Whether in the ring network power supply unit, box-type substation, or the end user's end-line high-pressure chamber, such as distribution transformer short-circuit fault occurs, the configuration can be quickly and reliably protect the removal of faults, the protection of 10kV high-voltage switchgear and transformers are very important. Protection mode configuration there are two: one to use circuit breakers; other is increasing the height of the load switch interdiction capacity back-up current-limiting fuse combination. These two configurations in the technical and economic advantages and disadvantages, the following two ways this comprehensive comparative analysis.
A ring form of power supply unit wiring
1.1 Composition of Central power supply unit
Central power supply unit (RMU) from the interval, generally at least 3 intervals, including two rings out of cable and a transformer circuit spacing interval.
1.2 ring configuration protection mode power supply unit
Loop feeder cable feeder and transformer load switch intervals are used, typically with a turn, cut off and ground features three-position load switch. Transformer feeder interval also increases high-breaking capacity back-up current-limiting fuses to provide protection. Actual operation proves that this is a simple, reliable and economical distribution methods.
1.3 Ring power supply unit configured to protect the characteristics of
Cut-off switch for the rated load of the load current, with a simple, cheap, etc., but not short-circuit breaking current, high breaking capacity back-up current-limiting fuses for the protection of components, can short-circuit breaking current, such as the two organic together to meet a variety of distribution systems under normal and fault operation mode operation protection requirements. Circuit breaker to determine the parameters and structure are designed and manufactured in strict accordance with standard requirements, operation and protection of both two functions, so its structure is complex, expensive, large-scale use impractical. Extensive use of RMU heightened interdiction capacity back-up load switch fuse combination unit, the operation of different appliances with protection by two simple, inexpensive components to achieve, that is complete with load switch to a high incidence of All sub-load operation, and high breaking capacity fuse back-up current-limiting devices on the rare short-circuit protective effect, a good solution to the problem, can avoid the use of operating complex, expensive circuit breakers, but also to meet actual operation needs. Three kinds of protection the technical configuration - economic comparison can be seen:
a) protection circuit breaker with function and operation of all functions, but are expensive;
b) load switch and circuit breaker performance is basically the same, but it can not short-circuit breaking current;
c) increasing the height of breaking capacity back-up load switch-type current-limiting fuse combination, you can disconnect the short circuit current breaking capacity fuse parts than the circuit breaker is higher, hence the use of load switches heightened interdiction capacity back-up current-limiting fuse combination poor than circuit breakers, but the cost can be greatly reduced.
1.4 increasing the height of breaking capacity back-up load switch fuse combination of advantages
Increasing the height of cover capacity using load switch fuse combination, has the following advantages:
a) opening and closing of the transformer no-load performance. RMU load types, the vast majority of distribution transformers, the general capacity of not more than 1 250 kVA, rarely up to 1 600kVA, distribution transformer no-load current is usually about 2% of rated current, with a larger power transformer no-load current is small. Ring opening and closing cabinets small transformer no-load current, good performance, does not produce a higher over-voltage.
b) effective protection of distribution transformers, especially for oil-immersed transformer, with heightened interdiction capacity back-up load switch current-limiting fuse type is more effective than the use of circuit breakers, and sometimes even the latter does not play an effective protection. The data indicate that when the oil-immersed transformer short-circuit fault occurs when the pressure increases and the arc generated by the formation of bubbles of gas will occupy the space originally part of the oil, the oil pressure will be passed to the transformer tank body, with short-circuit condition continues, the pressure further increased, resulting in deformation and cracking of the fuel tank. In order not to damage the fuel tank body must be removed within 20ms fault. Such as the use of circuit breakers, relay coupled with its own due time and the extinction time for action, the full-off time is generally not less than 60ms, which can not effectively protect the transformer. The high breaking capacity fuses back with the speed-limit-off function, with a limiting its role in the removal of fault within 10ms and limit short-circuit current, which can effectively protect the transformer. Therefore, high breaking capacity should be back-up current-limiting fuses and circuit breakers do not try to protect the appliances, even if the load is dry-type transformers, fuse protection action for fast, better than the circuit breaker.
