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#1
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A light shines where there was none
On Wed, 10 Sep 2003 14:03:12 +0100, Roland Perry wrote:
In message , Cast_Iron writes According to the report, the second fault occurred because automatic protection equipment shut off the power thinking there was a fault with the supply, because of the action taken to compensate for the defective transformer. Finally! Confirmation that the two faults were indeed related. As some of us insisted (against solid opposition) from the start. Not quite true. You conveniently snipped the *real* reason, which was almost certainly human error. "According to the report, the second fault occurred because automatic protection equipment shut off the power thinking there was a fault with the supply, because of the action taken to compensate for the defective transformer. The report adds that this occurred because "an incorrect protection relay was installed when old equipment was replaced in 2001". The second 'fault' seems to have been a protection malfunction. The key phrase is perfectly clear and obvious, at least to anyone with a knowledge of the industry - "an incorrect protection relay was installed when old equipment was replaced in 2001". |
#2
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A light shines where there was none
On Wed, 10 Sep 2003 15:11:48 +0100, Wanderer
wrote: On Wed, 10 Sep 2003 14:03:12 +0100, Roland Perry wrote: In message , Cast_Iron writes According to the report, the second fault occurred because automatic protection equipment shut off the power thinking there was a fault with the supply, because of the action taken to compensate for the defective transformer. Finally! Confirmation that the two faults were indeed related. As some of us insisted (against solid opposition) from the start. Not quite true. You conveniently snipped the *real* reason, which was almost certainly human error. ... The key phrase is perfectly clear and obvious, at least to anyone with a knowledge of the industry - "an incorrect protection relay was installed when old equipment was replaced in 2001". But triggered by the first fault, no? If the first fault hadn't occured, neither would the second one (at that particular time). I guess it all depeneds on how you want to define the chain of cause-and-effect... Sam -- Sam Holloway, Cambridge www.samholloway.co.uk |
#3
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A light shines where there was none
On Wed, 10 Sep 2003 15:17:25 +0100, Sam Holloway wrote:
On Wed, 10 Sep 2003 15:11:48 +0100, Wanderer wrote: On Wed, 10 Sep 2003 14:03:12 +0100, Roland Perry wrote: In message , Cast_Iron writes According to the report, the second fault occurred because automatic protection equipment shut off the power thinking there was a fault with the supply, because of the action taken to compensate for the defective transformer. Finally! Confirmation that the two faults were indeed related. As some of us insisted (against solid opposition) from the start. Not quite true. You conveniently snipped the *real* reason, which was almost certainly human error. ... The key phrase is perfectly clear and obvious, at least to anyone with a knowledge of the industry - "an incorrect protection relay was installed when old equipment was replaced in 2001". But triggered by the first fault, no? If the first fault hadn't occured, neither would the second one (at that particular time). I guess it all depeneds on how you want to define the chain of cause-and-effect... Or whether a member of the public would consider a protection malfunction to be a genuine fault, in quite the same way that they would seeing a bloody great hole blown in a cable or a transformer on fire. Certainly for the purposes of the National Fault reporting scheme it would be classed as a fault, but the implications in this particular case are quite far-reaching. If, in the final analysis it can be proven beyond all reasonable doubt that the outage happened because of negligence, which seems highly likely, then National Grid could be liable for substantial damages. Might be time to dispose of the shares... |
#4
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A light shines where there was none
In message , Wanderer
writes Finally! Confirmation that the two faults were indeed related. As some of us insisted (against solid opposition) from the start. Not quite true. You conveniently snipped the *real* reason, which was almost certainly human error. The *reason* for the second outage might have been human error [1], but the second outage was most definitely *caused* (ie triggered) by the first. It wasn't an "unrelated" incident. [1] Although you could argue that it was really caused by failure to implement a procedure that would have noticed and rectified that human error. -- Roland Perry |
#5
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A light shines where there was none
On Wed, 10 Sep 2003 15:21:57 +0100, Roland Perry wrote:
In message , Wanderer writes Finally! Confirmation that the two faults were indeed related. As some of us insisted (against solid opposition) from the start. Not quite true. You conveniently snipped the *real* reason, which was almost certainly human error. The *reason* for the second outage might have been human error [1], but the second outage was most definitely *caused* (ie triggered) by the first. It wasn't an "unrelated" incident. I'll concede that point, but the discussions that were going on at the time were much more of the nature that one 'bang' caused another 'bang' because the circuits were overloaded. It seems *that* wasn't the case. [1] Although you could argue that it was really caused by failure to implement a procedure that would have noticed and rectified that human error. Yes. Knowing the very strict and thorough commisioning and testing procedures that once were enforced, one is left wondering whether corners have been cut since privatisation. |
#6
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A light shines where there was none
In message , Wanderer
writes The *reason* for the second outage might have been human error [1], but the second outage was most definitely *caused* (ie triggered) by the first. It wasn't an "unrelated" incident. I'll concede that point, but the discussions that were going on at the time were much more of the nature that one 'bang' caused another 'bang' because the circuits were overloaded. It seems *that* wasn't the case. No, the debate was about whether the second 'bang' was related to the first in *any* way shape or form. Lots of people insisted it wasn't. One possible failure mode would be that the first 'bang' caused the second circuit to overload, and cut out. If the actual failure mode is the first 'bang' causing the second circuit to *think* it's overloaded, and cut out, then the difference is entirely academic to those people sat in the ensuing darkness. -- Roland Perry |
#7
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A light shines where there was none
Wanderer wrote in message . ..
