Overheated VTP motor

[sowhatso]

75HP motor for a vertical turbine pump is overheated afer 100 hrs of operation , the pump is running at the rignt side of the curve, inaddition , a high vibration can be observed. can any one tell me what may cause this overheat ?? I think that running at the right side of the curve with higher flowrate than the duty point (or BEP) will increase the required NPSH which will quicken impeller failure. but how can this cause the overheat of the motor .

Note : the absoverd shaft power (output power) at the running point at the right side of the curve is about 35 hp, which is still less than the rated power of the motor. can you please help me in any idea or expectation for this cause of overheating ????

 

[thewellguy]

we need more info. Were the amps normal at start up, whats the poewr supply and did it remain constant, define overheating ect

 

[TenPenny]

The most likely cause of overheating the motor is overloading. As stated above, do you know the running amp load it was drawing?

As to your 35 hp at runout on the curve...is this a single stage pump? Is the curve for a single stage? Oftimes, the curves provided are a single stage curve.

 

[JRLAKE]

Very good point TenPenny. Why would you select a 75 HP motor with a runout of 35 HP?

 

[sowhatso]

The motor is 75HP US Motor, Class F insulation , the motor is installed inside aroom , but it is located in an area that could be considered of hot weather , 35-40Cdeg .The nominal current of the motor is 100 Amp , and the current at the running point is 63 amp.the pump is multistage. the motor is little oversized as the owner is planning to change the pump with higher capacity.

Any other ideas regarding the overheated rather than the overloading ?

 

[Artisi]

What is overheated- have you measured the motor temperature?

If the motor is inside of a room, is there sufficient cooling air available to the motor?

 

[TenPenny]

If the motor is in an enclosed room which potentially could get hot, you'll need to find out what the maximum ambient room temperature is, then look up the motor data for the temperature rise for the highest expected load condition.

You'll need all the nameplate data off the motor. It is entirely possible that a motor with no special insulation can overheat if it is in an enclosed space.

Typically, a standard motor will be a Class B insulation, which is capable of a 90 deg C temp rise, in a 40 deg C ambient. A higher ambient will leave you less room for temp rise.

 

[dcasto]

HUMMM 63 amps is 48HP, pump spinning right direction? like TenPenny, how many stages?

 

[sowhatso]

The pump has 22 stages , 6" , the DESIGNED pumping point is 100m3/hr at 90m head . the owner of the well insist to run the pump with 110m3/hr , he doesn,t understand the bad effect of runing the pump at the right side of the curve , he just want to get the maximum capacity, so I expect that this farmer will operate it at higher discharge in the future which will destroy the pump very soon, but still the motor is ok as it is oversized and the maximum output power at maximum discharge ( when the owner open the valve fully)is still about 50hp.

The motor is of class F , AND 1.15 SF , WHICH allows 110c deg rise of temperature above the ambient. I didn,t reach this high tempreture yet but I,m still concern about this high temperature which is about 80 C deg.

Thanks for all your inputs

 

[Artisi]

Can't see any problem with this installation, running at 10% to the right of BEP will be ok and if the motor is allowed 110c rise above ambient and the operating temp is now only 80c where is your problem?