At 11:13 a.m. 4/02/2009, Dean Pemberton wrote:
They had n+1 They took down the +1 for regular maintenance leaving them n. Then one failed leaving them n-1. Then the remaining unit could not carry the load and shutdown to protect itself.
Actually they may have had (n+1)x2 or some factor like 2. On big transformers is common to have oil pumps and fans on the radiators. So you can turn a 15MW tranny into a 30MW tranny (or whatever the manufacturer has calculated). Of course if you were already running the pumps and fans, then it doesn't help.....and you can't run them for too long, apart from the noise, things do like to cool. Same goes for cables. Older cables (paper-lead) could be run in over load for several hours (like 50%+ overload). "Plastic" cables aren't as tolerant - they melt. You also need to keep an eye on road temperatures, some cables have to be de-rated if the roads are running too hot. Overhead lines are so much easier, they just sag under heavy load........