Grand Coulee Dam: Third Power Plant Overhaul Project

Underground, oil-filled cables currently transmit all power from the six TPP generating units to the 500kV switchyard (Photo 1).  In 1981, a single phase of an oil filled cable faulted, destroying all circuits in the tunnel that house the transmission lines for generating units G-22, G-23 and G-24.  This fire instantly removed 2,415MW of power from the grid.  It took approximately two years to plan, design and construct temporary overhead lines and another three years to replace the oil-filled cables.  Once the oil-filled cables were replaced, the temporary overhead lines were abandoned in place.  It has recently become apparent that the condition of underground oil-filled high voltage cables is degrading.  

Replacing these oil-filled cables with overhead transmission lines solves several problems:  Overhead transmission lines can be inspected and maintained more safely than oil filled cables; the new lines can support an up-rating of the TPP generators; and the replacement using an overhead route does not require long periods without generation to safely remove old cables and install new cables. Switching from the oil filled cables to overhead lines only constitutes a two week outage per generating unit while replacing the oil filled cables would take at least one year and cost over $250M in lost generation revenue.   In order to remove the risk of another tunnel fire, support an uprate of units G-19, G-20 and G-21 and reduce operation and maintenance costs, USBR made the decision to remove the oil-filled cables install and install overhead transmission lines (Photo 2 shows a simulation of the new towers and overhead lines).

The USBR approached Bonneville Power Administration (BPA) to assist in planning, designing and constructing the new 500kV overhead lines.  The $18.5M construction phased of the project was awarded to Wilson Construction (Canby, OR).  The new overhead lines were energized in December 2012 and the oil-filled cables will be removed by December 2013.

Each unit in the TPP has a single Fixed Wheel Gate (FWG), aka head gate. These gates need to be routinely inspected and overhauled, but this takes substantial manpower and unit outages.  The unit outages required for each TPP generating units’ mechanical overhaul are an ideal time to inspect and overhaul the gates.  

However, the FWG chamber is no longer in compliance with current life safety and electrical codes.  

At present, the wiring is not explosion-proof, ventilation is inadequate, separation from dam galleries is insufficient, and lighting is poor.  Compounded, each of these factors lead USBR to the decision to extensively modify the FWG Chamber to ensure it is fully compliant with all applicable codes and regulations.  The $4M project was designed by the USBR and is being constructed by Knight Construction (Spokane, WA).  The project was considered substantially complete in February 2013.

There are six cranes in the TPP, which will all be used heavily use during the TPP unit overhauls.  The TPP has two 275 ton upper bridge cranes, one 50 ton upper bridge crane, one 2,000-ton lower bridge crane, one 70 ton draft tube gantry crane, and one 275 ton forebay gantry crane. It is imperative that they all be in excellent working order prior to the overhaul work in order to prevent unplanned crane outages that could result in costly delays in the schedule.

Repairs and upgrades of these cranes in preparation for mechanical overhaul was the subject of an A/E crane consultants’ inspection and report that was completed in September 2008.  The A/E’s report stated that the cranes were all in good condition and recommended, in lieu of a complete overhaul of the cranes, to the limit the scope of the project to crane controls.  The $17M crane controls project was designed by CH2MHill, Inc. and the construction work is being performed by Dix, Inc (Spokane, WA).  The project was completed in February 2013.

Overhaul of the TPP turbines and generators requires lay-down space for all turbine and generator parts as they are removed. These and other incidental parts will occupy nearly all of the TPP floor space. There are a variety of spare parts and pieces presently being stored in the TPP that need to be removed in order to provide the needed overhaul lay-down space. These valuable and easily damaged spare parts need to be kept in a secure, climate and temperature controlled storage space. The new storage building was built adjacent to the TPP, providing a convenient location for movement of materials to and from the TPP. The building includes a 100-foot by 200-foot floor area with 30-foot walls, 30-foot by 28-foot door (same opening as the north TPP door), insulated walls and ceiling, heating and cooling, forced ventilation, power, compressed air, and a life safety system with fire suppression.  The building is also certified LEED Silver.

The GCPO facilities are considered part of a historically significant area. As such, this new storage building cannot detract from the overall appearance of the area. The storage building is significantly smaller than the TPP, but retains the historical perspective of the site.

A design/build contract was awarded to Graham Construction (Spokane, WA) for $5M.  The project was considered substantially complete in October 2012.  Grand Coulee forces have been moving material from the TPP into the Material Storage Building, freeing up lay down space for the TPP mechanical overhaul project.  

