A DAY IN THE LIFE OF...


go high impedance (open circuit, which means the load would not be supported in a mains failure), others develop low impedance, which can be far more dangerous. In this situation the increased current generates heat, allowing more current to pass – thermal runaway. The plastic casing melts and buckles, sometimes resulting in a fire. Over the years I can recall at least four occasions where companies have ignored warnings about replacing old batteries and this phenomenon has occurred.


usually when a system is just starting up – after maintenance for example. If the capacitor fails and the cabinet door is open, it can cause injury to anyone nearby.


Following from this, if sites do not have regular maintenance checks, capacitor failure can be a very real risk. In years gone by, you would see a capacitor fail catastrophically this way a few times a year. I’m pleased to say we have all but eradicated this amongst our customers as we encourage changing capacitors every five to eight years (depending on manufacturer and site conditions). Customers often question us as to why we are so keen to do this. I recently conducted a controlled experiment in a safe, cordoned- off outdoor space to show what happened as we slowly applied a DC voltage an old capacitor.


In this


way, we were replicating what would happen when a system was starting up. At a value well below the normal operating voltage, it was quite dramatic; not something you want to happen on a customer site.


twitter.com/TomorrowsHS “I MUST


BALANCE CLIENT EXPECTATIONS WITH REALISTIC


REQUIREMENTS AND PROVIDE THE BEST SOLUTION.”


Like all our engineers, I also conduct a visual check of the UPS system. We often hear of maintenance contractors performing diagnostics remotely; this is not sufficient. Relying only on remote diagnostics can mean some basic and major system issues are overlooked. Visually, I’m especially on the look- out for leaking capacitors, failed or noisy fans, changes to load levels and increased air temperature.


Batteries deteriorate at temperatures over 25 degrees. They can dry out, and while some


One example of a catastrophic failure was at an industrial site in Spain, when I was asked independently to assess a system following a major incident. The damage was so severe it was difficult to identify the initial cause. However, it became clear that cables in the rectifier were loose and had started arcing. As the battery was only protected by a 1000A fuse and not a protective breaker, the battery had continued to feed the arc. This melted the rectifier heatsinks and the continuous high battery current resulted in a large number of blocks literally exploding; fortunately, no-one was inside the battery room at the time.


In the past, I have been asked to perform load tests on UPS systems. Running a battery on full load is a good way to prove it is working, but is always a risk. Gloves, eye protection and avoiding standing in close proximity to the battery are a must. These days, we prefer to use battery impedance testing, which measures the internal resistance of the battery and alerts us to most problems.


When I’m not on a client site, time back at base is spent writing up quotes and dealing with the more awkward power and battery calculations as well as keeping tabs on any other technical challenges. The fact is, anything involving electricity supplies, batteries, cabling and suspended floors can pose a genuine health and safety risk. My job, and that of my engineering team, is not only to protect critical power supplies but also to prevent potential problems, keeping our own and our clients’ staff safe at all times.


www.mpowerups.co.uk 45


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