c) From the relay co-ordination is concerned, in most cases, there is no need for the use of the ring counter circuit breakers, this is because the first ring-side circuit breaker distribution network (ie, 110kV or 220kV substation of 10 kV feeder outlet circuit breaker) protection settings generally: instantaneous protection time for 0 s, over-current protection time for 0.5s, zero-sequence protection time for 0.5s. If the RMU used circuit breakers, even if the setting time of 0s action, due to the inherent circuit breaker operating time dispersion, it is difficult to ensure that the circuit breaker in the ring counter and not on a circuit breaker first action.
d) high breaking capacity back-up current-limiting fuses can be received after their equipment, such as current transformers, cables, etc. can provide protection. High breaking capacity fuses back-limit the scope of protection in the minimum melting current (typically fuse rated current of 2 to 3 times) to the maximum breaking capacity between. The current-limiting fuse - time characteristics, is generally steep inverse curve, short-circuit occurred, in a very short period of time fuse, removal of fault. If the circuit breaker for protection. Will enable other electrical appliances such as cable, current transformer, the transformer casing and other components of the substantial increase in thermal stability requirements, increased cost of electrical equipment, increasing the cost of the project.
Here, it is necessary that the introduction of increasing the height of breaking capacity back-up load switch fuse combination, to be a good match between the two, not three-phase fuse when the fuse when the firing pin to make the load switch fuse together immediately jump, to prevent missing running.
2 forms of end-user connection hyperbaric chamber
Standard GB 14285-1993 "relay protection and automatic safety device technical regulations' requirements, select the distribution transformer protection switching device, when the capacity is equal to or greater than 800kVA, should be used with circuit breaker protection devices. For this requirement, can be understood as based on the following two requirements:
a) distribution transformer capacity of 800kVA and above, most of the past use of isolation transformer, and is equipped with a gas relay, the relay using the circuit breaker can be compatible with gas, and thus the effective protection of the transformer.
b) For installations larger than 800
kVA of users, due to various causes result in single-phase zero-sequence ground fault protection action, so that circuit breaker tripped, separating failure, and will not cause the main substation feeder circuit breaker action, affecting other users of the normal power supply.
In addition, the standard also stipulates that even if this does not meet a single transformer capacity, but if the user's total capacity of distribution transformers 800 kVA, we have to meet this requirement.
Currently, most users of high-voltage power distribution room wiring scheme is the basic knot-line, on this basis can be a preparation derived from a main line or double line plus bus section, etc.. Circuit breaker is generally installed at A, B Department also installed in the circuit breaker, so that, depending on the relay is configured, you can use A or B to GB14285-1993 "relay protection and automatic safety device technical regulations," the two a requirement, in which a low Voltage Transformer need to quit running, the operation B can be realized at the circuit breaker.
According to the theory and field trials, in the B fuse as a protection device installed at a more reasonable and effective. I believe that, in the B at the height of load switch should be installed back-breaking capacity fuse combination, circuit breakers installed at A, both to GB14285-1993 "relay protection and automatic safety device technical regulations' requirements, and fuse installed at B as white short-circuit protection for each transformer, and the load switch can be used for each switching operation of the transformer, so the B is not commonly installed at the loading ring switchgear but switchgear, its low cost, small size, can effectively save power distribution investment. In addition, if the deal with the transfer of the load switch and fuse current and the transfer of current choice, not out of the B at each load switch with transformer zero-sequence corresponding to the possibility of protection.
3 Conclusion
10kV distribution transformer main circuit breaker protection configuration, load switch or load switch plus fuse, comprehensive technical - economic performance and operational management factors, both in the 10kV ring network power supply unit or in high-voltage power distribution unit end-user, using increasing the height of breaking capacity back-up load switch current-limiting fuse combination type protection configuration, can provide the rated load current, short-circuit current can be disconnected and with the opening and closing the performance of no-load transformers, distribution transformers can be effectively protected, this , recommended increasing the height of breaking capacity back-up load switch current-limiting fuse combination type configuration as a distribution transformer is protected.