Fan application 2

[krsh]

Hello friends,
Company bought a used fan from an abandoned factory which i was assigned to install in our factory. The problem is when i start the fan(DOL starting) the motor protection trips. The motor is a 3 phs, 5.5 kW 50 Hz 230/380, delta/star, 20.8/11.6 Amps which i connected in star and set the OL to 12 Amps. When i measured the amps with a clamp-amp it showed 60 A and it droped slowly to 40, 30, 20 and finally to running current 10.2 A in about 4-7 sec, the problem is that the OL trips in 3-4 sec. My opinion is to install a soft starter but i am a bit undecided if it can supply the needed starting torque.
Waiting for your opinions.

 

[electricpete]

The motor is a 3 phs, 5.5 kW 50 Hz 230/380, delta/star, 20.8/11.6 Amps which i connected in star and set the OL to 12 Amps.

If 2 winding configurations are suggested on the nameplate, it should be star-start / delta run.
We have many of these that we DOL/start in delta and leave in delta.
I would not try DOL start in star and leave it in star… if that’s what you’re doing. The motor would have reduced capability.

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(2B)+(2B)' ?

 

[rbulsara]

The current draw and acceleration time sound very normal. Set the O/L slightly higher. You can go up to 125% of the rate amps. If not replace the O/L relay with proper inverse time characteristics.

Star-delta would not be a good choice in this application for the reason you mentioned.

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

Hi Pete;
From the ratings, 50Hz, 230/380V, this sounds like an IEC motor. It is common practice across the pond to change connections between star and delta to change the voltage rating of motors rather than for wye/delta starting. The motor starts and runs on delta on 230V systems and starts and runs on star on 380V systems.

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

 

[electricpete]

Thanks Bill.... I missed the dual voltage rating.

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(2B)+(2B)' ?

 

[krsh]

i attached a photo of motor plate

 

[krsh]

...and the fan

 

[krsh]

So, if i have a 3 phase 220V between phase and neutral and 380V between 2 phases, how should i connect the motor for start.

 

[krsh]

I think i will connect the motor in delta to have full torque and buy a soft starter to ramp the motor to nominal speed.
Opinions?

 

[rbulsara]

Windings will see the same full voltage in either connection. 220V (380/1.732) and hence the same torque. No real point in getting a 220V delta service.

Plus that is not the real issue. Set the O/L correctly, this is not complicated.

Rafiq Bulsara

http://www.srengineersct.com

 

[Kiribanda]

krsh,
It looks like since it is a fan and running at STAR,the motor takes a long accelerating time.
1)Are you using an O/L relay with class 10 charateristics?Beacuse it is a fan and not like a cetrifugal pump,you may have to use Class 20,which will give sometime for the starting current to die down without tripping.
2)Also check your installation to see why it is taking such a long acc time.One reason may be the air discharge line is too long to handle by the fan.
3)No need to buy a soft starter.Use a star-delta starter and run at delta with class 20 O/L relay.

 

[zlatkodo]

Hi, Krsh,

If your line to line voltage is 380 volts then you can not start this motor with star-delta combination, because the motor may not be connected at all to 380 V voltage in the delta connection.
Zlatkodo

 

[electricpete]

You’re right zlatkodo.
I apologize that I got this thread off on wrong track talking about star/delta start.
It is not a motor designed for connection to 380 with star/delta start (as I originally thought)
It is a dual voltage motor – 230 connection in delta, 380 connection in star…. as you said.

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(2B)+(2B)' ?

 

[krsh]

rbulsara, the OL protection is set to 12 amps and the motor plate says 11.6.

waross what do you mean by "230V systems and 380V systems".

 

[waross]

rbulsara gave you the answer in the second response. 11.6 Amps x 125% is 14.5 Amps. Try that.
If that doesn't work change the overloads relay to a class 20 as Kiribanda suggests.
Actually, a long discharge pipe may drop the current on that type of fan. The fan may perform better when the discharge piping is installed.

If your line to line voltage is 230 Volts or close to it, you have a 230 Volt system.
If your line to line voltage is 380 Volts or close to it, you have a 380 Volt system.

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

 

[Compositepro]

I'm a little surprised that the fan (blower) takes so long to come up to speed. This indicates high inertia or high load. The load to accelerate the blower starts high and drops to zero at full speed. The load of moving air depends on the speed of the fan, if there is no restriction on the outlet.

It sounds as though your fan is installed in your system and it operates at close to full load when is in steady state operation. If you have a long ducting system the flow through the fan will be higher than normal while the ducts come up to full pressure. You might want to see if you need this full flow all the time. If you do, you could use a damper to restrict flow until the blower comes up to speed.

 

[rbulsara]

krsh:

the OL protection is set to 12 amps and the motor plate says 11.6.

That IS the problem. Not only it is low, the relay may be of wrong thermal class. Also see what Kiribanda said Or get an help of an experienced "electrician".

Rafiq Bulsara

http://www.srengineersct.com

 

[krsh]

I set the OL at 16 amps and still trips, only when i replaced it with a 20 amps OL than it runs OK and has the starting current of 60 amps and the running current of 13 amps clockwise and 10.2 CCW. The real problem is as compositepro said, high inertia, that is the reason why it takes so long to reach nominal speed and the reason why the OL trips. The bearings are ok you can spin the shaft easily with your hand and is nothing wrong with the pipes because i tested it not connected to pipes as you see in the photo in my previous post(maybe this is the reason why it has a high running current?). The question is to install a soft starter or use a OL which trips with a higher time delay.

 

[waross]

What is the voltage in your factory?

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

 

[krsh]

We have 3 phase 50Hz 380 V between 2 phase and 220V between phase and N.