Connections in energy storage and security issues

08.11.2021

 

Energy storage is an increasingly hot topic - it is worth knowing what dangers result from the improper connection.

If you are starting to read this article, you are probably interested in the topic of broadly understood energy storage. Maybe you already have appropriate applications on your offer, or maybe you are just recognizing the market when looking for a place to develop your own company in a promising industry. And that's good, because this topic will be ubiquitous in the market, in the media, and even in politicians' talks in the coming years (after all, the country's energy security is an important topic). It will also be undeniably important in the considerations of private users of home photovoltaic installations - since the possibility of "storing" energy in the operator's network is ending, many of them, wishing to become independent, at least in part, from a significant increase in energy prices, will look for the possibility of collecting it directly at home. The following content, however, will focus strictly on the safe use of the warehouse in terms of the device itself - apart from the price of the complete system, the smaller or greater popularity of a given manufacturer's solution will depend on it.

It might seem that making the connection is a trivial matter. There is a plug with a cable, there is a socket - plug one into the other and it's ready. However, let's try to break it down into prime factors and show potential risks.

First of all, let's focus on the initial assembly before commissioning. Energy storage usually consists of several battery modules/packages that we connect with each other - let's use the example in the graphic on the right.

Intuitively, of course, you can see which plug should be connected to which socket (color coding). However, is it enough? Not always. Sometimes the installation can take place in poor lighting conditions, we also never know how good the eyesight is or what the skill and diligence of the installer who took on this job looks like.

Already at this stage, there is (admittedly small, but always possible) the risk of a fatal mistake (e.g. damage to modules). Therefore, it is worth it that the selected connectors also have mechanical coding designed to prevent them from being incorrectly paired. Even if we choose elements with mechanical coding, some surprises may await here as well - it turns out that not every system available on the market allows for any positioning of the plugin in relation to the socket during connection!

Some solutions allow, for example, to connect only to the cable angled downwards. Of course, after connecting, you can turn the cable so that it points towards the next socket, but there again we encounter the same problem - to connect, the cable must also point downwards. The problem seems trivial - it is enough to make longer connection cables with a reserve to bend the whole thing properly. But here, too, there are at least a few disadvantages of such a solution.

First of all - a longer cable means more copper (thick sections are often required due to the high currents flowing through it). More copper means more cost. Multiplied by the thousands of cables that we are to produce and sell, it will effectively make the company's financial department nervous, or at least immediately indicate a possible place to generate savings.

Secondly - thick cables (eg with a diameter of 90 mm² or 120 mm²) are not so easy to bend - you need to put a lot of force into them.

And finally, thirdly - since we have to put a lot of force into something, we indirectly expose some parts of the structure to unnecessary (and sometimes unforeseen at the design stage) stresses that may lead to damage. And as we know from experience, even seemingly small cracks can generate considerable problems over time. After all, we care about the reliability of the system for as long as possible.

Another issue to consider is the secure locking of the connection point. As it is commonly known, each "loose connection" will one day become a source of more or less serious complications: depending on the "importance" of a given circuit (e.g. with signals or data transmission), the currents we deal with (the risk of local overheating) or voltage (sparking and burnout of contacts). Manufacturers design metal contacts in such a way as to obtain the lowest possible resistance after connecting them with the lowest possible pressure forces (ensuring ease of use and durability of galvanic coatings). The additional locking on the connector housing thus assumes all responsibility. And for this reason, it is worth focusing on solutions thought out in accordance with the idea of ​​Poka Yoke, i.e. in this case "connect in an easy way, without unnecessary complicating the operation, requiring additional instructions". And here I will use the graphics on the left again.

As you can see, it only takes one move - pushing the plug into the socket, which will automatically lock. To disconnect, it is enough to move the button located in the plug construction and remove the end of the cable from the socket. The lack of additional elements is an undeniable advantage of this structure.

Comparing the available versions of some manufacturers, they have, for example, an additional locking lever that requires closing. Unfortunately, this leaves room for an installer error, who may skip this step in a hurry or carelessly. Consequences? Risk of a loose connection due to vibration or unexpected/accidental cable tugging, leading to the effects already mentioned above. Therefore, it is also worth paying attention to this aspect when selecting components.

It is also important to protect the live components against accidental contact with a finger or short-circuit, e.g. against the metal housing of the device. Here you should choose only those structures that have appropriate protection (example - left side below). Appropriate design of both the socket and the plug guarantees that the isolated components of the connectors are properly hidden inside the casings. Thanks to this, both the installer and the equipment itself are not exposed to potentially dangerous situations.

A seemingly "easy" thing, such as mounting a plug on a cable, can sometimes turn out to be problematic. Typically, in applications of this type (with relatively large cross-sections and currents), crimp connections are used as the most reliable and durable. It is good if the very process of preparing the cable and pressing does not require too many operations, and the connectors themselves do not consist of too many elements.

To use an example - any additional metal sleeves that we must place indirectly on the stripped conductor before placing it in the terminal's terminal chamber are items that may be overlooked (or lost). And we must be aware that when designing their components, manufacturers designate them for assembly in a specific way that guarantees reliability. So it is better to choose what is easier to install and leaves no margin for error.

You should also take into account the mounting of the socket on the device housing. Is it safer (read: more resistant to possible damage) to screw the square socket flange in each corner, or is the situation where the entire insulation of the element is held on one pin? In the event of mechanical damage to the socket, we can risk all plastic falling off and the complete exposure of the live element, versus the possible chipping of a fragment of the plastic.

As you can see, device designers have many aspects to analyze and take into account when selecting the appropriate components. For this reason, it is worth focusing on companies that have many years of experience in a given field (e.g. connection systems), because they guarantee not only the right quality but also a well-thought-out structure of even newly emerging solutions, meeting the expectations of users (often even unaware of specific threats). And, as it usually happens in life, "the devil is in the details" - not always what at first glance looks similar, has the same refined functionality (we are talking about cheap copies of branded products). Reliability, the safety of installers, and users - these are just bonuses (but very important) that can outweigh the success of the final product in the market.

Source: https://tek.info.pl/

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