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Low Voltage Circuit Breaker Upgrade Options

Issue 7 and Volume 110.

Replacement circuit breaker can offer a viable alternative for increasing performance.

By Timm Smith, Square D/Schneider Electric

Management and maintenance personnel at power generating facilities face the same challenges operating their plant’s electrical distribution system as other large industrial plants-shrinking resources, limited planned outage time and aging plant equipment.

Today’s low voltage (LV) power circuit breakers allow older, often obsolete breakers to be replaced in less time and at a potential cost savings when compared to switchgear replacement. New circuit breakers have increased ratings, lower maintenance requirements and advanced capabilities, including power metering, monitoring and communication, which can help plant operators manage cost and resources. These breakers can provide power generating plants with several options for extending the life of existing electrical switchgear.


Manually operated circuit breaker replaced with a Square D Masterpact NT circuit breaker. Photo courtesy of Square D/Schneider Electric.
Click here to enlarge image

Increased demand for power plant operators to reduce maintenance costs and increase existing generation facilities’ reliability requires plant engineers to consider upgrades and different technologies that will improve performance. Circuit breaker technologies allow large electrical users to exchange older, often obsolete equipment, without disrupting existing switchgear. Over the years, power generation facilities have used different techniques to upgrade LV power circuit breakers. One example is to replace existing overcurrent protection on the breakers with new solid state trip systems. Following are details of three other methods that may help improve performance.

Although this article focuses on LV circuit breakers and switchgear, similar retrofill and replacement breaker options are available for medium-voltage equipment.

Replacement circuit breaker

The replacement LV power circuit breaker is a new breaker that uses a modular drawout assembly, intended to match components inside the existing switchgear’s breaker compartment. With this option, a new cradle interface is inserted into the existing breaker compartment. The cradle design typically includes a new racking mechanism, safety interlocks, primary and secondary disconnecting devices, truck operated contact (TOC) mechanisms, a new breaker compartment door and other provisions.

A replacement LV power circuit breaker matches the original circuit breaker in form, fit and function and is designed and tested in accordance with American National Standards Institute (ANSI) C37.59 and C37.09 standards. Because a number of circuit breakers manufactured more than 50 years ago remain in operation and are no longer supported, the replacement breaker often provides owners a viable alternative for increasing performance. New circuit breakers allow plant operators to exchange various older circuit breakers for one common breaker that is interchangeable throughout the plant. Another major advantage of replacement circuit breakers is that they allow plant operators to upgrade equipment without scheduling a bus outage.

Nuclear generating plants typically require recertification after 40 years. As part of the recertification, the U.S. Nuclear Regulatory Commission can require existing equipment to be replaced or upgraded. As a result, replacement breakers are prevalent in the nuclear industry. For example, a nuclear power plant in the Midwest recently began replacing more than 250 decades-old circuit breakers. The new breakers feature a digital electronic trip unit that produces electrical data to be used in operations, troubleshooting and energy management. The equipment change also reduced the inventory of replacement breakers and parts for the facility, translating to cost and space savings.

Benefits of replacement circuit breakers typically include:

  • Enhanced electrical system reliability.
  • Less cost and downtime compared to new equipment installation.
  • Reduced maintenance and operating costs.
  • No need for obsolete or hard-to-find spare parts.
  • Available for most manufacturers’ LV ANSI switchgear.
  • Various digital trip devices for short circuit and overload protection.
  • Extended range of short circuit and continuous current capabilities.
  • Increased safety by adding ground fault protection.
  • All applicable ANSI standards met.
  • Through-door racking and trip unit display.
  • Arc flash limiting breakers available.

Circuit breaker retrofill

An LV circuit breaker retrofill includes replacing the old breaker and related compartment components, such as the stationary primary and secondary disconnects, cell interlocks and racking mechanisms, with a drawout circuit breaker and cradle.

During the retrofill design and installation, the existing switchgear cell is modified and equipped with a new drawout cradle assembly. Significant changes are made to the structural components of the existing circuit breaker compartment as well as to the line and load bus structure and bus bracing. New isolating barriers are installed to conform to the latest electrical switchgear industry standard requirements.

Because the retrofill installation always requires a complete switchgear shutdown, some plant operators take this opportunity to implement a wider scope of switchgear upgrades. For example, during a planned outage, protective relays are often replaced with solid state or digital technology, control features are added and modern power monitoring equipment is installed, as well as new communication networks.


