Many hydropower plants have been in service for 60 or more years with circuit breakers that are well beyond their expected service life. Some of these circuit breaker designs require more maintenance over time and genuine replacement parts are often not available, potentially resulting in improper circuit breaker function, downtime and increased maintenance expenses.
Additionally, some circuit breaker designs require more and more maintenance over time and if genuine replacement parts are not available, this can result in improper circuit breaker function that can cause catastrophic failure.
The resulting conversions have simpler design, fewer components, reduced maintenance and readily available replacement parts. They also provide higher reliability, extended insulation life and can help increase safety for personnel.
Factors impacting a generator circuit breaker’s useful life
Circuit breakers used in generator applications can have various types of interrupting technologies, require special operating parameters and may have exceeded their original design life.
The circuit breaker’s performance and longevity depend on:
— Switching rates;
— Number of switching operations and current magnitudes;
— Maintenance costs;
— Availability and cost of renewal parts;
— Maintenance intervals;
— Maintenance outage times; and
— Environmental concerns such as oil, polychlorinated biphenyls (PCBs) asbestos and possibly sulfur hexafluoride (SF6).
These parameters not only affect system availability and reliability, but also impact the ongoing financial viability of the generating station. When considering whether to modernize power circuit breakers used in generator circuits, there are a number of options involving available technology upgrades to consider. In most scenarios, there will be some type of conversion involved.
Common terms for equipment life extension and modernization of generator circuit breakers
IEEE Standard Requirements for Conversion of Power Switchgear Equipment C37.59-2007 is a process standard that provides guidance and testing methodology for power circuit breakers.
The standard defines important conversion terms that should be noted and included in specifications that outline customer requirements for equipment life extension and modernization of generator circuit breakers. Familiarizing yourself with these terms will help ensure you are receiving the correct services to meet your needs.
— Conversion: The process of altering existing power switchgear equipment from any qualified design.
— Compartment adaptor: A removable device designed for insertion into a switchgear circuit breaker compartment that provides mechanical support and interlocking plus the primary and secondary electrical connections to allow insertion of a draw out circuit breaker that differs mechanically from that which originally occupied that circuit breaker compartment.
— Design verification: The process of design qualification, in accordance with all appropriate standards, of any conversion by means of design testing and/or evaluation, supported by justified technical evaluation and documentation.
— Modular assembly: A circuit breaker element, including interrupters, operating mechanism, and connecting terminals, or an alternating current contactor element, including interrupters, operating mechanism, and connecting terminals, that has been tested and qualified to the appropriate industry standards.
— Qualified design: Any power switchgear equipment that has been tested and certified to appropriate industry standards.
|This before and after image of a reconditioned breaker exemplifies how the life of vintage electrical equipment can be extended using only qualified design parts.|
— Racking: The act of moving a removable element physically between the connected position and the disconnected position in its compartment.
— Reconditioning: The process of maintaining existing power switchgear equipment in operating condition as recommended by the manufacturer’s instructions, using only qualified design parts. Reverse engineered parts (designs copied from existing parts by other manufacturers) are not considered to be qualified design parts unless specifically design verified.
— Replacement interchangeable circuit breaker: A circuit breaker that utilizes all new parts, has been design tested to IEEE Std. C37.09 or to ANSI C37.50-1989 or IEEE Std. C37.14-2002 as required, and requires no conversion of existing switchgear to maintain proper operation.
— Replacement non-interchangeable circuit breaker: A circuit breaker that utilizes all new parts, has been design tested to IEEE Std. C37.09 or to ANSI C37.50-1989 or IEEE Std. C37.14-2002 as required but requires conversion of existing switchgear to maintain proper operation.
— Retrofill: A conversion process that includes replacement of the circuit breaker and circuit breaker compartment functional components of a qualified design within a vertical section or compartment of a vertical section with functional components of a different qualified design.
— Circuit breakers used for generator service should also be design tested to IEEE Std. C37.013; and
— The term retrofit is not defined and is no longer used in IEEE Std. C37.59-2007.
Understanding different life extension and modernization solutions
Generator breaker conversion and modernization solutions are readily available from a number of sources. Site performance and financial requirements will drive the selection process. It is important to note the correct solution should provide the best long-range performance, so look for cost estimates and proposals from a number of sources. Typical solutions can be categorized as follows:
If parts are available from the original equipment manufacturer, outage time is not an issue, the circuit parameters are less than or equal to the circuit breaker’s rating and the switching rate is low, reconditioning of the existing circuit breaker may suffice for at least three to five years. If OEM parts are not available for a rebuild, then the circuit breaker’s performance will be affected and a failure can occur. Reconditioning using third-party reverse-engineered parts, as cautioned by the IEEE Std. C37.59-2007, can be dangerous. Reconditioning does nothing to update technology or increase the circuit breaker’s capabilities. However, this is the lowest cost solution for extending operating life.
New replacement circuit breakers
These will either fit directly into a draw out arrangement or require minor structure or control wiring modifications to complete their interface. Complete stand-alone designs can be manufactured to replace existing fixed-mounted oil circuit breakers. In many instances, the fixed-mounted design can be replaced with a draw out configuration to enhance reliability and reduce maintenance outage time. The new design would be tested to the appropriate IEEE Standards.
Retrofill conversions of existing installations
Retrofill conversions are often good solutions, provided the existing enclosure has the capability and room to accommodate the conversion components. Newer technology and circuit breakers with increased capabilities can be interfaced into the existing enclosures. When installations are unique, a retrofill conversion is often the best solution. The cost is usually between that of new replacement circuit breakers and complete replacement.
Installation of new switchgear with current technology circuit breakers is an always an option. Often extensive site preparation and reconfiguration is required to accommodate a different dimensional layout and new cabling is required. In addition, outage time, available space, conductor interfaces and total installed cost may rule out this option. This solution usually has the highest cost, but the cost difference for this option may afford increased efficiency and the safest equipment operation.
Simplifying circuit breaker maintenance through interactive training
To facilitate education and help address the knowledge gap, some vendors offer interactive video training modules to provide a starting point for circuit breaker maintenance and testing. Some of these available resources do not require any special software to operate and the vendors provide a portal for numerous test procedures, active animations and illustrations to guide personnel through maintenance and testing processes.
|To help simplify life extension and modernization, some vendors offer interactive training programs with animations and illustrations to guide personnel through maintenance and testing processes.|
Generator circuits may present special requirements for the circuit breakers intended to protect them. Industry standards are available to identify the requirements and demonstrate the required capabilities.
There are various methods available to extend the useful life of generator circuit breaker systems using reconditioning and conversions. Conversions also make it possible to modernize the system to current generator class circuit breakers. By incorporating newer interrupting technologies and other enhancements, a reduction in maintenance costs and reliability improvement can be realized.
Interactive digital training programs can also help accelerate the learning curve for maintenance personnel on new technology and existing testing techniques that are specific to generator class power circuit breakers.
Original Source: http://www.hydroworld.com/articles/hr/print/volume-34/issue-7/articles/extending-the-life-and-reliability-of-circuit-breaker-protection.html