In switchgear and control equipment, in order to achieve full insulation and full working conditions of the equipment

Insulation of bus

 

In switchgear and control equipment, in order to achieve full insulation and full working conditions of the equipment, reduce external short-circuit accidents and prevent electric shocks and prevent creepage caused by condensation and pollution. Insulating materials are generally used outside the busbar to cover the exposed part of the busbar. Bound. The main methods are insulated thermal shrinkable tube (or air shrinkable tube) and busbar vulcanization. The low-voltage busbar is mainly composed of insulated PVC tube.

The busbar insulation material is an insulating medium that cannot be recovered once it is damaged. Even an accidental overvoltage event may cause permanent damage. In the long-term use of bus insulation materials, it will encounter various situations, such as discharge accidents, and the insulation material itself will accelerate it due to various factors such as thermal stress, temperature, mechanical shock and other stresses accumulated over a long period of time. Aging process. In terms of insulating materials, due to the variety of varieties, although there are many indicators to measure the characteristics of insulating materials, they are not uniform. This brings certain difficulties to the selection and use of insulating materials, which is why other characteristics of insulating materials, such as thermal stress, mechanical properties, partial discharge, etc., are currently not considered from the international perspective.

In the structural design, it is not possible to simply use busbar insulation to ensure the factory power frequency withstand voltage test. Because there is no reliable insulating material that has passed the anti-aging test, the operating state is not the steady state that is imagined. The aging and failure of the insulating material will put the equipment in a dangerous state of poor insulation. According to Montsinger's rule T=Ae-mt, where:

T---Insulation material life (weeks)

A, m---The coefficient determined by the insulating material, for class A insulating material, A=372×104, m=0.368;

————Working temperature (C°)

The theoretical life of the insulating material will change with the temperature rise every time t=10C°, its life will be reduced to half of the original.

Bus support and fixation

(1) The support of the busbar must fully consider whether its bending strength meets the force effect requirements of the configured system.

(2) The bus bar is generally fixed with metal fittings, and bolts are not used to directly punch holes in the bus bar.

(3) When the insulator used to fix the busbar is subjected to large electric power (such as when the system rated peak withstand current is more than 40kA), it is necessary to verify whether the flexural strength of the insulator meets the requirements of structural design.

The verification of the force effect of the insulator can be as follows:

Fjs≤0.6Fph

Fjs=1.76KLich2×10-2/a

In the formula: Fjs-stress acting on the insulator, kg;

Fph—Bending strength of insulators copper bar bender, relevant samples can be checked;

L-span between insulators (support distance between busbars) (cm);

A—the distance between each other (cm);

Ich—rated peak withstand current (KA)

(4) Busbar clamps and fixed fittings should also be able to withstand the forces caused by the rated peak withstand current.

(5) The fixed fittings or other supporting fittings of the bus bar should not form a closed magnetic circuit.

(6) When the bus bar is horizontal, the upper pressure plate of the bus bar support plate should maintain a gap of 1-1.5 mm with the bus bar, and when the bus bar is standing, the upper pressure plate should maintain a gap of 1.5-2 mm with the bus bar.

(7) Between multiple rectangular bus bars, a gap of not less than the thickness of the bus bar should be maintained.

(8) The metal plywood (except fasteners) at the end of the wall bushing of the busbar of 600A and above should use non-magnetic materials, and there should be metal connection between the busbar and the contact should be firm, and the thickness of the metal plywood should not be less than 3mm When the bus bar is two or more, the bus bar itself should be fixed.

(9) The fixation between the busbar fittings and the post insulator should be flat and firm, and the busbars supported by it should not be subjected to additional stress.