550V AC Motor protection 1

[Electrical4life]

We have been losing motors lately due to wet insulation from high jet water ( our plant operates in very wet environment). I have installed earth leakage relays (CBCT) of 250mA but relay only operates after motor damage. Whay is the best electrical protection for this application?

 

[racookpe1978]

Physically, how do you (now) protect the motors from direct water impingment?
If you have no direct shielding, why not?

 

[magoo2]

What type of enclosure is used for the motor? An open driproof enclosure will protect from overhead water (like rain) but you might need something like a totally enclosed fan cooled (TEFC) design if you get too wet an environment.

 

[Electrical4life]

We have covered canopies on motors to protect mainly the terminal box, i want to find out if there is any electrical protection scheme suitable instead of physical protection?

 

[edison123]

For your type of wet environment, IP54 enclosure is a minimum. You may even require higher protection. See the Nema chart link below.

http://www.nemaenclosures.com/enclosure-ratings/ip-enclosures/ip54-enclosures.html

Providing a canopy over the motor will not prevent the moisture being sucked inside the motor by the cooling fan, if the motor is open type.

Muthu

http://www.edison.co.in

 

[Electrical4life]

Thanks edison123,
All our motors are currently IP54 enclosure, we mostly ABB and WEG motors, but somehow water gets inside. I want to implement scheme whereby motor should trip immediately water gets in touch with windings.

Any suggestion?

 

[edison123]

That's odd. Can you post some photos of the motor installation?

Muthu

http://www.edison.co.in

 

[waross]

It may seem like overkill, but at the end of the day,-
Is it feasible to pressurize the motors with dry air? Low pressure, just enough to maintain positive pressure.
Instrument air comes to mind as a readily available source of dry, low pressure air.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Electrical4life]

Edison,

Please see attached picture for one installation.

Waross,

We have over 200 motors installed in the plant so it will be costly and cumbersome to install instrument air.

 

[edison123]

That's is a IP 54 encl alright. But why so much wet gunk on the top of the motor?

My suspicion would be the wet gunk might seep some water into the terminal box, which, unfortunately in this case, is located on top. This could cause winding earth fault.

A removable slopey canopy might help keep off the wet stuff away from the motor. But the root cause of accumulation of that bad stuff on the top of the motor must be studied and eliminated.

Muthu

http://www.edison.co.in

 

[Electrical4life]

Dear Edison,
Yes this an IP54 enclosure ABB motor.

We operate in a cobalt process plant so sometimes we get pipe leaks and overflows that ends up on motors sometimes unfortunately, hence the junk on motor.

How do we prevent winding earth fault electrically? earth fault relay installed upstream on 11kv board only operates after motor damage.

Just now we lost another CG motor with IP65 encl.

 

[flexoprinting]

Hmm...interesting, is it possible your getting a sort of Capillary action drawing the moisture into the motor through shaft seals?, What about open hole's from OEM. Possibly hoist eyelets which
have been removed from motor. I do like the low pressure idea proposed above.

Chuck

 

[flexoprinting]

I know the low pressure idea would be a challenge considering how many motors you have however, consider the alternative with lets say GFI
protection. Motor faults out, now what disassemble to dry it or cook it out with low voltage or what ever, that's going to be a hassle as well.
I really think mitigating the intrusion is substantial.

Chuck

 

[jraef]

I agree that the first action would be to try to prevent that material buildup on the motor. That is also reducing the ability for it to cool itself adequately which may be contributing to the insulation damage. I would start there.

But you cannot "prevent winding earth fault" electrically. By definition, it is not an "earth fault" until it is a fault, so preventing it is preventing the physical deterioration of the insulation, which is not exactly an electrical issue. You MUST address the factors leading to that insulation deterioration.

