How Does an HRG System Detect Motor Ground Faults in 480V Pumping Systems?

Hi all,
I’m hoping this is in the right section, I am not an electrical expert.
I am a maintenance technician for a company that has many customer sites across a multi-state area. We have 480v pumping systems that utilize a primary and secondary pump. Today I was called to a site to fix a pressure leak, upon locking out the disconnect for the pump I was working on, I was met by 3 electricians who told me whichever pump I had shut off had a bad motor (imagine my surprise, I was just there to fix a leak). I was lead to their MCC building where they showed me their HRG system, I had no clue what it was but they explained that they had a fault for a while now and it just now cleared when I locked the motor out. 
After some more locking out, I opened the peckerhead on the motor to find the most charred and burnt wiring I’ve ever seen, and to think, this motor was operating a pump just hours ago!
You have to understand, the pumps and associated equipment is owned by my company, and a lease, so our customers never go inside our fence, maintenance is a part of our contract. They supply the power.
I’m not sure what caused the short in the motor but assuming insulation was rubbed through, water got into the conduit, or a connection broke loose. Is it a bad idea to have our systems run through HRG systems since we are not around to observe the fault? As a company should we require no HRG? It seems as though this should have tripped a breaker and possibly saved the motor. 
Just to be clear, they did not make any mention of investigating the fault. Seems these systems work well as long as the fault is investigated quickly.

Hi Steve-You had me baffled for a while there- I didn't know what "HRG" referred to.  After Googling it, I see it means "High Resistance Grounding". HERE is a simplified tutorial I found that explains it.Let me cogitate on this for a while and get back to you.  Meanwhile- If someone who is already up to speed on this wants to jump in- go for it!-Rick

Thanks for replying Rick, To be clear, I don’t think the HRG system caused the motor fail. My main concern is with it allowing the motor to run for way too long with a fault, with us having no idea there was a fault. This potentially could have been a very serious issue since the pumps are pumping liquid hydrogen, very flammable.

I don't think the HRG system made the fault any worse.  I think it could only have limited the damage (hard to believe, though!). I would be curious to know if the windings in the motor are still good.  Was the damage limited to the area inside the splice box only?  Was the inside of the motor full of water?It seems like a ground fault breaker would likely have limited the damage.  What kind of protective devices were installed?  If the Electricians already knew there was a bad motor, why didn't their protective equipment shut it down sooner?One clue is that since they said "Whichever pump you shut down" was in trouble, it hints to me that they may have one ground fault monitoring system that feeds several pumps.  A separate ground fault monitor (or breaker) on each pump should have prevented the worst part of the damage.-Rick