On Wed, 10 Sep 2003 15:21:57 +0100, Roland Perry wrote: In message , Wanderer writes Finally! Confirmation that the two faults were indeed related. As some of us insisted (against solid opposition) from the start. Not quite true. You conveniently snipped the *real* reason, which was almost certainly human error. The *reason* for the second outage might have been human error [1], but the second outage was most definitely *caused* (ie triggered) by the first. It wasn't an "unrelated" incident. On any interconnected system, the National Grid being a prime example, events are by definition related. This incident was caused by a classic very simple installation 'cock-up' made 2 years ago and not discovered or exposed since; system design, configuration and incident response were correct and supplies would have been securely maintained otherwise. The second outage (Wimbledon - New Cross 275kV circuit No.2) which caused the loss of supply was a 'phantom' overload trip, there was no equipment fault and total load was 33% of line rating. Overload detection relays, connected via 1,200:1 transformer, are rated 1Amp or 5Amp with a wide ranging multiplier, 5A was specified but 1A installed and through all the checks nobody spotted the error. This meant that tripping was initiated (time delay involved, irrelevant here) at 23% of rating and 20% of correct overload setting, so in the past 2 years this line can't have loaded above that level even at peak winter demand indicating the generous level of redunancy provided. It's accepted that when the system is being reconfigured, as it was after the first, potentially explosive, fault warning; there can be 5 to 10 mins 'switching time' when supply is via a single circuit. The risk of a second fault on that circuit during this time is estimated at 1:40,000 though that doesn't apply here with the system wrongly set-up. The engineers planning the switching could not have known the line would trip. [1] Although you could argue that it was really caused by failure to implement a procedure that would have noticed and rectified that human error. Yes. Knowing the very strict and thorough commisioning and testing procedures that once were enforced, one is left wondering whether corners have been cut since privatisation. They were carried out but I guess those engineers assumed they had been handed over correctly installed equipment and never thought to check the relay rating, pity they aren't brightly colour coded. Simulating real life faults is simply not possible or wise. Reading the full report my impression is of a well run and financed operation not obviously damaged by privatisation with London area investment running at £50m pa. Ironically the duplicate circuit, Wimbledon - New Cross No.1, is out from 1/7 to 28/9 for upgrade and refurb. Lessons have been, painfully, learnt and the relay error is not likely to happen again. All 45,000 are being checked (none found after 9,000). I would say the system is now secure, building extra lines would be very expensive. The LT loss of supply is rather laid on EDF, the London distribution operator, who chose to operate their Wimbledon 132kV Substation in a way that resulted in LT and others losing supply when the Grid was able to maintain the full load without interuption, and should have reconnected LT in a couple of mins at most. I get the impression there was only one engineer in their Control who didn't know what hit him... Source: http://image.guardian.co.uk/sys-file...on28082003.pdf |
#8
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A light shines where there was none
On 10 Sep 2003 15:31:14 -0700, robsignals
wrote in : detection relays, connected via 1,200:1 transformer, are rated 1Amp or 5Amp with a wide ranging multiplier, 5A was specified but 1A installed .... They were carried out but I guess those engineers assumed they had been handed over correctly installed equipment and never thought to check the relay rating, pity they aren't brightly colour coded. Given that there appear to be only two different ratings, an obvious question is, "Why not?" -- Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration, Brunel University. Room 40-1-B12, CERN KotPT -- "for stupidity above and beyond the call of duty". |
#9
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A light shines where there was none
On Thu, 11 Sep 2003 09:48:26 +0000 (UTC), "Dr Ivan D. Reid"
wrote: On 10 Sep 2003 15:31:14 -0700, robsignals wrote in : detection relays, connected via 1,200:1 transformer, are rated 1Amp or 5Amp with a wide ranging multiplier, 5A was specified but 1A installed ... They were carried out but I guess those engineers assumed they had been handed over correctly installed equipment and never thought to check the relay rating, pity they aren't brightly colour coded. Given that there appear to be only two different ratings, an obvious question is, "Why not?" becuase some pratt would probabably colour them red & green them employe colour blind engineers. -- This post does not reflect the opinions of all saggy cloth cats be they a bit loose at the seams or not GSX600F - Matilda the (now) two eared teapot, complete with white gaffer tape, though no rectal chainsaw |
#10
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A light shines where there was none
"Dr Ivan D. Reid" wrote in message ... On 10 Sep 2003 15:31:14 -0700, robsignals wrote in : detection relays, connected via 1,200:1 transformer, are rated 1Amp or 5Amp with a wide ranging multiplier, 5A was specified but 1A installed ... They were carried out but I guess those engineers assumed they had been handed over correctly installed equipment and never thought to check the relay rating, pity they aren't brightly colour coded. Given that there appear to be only two different ratings, an obvious question is, "Why not?" The cost of producing the item? Perhaps they aren't made? You'd hope that the maintenance engineers actually bothered to read things. Perhaps if the correct colour code was yellow they might stuff a banana in by mistake. |
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