European-style Cable Branch Box and American-style Cable Branch Box

The plug-in devices currently used in the high-voltage cable distribution box in our country are divided into two series: European and American. European-style devices refer to the cable connection concept of outdoor box-type substations introduced from Europe in the 1980s to the field of cable branch boxes, and American devices are the plug-in concept of the seat-mounted box-type substations imported from the United States in the 1990s. Refer to the cable distribution box.

1 The difference between European-style devices and American-style devices

There is no clearly defined boundary between European and American devices, and the understanding of people in the industry in my country is also inconsistent. They are slightly different in performance and price, and it makes sense for the selection work to clarify the difference.

1.1 The insulation structure of the device is different

The conductors of American devices are surrounded by three layers of rubber. The innermost layer is a semi-conductor shielding layer, the middle layer is the main insulating layer, and the outermost is a semi-conductor shielding layer with constant grounding, so it is called a shielded type and the price is slightly higher. The outer surface of the European-style device is wrapped with two layers of rubber, and there is no outermost ground layer.

1.2 The concept of branch circuit connection is different

European-style devices adopt a series branching method, that is, a number of silicone rubber insulated T-type devices are connected in series from the short arm direction one by one to form the main circuit, and branches are drawn from the long arm of each T piece. There are some shortcomings in this series branching method: if a T-piece branch circuit fails, then the series component must be untied, and the faulty T-piece must be removed and re-assembled before it can continue to run. Once the fault processing is over, the component needs to come again. It is troublesome to disassemble and reorganize at one time; the main circuit has many series connections, which affects the reliability of conduction and reduces the dynamic stability; when there are many series connected components, it is difficult to maintain the axis on the same straight line, causing some joint interfaces to deviate from the normal position , The dielectric strength of the interface and the ability to prevent water seepage will be reduced.

The American device adopts the parallel branch mode, which just overcomes the above-mentioned shortcomings of the series branch. Parallel branch is to fix a group of (three-phase) insulation device called busbar board on the box wall of the branch box, which acts as a busbar. There are a number of external cone-type connectors connected in parallel on the busbar board, regardless of the incoming line, outgoing line, branch line, etc. cables are all connected to the busbar board. The internal conductor of the busbar board is silver-welded, and the conduction is reliable, but the three-phase distance is larger, the phase cable is more difficult to bridge, and the three-phase busbar board is arranged in a row to make the length of the box larger.

1.3 The cone taper of the mating surface is different

The European style matching taper is designed according to German standard DIN47636, and the taper is small; the American style matching taper is designed according to the American standard IEEE386, and the taper is slightly larger. The difference in matching taper will bring about the following two differences:

a) The creeping dielectric strength of the bonding interface between the devices is different. The insulation strength of the bonding interface increases exponentially with its pressure rebound force. Silicone rubber has high elasticity, and the tighter the pressure, the higher the insulation strength. With a larger taper, the rebound force will be greater and the insulation strength will be higher. Therefore, the US-style interface insulation strength is greater than that of the European style.

b) Different anti-seepage ability. The greater the matching taper, the tighter the interface rubber material is pressed, and the better the water seepage resistance. Therefore, the water seepage resistance of American-style devices is slightly better than that of European-style devices.

4 Principles of distinguishing between European-style devices and American-style devices

Among the domestically produced plug-in devices, some manufacturers mix European and American structures with each other, which is difficult to distinguish. The following three basic concepts will help us make judgments:

a) From the perspective of the branch structure of the plug-in device, the parallel branch is the American cable branch box, and the series branch is the European cable branch box.

b) From the perspective of the insulation structure, the device with three layers of rubber (inner shielding layer, main insulating layer, and outer shielding layer) is American, and the device with two layers of rubber (inner shielding layer, main insulating layer) is European. As for those devices that use a spraying method to cover a layer of semi-conductive film on the outer surface of the two-layer rubber, because the semi-conductive thin layer is easily worn off during installation or use, the grounding performance is unreliable, and it cannot be regarded as a shielded type. It is a European-style device.

c) The size of the taper of the device’s matching cone surface cannot be used as a basis for discrimination. Because the taper size is only a geometric size issue, it only involves dielectric strength and anti-soaking ability. Regardless of European or American insulating devices, the matching taper can be designed according to American standards or German standards, so that American tapes and American tapes will appear. Different types of devices such as European cone, European cone with European cone and European cone with American cone.