1.1 Arc extinguishing and insulating medium
The arc extinguishing and insulating medium generally used in circuit breakers are: SF6 insulating oil, vacuum and air. However, for 220kV and above voltage levels, SF6 is now basically used as arc extinguishing and insulating medium, although SF6 has a greenhouse effect. Environmental problems such as poisonous decomposition after the arc, but there is no medium that can replace the superior position of SF6 in the field of high-voltage circuit breakers. Therefore, for high-voltage circuit breakers of 110kV and above, SF6 circuit breakers should be used if there are no special requirements. .
1.2 GIS and open equipment
In the big aspect, the selection can be divided into whether GIS equipment or conventional open switch equipment is used. GIS equipment is compact in structure, small in footprint, high in equipment safety and reliability, but expensive. It is generally only used in areas with small urban land area or underground substations, and is generally applied to 110kV and 220kV grades, 500kV grade GIS complete technology. Only a few large companies are mastered and expensive. They are generally used in underground power plants of large hydropower plants or in heavily polluted areas, and in areas where air insulation such as the sea is not easily reach the corresponding level. In addition, once a GIS device fails, the repair cost and time are more.
1.3 column or can
Whether the conventional open switchgear should be porcelain column or tank circuit breaker should be determined according to cost analysis, fault statistics and user habits. For the 500kV voltage level, the dielectric loss will gradually increase due to the traditional oil-paper insulation TA after a period of operation, and the 500kV class is SF6. The reliability of TA still needs long-term operation to verify (currently the fault rate of SF6TA is higher at 500kV level), so the use of tank-type circuit breakers increases the possibility of insulation faults in the circuit breakers, but greatly reduces the failure rate of TA. In terms of price, the tank circuit breaker slightly exceeds the price of the porcelain column circuit breaker plus the independent TA, and the land occupation aspect adopts the conventional wiring method of one and a half circuit breakers, and the difference between the two is small. The tank type circuit breaker can be installed in the outside of the tank, so it can be applied to severe cold weather conditions at the same SF6 density. In addition, the tank type circuit breaker has a lower center of gravity and relatively strong earthquake resistance; relatively speaking, the column type circuit breaker basically has no ground insulation problem, the structure is simple, the maintenance is convenient, and the price has certain advantages, and the selection should be comprehensive. consider.
1.4 New switchgear
New switchgear such as H-GIS, PASS, etc. are rapidly developed with high integration, flexible operation, simple structure, standardized secondary interface, unit assembly and commissioning in the factory, short construction period, and low maintenance. Relatively less expensive, it is recommended to try it in the North China Network.
2 closing resistor problem
In order to reduce the over-voltage of the long-circuit operation, the 500kV system is equipped with a closing resistor on the line breaker. When the closing is completed, the main contact is turned on. After the main contact is completed, the closing resistor is withdrawn. Non-circuit breakers such as main transformer breakers and busbar breakers should not be installed. Whether the circuit breaker is equipped with a closing resistor should be calculated according to the corresponding overvoltage calculation. In general, the lightning arrester for the line below 200km can limit the operating overvoltage to the corresponding level, and the line breaker can be installed without the closing resistor. More than 200km lines need to be calculated. The cost of the circuit breaker with the closing resistor is much higher, and the reliability of the circuit breaker mechanism is lowered, so it should not be installed where it is not necessary. Voltage levels of 220kV and below are not required due to the operating overvoltage, so the closing resistor should not be installed.
3 parameters of the outer insulation of the circuit breaker
The parameters of the circuit breaker should be selected to meet the DL/T615-1997 AC high voltage circuit breaker parameter selection guidelines. Its rated voltage, rated current, rated short-circuit breaking current and circuit breaker time characteristics shall comply with the corresponding standards. Here, the problem of the outer insulation creepage occurred in the equipment bidding is mainly explained.
The nominal creepage ratio of the outer insulation of the circuit breaker shall comply with the requirements of DL/T593-1996 3.1.2C.
The ratio of the nominal creepage ratio between the 500kV breaker breaks and the nominal creepage ratio to the ground is generally 1.15 to 1.35. If the nominal creepage ratio to the ground is larger, the deviation is smaller; if the nominal creepage ratio is smaller, the larger value is taken.
For the external insulation between the breaks of the 500 kV contact breaker, the creepage ratio should generally be 1.3 times the standard value of the corresponding pollution level, and it should not be considered that the creepage ratio of the circuit breaker to ground is 1.3 times. A contact breaker generally refers to a circuit breaker that can separate two independent grids after disconnection, and both ends of the fracture may be subjected to twice the maximum operating phase voltage. For example, a power plant sends a transformer high-voltage circuit breaker, two circuit breakers at both ends of the power line, and the general bus-coupled circuit breaker does not belong to this category.
