance, and can realize wide-area monitoring and diagnosis of substation.

(2) The improvement of computer technology and electromagnetic compatibility (EMC) level makes the intelligent measurement and control device more reliable than the traditional electromechanical measurement and control products. This has been proved by many years of operation.

(3) Based on the state maintenance technology to establish online monitoring technology and information technology, online monitoring projects can be determined according to actual needs.

(4) Switchgear cabinets used in important occasions should be equipped with intelligent fault arc protection devices.