Comparing Motor Starting Methods: Star to DOL vs. Star to Delta

[kautuksahni]

I need to understand the differences between the two motor-starting methods:

Case 1: Start with a Star connection and then switch to Direct Line [I know this is not standard configuration but trying to understand this].

Case 2: Start with a Star connection and then switch to Delta.

Please provide a detailed comparison in table format, including the following aspects:

What are the real-world differences between Case 1 and Case 2? Which method is generally better and why?

 

[Harald Kapp]

Sounds like homework.
Our policy is not to do your homework for you. Show us what you have found out so far and where you are stuck.

 

[kautuksahni]

@Harald Kapp ,
I'm puzzled as to why this is being considered homework, as I'm not currently enrolled in any university. I'm asking this question because we're in the process of buying an air compressor in our woodworking factory. The company handling the installation mentioned they'd be using a star-delta configuration, so I took the initiative to research the differences between DOL and star-delta configurations. While I understood why star-delta might be preferred over DOL, it led me to a new question: How would a Star-DOL configuration compare to star-delta?

Since Star-DOL isn't a standard configuration, I'm reaching out for expert opinions, as I couldn't find any relevant information online.

P.S.: I'm not an electrical engineer or a student; I'm simply trying to deepen my understanding. If you review the question carefully, you'll notice it's not just a comparison of DOL versus star-delta but specifically about how Star-DOL compares to star-delta.

To clarify, my question is:
-> Case 1: Start the motor on Star and then shift to DOL

1. -> Case 2: Start on Star and then shift to Delta
2. I am trying to understand the difference between Case 1 Vs Case 2.

 

[bertus]

Hello,

Then why do you have "school" as company name / institute?

Bertus

 

[kautuksahni]

Oh, I see where the confusion came from. The company name is 'School of Wood Mastery.' I hit enter early just after typing 'School'.

 

[Delta Prime]

The choice of starter depends on factors such as motor size, starting requirements, cost considerations, & application-specific requirements. You have not submitted any specifications of the motor being used. Because of this fact, & since your post has not moved from homework, I shall speak in generalities. Therefor It is inferred that a polyphase Direct-On-Line (DOL) starter is used, where the motor is directly connected to the full supply voltage at the start, resulting in a high inrush current which is OK for small induction motors,because that inrush current can be a much as eight times the amount of the motors current rating.
In a Star-Delta starter, the motor is initially connected in a star configuration, which reduces the voltage applied to each winding, also reducing the starting current & torque. After a predetermined time (typically a few seconds), the motor is then switched to a delta configuration for normal operation at full voltage & rated current. Star-Delta configurations are more complex & require additional control circuitry, but they offer smoother starting & reduced mechanical stress on the motor & connected equipment

 

[danadak]

This might help :

https://assets.new.siemens.com/siemens/assets/api/uuid:6ba7593d-d8d0-481c-b029-a5987c11366f/startingmotors-whitepaper.pdf

https://www.tmeic.com/sites/default/files/assets/files/library/Application%20Edge-v1i3-Starting%20Large%20Motors.pdf

https://mylearning.abb.com/config/mylearning.abb.com/sites/default/files/fileupload/1693294090-Motor+Startingp2C+Protection+and+Control.pdf

Regards, Dana.

 

[kautuksahni]

@danadak @Delta Prime,
Thank you both for reviewing and responding to my question. I may not have been entirely clear in my original query. I understand the difference between DOL starters and Star-Delta starters. What I'm trying to grasp is a hypothetical scenario where I start my motor with a Star configuration and, after reaching 60-70% of the motor's RPM, I want to:

1. ->Case 1: Transition from Star to DOL
2. ->Case 2:Transition from Star to Delta

So, this isn't a comparison between DOL and Star-Delta starters, but rather between Star-DOL and Star-Delta transitions.

 

[Bluejets]

Start with a Star connection and then switch to Direct Line [I know this is not standard configuration but trying to understand this].

This IS star-delta starting or commonly known as reduced voltage starting.
Usual configuration is bring out the six coils cables, connect in star for starting, then switch to delta for running.
There are uses requiring star connected run but not so common.

Current is limited during the run up time and the latter also varies depending on size.
However, most aim for around 70 to 80% full speed on switchover.

Large motors requiring starting control usually opt for auto-transformer starters.
I have also seen salt water probes used for start current limiting.

Many supply authorities disallow the use of dol over 5hp.
Exception to this would be in the mining industry where they have their own sub-stations(and massive dol contactors)