Electrostatic Precipitator

What's wrong with following the guidance already received, then?

Why we are hesitant to change insulators is even the supplier is not very confident and also it is a job which can be done in kiln stoppage.We have to procure new insulators also.But the same insulators with this type of small cracks worked well before ESP renovation.Hence,I thought whether any body help me with some different solution.Thanks.

If you have a short circuit when power is applied primary current will rise but the voltage won’t, you don’t mention current.

The insulators would have to be badly damaged to cause a fault before the voltage has a chance to ramp up.

More information needed.

Judgement call....what's the risk vs reward...

To replace the insulators isn’t a quick job and can’t be done with the kiln running. That is unless the OP totally ignores any emission limits and vents the cooler direct to atmosphere. Most of the recovered cooler exhaust material can be returned to the kiln as usable feed stock, a costly exercise if it’s vented, even worse if you get nailed for pollution.

Change the old support and shaft insulators, especially if they have developed very small cracks. Even without cracks, the insulators can form carbon traces on their surface that will leak off current to ground. Good maintenance practices should be observed to clean the insulator surfaces on a regular basis. With cracks in the insulators, it is much more likely that carbon traces will form and leak off current to ground.

Although I am not an electrician, I have another thought. Perhaps your three-phase service is old or rural like mine having only three incoming conductors. I believe this may be referred to as an ungrounded "delta" service. A consequence of having such a service is a "floating" neutral. A floating neutral means the neutral point is not earthed and is determined by the load on each phase, so it may virtually float around in potential. If the loads on each phase are perfectly balanced, the neutral point will be at zero or ground potential and will behave no differently than three-phase service having four incoming conductors, one of which is a neutral point to earth ("star" service?). However, in an ungrounded delta three-phase service, if the load is not balanced, or there is a short or "leak" to ground in one or more of the phases (such as a carbon trace on an insulator), the floating neutral point will not be at zero or ground potential. It will rise to a potential greater than zero volts. This will cause the voltage in the remaining phases to become much higher in value and, as a consequence, cause insulators to break down and possibly arc, creating new ground traces and a vicious circle of chasing such problems. How to "fix" such a system? I'll leave that to the electricians. I think I read somewhere that a corner of the delta can be grounded or a delta-delta transformer can be used and have a point between two legs taken to earth, but again, I am not an electrician, so don't go by what I say, let an electrician weigh in.

I was thinking the same thing, your new 3 phase service for the TR Sets probably has a power system ground reference your old single phase system did not have.

If the new TR Sets are auto-transformers, but the old TR Sets were fully galvanically isolated transformers, then your supplier cut a corner perhaps inadvertently, not realizing that your previously leaky insulators had only capacitive coupling to ground (ungrounded system).

With your new power system, a ground in the insulators systems is easily detected, thereby shutting down the supply when the leakage current gets high.

Going back to ungrounded operation may be possible, or you might add a transformer to isolate the TR sets from power system ground, or fix the insulators. The collection efficiency grounded/ungrounded should be the same, maybe a little better ungrounded, as you won't be charging the grounded precip casing, very small amount, depending on your ripple.

In my opinion gas temperature decrease the particle resistance.

If the new installation it is rated for less electrode number the reactor cannot limit the current at this elevated temperature and the voltage controller shuts-down the supply.

On the other hand the insulator cracks could increase the current -as if there are more electrodes than it was designed.

I think the manufacturer has to double check if the new installation corresponds the existing number of electrodes and the customer has to replace the insulators.

It may be also an equipment failure and the dissolved gas in oil has to be checked.

Do you progressively loose KV as the temperature increases or is all well until reaching 270° C and then a complete loss of KV (dead short)? With the field having been rebuilt I'm wondering if there is a thermal expansion problem within the chamber which brings emitting and collecting systems close enough to short at that temperature. For example a single collector plate with a minor variation in mounting location (or an un-slottted bolt hole) may be restrained relative to its neighbours causing it to bow out across towards the emitters. There are many close approach locations between the two where minor variations can lead to contact - and can be very frustrating to locate and correct.

270° C is well below fusion temperature of any carbon/carbonate dust in the insulators so not sure why insulator failure (tracking) would be affected by that temperature - would more expect to see an inability to reach full KV at any temperature. Unfortunately to find an expansion problem means not just shutting kiln but cooling sufficiently for internal entry to the chamber. If you do need to do this and know you already have some insulator cracking, then it would be prudent to at least be prepared to change them at the same outage.

You may also want to consider using airborne ultrasonic to "listen" for sounds of arcing / corona at the insulators while on line as one means to determine whether that may be the problem.

Further to continuance to my earlier topic Electrostatic precipitator,we have purchased new support insulators and we are going ahead with the replacement of old insulators job. Simultaneously,we have done open circuit test of the transformer and we have observed that the ESP controller panel is feeding 3 phase voltages with large variation to the transformer.

RY phase 389 volts

RB phase 369 volts

YB phase 461 volts

So,When we are increasing the voltage on primary side,when the primary voltage of transformer is attaining 380 volts and further,we are seeing voltage hunting and small typical noise from the transformer.The supplier says the voltage variation is alright for the transformer.But I am worrying it will have implications on losses,harmonics and transformer life.Kindly guide me with your advise.Supplier's point is when ESP field is connected to transformer,voltages are not full and that time,voltage difference between phase to phase will be around 30 volts only approximately.How much voltage imbalance is tolerable for power transformer.

Best Regards,

NVRSrinivas

As long as you're not running rotating machinery (induction motors) from that unbalanced source voltage, that is what will suffer due to unbalanced voltage. It is important to watch your supply system voltages in that case.

The harmonic content of your rectifiers and fields was already factored into the sizing of your transformer, assuming that the load hasn't really changed from design.

The heat load in your transformer is the sum of the 3 phases, but that 3 phase TR Set was designed for precipitator service, so the engineers who applied the equipment already understand the possibility of unbalanced field loading.

They may have a specification for what the maximum unbalanced load on the transformer is, which should allow some overload on a particular phase, providing the other two phases are lower than rated. There is some limit to the heat removal from one set of windings in the group, so would be limited that way.