By Ray Urbanic, Vice President of Engineering
Production systems continue to grow and evolve, but the electrical equipment providing them safe power eventually runs out of circuit breakers. The original switchgear that was installed when the facility was built 40+ years ago needs upgrading, but none of the new lineups seem to fit. Traditional switch-and-fuse protection used for decades now seems to create greater coordinationand arc flash issues today. Production demands continue to grow annually, but the maintenance budgets continue to get stretched thinner.
If any of these statements seem to apply to your facility, there is a need for your existing electrical protection system to be updated. The problem is answering the following:
- How much will it cost?
- Can it be installed within a short outage?
- Will it mesh well with the rest of the system?
The type of switchgear applied will have a profound impact on the answers to these questions and can be the difference between a project being approved or delayed.
Fused load-break switch lineups are among the most cost-effective and have the smallest overall footprint, but are not intended to be operated more than a few times annually. They can also often present coordination and/or arc flash challenges.
Traditional metal-clad circuit breaker switchgear is considered top-tier but is not only one of the most costly options but also requires significant footprint space.
Motor control centers offer high-duty operation as well as solid protection for frequently controlling motors but tend to be limited in amperage (650 A max) and voltage (7.2 kV).
Medium Voltage “hybrid” Switchgear can offer the best of all worlds. The design utilizes a common load-break switch as a visible disconnect, coupled with either a fixed-mounted circuit breaker or contactor, with added relay protection. This ends up being a “hybrid” between IEEE standards C37.20.2, 20.3, and UL 347, and can offer some significant benefits:
• Compact Design Applying fixed-mounted vacuum circuit breakers or contactors within the small footprint of a custom load-break switch enclosure allows for direct replacement of existing equipment, matching existing cable conduit layouts and pad dimensions. Installation time is significantly reduced as a result, allowing for shorter overall outage windows. The front-access design allows this equipment to be located against a wall or in limited space.
• Expanded Application Applying the “hybrid” load-break switch with a fixed circuit breaker can create a higher-capacity motor starter, rated up to a full 15 kV and 1200 A, instead of being limited to the power fuse and/or contactor ratings.
• Higher Duty Cycles Including a fixed vacuum circuit breaker or contactor with the load-break switch shifts the heavier duty-cycle burden to the breaker/contactor, preserving the life of the load-break switch.
• Superior Coordination Including independent relay protection with the fixed-mounted circuit breaker (in lieu of fuses) allows for greater sensitivity and allows for tighter coordination on the downstream substations.
• Reduced Arc Flash Energy This improved protection sensitivity can also allow for faster clearing times of lower-level fault currents, reducing the potential incident energy that can be available at the downstream equipment and reducing the level of required personal protective equipment (PPE) required by users.
Case Study #1: An original 11,000-480/277 V, 3750 kVA transformer is approaching its end of life, and is being upgraded with a 5000 kVA transformer for future expansion. The existing load-break switch protected the 3750 kVA transformer with three 300E-rated fuses, but there are no available fuses at that voltage that can protect the 5000 kVA transformer. The arc flash rating of the downstream 480 V equipment is already labeled “Dangerous” due to the incident energy being far above 40 calories per square centimeter. Metal-clad switchgear is being considered to protect the new 5000 kVA transformer.
Solution: A hybrid 15 kV-rated load-break switch with a fixed-mounted 600 A circuit breaker and relay can be installed in the same place as the existing fused load-break switch. Not only can the hybrid switchgear provide full over-current protection for the 5000 kVA transformer, but a coordination study shows that the new relay settings can also be set to greatly reduce the clearing time of any downstream arcing faults at the 480 V equipment, thus reducing the incident energy rating well below 20 cal/cm2.
Case Study #2: Three existing 2400 V, 3000 HP motors have been traditionally protected by upstream circuit breakers, being started across the line. The motors have each experienced significant stress on their windings and have failed several times. A new variable-frequency drive (VFD) is being installed to help start the motors with less stress to the system. Since there is limited space available, the drive is located near the motors, but there is not enough space for the new metal-clad switchgear needed to feed the VFD.
Solution: A hybrid 5 kV-rated load-break switch with a fixed-mounted 1200A circuit breaker can be applied within a compact, front-access enclosure close-coupled to the VFD. The VFD controls coordinate with the breaker control circuit to trip in case any issues are detected, with minimal impact on the existing floor space.
Southwest Electric has been creating and applying hybrid switchgear designs for a variety of custom solutions. Our team of engineers is happy to discuss your unique applications and offer custom solutions that meet your budget, outage window, and overall system needs.
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