Starter Type
Starter Type
(OP)
I think all of you in the electrical fraternity would agree with me when I say that a 45 KW Pump or AHU needs a suitable starter such as Star/delta or VFD to reduce starting current.
However, my company thinks different.They say and show me SLD's where they have fed 45 KW & Above AHU's,pumps(constant flow) etc with DOL starter.We work mostly for Petroleum company that follows Shell/DEP specifications.
I dnt have a clue as to how a DOL starter works perfectly for these large motors..
Can anyone throw some light?
Why is DOL preffered for AHU's,Pumps etc.?
However, my company thinks different.They say and show me SLD's where they have fed 45 KW & Above AHU's,pumps(constant flow) etc with DOL starter.We work mostly for Petroleum company that follows Shell/DEP specifications.
I dnt have a clue as to how a DOL starter works perfectly for these large motors..
Can anyone throw some light?
Why is DOL preffered for AHU's,Pumps etc.?






RE: Starter Type
RE: Starter Type
When should you use reduced voltage start?
A/ Voltage drop and disturbances to other customers on the circuit. Above a certain size the utility may demand reduced current start so as to avoid excessive voltage drop to other customers on the circuit. A residential distribution circuit may be feeding a group of homes with a 25 KVA or 50 KVA transformer. There would not be enough capacity to run let alone start a 45 kW motor. The transformer would have to be uograded to 75 KVA or 100 KVA. even then starting a 45 kW motor would cause objectionable voltage drops at adjacent homes. Most utilities would demand a reduced voltage start for the motor.
BUT
In a petro-chemical plant the electrical houses and MCCs are typically fed from 500 KVA, 1000 KVA or larger transformers. A 45 kW motor may easily be started DOL without an objectionable voltage drop.
B/ Inertia. industrial motors are typically suitable for a maximum number of seconds of starting duty per hour. Motors driving high inertia loads may be overheated by the starting current before the load is up to speed. Reduced current start must be used to avoid early failure of the motor. Most pumps and many but not all compressors may be considered low inertia loads for starting purposes.
C/ Reduced starting torque. Most loads will take the starting torque but there are exceptions. A more common issue is large belt drives that won't take DOL starting torque. I have seen high inertia applications in the 200 HP and 300 HP size where a slight mis-adjustment in the drive belts would result in the belts slipping and burning. A DOL start of these motors would probably result in the belts being destroyed in a few starts as well as the motor being overheated.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Starter Type
The motor accelerates rapidly with DOL starting so you also have to watch for torque shock in loads with slack in the drive system.
RE: Starter Type
A chart in my old IEEE Red Book indicates a 50 HP motor can start on a 75 KVA transformer with about 80% voltage drop on starting. If your transformer is bigger, it may be OK.
RE: Starter Type
RE: Starter Type
RE: Starter Type
Best to you,
Goober Dave
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RE: Starter Type
The issue not mentioned in regards to pump starting is that in many cases, there is a significant benefit in being able to soft STOP a pump motor and reduce the negative effects of water hammer. That is not so directly related to the motor, but it is significant to the pumping system as a whole.
"Will work for (the memory of) salami"
RE: Starter Type
Would you be able to share those studies? They sound interesting. My understanding was that Lionel's point was generally correct although there are probably specific combinations of motor and load and soft start where there is little difference. I'm more than happy to be wrong - it's all part of learning.
RE: Starter Type
The Chiller comes with inbuilt star/delta starter of each compressor motor(4nos in total).It also has a switch fused disconnector.
RE: Starter Type
RE: Starter Type
The first one I ever read was ironically published years ago by my current employer, but long befor I worked here. However I cannot yet locate it, likely because we recently reorganized our data storage systems and some archived papers have become difficult to find now. I will keep searching though.
IIRC, I was directed to that paper by someone in this very forum years ago when this exact subject was brought up before, and I believe I took the same position as LionelHutz at the time. Live and learn...
"Will work for (the memory of) salami"
RE: Starter Type
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Starter Type
RE: Starter Type
RE: Starter Type
I was unable to find direct reference to the studies behind this, but I did find the results stated in a white paper.
https://rockwellautomation.custhelp.com/ci/fattach...
The relevant section is starting on page 2
"Will work for (the memory of) salami"