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For all of you electrical operators out there does this scenario sound familiar? You are in a half power lineup on the port turbine generator. The Starboard Turbine Generator (TG)is ready to go and you need to bring the TG on the bus restoring the plant to a NFPL and restore the ability the answer bells on both main engines. You know the drill.
What are the things which must occur before you shut a breaker? For starters the voltage and frequencies of the incoming load and the running bus must match and the synchroscope needs to rotating clockwise prior to shutting the breaker within the gray area at the 12 o clock position on the gauge. Do you remember why? In short, varying frequencies on the generator could speed up or slow down causing damage or excessive power transients. Likewise a variance in voltages can result in transients as well. Proper shutting of the breaker using the synchroscopes ensures the two buses are on phase in addition to ensure the incoming bus picks up the load.
In any case, normally plant shifts are uneventful. I recall I was on watch as RO and the EO Under Instruction, (UI) was doing a plant shift for qualification. The shift qualified Electric Operator, UI, and the Engineer Officer of the Watch (EOOW) talked through the plant shift prior to operating the plant. Finally, the EOOW gave the order to perform the shift.
In retrospect, I am not sure of the synchroscope’s position when the UI attempted to shut the breaker. Let’s say the position was nowhere close from the loud boom everyone heard. After I looked at my panel my pump configuration I lost a pump on each side i.e.1 Slow- 1 Slow. I had two pumps running on each side before the shift.
After the restoring the plant E Div ensured no damage had occurred to the breaker. On this day we were lucky, for those of you who might not have been so fortunate what was the craziest thing you have seen during a messed up plant shift and what happened afterwards?
Image courtesy of http://metersandinstruments.yokogawa-usa.com/product/analog-switchboard-instruments/ab40-synchroscope-switchboard-meters
4 comments:
Worst end result of a poor shift was a loss of all AC. While standing my 3rd ever qualified watch at Prototype as AMR2UL during a set of staff drills.
A sea-returnee EO(UI) was doing a speed shift from HPLU on Prt TG to NFPLU. He was coming from a 688 (we were MTS S5W), so apparently there were some subtle differences in the behavior of the breakers. When the switch was turned (ours had to be held until fully shut/light lit) the breaker didn't actually shut at first, so as he was shutting and opening breakers, he inadvertantly shut a breaker ~180deg out of phase, the resulting transient caused teh running TG to trip completely off-line, the running MG tried to pick up too much load from teh TG, which slowed it down, so when the MT-TG breaker tripped, it suddenly over-sped and tripped. The remaining MG choked on the massive DC transient caused by the other MG under-speeding/over-speeding/tripping, and it also died.
I happened to be in the tunnel taking my logs when this occured, and to this day I swear I heard the rods hit the bottom in the ensuing darkness and silence.
I don't want to bore anyone with an aircraft carrier's electric plant, but the worst "shift" I've ever seen involved racking to test a 4160VAC breaker. The procedure has you rack it to test, then shut and trip it manually to discharge the closing spings. Well, a certain somebody forgot to rack it to test first and manually shut the breaker. This happened to be the 1040VAC, 15Hz Coolant Motor generator output breaker which is now in parallel with 4160VAC, 60Hz High Volts Shore Power. Hearing the thump and the CMG freak out he tripped the breaker back open. Not much visible damage was done, but in the months to come the CMG started having so many problems, that we ended up swapping out almost all of it. According to the perpetrator though, no damage to the CMG was his fault because he claims he opened the breaker so quickly that no electricity got through. Thusly why he is now dubbed "faster than electricity."
Every night on the boat (688 class) we had to conduct EP training, FPLU to HPLU and back. The thing is, we always energized the TG-TG bus tie on the midwatch to equalize equipment wear for those items powered off the bus. So we were in a FPLU with the bus tie energized from Port. Forgeting this, I select on the synco, the STBD TG-TG bkr and shut the bastard. Immediately we everything on the TG-TG bus, (feed pump)when the bkr tripped back open. I didn't want to admit that I screwed up, so all my fellow E-Divers had to get up and rack out the BKR and inspect it. Luckily no damage occurred, but the next time I made sure whether the bus-tie was energized or not.
688 Class Boat (almost last of species if you get my drift). Drill set preparing for ORSE. EO does flawless shift of bus. Breaker does not shut at time, but for some unknown reason shuts 180 out. Big boom, TG bedplate rocks violently. I felt the boom down in ERF (now you know my rate). No more drills that day, big investigation that turned up no clues. Glad I was not Edivver that day.
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