1. Introduction
With the domestic products going out and the construction of the Belt and Road, more and more Chinese switchgear are also actively participating in the competition of the international market, however, due to the lack of understanding and experience of foreign demand, only some large enterprises can really go out and expand their market share. Firstly, the product standards and parameters should meet the requirements of customers, and secondly, foreign customers have higher requirements for product safety. It is necessary to understand the demand comprehensively to be able to stand firm in the market and go out.
2. Parameters and standards
2.1 Except for North America, most of the countries in the world accept IEC standard products. Since GB standard is equivalent to IEC standard, many countries accept GB standard products.
2.2. Parameter requirements
IEC regional voltage levels in accordance with IEC622171-1 Table 1, the same Latin America and other regions using Table 2 provides 4.76, 8.25, 15, 27kV and other voltage levels. Table 1 is listed as common voltage and insulation requirements, there are other insulation requirements in the standard, you need to check the customer’s technical conditions.
Although the rated value of these voltage levels is less than GB 12KV, the lightning impulse withstand voltage is higher than the GB standard, so it is necessary to improve the overall insulation level of the switchgear to meet the requirements. Although IEC60071 defines the air static distance of the exposed conductor according to the impact withstand voltage of the product, and IEC60815 defines the minimum creepage ratio distance of insulators under different filth conditions, IEC products are more concerned about the type test of the product, based on the test report, rather than being overly entangled in the static distance, creepage distance, and other requirements, and heat-shrinkable tubing can be used as a way of narrowing the distance between phases. Material, according to RAYCHEM and other manufacturers to define the guidance distance through the test to meet the product requirements.
Table 1 IEC Common Voltages and Insulation Levels
| Rated voltage kV (rms) | Rated industrial frequency withstand voltage kV (rms) | Rated lightning impulse withstand voltage kV (peak) | ||
| Common value | Isolating break | Universal value | Isolated break | |
| 4.76 | 19 | 21 | 60 | 66 |
| 8.25 | 36 | 40 | 95 | 105 |
| 12 | 28 | 32 | 75 | 85 |
| 15 | 36 | 40 | 95 | 105 |
| 17.5 | 38 | 45 | 95 | 110 |
| 24 | 50 | 60 | 125 | 145 |
| 25.8 | 60 | 66 | 125 | 138 |
| 27 | 60 | 66 | 125 | 138 |
| 36 | 70 | 80 | 170 | 195 |
| 38 | 95 | 105 | 200 | 220 |
Latin America and other countries adopt 60Hz, according to IEC62271-1 and STL guideline, 50Hz circuit breaker can not be directly used in 60Hz system, must be verified by test, temperature rise and so on through the calculation of the test results and so on can be proved to be used in 60Hz system.
Table 2 50&60Hz circuit breaker and switchgear test frequency requirements
| Test item | Test frequency requirement | Remarks |
| T10,T30 | 50Hz or 60Hz | |
| T60,T100s, T100a | 50Hz and 60Hz | Do both frequencies |
| Single-phase grounding/dissimilar grounding | 50Hz or 60Hz | |
| Tolerance test | 60Hz | |
| Electrical life test | 50Hz or 60Hz | T100s peak current 2.6 times |
| Temperature rise test | 60Hz | 50% margin is required for 50Hz test. |
| Dynamic thermal stability test | 50Hz or 60Hz | The peak current of dynamic stability is 2.6 times of thermal stability in 60Hz test. |
At the same time on the circuit breaker breaking TRV also need to pay attention to some of the voltage rated voltage is low but TRV is higher than the GB standard, need to interpret the standard. As most of the domestic neutral point is not grounded system, so when the product is used in the neutral point directly grounded system, also need to single-phase grounding and opening test procedures in the grounding system test.
2.3. Type test generally requires products with KEMA, IPH and other international short-circuit alliance laboratory type test, with ASTA, TUV and other test and certification bodies in the domestic business expansion, some foreign customers also accept their test reports. Through the test witnessed in the third-party laboratory, ASTA, TUV and other type test reports issued in line with international standards, can greatly save the test and related logistics, personnel and other costs. For Africa and other countries, the type test reports of Chinese laboratories with CNAS in accordance with ISO17025 standards are also increasingly accepted.
3. Safety requirements
3.1 Safety interlock
Foreign customers have higher safety requirements, in addition to the conventional domestic requirements of the five mechanical interlocks, padlocks and industrial safety key locks must also be equipped.
For the middle cabinet, for safety reasons, customers require that the door must be closed to operate the circuit breaker and grounding switch, so the door must be closed to operate the mechanical interlock configuration. Not to avoid the hand to open the high-voltage contact valve, there must be a mechanical interlock to ensure that only through the circuit breaker and other functions of the hand car to open the valve.
Padlocks are mainly circuit breaker rocking into the hole cover plate, grounding switch operation hole cover plate, high voltage room door, etc. are required to install the locking rod diameter 8mm safety padlocks to ensure that the installation and maintenance of the marking locking requirements.
Safety interlocking technology ensures that personnel can only operate hazardous machinery and equipment under predefined programmes. The next operation can only be carried out if safety permits, thus maximising the safety of personnel and machine. Will also use the key box with a key or keys to exchange a number of other keys, to ensure that the switchgear cabinet itself, as well as between the cabinet and the cabinet, the switchgear high and low voltage side and the transformer compartment door between all the logic of the switchgear cabinet, through the use of the mechanical key exchange to achieve the requirements of the safety management of the power plant, the correct operation of the electrical equipment, and at the same time to ensure that mechanical interlocking device of the mechanical logic of the exchanger to leave the space can be expanded, can be achieved The interlocking of the new electrical equipment and the original system electrical equipment can realise the “five defences” of the whole system.
