Question about soft starters?

[Starforever]

Scenario;
In tunnel we are installing truly reversible axial smoke exhaust 2-speed fans (1450/750) with 5.5/1.1 kW to run on day to day ventilation (low speed) and to run during fire mode ( high speed).
But DOL is recommended by manufacturer because when the fan goes in to high speed fire mode as high speed will have to be achieved as quickly as possible.
Can we be able to use soft starters with two speed instead of DOL connection? Do we need to have the facility to bypass the controls ?
Appreciate feedback .

 

[flexoprinting]

Good morning

You can sign up and view codes here.

http://www.nfpa.org/codes-and-standards/document-information-pages?mode=code&code=502

Chuck

 

[eeprom]

Starforever,
I assume DOL means direct across line. I also assume these are 3 phase motors.

The fan appears to be going from 4 pole to 8 pole. The speed control is not related to the soft start. The only speed setting you can change (on most soft starts) is the ramp time. Given the small size of the fan, I don't understand why you need a soft start? Whether or not you use one, you don't need two. If you want to run at speeds, other than synchronous, you will need a VFD.

Given what little I can guess about your system, you will need a set of reversing contactors to establish the forward/reverse. But how is the fan speed changed? By switch or by changing T lead connections?

EE

 

[jraef]

I've done several tunnel ventilation fan systems using soft starters. Yes, you will need full bypass capability, safety codes will require it. But normal starting with the soft starter is often desirable because of the reduction in mechanical strain on the fan, and the reduction in starting kVA required from any backup generator power source.

A soft starter will not however do the switching from low speed to high speed, thst must still be done with contactors. If you select the right soft starter however, you can get one that is capable of locked rotor current in high speed, plus a "dual ramp" feature. So that way when it must go into high speed, you change the contactors to that configuration, and at the same time signal the soft starter to use "Ramp 2" that you have set up to
Be DOL, or nearly DOL. Overall it ends up as a very expensive arrangement, so first everyone must carefully evaluate the need for the soft starter. It usually comes down to the backup generator consideration, especially if the fans are running all the time.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

A possible contradictions.
If the codes require a bypass contactor, and a soft start must be used due to generator capacity limitations, then we may have a code violation.
If a bypass contactor is used then the standby generator must be capable of starting the fans DOL on the bypass.
How many fans are to be installed and will they all be required to start simultaneously?

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

 

[Starforever]

Hi eeprom,

Yes Direct on line with 3 phase motors with single winding with number of poles to be active during high / low speed mode

Guys I am Mechanical Engineer not sure about all the controls and codes.I think better to contact control specialist locally.


Hi waross

There are 110 Nos fans throughout the length of tunnel and all fans for ventilation run on low speed and all operating at same time.

Thanks

 

[waross]

A start signal that puts all 110 fans DOL simultaneously may be an issue. The added generator capacity above what is needed for a staggered start will be over 1 Mega-Watt. I would discuss this with the AHJ to see if he will allow staggered starting or staggered transitioning from low to high speed.
I would run the numbers on splitting the motors into about 5 or more groups and transitioning each group together. Stagger the groups.
This may be a suggestion to persue with your controls specialist.
If the tunnel is zoned on the fire alarm system, you may be able to group the motors in each zone.

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