One POSSIBLE electrical related solution would be to avoid allowing any internal condensation from forming as a result of the aforementioned wicking action of that wet material when the motors are turned off. While running, the heat from running will not allow that to happen, but when you shut down and the motor cools, the air inside of the connection box cools and shrinks, pulling air in from the conduit, or if sealed, through gaskets. If that air has moisture on it, the moisture will condense on the surfaces as they cool, which allows for hygroscopic absorption through the insulation. Then when the motor is turned on and heats up again, that moisture expands as vapor pressure and can start breaking down the insulation, creating a cascading failure. So to prevent this, you need top keep the motors warm when they are off line. The usual method is to use space heaters built-in to the frame or attached to it, but they need to be powered, which means conduit and wire added to all of the motor locations. Another method is a low voltage "motor winding heater" that trickles a small amount of low voltage current into the motor through it's own power leads, just enough to keep the windings above the dew point. This is done a lot in marine environments where the motors are constantly wet when off line. I suggest that you look into that.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[resqcapt19]

What wiring method is used to supply power to the motor? Water often enters the motor connection box via the conduit connection, if conduit is being used.

 

[itsmoked]

Dropping or splashing cold water/material on the warm running motor will drop the case temperature suddenly creating low pressure excursions in the motor. These will cause the motor to "take a breath" which sucks in moisture laden air.

Based on the the sopping nature of your plant, the questionable conduit breathing paths likely into every last motor in the place, and the hassle of providing heating power to hundreds of motors in the 'hope' that the windings remain dry, I believe you should reconsider your opinion on the plumbing of dry air to each and every motor. It's relatively easy and it will be absolutely effective. You just run a few distribution lines around the plant then you can use inexpensive 1/4" plastic pneumatic tubing you cut with scissors and John Guest fittings, that require no tools, to connect everything together.

You want only 0.1 or 0.2 inches of water column to keep the water out. Each motor would have a very low pressure regulator, a pressure relief valve(in case the regulator stuck on), and I'd include a little inexpensive floating ball flow indicator to quickly detect "problem motors". The distribution lines would only have 1 or 2 psi in them. Think of the whole thing as a gas appliance supply installation.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Electrical4life

Protection relays are fault-centric, they operate once a fault occurs (to prevent further damages) but they cannot prevent a fault from occurring. So, you need to mitigate the circumstances that lead to faults. And in your case, the motor is operating in an environment for which motors are not designed to operate.

Have you thought about rerouting the pipelines so that they don't cross over the motor? Yes, it's a pita but considering the no. of motors you are losing, it might be worth a shot.

I had faced similar problems in a thermal power station in which ID/FD fan motors which were located outside and the flyash would collect on the motor surfaces and would create earth faults whenever there was rain. Upon my suggestion, a removable light weight canopy was installed over these motors and the motor failures dropped dramatically. But in your case, I don't know what kind of canopy would withstand hot(?) cobalt droppings.

To the eng-tips site admin: Edits to the posts don't stick. Repeated error messages.



Muthu

http://www.edison.co.in

 

[waross]

Heat cycling will cause internal pressure cycling. If there is any path for leakage some air will be forced out when the motor is hot. Then when the motor cools the internal pressure will go negative and air will be drawn into the motor housing. Matter piling up on the motor and impeding cooling air will cause the motor to run hotter and increase the amount of temperature and pressure cycling.
If you do go with the air option, you may consider an initial test with low pressure freon and a halide leak detector to locate motors with bad seals and excess air leakage.
You don't have to avoid very many motor burnouts to justify the cost of an air system.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

I have installed earth leakage relays (CBCT) of 250mA but relay only operates after motor damage.

- Maybe, you can try with a more sensitive relay with significantly lower leakage current?
- Another thing you can try (at least during rewinding) is improving the insulation (quality and thickness) and varnishing (twice to get thicker layer).

Winding Repair and Design

 

[robert122]

In your case Earth fault relay operates only when the insulation of motor is broke down. It is adviceable to use IP rated motors for operating in wet environments. Earth fault protection is not going to help you.