John Outram, Outram Research Limited
Power quality problems can be caused by many different phenomena and are often difficult to identify. These difficult power quality problems, however, can be very expensive especially when multiple contractors are involved as nobody is keen to take the blame. Sometimes it might feel as if some supernatural force is at work, but with the right equipment trained engineers can identify almost any power quality problem ‘and lay the ghost to rest’.
A particularly challenging power quality problem existed at a pub in Kent. Part of a new development, the pub was a new building that suffered problems with its power supply soon after it opened. After only three months an extractor fan in the kitchen failed, requiring a new inverter, and then a few weeks later the fan itself failed. Subsequently the landlord had to deal with computerized tills going down, lights failing, and the burglar alarm sounding whilst the pub was open.
The pub had a three phase supply, with multiple three phase distribution boards, although most of the systems within the pub ran from single phase supplies. One theory was that there were problems on the incomer. Initially a UPS was installed to supply the computerized tills, which helped to solve the problem of the tills failing. Then a generator was brought in at significant expense to supply the extractor fan, but the generator itself failed. The problem clearly wasn’t straightforward.
Extractor fans are critical to a pub’s operation as any premises that serves food is required to close if the kitchen’s extractor fan fails. So the continual electrical problems meant that the pub often had to close early and unexpectedly and sometimes couldn’t open at all. The landlord even had to deal with people hammering on the door to get in; when the systems were down the pub had to turn customers away. Naturally the brewery wanted this expensive and embarrassing situation resolved quickly, but although the electrical contractor, building contractor and the consultant hired to resolve the problem had ideas of what might be the cause, the lack of visibility of what was happening to the power made it impossible to identify it.
After several particularly awkward days, Outram Research was called in to deploy its power quality analysers to monitor the supply and analyse the results.
While the initial monitoring was taking place the speculation continued. For instance a number of electrical systems were installed on the roof of the pub, one of which was a distribution box that turned out to be letting rain in. Disappointingly for the speculators (but possibly not for the provider of the distribution box) once the leak was fixed, the erratic power quality problems continued.
In general the power quality was good, apart from these major events that happened around once a week.
The Outram power quality analysers were ideally suited to identifying such a rare event, as they don’t require thresholds to be set, but rather record the most “interesting” events that happen on the supply. Eventually 10 loggers were deployed at the pub, giving a very detailed view that allowed the problem to be narrowed down step by step to the public access distribution board. Patio heaters were supplied from this board, and quickly fell under suspicion as they drew a current spike of 130A for 0.5s when first turned on. Despite this high inrush current, the data from the loggers showed there was no correlation between the heaters turning on and the power quality problems that were seen.
At this point the jokes made by the staff about the pub’s poltergeist began to take on credibility. The electrical contractor was sure that the quality of the installation was good, yet without identifying the root cause, it was impossible to prove his team had done its job well.
But matters took a more sinister turn as the brewery began to consider seriously the possibility of sabotage.
Security cameras were already installed at the pub but so far they failed to show any wrongdoing. However the Outram analysers went on providing more information about the problem. The breakthrough came when short power outages were identified that could only be due to the operation of a particular circuit breaker. The recorded data showed however that the power was restored within a couple of seconds. How could a circuit breaker trip and then be switched back on so quickly? It was inconceivable that someone would be able to realize a problem had occurred and restore the power in such a short time; people simply weren’t likely to be near the distribution board.
The analysers provided a valuable insight into the problem by revealing that the three phases went out in sequence. By examining the data for the sequence and timing of breaking and restoration of the power at different points in the pub, then comparing this to the effects of deliberate controlled manipulation of the relevant breaker, it appeared likely that the faults occurring were due to manual disconnection at that breaker. The contractors subsequently confirmed there was no automatic restoration process.
With this information, and the knowledge that the problem was associated with the public access distribution board, the security camera footage was reviewed again. Although the cameras did not cover the distribution board, they did cover a nearby door. From the opening and closing of the door, they were able to confirm that someone was in the vicinity of the board each time the problems occurred. Although the individual could not be identified from the camera, the brewery was able to reconcile the times of the fault incidence with the presence or absence of staff elsewhere.
Once staff changes had been made, the pub reopened and the power quality problems were not encountered again.
Sabotage is often one of the most difficult causes of power quality problems to identify, but can still be incredibly costly. Not only had the brewery lost money and good standing with their customers through the pub being closed, and arbitrarily, but the contractors and consultants involved stood to lose their good reputation with the brewery and might not have been awarded contracts in the future. By the use of power quality analysers, the ‘ghost’ was ultimately identified and the reputations and business of everyone involved remained intact.