See Also: Blow-up Reports
This report was written by Steve Hunt.
Introduction
On Monday, August 28, 1995, Switch - Air Break 1107 at the Henry Substation burned in two at the switch contact and at the end of the switch blade. This
switch was on the A-phase part of the Electric Circuit and was the reason for the low Voltage on the 13.2 KV side at Cull. Unfortunately, Sho-Me didn’t find this out until it was too late.
Events Leading to the Burnout
In actuality, the problem started on Sunday when the dispatcher (see Dispatching) received a high voltage alarm on the C-phase at Cull. Larry Langdon was
notified and he found that both B- and C-phase were running high. At this Time, the 450 KVAR Capacitor bank at Cull was turned off to see if this would alleviate the problem. It
did not and Larry relieved the higher voltage by changing the tapchanger. This
brought the phase voltages out of alarm.
The reason for the high voltages were due to which phase was being regulated.
In this case the A-phase was being regulated and its voltage was too low.
This caused the tapchanger to increase the voltage on the A-phase which in turn
increased the voltage on the B- and C-phases. This of course put B and C into a
high voltage alarm.
On Monday at 1:00 p.m., the B- and C-phases again were too high on the 13.2 KV
side. Ed Terry checked the high side and discovered that the voltages were
also too high. At this time, he began to sectionalize to see if he could either
alleviate this problem or actually find out what the problem was.
The first thing done was the trip Circuit Breaker 652 at Alton. This actually made the problem worse and it increased the B
and C voltages even higher, so Ed closed the breaker back in quickly. Next,
breaker 1504 (Mountain View line) at Cull was opened and it had the same result as
Alton. After 1504 was close back in, Ed tripped breaker 1505 and that was when
breaker 1050 at West Plains #3 tripped on its own. When 1050 was closed back
in again it tripped right back out. By this time, Jeff and Max had a suspicion
that we had a bad switch. Now Sho-Me had a fault (see Fault Current) on their line between Cull and West Plains #3. The key now was to isolate
the fault or actually find out where the fault was located. This was done by
opening switch 1107 at Henry and closing breakers 1050 and 1505 at West Plains #3
and Cull, respectively. Crews were dispersed at that time and at 3:45 p.m.
Monte Housley reported that switch 1107 at Henry had burned in two.
Concluding Remarks
It is important to note that 1107 had probably been faulty for some time but
was not discovered until a higher load was applied to it. For many years the Relay department was getting operations that did not make any sense. No relay
operations were taking place at Cull and even after extensive testing no troubles
could be found.
Lessons we can learn from this should be two fold. First, when we have a
voltage problem on the low side we should automatically check the high side to see
if similar problems exist. If not, then we know that the trouble exists on the
low side and can be pursued from there. Secondly, we should keep our minds
open to the fact that a problem at a substation might not be caused from within
the substation but might actually be a problem at another location.