[application of box-type substation in agricultural network]: the gradual implementation and development of dispatching automation system of agricultural network have promoted the construction of unattended substation, and in the construction of 35kV unattended substation, box-type substation is more and more favored.

Box substation (hereinafter referred to as box substation) has many obvious advantages, such as, small area, construction...

The gradual implementation and development of automatic dispatching system of agricultural network have promoted the construction of unattended substations, and in the construction of 35kV unattended substations, box-type substations are favored by more and more people.

Box substation (hereinafter referred to as box substation) has many obvious advantages, such as, small area, short construction cycle, flexible configuration, etc., but in practical application, there will be some problems.

1. Reasonable allocation

According to the actual situation, different box transformer configuration schemes can be adopted. In general, oil charging equipment such as main transformer and capacitor can be placed outside the box body. Two boxes, one 35kV box body and one 10kV box body can be set.

To save money, 35kV circuit breaker and other equipment can be placed outdoors and only 10kV box body can be set.

The base and frame of the box body are generally welded with channel steel and Angle steel, and the top cover and four walls are pressed with flame retardant materials lined with metal plates, which can play the role of heat insulation.

According to the local actual situation, the main structure of the order can be put forward corresponding requirements.

Our county is located in the salt and alkali zone, the corrosion resistance of the equipment is required to be higher, so in addition to the main frame of the anti-corrosion process, the overall outer lining plate of the box body adopts a 0.5mm thick stainless steel plate.

When considering the structure of the box body, should focus on some special parts, such as the switchgear in 35 kv box change many adopted handcart form, handcart in and out of the body has enough strength requirements, to ensure its smooth operation, if the enclosure in the handcart, produce large deformation, not only operating easily, may also appear handcart switch position response anomaly such as a series of problems.

Maintenance corridor is an important link in the normal operation and maintenance of the box, a defect of the box is narrow space, manufacturers from the cost and equipment compactness, maintenance corridor is generally compressed as far as possible.

Maintenance corridor should be considered as an index in the selection of model, otherwise it will cause great trouble to the future operation and maintenance.

The sealing and dustproof of the box is an important aspect, especially the protection device has higher requirements on dustproof and other indicators, which should be paid attention to.

The bottom plate of the box body is generally used as the cable room. When considering the design of the box body foundation, the installation and maintenance convenience of cables should be taken into account, and the requirements of personnel access, ventilation and lighting should be taken into account.

2. Device selection

(1) primary equipment of the box:

(1) the box changes the equipment, should be no oil, no maintenance or less maintenance equipment is appropriate.

Vacuum circuit breakers may be used for circuit breakers, and dry equipment shall be used for current transformers, voltage transformers and station transformers.

(2) due to the small space inside the box change, the actual operation of the grounding wire is very inconvenient, so many box change in the switch cabinet unit installed a grounding switch, but due to space constraints, some box change manufacturers will grounding switch and isolation switch adopted the form of linkage, open the isolation switch, the grounding switch is closed;

Close the isolation switch, then the ground switch is opened.

In actual operation, this operation mode will bring a lot of trouble when executing existing procedures, and the operation mode of equipment is not clearly defined.

If possible, a separate grounding switch will make it more flexible and convenient to operate.

(3) box change in the five anti locking is an important aspect, in the selection, to consider the isolation switch between the mechanical locking and electrical locking, see if it can meet the needs, and reliability can meet the requirements.

(4) box change inside the switch cabinet should leave an appropriate observation window, in order to observe the condition of the operation of equipment, in view of the actual needs of operation, in the selection of model, this should also put forward requirements, so as not to bring inconvenience in the future operation.

(2) primary incoming and outgoing wires of the box:

(1) the box change of a line and line can be used overhead or cable.

The use of cable can effectively save space.

(2) selection must be combined with the actual situation, consider the wiring mode of the incoming and outgoing lines, otherwise it is not conducive to the future installation.

(3) due to the box change internal space is limited, the cable head should be generally done under the bottom plate of the box body, through the hole on the bottom plate of the box body to introduce.

According to the requirements of the regulations, the three inlet holes on the metal floor should be connected with each other, so as to avoid eddy current on the metal floor during the cable operation and damage to the equipment.

Some box changes in the design, to this aspect of the requirements of insufficient consideration, will affect the cable installation and operation.

(4) for the 10kV feeder cable installation, if the cable head is done in the box under the floor, the position of the zero sequence transformer should also be considered.

If the zero-sequence transformer is installed above the cable head, the grounding wire of the cable shall not pass through the zero-sequence transformer again, which is different from the normal method of connecting the zero-sequence transformer under the cable head.

(3) protection device in the box transformer.

Box change in the general use of integrated automation device as protection, some box change manufacturers at the same time production of integrated automation device, if the choice of such a box change and protection of integrated products, will bring convenience to the design and construction and debugging, from many intermediate links.

If the strength of the box manufacturers allow, but also to meet our needs, this can yet be regarded as a better choice.

The selection of integrated automation device, to consider the characteristics of box change, and strive for simple wiring, complete function.