Bhavya Kapadia, Kiran Bhattar, Harshada Nagare ABB Smart Power Hyderabad, India, bhavya.kapadia@in.abb.com, kiran.bhattar@in.abb.com, harshada.nagare@in.abb.com; Tim Ford ABB Smart Power Cary, NC, United States, tim.ford@us.abb.com; Steven Greenwald ABB Smart Power Plainville, CT, United States, steven.greenwald@us.abb.com
The majority of electrical connections in industry are made by plug-in or bolted connectors, both of which have their issues. Bolted connections, for instance, are susceptible to loosening over time, which can lead not only to high-resistance effects like heating but also to arcing and short circuits. Because the state of the electrical connections in an installation plays a uniquely critical role in its safety, efficiency, reliability and longevity, ABB has introduced the new ReliaGear plug-in design to ensure optimal connection performance →01.
ReliaGear neXT And ReliaGear SB plug-in connections
ABB’s ReliaGear plug-in design represents a significant improvement over the classic bolted-joint method of device installation and connection. The central novel feature of the ReliaGear neXT and ReliaGear SB design is the fixed (vertical) panel board bus and the slots it incorporates →02. Correspondingly, the connectors on the associated circuit breakers (ie, the line-side connectors) feature a clip with matching geometry that engages the slots in the vertical bus assembly →03. Further, while the forces generated during fault currents can loosen traditional connections, ReliaGear cleverly harnesses these forces to tighten the connection.
ReliaGear plug-in breaker assemblies incorporate the circuit breaker and the line-side connector assembly into a single, factory-assembled item. There is no strap kit with multiple conductors and no hardware kit, and the line-side connector is pre-assembled in a single unit. With no field assembly required and no complex kit of parts for connection, installation is straightforward and simple.
Mounting
The ReliaGear neXT panel board’s modular design is the key to faster installations. A steel mounting bracket, affixed to the circuit breaker, provides a fulcrum on which the circuit breaker is levered into position, engaging the plug-in fingers with the vertical bus. The circuit breaker is then secured in position by easily accessible mounting screws, attached through the steel mounting bracket. There is no torque to check on the electrical connection and no special tools are required. The line-side connector design helps to ensure proper alignment and supports the clips during installation and removal.
The neXT rail system allows easy and straightforward installation of devices of various widths and lengths due to its equally spaced slots. Any device with back-bracket slots that fit into the openings on the rail and install into the bus stack may be positioned there. Conversely, and by design, the largest devices will not engage the slots or vertical bus if the panel cannot accept the device.
The slots are designed so that the “X” spacing (the number of mounting positions available) can accommodate the various circuit-breaker widths. Each circuit-breaker frame and bus-stack-mounted accessory has specific requirements for X-spaces. The frame also accommodates blank spacers to fill in gaps.
When a device is installed in the rail system, the underlying frame hole will align with the bolt hole at the back bracket, allowing installation of the screws. This efficient design ensures that the devices being installed are positioned correctly and fully engaged.
The ReliaGear neXT and SB system has been thoughtfully designed so that insertion is as easy as possible while helping to achieve contact integrity. Given the plug-in nature of the design, the insertion forces scale with the current-carrying capacity of the device being installed. For low-ampacity breakers, the insertion will be an easy operation requiring minimal hand force and support. For larger-frame circuit breakers, the ReliaGear neXT power panel is designed so that the breaker’s weight is supported until final insertion.
Investigation revealed that, on average, installation of a circuit breaker and strap kit, completed by an experienced technician, can take 10 minutes or more to complete and requires the proper torque wrench to ensure a suitable connection. Adding a similar circuit breaker to the ReliaGear neXT panel board took under 30 seconds, left adjacent devices unaffected and required only basic hand tools.
Performance at rated load
The circuit-breaker line-side connector includes a compression spring inside the clip, secured via features in the clip itself, that achieves the required contact pressure during typical operating conditions. As a spring-loaded connection, this joint does not loosen over time; there are no threaded connections to inspect or maintain; and the contact pressure is maintained by the spring. The ReliaGear clip assembly is a patented solution that provides a repeatable and reliable force to the connection, helping to ensure a secure and robust connection.
When considering the contact area of electrical connections, it is important to take into account the ratio of apparent contact area to true contact area. While common sense might suggest that this ratio is higher with a perfect surface than with a line contact, experimentation and calculation reveal the reverse to be true: A ReliaGear neXT clip assembly held by the embedded compression spring increases the ratio from around the 20 percent seen in the traditional approach to over 40 percent →04. Attaining an equivalent contact area using a classic bolt-on style connection requires highly torqued, high-strength fasteners – a particularly vulnerable arrangement in the field.
Performance under short-circuit conditions
The electromagnetic forces generated during fault currents can impact joint resistance on bolt-on connections, thereby impacting thermal performance. Here, the ReliaGear plug-in clip design turns the tables and exploits these forces to create the opposite effect. With ReliaGear, the repulsive forces between the clip and the panel board bus are overcome by the repulsive forces generated in the arms of the clip itself →04. What might be described as “blow-off” forces are harnessed and turned into “blow-on” forces. With this arrangement, the contact force is intensified proportionally with the magnitude of the current, allowing the clip assembly to remain in place during faults and short circuits.
Vibration testing
Vibration is a significant cause of connector failure in the field so the structural and functional integrity of the ReliaGear neXT assembly system was verified by thorough vibration testing. The test was conducted by rigidly mounting a neXT assembly on a vibration table and subjecting the assembly to values that met or exceeded those required by the relevant code: International Code Council – Evaluation Services Acceptance Criteria (156ICC-ES AC156).
Ingress protection (IP)
An ingress protection (IP) code, according to the IEC 60529 standard, defines a mechanical housing’s degree of protection against the intrusion of dust, accidental contact and water. The patented IP20 ReliaGear neXT design incorporates a molded-in mechanical barrier that protects certain configurations of the main bus stack against accidental contact of solid objects of sizes larger than 12.5 mm. This complies with an IP20 level of protection, generally recognized as “finger safe.” The design also minimizes the risk of a foreign body contacting the bus system →05.
Safe and reliable connection
Safety and reliability are the most important aspects of any electrical connection scheme. The ReliaGear neXT panel board has been designed and tested to enhance safety and to provide long-term reliability. ReliaGear’s plug-in connections improve on the plug-in connections that have a long history of use in power distribution and control equipment, providing a better true contact/apparent contact ratio at rated current than bolted equivalents. The design even exploits electromagnetic forces created during fault conditions to improve the electrical connection. In short, the ReliaGear design makes installation safer, easier and faster while ensuring long-term, high-quality performance.
ReliaGear is the property of ABB Inc., all rights reserved; SACE and TMax are the property of ABB S.P.A., all rights reserved.
