OverviewSCT-PPT excitation systems were supplied for gas and steam turbine-generators from 1960 through the 1980s in the 5 to 250 MVA range. These compound type exciters have both a Saturable Current Transformer (SCT) and a Power Potential Transformer (PPT). Their primary attribute is the ability to support transients in generator load due to single or 3-phase faults or starting large motors even with reduced terminal voltage.Control PlatformReasons to UpgradeCurrently, these systems are typical of any aging control system, with difficulty in parts and service availability, relatively high maintenance, and limited data access for operations and maintenance. In addition, the SCTs are subject to high levels of heat and vibration and are difficult to repair. Rewinds are occasionally unsuccessful and replacement SCTs are long-cycle deliverables contributing to prolonged outages. Retrofit OptionsGE offers an array of EX2100 retrofit options to varied needs of our customers. A SCT-PPT Voltage Regulator Retrofit - replaces the existing SCT-PPT regulator with the new EX2100 AVR, eliminates the motor operated voltage adjusters, and adds digital protection functions at a low project cost. A Partial Compound Retrofit - replaces the aging analog control and the original power rectifier bridges with a new EX2100 system, but reuses the existing power magnetics. Retains the fault support of a compound system and increases performance to high initial response, with a lower cost and shorter outage than a full compound retrofit. A Full Compound Retrofit - a complete system modernization with new EX2100 control and power conversion bridges as well as new power magnetics (i.e. SCTs, PPT, Linear reactors). It retains all of the benefits of the compound system performance, fully digital controls, and magnetics manufactured with modern materials and methods. A Potential Source System Conversion - removes the compound magnetics and converts the system to a potential source static EX2100. A simplified and cost effective alternative when the compound system transient support is no longer needed. ValueGE provides the widest range of SCT-PPT retrofit options in the industry. Our engineered retrofit packages can provide the design and implementation support needed to retain the performance benefits of the original system, while integrating the EX2100 into the existing plant infrastructure. Operational benefits include improved parts and service availability, powerful programming, maintenance and diagnostic software tools, and improved performance and protection of the generator. |
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SCT-PPT Excitation System Retrofits
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