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  Wuhan Yue Neng Gao Measure Power Equipment Co., Ltd. is a collection of power testing equipment, instrumentation research and development, production, sales, service in one of the high-tech enterprises. Always adhere to the product quality as the lifeline of the enterprise, the company's all products strictly comply with the ISO9001 quality management system standard.
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Relay protection technology is very important for the safe and stable operation of HVDC transmission lines. As the current commonly used technical means have certain deficiencies, we should increase research efforts and develop a relay protection scheme that is more suitable for my country's DC transmission requirements , Thereby promoting the long-term development of the power system. Here are four common relay protection technologies. Traveling wave protection In the process of HVDC transmission, the main protection measure is traveling wave protection. The protection principle is as follows: When the line fails, the fault point will propagate the anti-traveling wave to both ends of the line, and the traveling wave protection can pass the reading Identify and judge the situation of the fault-related area. At this stage, when using traveling waves to protect HVDC transmission lines, two more schemes are adopted. One is the ABB scheme. The fault detection of this scheme is carried out by pole waves, and at the same time, the fault pole is determined by ground model waves; the other is Siemens In the scheme, the starting criterion of the scheme is voltage differentiation, but the fault determination method is to observe the sudden change of the reverse traveling wave within 10MS. The above description shows that the two schemes adopt different detection methods, and there are certain differences in effect. Because the differential link exists in the Siemens scheme, the detection speed is relatively slower than the ABB scheme, but it is precisely because of this link. Makes the Siemens solution has better anti-interference ability. However, these two schemes have certain shortcomings, such as insufficient resistance to excessive resistance, high sampling requirements, and lack of good anti-interference ability. Since many problems exist in the traveling wave protection technology, a traveling wave directional protection scheme based on wavelet changes is proposed; another example is to optimize the sensitivity and study the principle of polarity comparison equation.

Differential undervoltage protection In DC transmission lines, differential undervoltage protection belongs to the main protection. At the same time, when using traveling wave protection, it also acts as a backup protection. The main way to realize protection is to detect the voltage differential value and voltage amplitude level. From the protection principle, the differential undervoltage protection is the same as the ABB scheme and the Siemens scheme. Both are the determination of the polar voltage differential and amplitude, and the voltage differential setting is consistent with the traveling wave protection. The difference is that the original 6ms is extended. It becomes 20ms. As a result, when the traveling wave protection exits or there is no sufficient rising edge width, the differential undervoltage protection can fully exert its backup protection function. Compared with traveling wave protection, differential undervoltage protection has a slower operating speed, and its accuracy is significantly improved. However, it is still not ideal in terms of resistance to excessive resistance and is very limited.

Low-voltage protection For the first two protection technologies, low-voltage protection is a backup protection method, and the relay protection function of the fault pole is determined by voltage amplitude detection. According to its design, after a high-impedance fault occurs, when the traveling wave protection and differential under-voltage protection fail to act, the low-voltage protection will cut it off. However, from the actual application situation, the low-voltage protection mirror is equipped in the extreme In a small number of HVDC transmission lines, there are two types of low-voltage protection, one is line low-voltage protection, and the other is pole-controlled low-voltage protection. Compared with the latter, the former has a higher protection rating, and the former acts After that, the line restart procedure will start, and after the latter action, the fault will be blocked. Although the low-voltage protection has a relatively simple principle, it also has many problems, such as poor selectivity and inaccurate discrimination of high resistance faults. Pilot current differential protection In HVDC transmission lines, pilot current differential protection is a backup protection scheme. The principle is to promote insulation selectivity through double-ended electrical quantities. According to the design, high-resistance faults can be cut off. Judging from the existing longitudinal current differential protection, because the capacitive current problem has not been fully considered, the differential criterion only uses the sum of the two ends of the power, which leads to a relatively long waiting time and relatively slow action speed. For example, the Siemens scheme of longitudinal current differential protection has large current fluctuations at the beginning of the fault, and the differential protection will have a delay of 600ms. At the same time, the delay of the differential criterion itself is 500ms, that is, the differential The action will not appear until at least 1100ms after the fault occurs, and during this period, accidents where the fault is directly blocked may occur many times, causing the equipment to fail to start, and the backup actions of the longitudinal current differential protection can not be fully performed. . In order to enhance the effect of this protection technology, improvements can be made from multiple aspects, including compensation capacitor currents to promote the sensitivity of differential protection; upgrading high-frequency channels to fiber channels to speed up the protection action.

structure

The iron core of this series of products is a single-phase core type, which is made of high-quality cold-rolled oriented silicon steel sheets, and the fastening method uses steel as a clamp. The high-voltage coil is a cylindrical multi-layer tower type, wound by high-quality polyester enameled wire and high-voltage insulation material. The low voltage coil is outside, and the instrument coil is an independent winding, generally 100V. The shell is octagonal, and test transformers above 10KVA are equipped with movable iron wheels. It has light weight, small size, convenient movement and superior performance.

