3 PHASE 180KW STEAM GEN BLOWING FUSES

[retirede]

It would take a huge spike to cause a catastrophic heater failure. Not impossible, but I’m skeptical.

 

[synchro]

Wow! Great suggestions. To answer a couple of your questions... The fuses and elements that are failing are in the generator that remains powered. The fact that the failures occur only when the other generator is taken off line would seem to indicate that water quality in this case is not an issue.

The one thing that does intrigue me is the PF correction idea. That is a question I think the facilities folks probably would not even know, but I can see how that might affect this. Would it matter at what point in the sine wave relative to voltage and current the power was interrupted? I really need to look at this one... again.... thank you ALL for your feedback.

A power factor correction capacitor by itself would probably not cause this issue. But of course the reason you would have such a capacitor is because there are inductive loads present. Then you have an LC circuit, and it could ring and overshoot when a load is shut down.
The remaining delta connected load should provide some damping though. Are the elements that fail across the same pair of phases as those that are shut down, or they across a different pair? Or do all phases maintain some loading?

Also, it's possible that the common mode volage of a delta or ungrounded wye transformer secondary could be ringing or overshooting.

 

[kwired]

===============
My apologies for the delay. You are all very kind to even give this thought. We have had some "fires" lately and this is only one of them.
I did mention today in a thread above it is a CES Chromalox generator, but the design is considered proprietary. I can tell you there is nothing special about it. We have them in use elsewhere and we service them with our medical equipment in many places. The water level control is via a Warrick control board and the elements are controlled via standard contactors.

I tend to believe there is an issue with the overall system not the generators specifically and that is what I'm trying to get our techs to discover. I tend to think there is something happening between ground and the phases, but we have yet to discover that. It is a delta heater configuration, but I do not know if the feeds have a neutral or not coming from a wye source. What if there is a neutral and it is tied to ground....? Thank you all again... I will definitely post to this when we discover the cause.

Neutral point of the wye source is the point that is grounded. No problem if it is going straight back to source or point where the system bonding occurs, that is exactly where the EGC is going and it will just function same as an EGC. If it is tied to other current carrying neutrals beyond the system bonding jumper then it can be carrying some neutral current from those circuits which creates some code issues, but probably isn't going to effect your heating elements.

The wye system will have 120 volts to neutral/ground. If you supply it with a corner grounded delta you will have full line volts to ground. (usually going to be 240 or 480 volts if corner ground delta)

 

[Barbqranch]

This is probably a silly question from one who has never dealt w/ large electric boilers, but, how do you know when it fails? Is there an alarm, or a loud bang, cloud of smoke, or gush of water?

 

[Russs57]

I am not inclined to share your belief that failure of the elements occurring with the boiler that stays on-line rules out water chemistry.

When you take one boiler off-line the other will increase it's firing rate. If water chemistry is poor you will have contaminates at the steam/water boundary layer. This can lead to foaming and surging which gets worse at higher firing rates.

There is a difference between bottom and surface blow down and their intended purpose.

Do these boilers have a surface blow down controller and does it work correctly? Are the elements that are failing nearer the bottom or the top of the boiler?

There are many questions like percentage of condensate rate vs makeup water. Also how the makeup water is treated and it's type. Then we get into operator areas like blow down frequency, water testing, operating/safety control testing, etc.

Boilers that are part of a "packaged" sterilizer are often considered not the "maintenance" people's responsibility and the sterilizer service contract people don't come often enough, nor understand boiler operation well enough, to insure safe operating conditions (in my experience).

I wish you luck in solving this problem but I think you wouldn't be doing your "due diligence" if you are convinced, without evidence, it is only electrical in nature.

 

[gadfly56]

I am not inclined to share your belief that failure of the elements occurring with the boiler that stays on-line rules out water chemistry.

When you take one boiler off-line the other will increase it's firing rate. If water chemistry is poor you will have contaminates at the steam/water boundary layer. This can lead to foaming and surging which gets worse at higher firing rates.

There is a difference between bottom and surface blow down and their intended purpose.

Do these boilers have a surface blow down controller and does it work correctly? Are the elements that are failing nearer the bottom or the top of the boiler?

There are many questions like percentage of condensate rate vs makeup water. Also how the makeup water is treated and it's type. Then we get into operator areas like blow down frequency, water testing, operating/safety control testing, etc.

Boilers that are part of a "packaged" sterilizer are often considered not the "maintenance" people's responsibility and the sterilizer service contract people don't come often enough, nor understand boiler operation well enough, to insure safe operating conditions (in my experience).

I wish you luck in solving this problem but I think you wouldn't be doing your "due diligence" if you are convinced, without evidence, it is only electrical in nature.

How does that happen with an electric steam generator? :?:?

 

[zbang]

How does that happen with an electric steam generator?

firing rate often indicates the energy input to a boiler, which isn't always fire

If the steam consumption does not drop by as much as the 2nd boiler was contribution, then the 1st has to make that up. Once the pressure drops enough to start "firing", the control system will start/increase the heat input and hold it on for longer (higher firing rate) than it would have before.

OTOH if the steam consumption has already been cut, then even the 1st may not fire as much.

 

[kwired]

This is probably a silly question from one who has never dealt w/ large electric boilers, but, how do you know when it fails? Is there an alarm, or a loud bang, cloud of smoke, or gush of water?

How does that happen with an electric steam generator? :?:?

firing rate often indicates the energy input to a boiler, which isn't always fire

If the steam consumption does not drop by as much as the 2nd boiler was contribution, then the 1st has to make that up. Once the pressure drops enough to start "firing", the control system will start/increase the heat input and hold it on for longer (higher firing rate) than it would have before.

OTOH if the steam consumption has already been cut, then even the 1st may not fire as much.

If the element had a variable rate controller ahead of it I guess it would have variable firing rate, otherwise if controlled by simple contactor it has either zero or 100 percent firing rate.

 

[synchro]

===============

I did mention today in a thread above it is a CES Chromalox generator, but the design is considered proprietary. I can tell you there is nothing special about it. We have them in use elsewhere and we service them with our medical equipment in many places. The water level control is via a Warrick control board and the elements are controlled via standard contactors.

Make sure that there's a good dedicated ground wire connection between each control board and its respective boiler.
This is necessary to have the water level sensors operating correctly on a consistent basis.
It's simple thing but could still cause problems.

By the way, how soon after a boiler is shut off does a fuse blow on the one that's still online? A low water sensing problem would take some amount of time before water is consumed and it causes a heating element to overheat and fail, but element damage due to a voltage surge (if it's happening) would likely blow a fuse more quickly.