Exploring switchgear maintenance options

Key concepts Alternatives for maintaining electrical switchgear include reconditioning, converting, replacing, or retrofilling.

02/01/2001


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Alternatives for maintaining electrical switchgear include reconditioning, converting, replacing, or retrofilling.

Power circuit breakers can remain in service for an extended period if they receive annual routine maintenance.

In-shop reconditioning, replacement, or retrofilling circuit breakers reduce downtime and improve equipment reliability.

It wasn't too long ago that aging electrical equipment was repaired or replaced. But, in today's business environment, maintenance staffs face increasingly intense pressure to reduce costs and defer expenses. This trend has led many plant engineers to find less expensive ways to maintain equipment and extend its life.

There are many alternatives for maintaining electrical switchgear-reconditioning, converting, replacing, or retrofilling.* With so many options, it is difficult to know when you should replace a power circuit breaker, versus converting or retrofilling the unit. What are the pros and cons of each option? More importantly, what are the costs of each possibility?

Extending equipment life

The traditional ANSI power circuit breaker was designed to make periodic onsite maintenance simple to perform. Major electrical equipment manufacturers generally require annual maintenance for power circuit breakers to ensure proper operation and maintain equipment warranties. Annual maintenance typically involves inspection and cleaning of primary and secondary disconnects, racking mechanisms, and cell interlocks. Power circuit breakers can remain in service for an almost indefinite period of time, if they receive annual routine maintenance.

Even with annual maintenance, however, power circuit breakers may need additional upkeep or upgrades. The need for additional maintenance varies due to factors such as ambient operating temperature, humidity, cleanliness of the operating environment, operating duty cycle, and frequency of maintenance the circuit breaker has received. Under stressful conditions, circuit breakers only 5-yr old can be candidates for complete reconditioning.

The service industry has developed its own terminology for various types of refurbishment and upgrades performed on electrical equipment. However, this terminology can vary from supplier-to-supplier, which creates problems in communicating the types of offers available.

The following definitions, based on ANSI standards and industry common practice, may serve as a guide.

Onsite maintenance is the periodic performance of recommended maintenance or repair procedures by a staff person or technician from an outside firm. Onsite maintenance may include the use of new or refurbished parts or subassemblies to return a circuit breaker to good operating condition. This activity typically involves only partial disassembly of the circuit breaker. The existing switchgear structure is generally not affected.

In-shop reconditioning is the removal of a circuit breaker from the electrical equipment and sending it to a service shop location where it is tested against ANSI standards. The breaker is completely disassembled, cleaned, and inspected. Damaged parts are refurbished or replaced, and pivot points are relubricated before the circuit breaker is reassembled. The reconditioned breaker, including the new assemblies, is retested against ANSI standards. The existing switchgear structure is generally not affected by this activity.

Conversion is commonly performed while reconditioning a circuit breaker, and involves replacing out-of-date components (such as traditional trip units with solid state trip units or arc interrupting elements with vacuum or SF6 technology). Current transformers are generally replaced when a solid state trip unit is replaced on a low-voltage power circuit breaker. Also, replacement of a solid state trip unit and associated current transformers on a lower voltage power circuit breaker is commonly called a "low-voltage retrofit" by the service industry.

Replacement is the removal of the old circuit breaker and replacement with a completely new unit, truck, and carriage assembly. Designed and tested against ANSI standards, the new circuit breaker mounts in the existing cell of the switchgear. Existing cell interlocks, racking mechanism, and switchgear structure are not modified.

Retrofill is the removal of the old circuit breaker, cell interlocks, and racking mechanism; and replacement with a new circuit breaker, truck, and carriage assembly mounted in a new cell, including interlocks and racking mechanism. The new circuit breaker assembly and cell should be tested against ANSI standards. The existing switchgear structure and bus are modified to mount the new circuit breaker and cell within it.

Each solution has its advantage

The state of the equipment and cost to do the work, including labor to complete the job, should be the determining factors in deciding which solution is best. Another consideration is the need for integrating new technologies to improve the performance of the circuit breaker and overall electrical system, such as a new solid state trip unit to replace an existing trip relay.

The drawing compares the total installed cost, from the customer's perspective, for a range of solutions available to extend equipment life for low-voltage switchgear installations. The drawing also shows when an upgrade in technology is included in the solution.

Comparing benefits

The most obvious benefit of pursuing options, such as in-shop reconditioning, conversion, replacement, or retrofill, is the significant savings on costs that would have been dedicated to buying new equipment-and not just the physical equipment, but the time and labor involved in specification, procurement, installation, testing, and commissioning. In-shop reconditioning, replacement, or retrofilling circuit breakers can mean reduced downtime and improved equipment reliability because damaged or worn components are usually discovered before they can cause a piece of equipment to fail. Conversion allows plant engineers to modernize existing equipment at a fraction of the cost of procuring new items embedded with the latest technology.

Electrical equipment manufacturers normally offer only new equipment to a customer seeking to upgrade an electrical system. But before buying that new switchgear, consider the options. The company may just save a lot of money.

-Edited by Jack Smith, Senior Editor, 630-320-7147, jsmith@cahners.com

* There is a distinction between the words retrofill and retrofit . Within the context of this article, retrofill means the removal of the old circuit breaker, cell interlocks, and racking mechanism; and then replacement with a new circuit breaker, truck, and carriage assembly mounted in a new cell, including interlocks and racking mechanism. Retrofit is also commonly called a "low-voltage retrofit" by the service industry and refers to the replacement of a solid state trip unit and the associated current transformers on a lower voltage power circuit breaker.





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