Generator Circuit Breaker (Explosion)
The more interesting findings during our assessments are related to poor commissioning practices. These items tend to be more complex than construction defects and typically more serious from a safety, equipment protection, and reliability perspective of the asset.
One case involved an "explosion" of a generator circuit breaker. The event took place about one year after COD, destroyed the GCB and damaged an F-class turbine generator (both stator and rotor).
The Event: During a unit start the operator was at the elevated GCB panel. The generator field breaker was closed, so the generator exciter was energized. The operator inadvertently pushed the earthing switch button which activated. The earthing switches are NOT designed to be activated when the generator/exciter is energized. The switch exploded (vaporized) with the GCB housing being damaged and opened like a tin can. The operator was shielded from bolts and other shrapnel, but luckily did not fall from the platform.
Background: The GCB vendor provided a set of dry contacts on each earthing... Read more
Possibly only a time savings, but doubtful.
Unit was out of service for 6 months. New breaker, rewound stator and rotor, recommissioing of unit... All-in costs between contractor, owner, an insurance company was about $8mm.
Electrical Zip(less) Ties
Recently EPR evaluated a facility, which among other difficulty, suffered from a condition that is unusual but serious in that essentially all the nylon cable (zip) ties were defective. While the zip tie is a wonderful time saving and usually effective component widely used to affix electrical cables, it must remain unaffected by its environment to remain durable over time.
In this instance, the plant was less than two years old and located in a high UV zone. This defect was so severe that gently touching the installed tie would cause a brittle failure. The plant was littered with failed zip ties that had fallen from tray systems and cable installations.
One supplier used by the contractor indicated in the technical literature that the ties are compliant with NEC, meaning Nylon, UV, weather, seawater, and oil resistant type from Panduit /T&B or equivalent. However, those ties have failed almost universally. While some cursory research was performed on the ties, it is not clear exactly why the ties were brittle and failing, but they certainly all needed replacing. The real... Read more
Negligible material savings.
Contractor: Somewhat time consuming especially in an operational plant. Owner: Outage events and unpredicatblity are hard to quantify, but even a single lost generation day is expensive.
Faked Electrical Ductbank
There are several important reasons to concrete encase underground raceway (rigid and PVC conduit) that carry power and control cables.
At a newly completed powerplant, the EPC Contract clearly stated: “All underground cables are installed in underground duct bank consisting of concrete encased duct: Hard polyethylene or rigid galvanized steel conduits as per ANSI C 80.1.” It goes further with detail, but does not allow direct bury cables and also articulates a minimum depth of cover. Engineering understood the implications and cascaded the contract/code requirements into the construction drawing details, which were available to the construction team.
Upon casual observation, the ductbank risers (concrete exposed above grade) did not appear "correct". Detailed investigation revealed there was effectively no ductbank. In some cases, rigid conduit was inserted into soil, perhaps 24” deep and then simply ended, leaving a direct bury cable condition. In other cases, groups of conduit were encased in concrete risers, giving the “impression” a ductbank existed. However, upon removing 6” of... Read more
Certainly some marginal cost was saved, as well as, some time early in the project. Almost certainly not a critical path activity (No LD savings).
Owner: Unpredictable unit operation. At ~$35,000/day finding/repairing cable problems is costly. Contractor: Full remedy would cost millions.
Galvanized Hardware (Or Not)
When a plant is built in a moist, heavily polluted, and/or salt laden environment, corrossion protection is a serious consideration. At a minimum, hot dipped galvanized hardware (nuts, bolts, washers, clips, etc.) is usually specified for outdoor service.
In a recently visited new facility, agressive corrosion was exhibited almost universally on the hardware. What was discoverd is that wherever galvanized was specified, electro-galvanized, electroplated zinc, or zinc plated, (different terms, same thing) was substituted by the contractor. This results in a 3 to 12 micron coating that gives it a much lower degree of corrosion protection than hot dipped galvanized with an 85 to 90 micron layer of zinc.
IEC indicates these coatings degrade (in this environment) at 4-8 microns/year. It's then easy to see why there is so much agressive corrosion and advancing stages of metal loss after only a couple years.
In the rare cases where hot dipped galvanized was provided, it... Read more
Marginal material cost savings; No labor savings.
Contractor: Substantial cost (Labor/Material) to replace fasteners in bulk. Owner: Fasteners failing is significant. Electrical system risks increase over time.