Six kinds of problems in the operation of distribution box

  Outdoor low-voltage power distribution box (hereinafter referred to as “ distribution box ”) It is a low-voltage distribution equipment used to receive and distribute electric energy in 380/220 V power supply system
It is generally installed at the low-voltage side of distribution transformer and other places
The box is usually equipped with fuses, leakage protectors, lightning arresters and other protective appliances, contactors, circuit breakers, load switches, disconnectors and other control appliances, current transformers, electric energy meters and other measuring appliances, capacitors and other compensation equipment
With the implementation of urban and rural power grid construction and transformation projects, the widespread use of distribution boxes, the continuous increase of social power consumption, some problems in operation have been exposed, which should be paid attention to
1
The service life of electrical equipment in the distribution box decreases due to high temperature   The upper limit of the ambient temperature of the electrical equipment designed and manufactured according to the national standard during operation should not exceed 40 ℃, while the temperature of the operating distribution box exposed to the hot sun in midsummer sometimes exceeds 60 ℃ due to the direct sunlight, the reflection of the heat of the cement ground and the heat generated by the equipment in the box itself
Such a high temperature can easily cause the insulation aging of electrical coils and leads to breakdown and burnout; The contact resistance of electrical contacts increases due to high temperature, and the increase of contact resistance intensifies heating
Such a vicious cycle eventually leads to contact burnout; At the same time, too high temperature will also affect the stability of electrical protection performance, the reliability of action, and the accuracy of measurement
For this reason, it is suggested that: (1) distribution boxes with shutters on both sides and incomplete separation in the middle should be selected as far as possible to form air convection and heat dissipation; (2) The box body shall be made of natural color stainless steel as far as possible, which is not easy to rust and has heat reflection effect
If the coating with heat insulation performance can be sprayed regularly to reduce heat radiation, the effect is more ideal; (3) In addition to ensuring ventilation, the box should try to avoid direct sunlight at noon, and the ground should be non gravel; (4) Avoid overload operation of equipment in high temperature season, and try to reduce the heat released by the equipment in the box 2
Only install lightning arrester on the incoming side, and lightning protection cannot cover the whole equipment   Usually, fuses and other equipment are installed between the incoming and outgoing lines of the distribution box and its bus
When the outgoing line is struck by lightning, if the incoming fuse is blown first, then the whole distribution box will lose lightning protection, and many distribution boxes are damaged by lightning every year It is recommended to install zinc oxide arresters at the inlet and outlet sides of the distribution box
3
Improper use of products increases the failure rate of distribution box   It is recommended to select high-quality low resistance products (such as low resistance fuses), which can not only reduce the loss, but also reduce the heat accumulated in the distribution box and prolong the service life of the equipment
In addition, the safety margin of some equipment should be appropriately increased
Due to the high ambient temperature in the box, the margin of conductor ampacity should be enlarged by one more specification; Without changing the rated current of the fuse, if the size of the fuse is appropriately enlarged, the probability of its base burning out will be reduced
4
Improper installation process causes overheating and burning loss of the connector   Some electricians do not press the wiring nose when replacing the lead, but use multi stranded wires to wind the wiring nose and screw it
As a result, the lead is burned out soon after changing the wire
The distribution boxes produced by some manufacturers are overlapped and bolted on the bus, so the heat dissipation is not good, and the load is heavy, which naturally causes continuous faults It is recommended to install a branch line at the load side of the bus, and each branch line is led out by the branch line, which is not only conducive to heat dissipation, but also beautiful, clear and easy to fix
5
The distribution box is put into use without inspection, leaving hidden dangers for safety   Although the products provided by the equipment manufacturer have been strictly inspected before leaving the factory, due to the bumpy road and loading and unloading vibration, some connecting bolts may be loosened to a certain extent after they are transported to the site, resulting in overheating of the lead joints of some distribution boxes shortly after they are put into operation It is recommended to check and retighten before putting into operation
6
Other problems   The improper installation position of the distribution box will not only affect the appearance of the city, but also be vulnerable to external forces
It is suggested to comprehensively consider and select the appropriate installation position Some power supply systems with protective neutral connection still adopt the three-phase four wire power supply mode
The zero line of low-voltage power grid is long and has large impedance
When the three-phase load is unbalanced, the zero line will have zero sequence current passing through
At the same time, due to environmental deterioration, wire aging, moisture and other factors, the leakage current of the wire also forms a closed loop through the zero line, resulting in a certain potential in the zero line, which is very detrimental to safe operation
Three phase five wire power supply mode is recommended
Since the working zero line and protective zero line connected to the electrical equipment are laid separately, which can effectively isolate the dangerous voltage caused by the three-phase four wire power supply mode, the shell of the electrical equipment is always at “ Ground potential ”, So as to eliminate the hidden danger of dangerous voltage generated by the equipment The spacing of distribution boxes is too small, the gap between electrical appliances and between phases is small, and some have no obvious disconnection points, which not only brings danger to electricians' operation, but also makes it impossible to replace fuses with electricity in rainy and foggy weather; The distribution box is generally lack of phase failure protection, and the motor is burned out due to phase failure from time to time; Some distribution boxes do not use electronic watt hour meters, so it is impossible to implement remote centralized meter reading; Some distribution boxes are closed all year round, lacking routine maintenance Manufacturer of distribution cabinet: http://www
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