Several questions about insulation in the introduc

Several problems of insulation in the introduction of 10kV switchgear ring cabinet

Abstract: in recent years, there are many cases of using imported 10kV switchgear and ring cabinet. It is summarized that when importing this kind of equipment, we should improve the requirements for its insulation level according to the specific situation, pay attention to the weak insulation links of the ring and the performance of SF6 switchgear under zero gauge voltage, and other related insulation experience, so as to ensure the long-term safe operation of this kind of equipment. Since the 1980s, imported switch cabinets and ring cabinets from different manufacturers have been used in 10kV power and some user switch rooms. This article intends to talk about my experience and views on several technical issues

key words: 10kV switchgear ring cabinet insulation problem Untitled Document in recent years, imported 10kV switchgear and ring cabinet have been used more. It is summarized that when importing this kind of equipment, we should improve the requirements for its insulation level according to the specific situation, pay attention to the weak insulation links of the ring and the performance of SF6 switchgear under zero gauge voltage, and other related insulation experience, so as to ensure the long-term safe operation of this kind of equipment. Since the 1980s, imported switch cabinets and ring cabinets from different manufacturers have been used in 10kV power and some user switch rooms. This article intends to talk about my experience and views on several technical issues. 1. Requirements for insulation level. In the initial stage, the electric power industry bureau selected such equipment according to IEC 12 kV level, and the power frequency/impulse withstand voltage was 28 kv/75 kV. There were two insulation accidents in actual operation: one was due to the breakdown of the cable joint of the user's dedicated line, and the breakdown process may be intermittent, thus inducing the external insulation flashover of the current transformer (hereinafter referred to as TA) of the bus coupler cabinet, and then causing phase to ground and phase to phase short circuit. In addition, there is no separation between the busbar chambers between cabinets, and the busbar is exposed. Once the arc is swept to the end, except that the busbar coupler cabinet is burnt out and needs to be replaced, other cabinets also need to be cleaned, and the power transmission can be restored the next day. The other was due to creeping flashover of insulation outside the voltage transformer cabinet, causing ground and phase to phase faults and burning out the cabinets on both sides. It can be seen that for the humid tropical climate in the south, although the new cabinet selected according to the above insulation level can successfully pass the handover acceptance test, due to the influence of various external factors on the insulation, it can no longer meet the requirements of long-term safe operation. We should improve the requirements for imported equipment from three aspects: a) no longer choose IEC 12 kV gear, but IEC 17.5 kV gear, and its power frequency/impulse withstand voltage is 38 kv/75 kV or 95 kV. In order to be roughly in line with the requirements of domestic orders (42 kv/75 kV), 38 kV (100%) is required to be taken during the site acceptance test. b) The busbar room is required to use fully insulated busbar (PVC material is not allowed for the wrapping layer), and the clear air distance between the primary conductor of each cabinet and the ground and between phases is required to be 125 mm or more. c) It is required that the creepage distance of organic insulating materials should reach 230 mm and the porcelain parts should reach 210 mm, and it is clearly put forward that the key parts that should meet the requirements, namely, bus support insulator, arc extinguishing chamber moving contact rod insulator, voltage transformer outlet bushing, static isolation plug support bushing, circuit breaker pole support insulator and outlet insulator, grounding knife static contact support insulator, etc. 7 places, which will be implemented one by one in the meeting and the manufacturer. 2 pay attention to the weak insulation links of the ring cabinet

the supplier often introduces that its ring switch is designed according to the insulation requirements of 24 kV voltage level. It should have a large margin in insulation, but there are still places to pay attention to. 2.1 creepage distance of the connection part of the cable head

the structure of S company here is "pipe type" cable head. In the actual construction, some teams and groups changed to the general-purpose heat shrinkable head of Raychem company, resulting in the cone of the outlet sleeve not being covered by a "pipe", and there was a discharge phenomenon here after being charged. After switching back to the "pipe type" cable head of the factory, everything was normal

2.2 fault indicator perceives the insulation of TA

since single core cables are often used in Europe, the fault indicator perceives that TA is covered outside the cable sheath, and there is a complete cable insulation layer between it and the surface Rockwell hardness test, one of the cable cores. Therefore, the insulation of this TA is very simple and weak, and generally only a few layers of insulation tape are wrapped around the iron core. However, three core cables are mostly used in China. The fault indicator senses that TA is placed on the cable core with the main insulation after the Trident head is stripped of the protective skin/armor layer and grounding shielding layer, and separated by the heat shrinkable insulation sleeve, the following problems may occur: a) there is the accumulation of free charge on the heat shrinkable insulation sleeve, and after a certain degree, the TA core will be discharged; b) After long-term operation, the sharp edge of the iron core may cut the heat shrinkable insulating sleeve and the main insulating layer, causing a short circuit between high voltage and ground. This is a potential threat to equipment and personal safety (especially in the occasion of using microcomputer to realize distribution automation). Generally, the touchable cable head with sheath grounding can be used, and the TA can be properly fixed with insulating support. In the occasion of implementing distribution automation, the measures should be more perfect. For example, the sensing TA can be required to be set on the outlet sleeve of the cabinet instead

2.3 quality of grading cover

m company uses grading cover to solve the interphase distance at the connection of cable head, waiting for downstream demand verification; Macroscopically, the two sessions are not enough. According to the computer simulation of electric field distribution provided by them, this practice should be reasonable. However, in February, 1998, a burning failure occurred in a ring cabinet of M company in a building in Guangzhou. One phase voltage equalizing cover fell, and there were discharge traces on the surfaces of the two phases. Up to now, the analysis conclusion of the manufacturer on this accident has not been seen. Therefore, some people suspect that due to the dispersion of manufacturing, assembly and other aspects, the effect of the pressure equalizing cover may not achieve the expected effect. Therefore, it is proposed that, in order to be safe, it is best to wrap an insulating sleeve outside it. There is a button type insulating sleeve suitable for this purpose. At first glance, this is a concern when the voltage level is 110 kV and above. However, from the perspective of safe operation, it is equally important for 10 kV for the following reasons:

a) whether it is a circuit breaker or a load switch, the structure of this voltage level is very simple, and there is no pressure gauge or pressure switch monitoring for SF6 pressure (or there is only a simple pressure gauge indication, and this gauge sometimes fails). The actual operation shows that although the imported equipment has good sealing performance, air leakage also occurs. Since there is no gas monitoring device, the user does not know if there is a gas leak, which can minimize the heat generated by the hydraulic system and easily become a potential accident hazard

b) for such products, they will be able to charge at the speed of lightning - the type test of products in the order of seconds or minutes, even the products of large companies are often not done well, especially the performance (insulation, switching, etc.) and durability under zero gauge voltage