Choosing the most appropriate circuit protection solution can be critical to success
by Brian Moran, Supplier Marketing and Product Manager at Sager Electronics
Many power supply products have current-limiting or other circuit protection mechanisms built into the device. However, most circuit protection is located on the line side of the power supply, and its circuit protection typically involves a thermal element that monitors current.
That type of protection is sufficient for some applications; however, with an expanding variety of power feeds (line side) and power distribution (load side), simple thermal current protection may not be adequate.
While power supplies have some internal circuit protection, most electrical equipment powered by them has minimal, if any, electrical protection. Circuit protection products serve as electrical guardrails for motors, compressors, light fixtures, and a wide range of other products that require electrical power to operate. These systems, left unattended, would eventually damage or destroy themselves.
Some circuit protection examples in general industrial applications include motor loads, lighting loads, and compressor loads. These applications create an in-rush current at startup or turn-on states. This in-rush current can reach a level 50% to 80% higher than the equipment’s rated operating current for up to five seconds. While this is quite normal, a typical thermal breaker, set to react at 20% to 30% above the rated load, could trip.
These “nuisance” tripping events would significantly disrupt normal industrial operations. Additionally, if the power supply is feeding multiple loads, a fault from one of the outputs will put an additional burden on the remaining power supply outputs. In short, the interdependence between circuit protection and power supplies has become increasingly critical.
In addition to product and feature considerations, several key elements must be taken into account when evaluating the proper circuit protection for your power distribution scheme. Total solution size, cost, proper load balancing, type of circuit protection, and system communications are just a few of the basic challenges related to designing an optimal power management solution.
When an event occurs, such as an overcurrent, overvoltage, or fault, the circuit breaker will trip or the fuse will blow. In a large industrial setting, identifying the location of this fault can be challenging. However, in most cases, it is crucial to identify the issue and correct it promptly. Most circuit protection devices do not communicate a fault other than moving the breaker handle to a neutral position or illuminating an indicator light on the panel housing the breaker. Communicating with a remote system panel would enable a maintenance team to quickly find and address the problem.
E-T-A Engineering Technology offers a unique protection system capable of communicating with remote locations, such as a control panel, a maintenance center, or even a production supervisor. The REX12D is a multi-channel 24V circuit protection module that provides instant communications, remote maintenance, and remote access. Due to the REX12D’s modular architecture, users can add required functionality, such as various trip mechanisms, communication functions, and remote reset, among others.
There are several other types of circuit protection. Thermal Circuit Breakers, for example, are commonly used in a variety of applications. A bi-metal strip inside the breaker is engineered to bend or deflect in response to the heat generated by a certain amount of current. If the current becomes too high, the heat generated causes the bi-metal strip to bend to a point where it trips the breaker. This method is very common, but the trip mechanism can be affected by ambient conditions and other factors that compromise the device’s accuracy. However, a Thermal Circuit Breaker is sufficient to protect various loads if ambient conditions are predictable. Additionally, thermal circuit breakers are generally a less expensive option when selecting a resettable breaker.
Hydraulic Magnetic Circuit Breakers, meanwhile, offer unique features that not only protect equipment but also help optimize the operating continuity of the equipment they are protecting. Sensata-Airpax, E-T-A, and Littelfuse’s Carling Technologies are three of the primary manufacturers of Hydraulic Magnetic Circuit Breakers. Each of these circuit breaker brands offers unique features and a breadth of portfolio.
The name Hydraulic Magnetic Circuit Breaker is derived from two key mechanisms within the breaker. Propelled by an electrical field, a magnetic core moves in a tube toward a trip armature as current increases. This method of moving the core is unaffected by changes in ambient temperature. When the current becomes sufficiently large (typically 125% of rated current), the core moves against the armature, causing the breaker to trip. This tube contains hydraulic silicone fluid. The type of fluid slows down or speeds up the time it takes for the core to reach the trip mechanism.
The two primary benefits of a hydraulic magnetic breaker are that ambient temperatures do not affect the trip mechanism and that different trip delays can be implemented. These benefits are achieved by the movement of the magnetic core not being affected by ambient temperature, and by the hydraulic fluid, which creates a delay in tripping the device. This delay can be adjusted depending on the viscosity of the liquid in the travel tube. These benefits are not easily achievable with thermal breakers.
Given all the advantages of resettable circuit protection devices, there are several considerations when choosing a fuse as a circuit protection device, as follows:
• Fuses are the most commonly used device for circuit protection.
• Fuses open much faster than a circuit breaker in an over-current condition. This is especially valuable if you are protecting sensitive electronic equipment.
• Fuses have very precise voltage and current ratings if precision protection is needed.
• Fuses tend to be smaller than an equivalent circuit breaker, which is advantageous in an application where space is limited.
• Fuses tend to be chosen if the product has a one-time use, like disposable items, or even tamper-proof devices.
• Fuse trip conditions can be more precisely set if several devices need to have a coordinated protection scheme.
Choosing the most appropriate circuit protection solution can be just as critical as selecting the device or equipment that requires protection. Considerations and choices made for protecting equipment should be as important as the equipment’s function, the information it contains, and its role within a system or organization.