Are High Speed VFD Fuses Worth It?
Why be concerned about high speed VFD fuses?
A few weeks ago I was walking through one of our warehouses and noticed a stack of variable frequency drives (VFDs) awaiting repair.
You may be aware that we offer repair services for industrial electronics, and so it is common to see I/O boards, instruments, and drives going out for repair from our warehouses. But this was a large stack of drives from several different manufacturers and I could not help but wonder – what happened? A few phone calls later we found ourselves in a week long venture to understand why drive components fail - and quickly learned the value of high speed VFD fuses.
For example, what makes IGBTs fail and so violently rupture? After some investigation one thing we learned was that many VFDs are not protected as well as they could be. Many drives, like the ones I mentioned earlier, run successfully for years but then endure a serious fault that circuit breakers are not fast enough to respond to. High speed VFD fuses can be critical to reliability.
VFD fuse selection - The value of high speed VFD fuses.
To summarize, standard fuses (even class J) and especially circuit breakers allow too much let through current during a fault. This can lead to a ruptured IGBT, which often damages other drive components and leaves the VFD unrepairable.
Regardless of what VFDs you purchase or who you purchase from, we would like to offer you an opportunity to upgrade to high speed drive fuses. If you are using fuses today you can easily make this upgrade and enjoy the benefits of the added protection.
You may have questions about this, and a few that we get often are:
What if you are using circuit breakers? - A breaker is a great disconnecting means and can provide both short circuit and thermal overload protection. But it cannot protect your drives as fast as a fuse, so you may want to consider adding the fuse protection, especially on critical applications.
- Why upgrade when my drive manual says that standard branch protection is okay? - That is because drive manufacturers are accepting the minimum level of branch circuit protection required, and yes they will honor their warranty at that level. Branch circuit protection is acceptable for the circuit– we are making a recommendation to improve beyond that level for protection of drive components.
- How much are these fuses going to cost me? - Hopefully you are using a minimum of a class J fuse today on your motor circuits, which is our longstanding recommendation. Taking that into perspective, you could expect an estimated 30% premium for high speed VFD fuses.
- Given the premium, are these fuses really worth it? - Prior to purchasing and testing yourself, the best visual aid for your decision may simply be the energy let through curve. A comparison between the standard class J and a circuit breaker is illuminating.