The generator step-up transformer banks for generators G-19 and G-20 have been in continuous use since 1975.  Identical transformers for G-21 were replaced in 2002 because of deteriorating conditions, and it was recently noted that the transformers for G-19 and G-20 are also beginning to show signs of deterioration.  When these types of transformers deteriorate they produce flammable gases within the cooling oil. Close monitoring is required to prevent gas build up and the potential for explosion. Due to potential for explosion, access to this transformer area has been restricted. An explosive failure could damage cable circuit terminations and adjacent transformers which would compound immediate power loss and lengthen recovery time.  Spares for these transformers are not available in the Northwest.  An additional motive for replacing these transformers is the forthcoming uprate of generating units G-19 and G-20.  In order to uprate G-19 and G-20 from 690 MW to 770 MW, the single phase step up transformers required an uprate from 236 MVA to 276 MVA.  

The $28M project was designed by the USBR and the construction phase was awarded to Gardner Zemke (Albuquerque, NM) for $26M.  The project was substantially complete in December 2011.

There are two freight/personnel elevators which will be in continual use during the TPP mechanical overhauls. One elevator is in the Turbine Erection Bay at the southern end of the TPP and the other in the Generator Erection Bay at the northern end of the TPP. It is imperative that both are in excellent working order prior to the overhaul work in order to reduce potential for elevator outages and costly delays in the overhaul schedule.  The $2.3M project was designed by CH2MHill, Inc. and the construction phase was awarded to ThyssenKrupp, Inc (Spokane, WA).  This project was completed in February 2013.

The TPP generators have a major role in reacting to normal load swings but also in reacting to power system transient conditions such as loss of critical transmission paths or varying load. However, the units have been experiencing failures and erratic behavior, therefore not responding as quickly as possible. The electric-hydraulic governors are also showing problems with obsolete electronic components. The printed circuit cards used epoxy-based operational amplifiers which are no longer being manufactured.

The six TPP governor control systems are currently being replaced with new digital governor controls.  The new, faster responding governors allow for a more stable response to load rejection. The TPP governor hydraulic systems are in good condition and have not experienced major problems, so the scope of the governor replacement project is limited to replacement of the electronic components and pilot valve. Four of the new governor systems are currently online, one is being installed and the final unit is scheduled to be installed in January 2013.   The construction phase of the $3M project was awarded to American Governor, Inc. (Amherst, WI) and is scheduled to be complete in May 2013.

The TPP generators have a major role in reacting to both normal load swings and to power system transient conditions such as loss of critical transmission paths. Generation dropping opens generator breakers and is used to decrease supplied power to compensate for loss of a similar quantity of load.  In addition, the new modern, faster responding exciters have contemporary power system stabilizers which will enhance the overall stability of the units and the power system. Between generation drop and the power system stabilizers, the stability of the northwest power grid will be enhanced.

The excitation systems and associated equipment for the six TPP generators are being replaced with more robust and modern equipment. The previous excitation systems were state-of-the-art when first supplied in the late 1970s but the components have become obsolete and are difficult to replace. In addition, failures associated with the older excitation systems have created frequent unscheduled, forced outages of the TPP generators.  Recently, one of the 805MW generators was forced out of service for several days by the failure of a small choke coil in the exciter regulator circuitry. Lost revenue is dependent upon time of year and availability of other TPP generators. However, an average one week forced outage of one TPP generator costs about $250,000 in lost revenue and approximately $800,000 if an additional unit is also forced out of service.  

Four TPP units are currently operating with the new excitation system, one is currently being installed and the last unit is scheduled to be installed in January 2013.  The construction phase of the $22M project was awarded to ABB., Inc (Montreal, Quebec) and is scheduled to be complete in May 2013.

The Contractors performing work on existing equipment need may encounter asbestos or lead paint on some of the existing components. This is typically not an issue for components manufactured after 1980, however, these units were completed prior to 1980. Tests have confirmed that lead and asbestos do exist. The units will be cleaned prior to the overhauls by USBR and contractors who specialize in this field. The overhaul Contractors must be prepared with appropriate safety equipment, procedures, and trained staff to test for, handle and dispose of hazardous materials should they be encountered.

The TPP unit overhauls will provide an opportunity to inspect and, if necessary, to repair the draft tubes. A specialize work platform is needed to complete the repairs, and the contractor performing the overhaul work will be responsible for fabricating it. The platform will be suitable for use on all three units undergoing overhauls.

Last Update: March 11, 2013 10:56 AM