The A/C Blew Up the Earth Station

DN Staff

November 29, 2013

4 Min Read
The A/C Blew Up the Earth Station

Problems can always arise with sub-contractors. That was certainly true at the earth station in Kenya's Rift Valley. Building a complete satellite earth station from scratch is a major project involving civil, electrical, and electronic engineering. You have the buildings and all their services, as well as the actual antenna and all the telecom equipment, not forgetting standby diesel generators and water boreholes and septic tanks.

It made economic sense to employ local sub-contractors where possible as it was usually cheaper than shipping everything from the UK.

We employed the local branch of an international air-conditioning company to design and install all the A/C and ventilation systems. Everything seemed to go well at first. The A/C plant was tested and signed off in a timely fashion. We finished the installation and commissioning phase and went "on-air." Then, we started to prepare for the opening ceremony where President Jomo Kenyatta would declare it officially open.

Just a few days before the ceremony, most of us were in the control room when a deep "boom" echoed round the building. The floor shook and the normal background rush of cooling fans slowly died away. The power turned off completely, leaving us in total silence and half-darkness. The sound appeared to have come from the corridor, so we ran to the sliding glass doors that led from the control room. Without power the automatic doors remained shut. We found a screwdriver and pried the doors apart enough to get fingers into the gap, after which a couple of guys were able to slide them far enough apart to get through.

I ran down the corridor to the southern end of the building leading to the stores and various offices. I came to the door to the A/C plant room and noticed curls of smoke coming from the ventilation grille. Mindful of the possibility of fire, I opened the door a tiny crack. It seemed to be just acrid white smoke and no sign of flames, so I cautiously peeped into the room.

As the smoke cleared, I could see the far wall of the room which supported half a dozen big control cabinets and switch boxes. Most of the front panels had been blown off and some were still swinging, hanging at crazy angles from broken hinges and festooned with dangling wires. Below the cabinets was a run of trunking around the room with most of the lids blown off and the bundles of wires inside just smoking, half-molten messes of burnt PVC with the tell-tale bright red of overheated copper strands.

With the immediate danger located and contained, it took just a few minutes to isolate the entire A/C system, start the diesels, and reset the main breakers, after which we had the station back on air quite quickly. Within hours the sub-contractors were back on site for the inevitable hard questions. We needed to find out what caused the catastrophic failure and what the subcontractors were going to do to sort it out before the President's visit. The first question was answered quite quickly when the senior contractor showed us the wiring diagram for the A/C controls.

To his embarrassment and our amazement, there wasn't a single fuse between the incoming 300 amp feeder and the thinnest control circuit wires (28AWG), i.e., no systematic discrimination at all. We never found what the prime failure was but once the first failure had occurred it gave rise to an inevitable cascade of faults, leading to complete destruction of all the wiring in the trunking and trip of the incoming HV feeder.

The words "President" and "in five days' time" clearly carried much weight. The next day we heard that the hapless young engineer who had designed the installation had been sacked and sent back to UK in disgrace. Then the contractor began work to clean up the mess and replace all the wiring with the addition of fuses and MCBs at strategic points to ensure correct discrimination. Much to the credit of the contractor, soon it was all working again and the opening ceremony went off without hitch, much to our great relief.

Maybe our contract engineers should have asked to see the installation drawings before the job went ahead. If they had, the obvious oversight might have been spotted. Or was it reasonable to assume that the contractor would actually employ competent designers? more than 40 years later, we now have much more emphasis on quality control and procedures for certification, so I'd like to think it wouldn't happen again in such an egregious fashion. The company is still listed in trade directories as an international air conditioning contractor.

Rod Hine graduated from Churchill College in Cambridge, England. He worked in satellite communications, meteorological telecoms, and then general automation, machine tools, and industrial control systems. He has also lectured in electronic engineering and cybernetics.

Tell us your experience in solving a knotty engineering problem. Send stories to Lauren Muskett for Sherlock Ohms.

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