Explosion in Power Factor Correction Panel

Your best bet, Mildred, is to ring the original equipment manufacturer and arrange for a call-out. Seriously!

Since we cannot see the power factor correction panel from here, and don't know any of its history, some of the questions a qualified testing and repair contractor will ask would be: 1. What is the environment in which the panel is installed? Is there air filtering to prevent cement dust from entering the panel and contaminating the components? Is it in a location in which the temperature, humidity, and other environmental conditions are within its specifications? 2. What are the electrical conditions to which the panel is exposed? Is the electrical service (voltage, frequency, etc.) within specified limits? Were there any excursions of the electrical service outside of limits before the panel failed? 3. What routine maintenance and testing was done on the panel to assure that all its components were clean and operating properly? Were all connections properly tightened and insulated? Had anyone inspected the panel prior to the failure to determine if there were any conditions that need correction? 4. Were personnel properly trained in the operation and maintenance of the panel, and was it operated within its design specifications? Was the panel properly specified in the first place, with regard to the operating conditions and purpose? So many questions, so little information. If you answer these, you may come upon the answer you are looking for by yourself...

That would make CR4 completely superfluous!

Preface: I absolutely HATE Power Factor Control done this way. It NEVER ends well in my opinion, the best you can hope for is that the expected catastrophic failure happens after you retire...

I agree on the issue of the contactors. Switching of capacitors is a special kind of duty, you need contactors rated for the task. In addition, these contactors must have a "dampening resistor" across each pole to prevent the inrush of capacitor charging current causing damage to everything in the circuit. The dampening resistors are controlled by separate parallel contacts interlocked with the main contacts in such a way as to allow the resistor to be in series just BEFORE the main contacts close, then shunted or opened when the main contacts close (because they are only needed for a few cycles).

This is what those special contactors and the circuits should look like:

The extra block on the top that has the coiled wires on it contains the dampening resistors and the early-make contacts. The wires are coiled because that inrush current will attempt to flow AT THE AVAILABLE FAULT CURRENT LEVEL for those few cycles, which makes the wires "dance" from magnetic forces. The coils act like shock absorbers so that they don't pull out of the terminals. Your system may or may not have the exact same physical arrangement, but the dampening resistors SHOULD be in the circuit somewhere.

Something that happens all too often is that the resistors eventually fail, and they fail open. Once they are not there, the rest of the components get all of the stresses associated with the extremely high inrush current of the capacitors. So the contacts of the contactors burn more, the main power leads start to "dance" and stress their terminations, and eventually, the capacitors themselves can swell and fail.

One thing that can cause the resistors to fail is that the system design itself is inappropriately selected, or something has changed. What that means is that the PF changes so dynamically that the controller is stepping caps in and out very rapidly; more rapidly than it should. the contactors are not supposed to be allowed to close until the caps have bled down to less than 50V, and that takes time. The controller usually has minimum time between step settings, but someone may have changed the setting because they (incorrectly) though that it was not tracking the power factor closely enough. That is actually the result of someone not understanding how it works and what the ramifications might be of making those changes.

You have your work cut out for you...