Motor & Pump Protection

[zaza123]

If there is a fault at the Drive end side bearing of the pump, the bearing & the shaft gets overheated & damaged.Should the induction motor does not trip before this condition.The motor thermal overload shall operate to prevent such condition.please clear my doubts

thanks in advance

 

[itsmoked]

Is this motor run with a VFD?

What size motor?
What type of pump?
What is the pump pumping?

How long does it take to heat up?

And the general motor housing does not seem to heat up too much?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

The motor overload protection protects the motor from thermal damage.

It cannot protect against bearing damage in a driven machine or in the motor for that matter.


Bearing damage can lead to shaft damage from scraping/wear/heating.

The motor shaft should not be damaged from any associated torque overload since worst-case torque overload is typically locked rotor and shaft can withstand that (and motor would trip on overload within a short period with no winding thermal damage expected).

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[electricpete]

and shaft can withstand that

I should clarify motor shaft can withstand locked rotor torque. Pump shaft normally will be I'm not sure that is a guarantee. I have seen vertical pumps with long shafts that were a heckuva lot thinner than the motor shaft.

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[waross]

I recently did some work installing vibration elements and temperature elements on a group of motors throughout a plant. The intention is to log the temperature and vibration signature of the pump bearings to anticipate failures. All bearings have vibration elements. Some pumps in hot product service with oil circulation and cooling do not have temperature elements.
These signals are transmitted to trending software in the control room.
Short answer:- No, motor overload protection will not protect pump bearings.

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

 

[zaza123]

Thanks for the answers, While the Pump bearings are damaged & pump shaft is getting damaged will the motor current will increase or not.
The motor is 900 KW & not run with VFD, voltage level 4.16 KV, Rated current 156 A.
Is it normal for the motor to take 1MW load.

Zaza

 

[waross]

will the motor current will increase or not.

The motor current may increase but not enough to be a useful protection indicator.
A change in the dynamic head, a change in the temperature of the product, a change in the SG of the product and a lot of other things will make more difference to motor current than the increase in current caused by failing bearings.

Is it normal for the motor to take 1MW load.

It depends:
Does the motor have a service factor greater than 1?
Why do you think that the motor is taking over 1MW load?
How are you measuring the load?

For bearing protection look here:

http://www.omega.com/toc_asp/subsectionSC.asp?subsection=K&book=Pressure&all=1

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

 

[jraef]

You did not describe the details of what you are using for motor overload protection. But assuming the worst, a simple bi-metal thermal overload relay, the overload protection is based on an inverse I²t time-current curve, meaning that the time to trip will decrease at the square of the increase in current. The cheapest will have an OL pickup point of 125% of FLA setting as well. So if you have a 900kW motor and the load increases to 1MW, then the motor is going to be overloaded by only 11%. At an 11% overload, I would expect a basic cheap Class 10 OL relay to trip in hours, if it trips at all.

An OL relay will pick up a bad bearing only after the friction it causes increases the motor loading into that OL detection range, in other words, LONG after the damage is done. That is not what a basic OL relay is designed to do.

If I had to guess, I'd say you have an OL relay selected based on the lowest cost, not the best protection of your motor investment. You need something more sophisticated, what we refer to as a Motor Protection Relay, along with the proper sensors as mentioned above.


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[edison123]

You are asking electrical protection to act for mechanical failures. Unless the bearing failure resulted in a locked rotor condition, your electrical protection will not act.

Provide Bearing RTD's and Vibration sensors to protect your motor as well as your pumps mechanically.

 

[LionelHutz]

Think of it this way, you need to add significant extra load to the motor for the overload to trip. Say you need at least 20% extra load and even then it could take hours to trip. The only way a bearing could add 20% extra load is to dissipate 20% of the motor power as heat. Do you really want 180kW, as a minimum, dissipated by the failing bearing for a long period of time? Dumping that amount of power power into the bearing will cook everything and destroy parts.

You need to add bearing RTD's and a monitoring relay.