Although the MNS low-voltage cabinets, KYN28 middle cabinet mechanism, appearance is similar, but the specific implementation of the project, large to the current specifications cabinet size, small to the transformer indicator and other control circuits may be different.
Switchgear project first need to project how big, how many incoming, incoming transformer capacity, how many outgoing, how many transformer outgoing, transformer out of how much, transformer out of the capacity is how much and so on.
According to the capacity, you can roughly calculate the current how many amperes, short-circuit breaking how big, what special requirements, such as environmental parameters, and then decided to use what type of cabinet, according to the number of in and out of the line can be roughly estimated the number of switchgear, for the middle of the cabinet in general, in addition to in and out of the line switchgear, but also need to be the bus pressure transformer cabinets, a section of buses need to be one, whether you need to measure the metering, metering cabinets are generally required to use two sets of supporting! That is, a metering, a bus lifting, such as some areas into the use of isolation trolley, that is, the lead cabinet, and then the inlet switch through the inlet circuit breaker will be the main bus turned over to the lower part of the cabinet, and then the metering cabinet through the metering of current transformers will be the main bus to return to the upper part of the main bus position, and then followed by the bus pressure change, N outgoing cabinets, and so on.
For more than one incoming line, generally use the sectional form, each section needs the upper lead, incoming switch, metering, voltage transformer and N outgoing cabinets, in addition, between the two sections of the busbar through the busbar contact switch, the busbar isolation cabinets, connect the two segments, each other as a standby. Multiple incoming buses, will be divided into multiple sections, each section is connected through bus link switch, isolation link.
Some of the outgoing lines from the centre cabinet are directly connected to the transformer and transformed to 400V low voltage, which is used for power control and distribution to the next level of loads or distribution box or power box for power loads such as lighting, pumps, etc. through the low voltage switchgear.
There are also through the ring network cabinet further power to the load centre, substation in the cabinet capacity, the number of large, far from the load centre, in the cabinet out of the line through the underground cable connected to the application of the load close to the ring network cabinet, ring network cabinet, the maximum current is generally 630A, the use of two into the form of one or two into the form of more than one out of the power supply, hand in hand, power supply from the two different out of the line of the power supply to ensure continuity of power supply.
Ring network cabinet outlet line connected to the transformer, directly to the load power supply, such as residential power supply, street lamp power supply. Community power supply generally has more than one outlet, such as two into four for six units.
There are also such as construction sites and other temporary power supply through the box variable power supply, box variable is generally equipped with 12kV ring network cabinet, transformer, low-voltage cabinets, ring network cabinet is generally one into one out or two into one out, transformer capacity is generally not large, low-voltage cabinets to the main plastic-case circuit breakers, but also need to be equipped with reactive power compensation.
The number of low-voltage cabinets in the project will be very different according to the type of user, in addition to the conventional inlet, segmentation, reactive power compensation and other switchgear, the number of outlets will be very different, for industrial users, infrastructure, data centres, etc. The difference between the industrial users have a large number of motor circuits, a large number of drawer cabinets, while the capacitor compensation requirements are high, the contactor, thermal relay, soft start and other industrial control products. And for residential power distribution, the number of switchgear is basically fixed, its standardised design of the Chinese network has been defined, commonly used frame circuit breaker out.