Fused contactor conversion for an electrically operated circuit breaker uses a Square D FB600E retrofit kit. Photo courtesy of Square D/Schneider Electric.
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An LV circuit breaker retrofill is used when and where the power generation plant can afford modifications that require extended switchgear shutdown (at least 16 to 24 hours). When the available fault current is higher than the withstand capabilities of the existing switchgear, a retrofill solution may be preferred to replacing LV circuit breakers. In such cases, the entire switchgear bus structure and bus bracing must be evaluated and upgraded, requiring the switchgear to be de-energized during modifications.

The retrofill solution is also recommended for LV circuit breakers exceeding 2,000 A continuous current rating due to primary current path interface complexity and the temperature increase generated by the primary conductors. Because breakers above 2,000 A are typically the main breakers, they always require a bus outage. This may make a retrofill approach as advantageous as a direct replacement.

For example, an industrial facility that owns and operates its electrical distribution system had to upgrade obsolete switchgear and circuit breakers. The original job specified new equipment. Because the switchgear was not readily accessible, substation modifications (including removing a concrete wall) were necessary. The facility engineer chose to work with an OEM service group to complete a retrofill, avoiding excessive downtime and reducing costs associated with removing equipment, testing and potentially replacing cables and installing the new equipment.

Power plants have plenty of LV equipment that could benefit from such a retrofill process. More importantly, utilities are migrating to more time between outages, as well as shorter outages. Therefore, extending the life of replacement equipment is a top priority.

Benefits of a circuit breaker retrofill typically include:

  • Reduced costs and downtime for equipment upgrades compared to new switchgear installation.
  • Cost-effective electrical system upgrade.
  • Continued electrical system integrity during upgrade.
  • Need for obsolete or unavailable spare parts eliminated.
  • Switchgear upgrade can be expanded beyond the circuit breaker compartment.
  • Replacement of the original integrally fused circuit breakers with modern non-fused breakers possible.
  • A universal solution for any switchgear modification, regardless of short circuit and continuous current ratings.

Fused vacuum contactor conversion

Some power generating facilities use circuit breakers in motor starter applications. Here, a circuit breaker may be converted to a fused vacuum contactor, which can promote longevity, reliability and performance in motor starting applications. Most early-generation LV power circuit breakers were designed primarily to protect loads during short circuit or overload events, rather than for a high number of repetitive switching operations with high inrush current, which are required for motor starting applications. Circuit breakers in such applications require an intensive maintenance schedule as well as a large replacement parts inventory.

Conversely, modern vacuum contactors are specifically designed for high numbers of low-current switching (amounting to hundreds of thousand of operations). Vacuum contactors also perform reliably in repetitive capacitor switching applications. Converting LV power circuit breakers to integrally fused vacuum contactors can enhance system reliability by increasing the number of operations between maintenance cycles.

One Southeast utility recently faced using circuit breakers in motor starting applications for a number of its power generating facilities. Many of the breakers were used in the coal handling area; some were performing as many as 20 operations a day. Contaminants were invading the breaker mechanisms leading to frequent bearing and bushing failures. To resolve the situation, the utility replaced many circuit breakers with fused vacuum contactors, which are rated for many more operations and are better protected against contaminants.

Benefits of an LV contactor conversion typically include:

  • Existing switchgear devices upgraded to vacuum switching technology.
  • Existing motor controls are improved and upgraded through integration of modern protective relays with the converted breaker.
  • Improved coordination of motor protection.
  • Additional communication and power monitoring capabilities.
  • Additional ground fault protection available.
  • No circuit breaker compartment modifications required.
  • Standard designs available for 480V-600V switchgear for most original equipment manufacturers.

Power generating plant owners must decide how long they can operate their electrical distribution equipment before it needs to be upgraded. New switchgear is an option, but the potential benefits of reduced costs and shorter outages available through upgrades are hard to overlook. Additionally, in many cases the existing switchgear is tightly surrounded by other equipment and has limited accessibility. In such instances, replacement becomes difficult and potentially much more costly.

The options discussed here do not displace the need to properly maintain a power generating facility’s electrical distribution system. However, because of existing equipment replacement costs, as well as rising maintenance costs, plant operators should consider these options.

Author

Timm Smith is the National Marketing Manager of Square D Services. He has worked 20 years in the electrical industry, including 12 years with Dayton Power & Light, primarily in the T&D group, and the last eight years in sales and marketing for Square D Services.