The grounding switch and circuit breaker key locking requirements of the switchgear are shown in Figure 1 and Table 3. Figure 2 is an example of a switchgear key interlocking system, where the two incoming and outgoing circuit breakers and the corresponding earthing switches need to meet the conditions and exchange the specified keys through the key exchange box to perform the corresponding operations.
Internationally recognised industrial locks such as FORTRESS, CASTELL etc. are usually required.
Table 3 Switchgear circuit breaker and earth switch key locking requirements
| Description of the key locking system | Key status |
| Function Handcart locking in working position | The key can only be withdrawn when the handcart is in the test position. |
| The key cannot be turned to the withdrawn position when the handcart is in the working position. | |
| Functional trolley locking in working position | The key can only be withdrawn when the handcart is in the working position. |
| The key cannot be turned to the unplugged position when the trolley is in the test position. | |
| Ground switch blocking in closed position | The key can only be withdrawn when the earth switch is in the open position. |
| The key cannot be turned to the pull-out position when the earth switch is in the closed position. | |
| Ground switch opening position blocking | The key can only be withdrawn when the earth switch is in the closed position. |
| The key cannot be turned to the unplugged position when the earth switch is in the open position. |
3.2. Internal fault protection level Switchgear must have an anti-internal fault level, which is generally required to be A FLR, consistent with the product opening current, and the time is 1 s. At the same time, some projects are affected by the height of the switching room, etc., and it is necessary to avoid the injury of personnel due to the flames arriving at the roof and then bouncing back, and some customers require that there is no fire or fire-carrying objects to be sprayed out, and that the pressure, arc, etc., from internal faults should be released to the switching cabinet through a special pressure-release channel. Pressure, arc, etc. generated by internal faults need to be released to the outdoors through dedicated pressure release channels, the switchgear cabinet with pressure release channels shown in Figure 3; or an arc absorber made of a large amount of ceramic filler to filter the fire and the airflow and minimise the injury to personnel.
For safety reasons, arc protection devices are also a requirement for many customers, requiring the installation of light sensors in the three high-voltage compartments, arc protection relay through the logic control of the corresponding circuit breaker to achieve when an internal fault occurs, you can quickly cut off the power supply to reduce losses. Typical arc light protection relays such as UTU-Falcon.
3.3 Environmental requirements
For the Middle East due to high ambient temperatures, switchgear sometimes need to meet the requirements of the ambient temperature of 50 degrees, this use of the environment, not a simple reduction in the use of capacity can be, too high a temperature on the mechanism of the spring, lubricating oil, rubber seals and so on will have an impact on the need to carry out the necessary tests to ensure that the use.
For Latin America and other countries with frequent earthquakes, anti-seismic grade requirements are higher, need to compare our seismic standards and customer requirements for seismic standard grade requirements, if necessary, need to test and verify.
4. Usage habits
For the primary system design, foreign products require more compact, a typical scheme as shown in Figure 5, the feeder cabinet 05/09 need to be grounding switch and voltage transformer for cable grounding and input voltage measurement or to provide operating power, and each section of the bus needs to be grounding switches and voltage transformers for bus maintenance grounding and bus voltage measurement, the left section of the bus in the figure, the bus grounding switches and voltage transformers are installed in the lifting cabinet 06, the other section is set separately 06, the other section of the separate voltage transformer grounding switchgear 09. There are also more compact design requirements that the bus grounding switch or voltage transformer installed in the top of the outlet cabinet, as shown in Figure 6, which can reduce a switchgear.
Many foreign projects are pre-assembled substation (E-House) projects, the switchgear is installed in a separate outdoor box, the compactness of the switchgear is very important for operation and maintenance of the space is also very small, some need to be installed in front of the cabinet, the replacement of components, so you need to consider the convenience of installation in front of the cabinet.
Foreign customers operating force are relatively large, mechanical interlock design must have sufficient strength, otherwise it is easy to be destroyed resulting in interlock failure. For example, the rocking-in of the middle-mounted circuit breaker trolley, if in the closing state, the circuit breaker cannot be rocked out in the working position, which is realised by locking the rocking-in screw through the top plate, but if the operating torque is greater than 50 or even 60 N.m, it is very likely that the top plate will be destroyed and the circuit breaker will be rocked out.
The use of active, visual, programmed interlocking can effectively avoid misoperation, resulting in interlocking damage. That is, if the operating hole of the ground switch is blocked, i.e. the operating handle cannot bite with the operating shaft, it cannot cause misoperation.
5. Marking and labelling
The switchgear needs to have obvious signs to ensure customer safety and correct operation, generally divided into danger, warning, attention, instructions and other signs. Signs should be made in accordance with customer requirements or relevant ISO 3864 standards, such as high-voltage danger.
Should reduce too many operating instructions class logo, the content is simple and concise, emphasise the content of special attention, such as the above circuit breaker trolley rocking into the operating force is too large damage, can be added in the rocking hole “operating torque ≤ 25N.m” logo.
6. Conclusion
China is becoming the world’s leading power transmission and distribution products, many multinational companies also take China as a global R & D centre for power distribution products, and constantly design products for the regions around the world to meet different standards. And local enterprises can learn from the experience of these multinational companies in product development, a true understanding of customer needs, design and export to meet, this paper is only an introduction to the primary system and structure, the same specific project there are a lot of specific requirements on the control, protection and secondary wiring, etc., you need to carefully read the customer’s technical conditions and other information, to make the right product. You can also refer to some multinational foreign products sample information as a design reference.