In recent years, 10KV distribution transformer protection and control of the selection switch, because of load switch - in comparison with the circuit breaker fuse combinations of simple structure, convenient operation and maintenance, low cost, reliable operation, etc.
, So that the combination of electrical access to a wide range of applications. In practice, how to choose the right combination of appliances, load switch, fuse and transformer how reasonable matching parameters, is related to the ability to play the role of combination appliances,
Ensure the safe operation of the system's key issues.
1, the transfer current calibration
The combination of the three-phase electrical melting fuse melt with the time difference, three-phase fuse in one phase First off, the impactor moves, this time may be the other two phases have not yet put out the fuse breaking arc, while the impactor attack formation
Fault current from the load switch off phenomenon, which was originally undertaken by the fuse breaking tasks transferred to the load switch commitment. Therefore, current is the transfer of load switch fuse with the conversion functions of the three phase current. Less than
The value, the first open phase current from the fuse breaking, the other two-phase current from the load switch breaking. Greater than this value, the three-phase current is breaking from the fuse. Transfer current is that we should pay attention in the selection of a combination of heavy electrical
To index, if used properly, can bear the load transfer switch current is not enough to afford the two-phase short-circuit breaking current task switch caused the explosion.
Load switch is usually divided into two general types and frequent type, with air as gas insulating medium pressure gas type and general type of load switch, vacuum and SF6 load switch as frequent type, a different load switch, the transfer current means
Standards vary, the general-type load switch current in the transfer of about 800 ~ 1000A, frequent patterns of up to 1500 ~ 3150A.
Different distribution transformer capacity, the corresponding transfer current is not the same, the actual transfer of the current estimate by the capacity of the transformer. General S9-800ö10-type distribution transformers transfer current of 978A.
And in accordance with the definition of transfer current load switch-off time and features an open, load switch to avoid the transfer current maximum short circuit current, control 70% of the maximum short circuit current is less than the actual transfer of current is about 978 × 70
% = 685A. Made in the analysis of the load switch and fuse on the basis of technical coefficients, taking into account the discrete nature of the product, according to transfer current checking results to the experience of a city, within the capacity of 800KVA transformers, can be
Choose the general type of air insulated load switch, the capacity in the range of 800 ~ 1250KVA transformers, vacuum or SF6 insulated generally used frequent type of load switch. The transformer is larger than 1250KVA be selected off
Breaker protection and control. From a combination of electrical appliances for many years running the city situation, safe, reliable, good condition, there has not been an accident due to improper matching.
2, matching the transfer of current indicators
Partakers of certain load switch with shunt trip for overload protection trip with an overload protection means that when the load through the trip without burning fuse switch, fuse for short circuit protection only. Action by the shunt release
The operating characteristics for the relay and fuse time - current characteristic point of intersection called the "transition current." Current is a transfer of over-current value, lower than the current over-current transfer from the shunt trip action to make the load
Switch off, higher than the transfer of current, the fuse protection action. Optional parameters for this transfer of high current load switch, which can effectively reduce the number of fuse action, thus greatly reducing the number of replacement Fuse
It has some technical and economic significance. For vacuum and SF6 load switch, the transfer of relatively higher current value, can improve the transfer of current close to the transfer of current to full load switch such as a frequent
The advantage of breaking ability.
3 Matching limiting fuse
In the load switch - fuse combinations, the load switch is responsible for the normal current or transfer current breaking, fuse overload current and short circuit assumes current breaking, breaking capacity of two appliances complement each other, can be successfully
Completely breaking task, so the matching is critical limiting fuses. Limiting fuse selected should have high breaking capacity, the minimum breaking current, low operating temperature, time - current characteristic curve steep error curve
Poor and small properties. Aging should also be met, the installation forms, dimensions and other requirements appropriate. It should be noted that when the ambient temperature of 40 ℃, the power loss breaker shall not exceed 75W.
Selection of fuse, the fuse's rated current to match the capacity of the transformer. Some people think that a large selection of fuse rated current is safer is wrong, it will not only lead to economic waste, but also fuse
"Time - Current Characteristics" worse, protecting a decreased rate of correct breaking fuse protection.
4, should pay attention to other issues
(1) For more than parallel operation of the system of distribution transformer, in the selection of combination of electrical current when particular attention to the calibration transfer problem, as mentioned earlier in the checksum calculation, if the same for the two models side by side of distribution transformer capacity run, false
Such as the transformer secondary terminals short-circuit, this time only a single transformer impedance will change the system with half the high side so that the maximum three-phase short-circuit current to double current transfer should be possible also will be doubled.
So for more than one distribution transformer parallel operation of the system should be used when the combination of transfer electrical current checking and transfer of current indicators used to meet the requirements of the combinations.
(2), one of the following requirements, the combination of electrical shunt trip shall be configured to achieve fast load switch power sub-gate:
① need to set the protection of the heavy gas oil immersed transformers. Under normal circumstances, the capacity of 800KVA and above the heavy gas oil-immersed transformers shall be provided with trip protection.
② dry-type transformers tripping over temperature protection.
③ dry type transformer with cover open error live tripping protection.
④ with remote operation control requirements.
In short, on the load switch - fuse combinations of selection should be based on actual use cases, in accordance with the transformer capacity and the operation mode of the load switch with all kinds of technical parameters and breaking capacity, to strike a transfer current
And the transfer of current to the load switch, fuse and transformer reasonable matching parameters, and thus make the right choice switchgear to ensure safe and reliable operation of electrical appliances combined.
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