Winding Temperature for Motor-Driven Air Compressor

My first thoughts are is the motor overloads in the starter tripping assuming they are sized properely, somewhere about 15% above the motor FLA. What is the temperature rise rating on the nameplate. Reason being, service factor. Is it 115%? Tell you what I did in an emergency condition with a transformer until we got a new one, I put a fan blowing directly on it! Worked to!

V=4160

60hrz

671KW

FLA=114

Amb temp 55: Max temp rise 80K/1.0 900hp

What I believed is that your air compressor motor is designed and using up all the motor Service Factor to its maximum capacity. Just do a simple calculation by using this formula,

Power = V*I*1.732*0.85

Power = KW of the motor

V= Applied Voltage

I = Motor Current

Check your motor KW and calculate the actual motor nominal running current and compare to your actual measure current at the compressor. I am sure that your measure current is higher than your nominal motor running current.

If that is the case, there is nothing you can do you have to replace the unload or solve the problem of the unload valve. At the mean time, you have to put some fans to cool down the motor. Running the motor too long will cause the motor winding to burnt. The outside of the motor may be 90c but the internal of the motor winding may be higher than 90c. So I suggest you better take all the precaution needed to protect your air compressor motor.

Actually Motor current is varying during loading 105amp and unloading 35amp. But after the valve defected, during loading current is 105amp and during unloading 80amp.

When your air compressor is loading the motor will run at it maximum amps. Since your unloading valve have some problem, from the unloading amps of 80 A indicated that your air compress motor (during the unloading stage) is still between the loading and the unloading stage.

Well, you have to replace the valve. What is your air compressor motor rated KW (Power) and your Voltage. It is 380V or 415V

I'm not too familiar with this compressor, but if I understand correct the unload valve take load of the motor once certain criteria in the compressor is met?

My question (if my assumption is correct): what is the winding temperature if the motor is under full load?

It's there probably already some hot climate where the compressor is positioned for a fan to cool it. Maybe use a mobile air conditioner ? (recirculating cooling air around the motor). Also maybe it's possible to reduce somehow in other way the load on the comp (let's say - my arbitrary numbers - make it handling not 100 cub meters per minute, but 75, maybe by just slightly closing the air ingress) ?

My first question about your compressor would be in regards to set up. It seems odd that your motor is overheating in unload and not in load when it is doing more work. So I must ask about the machine's electrical input requirements, the overload protection provided to it and the line size providing service. Most times I've been called out to diagnose some ones install problems I encounter something in these three areas. Most commonly I'll walk into some ones shop and quite simply management would not provide for their maint. dept. either time or proper materials to do the job correctly. The number one problem I find is that the electrical run is insufficient. Owners don't like to hear that the run they put in for the last unit is insufficient for their new one. (But it's only 35% larger than the last one!) Most equipment comes with its own overload system however selecting the correct element size is still up to the guy in the shop. Next up on the list would be your air lines to the shop to make sure that they are sized appropriately. (I hear the same response as with the electrical run). Then there is environment to consider. I don't know to many company's that do not put their compressors in the mechanical room. (with the heat, and the dirt, and the nasty stuff on the floor...) any how compressors like the cold. (funny how things work like that) If its stuck in a hot room with plenty of dirty air to choke up the filters then expect problems. All of these could lead to the motor overheating. and with a restrictive air system it could effect the proper operation of the load unload valve.(excessive cycling, etc.)

Now I'm not saying you've got a dirty shop. I'm also not saying you did the install wrong. I have no way of knowing these things without being there. I'm just saying that these are things I see on occasion and would likely start there.

Good luck!

yes it is in close silencer as shown in picture

I might take a different approach to solving this problem. First, you might remove and repair the unloader valve. If repair is out of the question, you might install a temporary unloader bypass valve, either solenoid or manually operated until the automatic valve is replaced.

When you say it is tripping, do you mean you have to reset the motor overloads due to the motor overheating or is it tripping due to a high air temperature from one of the other sensors ? It looks like when you are getting a current of 80 amps during unloading you are not fully unloading and may still be building some heat from compression, thus increasing the discharge temperature at one of the sensors, most likely at the airend discharge. It may be hard to believe, but when a screw compressor runs partially loaded it will run hotter. I have had situations with my customers where I have told them in similar cases to open an airline and waste some air to make to the compressor run fully loaded and the temperature actually drops until we can get them a new valve shipped in and replaced.

It is typical for air compressors to be overload if unloading solenoid is not working. If you can not fix unloading solenoid try to fit valve to open it for unloaded start. But if your compressor runs in auto mode there is no help.

Its Really simple.See what is the insulation used on the name plate.Normally it should be Class F.See Design ambient which should be 40Deg C (Again On name plate)If Its class F , Check ambient let's say its 45 Deg then you can go as high as 100Deg C Rise that means total 145 DEG c .If it is class B you can allow up to 120Total including ambient.Though it is normal to have rise decresed by 10Deg C for measurement by thermometer as compared to measurement by winding resitance in this case its ok.All u have to do is to check the temperature over a period of time and then reset the trip.Since it is a compressor motor motor it will also have a service factor 1.1 or 1.15 Check that on name plate.I hope its clear.

There has been some very good answers given since you first ask this question! I know the starter overloads would have certainly protected your motor or you would have more questions. My question is, what the hell is taken FedEx so long to get you a new unloader valve? Just asking?