On Wednesday, March 23, 2022 IEEE PSES Chicago hosted a virtual meeting with some brief updates followed by a presentation via Teams (due to problems with Webex), which was well attended. The meeting began with PSES Chair, Barbara Kelkhoff, providing some brief business updates on the IEEE PSES Chicago schedule of technical topics and other items of interest. There was a reminder to members that the chapter records are stored in the PSES website. The April 2022 meeting will be on the topic of Market Surveillance discussing issues in the field (UL). There is also a speaker in the works on H2 refueling station criteria (UL) TBD for date of presentation. The chapter is looking for speakers on tech topics for future meetings and the committee is also open to proposals from members for topics of interest.
Events of interest to IEEE PSES:
- September dates are on for ISPCE 2022 for September 20-22, 2022 in San Diego CA
- SPCE 2022 – Atlanta GE (date TBD)
A technical presentation was then provided by Ray Zumbahlen (technical services) and Tyler Klassen (sales engineer manager) and Josh Lueders (sales engineer) both of Littelfuse, entitled, “Fuseology”, which looks at industrial power fuses and their applications. Ray Zumbahlen has a Bachelor of Science degree in Electrical Engineering from the University of Illinois Urbana Champaign and has worked at Littelfuse for over 10 years where he has been involved in various engineering functions focusing on industrial fuse validation, design, and applications. Tyler Klassen has a Bachelor of Science degree in Electrical Engineering from the University of Saskatchewan and has over 25 years of experience specializing in system grounding, ground-fault protection, arc-flash protection, and electrical distribution used in mining, oil and gas, and other heavy industries. He is currently registered as a Professional Engineer in Canada.
The presentation began with an overview of the purpose of a fuse as the planned internal weak link of a circuit and what it protects. Comparing the benefits of fuses when compared to circuit breakers, they speakers noted that the fuse is a simpler, requires no maintenance, operates quicker, is more reliable, and is smaller. They also noted that it is simpler to coordinate fuses in a circuit of multiple fuses than using multiple circuit breakers for the same purpose.
The two types of overcurrent protection are short circuit protection and overload protection. Examples of when these two conditions would occur:
- Short Circuit – a fault flowing outside of the intended path (e.g. a screwdriver shorting over a circuit during servicing)
- Overload – current within normal path, but the current load is drawing more current than it normally would (e.g. a damaged bearing of a motor). An overload current is typically less than six times the rated normal current.
The fuse will quickly clear a short circuit condition such as described above. For an overload, the fuse will have a different section that responds to lower levels of current (overcurrent), which is a dual element fuse. This design approach was developed to meet the code per NEC 240.2 and NEC 240.4, and represents good engineering design.
The presentation also covered details on dual element fuse design, which has no moving parts, no air chambers, is sand filled (quenching arcs), clears faster, etc. For short circuit (a high level of current over a short amount of time) there is a metal ribbon in the center with weak links, and for overload protection (as defined above) the design is a solder pellet typically, that heats up and melts with a rubber plug squeezing it and opening the circuit. The presentation also noted diffusion fuse design, which combines different alloys to create different time-current characteristics.
Industrial fuses are classified into several different categories: Class RK1, Class RK5, Class J, Class L, Class T, Class G, midget, Class CC/CD, Telcom, Medium voltage fuses. The presenters noted that when designing for fuses, the circuit designer needs to consider the following: voltage rating, current rating, interrupting rating (SC rating 10 – 200 kA), fuse characteristic (time delay, fast acting), physical size, current limiting (varies), indication (open indication that they have operated. The presenters gave some details from each of these fuse classes including explaining what type of circuits they would be protecting. The presentation also covered the fuse ratings and operating curves. The ratings for fuses are current, voltage, operating currents and fuse reaction times (time delay fuses). The curve specifications include the fuse characteristic curve and peak let through curve.
Current limiting aspects of fuses were also described in the presentation. Current limiting devices open and clear within the first half of the electrical cycle, and must have a rejection feature. For example a fuse holder designed to only accept fuses with this feature would be a type of rejection feature. These types of fuses operate by stopping the flow of current and by reducing I2T. They need to have a defined peak let through current and defined I2T to meet class requirements for the fuse. Class CC is the most current limiting type.
The presentation was followed by short Q & A session. It was noted during the Q & A session that differences between UL and IEC criteria (e.g. IEC 60269-6 and UL 248-19) are small but impactful, such as protection range. It was also noted that UL standard fuse classifications are quite different from the IEC classifications. It was also noted that the designer should never use a fuse with a lower operating current than the circuit fault current. Finally, there are no UL standards for battery fuses, but that the IEC had developed criteria for fuses that are intended for battery protection.
Littelfuse provides a lot of support for their products and they have online tools and whitepapers readily available on their website.