The working principle of TWSB high voltage test transformer

1. AC, AC and DC test transformers:

Input the power frequency power into the operation box (or console), adjust the voltage through the auto-voltage regulator and input it to the primary winding of the test transformer. According to the principle of electromagnetic induction, power frequency high voltage can be obtained in the secondary (high voltage) winding. After the power frequency high voltage is rectified by the high-voltage silicon stack and capacitor filtering, the DC high voltage can be obtained, and its amplitude is 1.4 times the effective value of the power frequency high voltage. It's just that the short-circuit bar should be drawn out when using DC, and the short-circuit bar should be inserted when using AC.

2. Transformer with tapped test:

In order to satisfy the contradiction between a transformer with a higher voltage and a lower voltage and a lower current and a higher current, the high-voltage winding is divided into two windings, one is the winding with the larger current, the other is the winding with the smaller current, and then Two windings are connected in series and lead out separately, schematic diagram

3. Cascade test transformer:

In order to obtain a higher voltage test transformer, a cascade method can also be used to obtain a higher voltage. Figure 2 shows the principle wiring diagram of a three-stage cascade test transformer. The relationship between the capacity and voltage of the three transformers satisfies: P1=2P2=3P3, U(total)=1U+2U+3U.

characteristics

◆ Data such as voltage, current, time, status information and prompt information are displayed on a 4.7-foot large-screen LCD with clear and intuitive readings;

◆ All Chinese interface, simple and clear operation, can adapt to a variety of applications;

◆ Light touch button operation, all functions can be set by buttons, which improves the safety and reliability of the product;

◆ All-digital calibration method, abandoning the old potentiometer adjustment, extremely convenient on-site use, and easy to control accuracy (this function is protected by a password);

◆ Press the button to directly set the transformation ratio of the test transformer (this function is protected by a password). When connecting testers of different voltage levels, the application is flexible and free, and it is true that one control box can be matched with multiple transformers;

◆ Status reminder function, full Chinese-guided operation, even if there is no manual, it can be manipulated skillfully;

◆ During the test, there are flashing high voltage symbols on the screen to remind the operator to pay attention to safety;

◆ Test result display function, which can automatically judge the test result (test passed or failed), and can reliably record the overcurrent, flash or breakdown voltage of the sample;

◆ Test result sound alarm function, when the test passes or fails, the equipment will emit different alarm sounds, and the test personnel can directly identify the test results by the alarm sound;

◆ Pause function, under automatic control, this function can realize the pause of boosting or depressing at any point, and the time of the pause can be flexibly controlled by the tester to facilitate the observation of the state of the test product;

◆ Automatic timing function. In automatic control, when the voltage automatically rises to the set value, the device automatically starts timing. When the timing expires, the test result is displayed and the device automatically returns to zero;

◆ Manual timing function. When manually controlled, the timer can be started manually. When the withstand voltage time is up, the device will automatically return to the zero position (only desktop devices have this function);

◆ Manual control mode, this mode is similar to the traditional electric boost/decrease method, the up/down is controlled by the button, the device automatically judges the upper/lower limit, there is overvoltage protection;

◆ The boost speed is intelligently controlled. When the voltage reaches 80% of the target voltage, the boost speed will automatically slow down. When it reaches 90% of the target voltage, the boost speed will further slow down;

◆Optional remote communication, door interlocking warning light alarm bell, external voltage divider verification interface, etc.;

◆ Using the combination of hardware and software anti-interference technology, stable performance and strong anti-interference.

Transformer drying method

induction heating method

This method is to put the body in the oil tank, and pass the power frequency current to the outer winding coil, and use the heat of the eddy current loss in the oil tank wall to dry. At this time, the temperature of the box wall should not exceed 115~120℃, and the temperature of the body should not exceed 90~95℃. For the convenience of winding the coil, try to make the number of turns of the coil as small as possible or the current is smaller. Generally, the current is 150A, and the wire can be 35~50mm2. Multiple asbestos strips can be placed on the wall of the fuel tank, and the wires are wound on the asbestos strips.

　　 hot air drying method

　　This method is to put the body in a drying room with hot air for drying. The inlet hot air temperature should gradually rise, and the temperature should not exceed 95℃. A filter should be installed at the hot air inlet to prevent sparks and dust from entering. Do not blow the hot air directly to the body, as far as possible from the bottom of the body to blow evenly in all directions, so that the moisture is released from the vent of the box cover.