Limiting startup current
Limiting startup current
(OP)
Hello Folks,
what practical (and cheap) solutions are there to limit the startup current of a 0.8MW fan? It is directly connected to the network and the high startup current causes a lot of trouble for me and customer. I have been thinking of inserting some resistance during startup and removing them once the fan is stable but did not find any detailed technical information of that. Any thoughts appreciated.
R
what practical (and cheap) solutions are there to limit the startup current of a 0.8MW fan? It is directly connected to the network and the high startup current causes a lot of trouble for me and customer. I have been thinking of inserting some resistance during startup and removing them once the fan is stable but did not find any detailed technical information of that. Any thoughts appreciated.
R





RE: Limiting startup current
With an 800KW fan i'd be surprised if the fan supplier did not have some ideas for you so its worth trying them.
If its supplied from some sort of VSD then you could maybe code in some kind of soft start.
Alternatively, switching out resistors just after start-up as you say sounds good.
RE: Limiting startup current
Do you happen to have (or know of) some online technical information on resistor switching technique? (Dimensioning etc.)
RE: Limiting startup current
You have to make sure the motor will provide enough torque at reduced voltage regardless of what starting method you choose.
RE: Limiting startup current
If the pump is connected in wye, then a delta-wye starting method will usually reduce the starting current - might possibly be cheaper than the electronic soft start although also can cause some problems with switching transients and incorrect timing of the switchover.
To get more ideas, google "reduced voltage start" and you should get a bunch of ideas. I defer to people like dpc and others on the forum on which is the best. My experience is limited to power plants where no reduced voltage starts are required.
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RE: Limiting startup current
RE: Limiting startup current
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RE: Limiting startup current
But, you need to study the system to see if a soft-starter can reduce the transients enough to fix the problems.
RE: Limiting startup current
Sometimes old technologies sound better.
O,8 MW fan looks to be a medium voltage motor and a fan requires more severe starting torque.
Please check an autotransformer starter (closed transition=Kondorfer connection)
RE: Limiting startup current
Late reply, but the 'cheapest way' would be to add a series, iron-core current limiting reactor with a bypass contactor. (A resistor would be too big and expensive and doesn't give you di/dt advantage). The bypass contactor can either be timer, or current sensing switched. Generally speaking, you can look at the speed-torque curves of the motor and the fan and design the reactor voltage drop so as to maintain acceleration torque until the point of bypass. Inrush current is usually limited to 50% or less.
Regards.
RE: Limiting startup current
Intresting idea of Swgrmfg.
It's also old-technologies as AT starter. Are still used?
Regards.
Slava
RE: Limiting startup current
Options in order of ability to limit voltage drop:
VFD
Autotransformer
Solid State Soft Starter
Reactor
Star-Delta
Options in order of initial installed cost (lowest to highest):
Open Transition Star-Delta (assuming the motor is wound for it)
Reactor
Closed Transition Star-Delta
Autotransformer
Solid State Soft Starter (ofetn similar in price to AT)
VFD
Options in order of flexibility to adjust to unknown starting parameters:
VFD
Soft Starter
Autotransformer (limited)
All others are not adaptable at all
I tend to still recommend Soft Starters because of the ability to adapt to unknown starting parameters, but it depends greatly on your mains capacity. What you really need to do it so gather all pertinent data on your load, motor and power system, then do a Transient Motor Starting Analysis using the available choices outlined above. On these high cost medium voltage systems, guessing can be an expensive endeavor.
RE: Limiting startup current
I will be concerned, if I have to use any reduced voltage start for a system originally designed to start DOL. More so, when the driven equipment is a Fan with high torque requirement.
It is true by clsong the input dampers before starting the fan you can reduce the torque reqiurement. May be it is worthwhile talking to the Fan vendor and motor vendor and have the curves ready for analysis.
I guess it would be worthwhile to order a different motor that comes with start current limited to say 3.5pu. Such motors are available in the market. The demerits of this option could be cost (when compared to standard motor) and the efficiency. But you have advantage with regard to reliability and O&M costs.