4 operating mechanism selection
Statistics show that about 60% of faults and obstacles in high-voltage circuit breakers are operational failures or obstacles. The operating mechanism is an extremely important part of the circuit breaker. At present, the operating mechanism of the application can be roughly divided into several types, such as a spring mechanism, a hydraulic mechanism (including a spring hydraulic mechanism), and a pneumatic mechanism.
4.1 Spring operating mechanism
The mechanism is in the form of a mechanism that directly operates the circuit breaker with a spring that stores energy. The utility model has the advantages of simple structure, small maintenance amount, simple secondary storage positions and simple locking contacts. The spring mechanism is generally an electric closing spring energy storage, which can meet the requirements of energy storage time. 0--0.3 s--combination--3min one-time operation timing, that is, the required energy storage time is less than 3min. Such a mechanism closing spring is always in a state of energy storage during operation, and long-term operation may cause problems such as spring fatigue, deformation, fracture, etc., and generally cannot be predicted in advance, so the spring material is extremely demanding. At present, the spring operating mechanisms produced by various manufacturers have passed the mechanical life test of 3,000 times or higher. However, the influence of the spring mechanism on the deformation of the split and closing springs and the parameters such as the time and speed of the circuit breaker are still needed. Research and time testing.
4.2 Hydraulic mechanism (including spring hydraulic mechanism)
The high-pressure hydraulic oil drives the piston of the working cylinder to drive the contacts to perform the split operation. This type of operating mechanism is mature in technology, large in operation and reliable in operation. The common problem is that the original domestic hydraulic mechanism has low machining precision, and the quality of the seal is poor. Long-term operation will result in leakage oil and frequent pressure. However, the integrated hydraulic operating mechanism currently produced has been greatly improved, in which the reduction of the pipeline, the reduction of the number of sealing components, and the integration of the valve body make the probability of oil leakage greatly reduced.
4.3 Pneumatic operating mechanism
It is a mechanism that performs switching operation with compressed air as power. Its advantage is that air is the medium, no environmental pollution, the cost is relatively cheap, and the output operation is large. The biggest problem with pneumatic mechanisms is that the water in the air becomes compressed after being compressed. In the cold season, freezing will block the pipelines, valve bodies, etc. Therefore, it is necessary to strictly implement the regular water discharge system. If necessary, automatic dewatering devices and automatic sewage disposal can be added. Valves, etc. Pneumatic mechanisms require high air compressors, and high quality air compressors should generally be used.
5 Spare parts/spare parts and special tools
In order to facilitate the operation, maintenance and test of the circuit breaker, a certain number of types of spare parts/spare parts must be selected when ordering the circuit breaker. Generally, the following contents should be included: split coil, valve, pressure gauge, hand operated tool, lifting tool Etc. For pneumatic mechanisms, consider whether to order a spare air compressor. If there are more circuit breakers of the same type or the fault recovery time is higher, consider the standby single arc extinguishing chamber and single-phase operating mechanism. In a 500kV system, when a half-switch connection is used, the possibility of simultaneous failure of two circuit breakers is extremely low, and the emergency spare parts can be ignored. However, for a 220 kV system, a single circuit breaker failure can directly force the unit or line to be shut down. Therefore, it is possible to consider accidental backup circuit breaker equipment, which is especially important for imported GIS products.
To facilitate on-site circuit breaker speed testing, users should also order speed measurement brackets, sensors, etc. that can be used for the switch test instrument used to perform speed checks during handover or if necessary.
6 Factory test
The high voltage circuit breaker shall be tested in accordance with the corresponding standards such as GBl984-89. In the low-voltage operation test in the mechanical operation test project, some manufacturers only perform 30% voltage non-dividing, and 65% voltage is reliably passed, that is, it is considered to pass, and the specific operating voltage value is not measured, and after the handover and pre-test It cannot be compared with the factory value, so we recommend that the manufacturer be required to determine the specific minimum operating voltage value at the time of shipment.
7 The problem of matching the new circuit breaker with the original protection system in the renovation project
In the circuit breaker renovation project, the resistance and current requirements of the circuit breaker coil are often proposed in conjunction with the original protection system. The manufacturer is required to change the original standard configuration with a non-standard coil, which requires rigorous calculation and testing. It can be implemented, and it also involves the problem of spare parts when the coil is replaced after operation. Therefore, we recommend that the circuit breaker coil should not be forced to match the original protection system, but the interface board in the original protection system should be replaced.
In addition, for the circuit breaker of the RC parallel acceleration circuit of the opening circuit, since it needs to obtain tens of amps of DC current at the moment of opening, it should be specially designed in terms of secondary protection, increase the DC cable diameter and reduce the trip relay. The contact resistance of the contact prevents the circuit breaker circuit from failing to obtain sufficient terminal voltage and refuses to move.
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