What is an explosive compound in the energy sector? 

BB connection is not just “some kind” contact in a cable line, and often the weakest link, which either provides decades of trouble-free operation or becomes the cause of an unscheduled outage. Many people think that this is just a “coupling”, but in practice it is a whole system where there are no trifles.

What is hidden behind the abbreviation BB?

When they sayBB connection, usually mean a connection for cables with impregnated paper insulation for a voltage of 6-10 kV. Letters ?ВВ? - this is an “inner sleeve”, to put it simply. But the point is not in the title. The main thing is a sealed transition from one core to another, which must withstand not only operating currents and voltages, but also thermal expansion, mechanical loads in the trench, and, critically, prevent access of air and moisture to the paper insulation. If the insulation begins to “breathe”, it’s a disaster—moisture leads to aging and breakdown.

At one time, we came across a batch of connections where the problem was not in the main body, but in the sealing system. It would seem like a small thing - rubber cuffs. But the supplier saved on the material, and six months later partial discharges began in the raw collector. Diagnostics showed increased humidity inside. We had to open and redo dozens of units. This is the case whencable accessoriesfrom ?consumables? become a key element of reliability.

By the way, about suppliers. Not all manufacturers understand what they are dealing with. I have seen supposedly “analogs”, where instead of cast epoxy insulation they used composite shells that were not designed for long-term heating from the core. In theory, everything fits; it is being tested on the bench. But in real soil, with a constant load close to the maximum, peeling begins after a year or two. Therefore, now we always look not only at certificates, but also at real experience of application in similar conditions, for example, from colleagues with thermal power plants.

Design: where the pitfalls lie

ClassicBB connection- this is a steel or brass housing into which the end of the cable is inserted. The core is connected by crimping or welding. Then all this is filled with a compound - usually a mastic based on petroleum bitumen or modern epoxy compounds. Here is the first nuance: preparing the surface of the core. It must be thoroughly cleaned of any remaining impregnating mass, but not damage the wires themselves. If the film remains, the contact resistance will increase and the point will heat up.

The second point is filling. It would seem that I filled it in and forgot about it. But if you pour it at a low temperature into an unheated housing, air bubbles or, worse, non-spills will form in the mastic. The cavity must be filled monolithically, without cavities. Otherwise, partial discharges will begin in these voids over time, which will slowly but surely destroy the insulation. I myself saw such “caves” at the autopsy. inside, filled with soot from discharges.

The third stone is thermal cycling. The cable heats up under load and the connection expands. The load drops - everything cools down and contracts. Over the years of such cycles, poor quality filling or ill-conceived design can cause microcracks. Moisture is sucked in through it. This is especially critical for cables laid in areas with high groundwater levels. Here we already need solutions with additional sealing shells, maybe even double ones.

From practice: a case at a 35/10 kV substation

A good example is the story at one of our old substations. 10 kV cable line from the power transformer to the 10 kV switchgear. The connections were made twenty years ago, using the technologies of that time. Last year, zero-sequence protections started tripping—a clear sign of insulation breakdown to ground. A search with a portable partial discharge detector yielded nothing - the background was high. We decided to turn off the lines step by step.

In the end, the ?culprit? it turned out justBB connectionin the end coupling. Upon opening, we saw a picture: the paper insulation at the end of the cable was dark, fragile, and obvious overheating. The reason is poor contact at the crimping point of the tip. Apparently, during installation they used the wrong tool or the dies were already worn out and did not produce the required pressure. The contact resistance was increased, the point was heated, the insulation aged and, as a result, carbonized. It’s good that it didn’t lead to an interphase short circuit.

After this incident, we tightened control over installation. Now we be sure to measure the contact resistance with a microohmmeter after crimping and compare it with the resistance of the whole core. The difference should be minimal. And, of course, thermal imaging monitoring of all connections after commissioning and during scheduled inspections has become mandatory. A trifle, but it saves thousands on unscheduled repairs and downtime.

Manufacturers and materials: what to look for

The market is now saturated with offers. From cheap ?noname? products to systems from companies such as e.g.Shijiazhuang Hist Electric Co.,Ltd. Their website (histe-ru.com) positions them as a professional manufacturer with patents in the field of isolation switches andcable accessories. This is an important signal for me. If a company invests in development and has expertise in related fields (the same insulators, fuses), it means that most likely they understand the physics of processes in power equipment, and do not just cast housings.

At one time we tried to work with different suppliers. I had experience with very low-cost explosive couplings. Everything looked decent: the case was durable, the equipment was complete. But when installation began, it turned out that the geometry of the internal insulating sleeves did not correspond to the declared cross-sections of the cores. I had to “finish it with a file,” which, of course, is unacceptable for high-voltage equipment. Since then, for critical facilities, we only take products from trusted brands where quality control is at a high level.

Modern materials also play a role. Traditional bitumen casting compounds are gradually giving way to epoxy ones. They provide better adhesion and less creep. when heated, they have more stable dielectric properties. But you also need to be able to work with them: precise adherence to the proportions of mixing the two components, a limited lifetime of the mixture. Automatic dispensers and mixers greatly simplify life, but they cannot be used everywhere, especially in cramped conditions of a cable well.

Editing: an art, not just a job

You can have the perfectBB connectionfrom the best manufacturer, but spoil it during installation. Cable preparation is a ritual. It is necessary to remove the outer shell, armor, and screen without damaging the waist insulation. Then carefully separate the wires and remove the paper insulation from them to a strictly defined length. People often make mistakes here: if you remove a little, the required length for contact in the sleeve will not be provided; if you remove a lot, a section will be exposed, which is then difficult to properly insulate inside the sleeve.

Pressure testing is a separate issue. The sleeve must be of the correct type and section. The tool is certified, with calibrated dies. The crimping force is according to the instructions. If you don’t hold out, there will be a bad contact. If you pinch it, you can bite through part of the wires in the core, reducing its cross-section. I saw how ?experienced? The installers did this with a makeshift hydraulic press without a pressure gauge. The result, alas, is predictable - failure after several years of intense load.

The final stage is assembling the body and pouring. Cleanliness is critical here. Any dust, chips, or moisture inside is a potential discharge center. Before pouring, everything needs to be degreased and dried, sometimes even blown with warm dry air. It is better to carry out the pouring process itself continuously, allowing the mastic or compound to flow down the walls to displace the air. After pouring, wait until complete polymerization. No “let’s speed up the process, turn it on earlier?”. Patience is the main virtue of a power engineer.

Instead of a conclusion: thinking out loud

So what is itBB connectionin energy? This is not just a part from a catalog. This is the point where materials, design, workmanship and human craftsmanship converge. This is a story about how attention to a seemingly minor “muff?” determines whether a cable line will serve its useful life for 30-40 years or become a headache for the next five.

Now, with the advent of cables with cross-linked polyethylene (XPE) insulation, classic explosives for paper cables are gradually becoming a thing of the past. But there are still thousands of kilometers of them in the ground, and they require maintenance, repair, and replacement. And while they exist, knowledge of their “anatomy” and ?physiology? remains critical to any cable or power engineer responsible for networks.

For me personally, working with such compounds is always a bit of alchemy. You need to feel the material, foresee how it will behave over the years. And always remember the old truth: the reliability of a system is determined by the reliability of its weakest link. And in a cable line, this link very often ends up exactly where two cores meet in order to continue the current path further.