Can we start an ID fan motor 700 kW 690 Vac direct on line? 5

[SA07]

Hi
Our VSD is faulty. Our spare soft starter is being used on a second plant. We do not have another spare VSD or soft starter

The motor is supplied from the following double winding transformer transformer

3.63 MVA 11kV/400V 630 kVA 690V/3MVA Dynyn11 50 Hz Primary 1 11500 2. 11275 3. 11000 4. 10275 5 10450 Sec BT1 715V BT2 415V Current 190.5 A 2422A

 

[LittleInch]

Also could you run a cable from another 690V supply into the switchboard from another TX or source?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[seanleed]

"The boiler is operating well now although with a VSD the kW consumed would be much less."

Has anyone confirmed this?

We found that up to 80% nominal speed a VSD saved anergy and after that it tailed off until it cost more to run it through a VSD. At 50Hz, we were using 1.2x the energy that would be used DOL. For motors that were running at their rated speed we used a soft starter with bypass.

 

[jraef]

At 50Hz, we were using 1.2x the energy that would be used DOL.

VFDs are generally about 95-97% efficient. So yes, at full speed there are losses, but 20%? I find that difficult to believe. There has to be more to that story...

Still, it's a valid point in that if you are going to run a motor at full speed most of the time, a VFD may cost you in energy losses. The energy saving value is in being a more efficient way of VARYING the flow in a centrifugal machine. If the flow is not varying, don't use a VFD (unless there is no other way to accelerate it, which happens sometimes).

This is the first time that I can remember disagreeing with you Jeff.
Transformers saturate from over-voltage not overload.
As the impedance of the load drops, the current increases and the terminal voltage drops until the load impedance reaches zero Ohms and the current reaches the available Short Circuit Current as determined by the the transformer impedance.
Apart from that I am in agreement with you.

Bill, to be quite honest, I never really thought that through too much, I simply observed it (the first time on the motors for the drawbridge at Ford Island, going to the USS Arizona memorial at Pearl Harbor**) and made the leap to comparing it to a reactor start. I will, in the future, stop using that explanation in favor of yours. Makes a lot more sense.


**I built Soft Starters for the twin 75HP drawbridge motors for that back in the late 90s. I got called out there to troubleshoot them after installation, because they "weren't working". Turned out they put 75KA transformers feeding the 75HP motors, thinking that the soft starters would "magically" fix this problem. They of course didn't, because by the end of the ramp time, there was still no voltage to give to the motors and the OLs would trip out. So we bypassed the OLs for 30 seconds and it allowed the motors to come up to speed. I basically turned the ramp time to near zero, because the Soft Starter was not doing anything useful anyway, but I never told them that... Since then I have seen similar situations with under sized transformers resulting in a quasi-soft starter arrangement, but only if the motor is the only load affected.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

I suspected that the old auto-transformer starters had a series impedance component as well as the transformer action.
Unfortunately for my research, by the time that the suspicions developed I had drifted away from plants with auto-transformer starters and never got the chance to do a voltage during a start.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SilverfoxUK]

I really can't see this working.
If you can't get a VSD you might try a soft start.
Its usual to put a bypass around the soft start once it has done its job to cut losses.
I've seen largish LV pumps on a 415V system but the motors were specials and had resistance starters on them.
Swapping drives around etc and you mention gasses is it safe to assume we don't have any hazardous gas conditions.
A fan is a horrible thing to start and connecting the fan as a DOL I would suggest having a large fire extinguisher to hand for the MCC.

 

[SA07]

3 blocks have been replaced on our VSD 1.
Unit 1 is operating with VSD on ID fan
Unit 2 is operating with Soft starter on ID fan
For info

Both units are exporting same MW

we have
844 kW on aux transfo unit 1
1306 kW on aux transfo unit 2
VSD ID fan 2 operating at 36.3 Hz consuming 221 kW
ID fan 2 operating fixed speed
Unit 2 is consuming 462 kW more

 

[waross]

Thank you very much for the update.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!