Star-Delta Starter Operation
A star-delta starter is a widely used method for starting electric motors, particularly in industrial applications. It reduces the initial starting current and torque, ensuring smooth motor operation and protecting electrical components. This post explains the operation, working principles, and considerations for star-delta starters in detail.
What is a Star-Delta Starter?
A star-delta starter is a starting method designed to reduce:
- Starting Current: Approximately 30% of the current during a Direct-On-Line (DOL) start.
- Starting Torque: About 25% of the torque available at a DOL start.
Key Components:
- Three Contactors: Control the star and delta connections.
- Overload Relay: Protects the motor from excessive currents.
- Timer: Sets the duration of the star connection during the start.
How Does a Star-Delta Starter Work?
1. Starting in Star Configuration:
2. Transition to Delta Configuration:
- After the motor achieves approximately 80-90% of its operational speed, the system switches to delta connection.
- In this configuration, the full line voltage is applied to the motor windings, providing full torque for normal operation.
Key Features and Benefits
| Feature | Description |
|---|---|
| Reduced Starting Current | Minimizes electrical stress on the motor and supply network. |
| Lower Starting Torque | Protects connected machinery and reduces mechanical stress. |
| Cost-Effective Solution | Simple design with standard components, making it affordable and easy to maintain. |
| Ideal for Light Loads | Suitable for applications with low initial load and gradual torque requirements. |
Applications of Star-Delta Starters
This starting method is ideal for:
- High-Inertia Loads: Fans, pumps, and blowers.
- Low Starting Torque Requirements: Conveyor belts and compressors.
- Machinery with Delayed Load: Applications where the load increases only after the motor reaches operational speed.
Detailed Operation Steps
- Star Connection:
- The main contactor connects the mains to terminals U1, V1, W1.
- The star contactor shorts terminals U2, V2, W2, creating a star configuration.
- Transition to Delta Connection:
- The star contactor disengages.
- The delta contactor connects terminals:
- U1 to W2
- V1 to U2
- W1 to V2
- Phase Sequence Considerations:
- Correct phase sequence ensures smooth transition without high current peaks.
- Improper phase sequence can lead to torque reduction, high peak currents, or motor damage.
Advantages of Star-Delta Starters
| Advantage | Description |
|---|---|
| Reduced Inrush Current | Lowers stress on the motor and electrical system during startup. |
| Improved Power Quality | Minimizes voltage dips in the power supply network. |
| Enhanced Motor Protection | Avoids excessive torque, extending the motor’s lifespan. |
Disadvantages
While star-delta starters are effective, they have limitations:
- Not Suitable for High-Load Applications: Insufficient torque during start may fail to accelerate heavy loads.
- Complex Wiring: Requires precise wiring and coordination of multiple contactors.
- High Current Peaks During Transition: Improper phase sequence can cause damage to motor windings.
Important Considerations
- Duration of Star Connection:
- The star connection should last until the motor reaches close to its operational speed.
- Overextending the star phase may result in insufficient acceleration.
- Phase Sequence Check:
- Ensure the motor runs in the correct direction.
- Incorrect sequence may cause high current peaks and operational failures.
- Switching and Rotation:
- Switching the phase sequence can reverse motor rotation if needed.
Practical Tips for Star-Delta Starter Usage
- Monitor Load Requirements:
Ensure the motor’s load matches the torque capabilities of the star-delta starter. - Proper Wiring and Maintenance:
- Follow the motor manufacturer’s wiring diagrams for correct termination.
- Regularly inspect contactors, timers, and overload relays for wear and tear.
- Use an Automatic Timer:
Automate the transition from star to delta to minimize errors and optimize performance.
Conclusion
Star-delta starters are an effective and economical solution for starting electric motors in applications with low initial load. By reducing starting current and torque, they protect both the motor and the connected electrical system. However, proper configuration, phase sequencing, and load assessment are critical to ensure smooth operation and prevent damage.
For detailed diagrams, wiring techniques, and troubleshooting tips, check out related posts on Star-Delta Motor Connection and Electro-Mechanical Star-Delta Control Circuits. Stay informed to optimize your motor operation and system reliability!
Good informations in this site. how to to find out the wrong termination in star delta connection. for example in star delta connected motor star in star mode but after change in delta mode contactor of delta and main are in pick up condition but motor got off not in trip. can u explain this
Are u already confirm your motor connection true or not?i think your motor terminal connection maybe wrong..please refer my last post about star delta motor connection
please give a diagram of star-delta starter with transition resistors(Kondorfer)
hi,
The artical which is above is more enough to understand and knowledge of particular thing.
please refer to my post : http://www.electricneutron.com/motor-control/electro-mechanical-star-delta-starter/
very usefull
plz send to my email a control circuit of forward reverse connection…A.S.A.P….thank you…
i will discuss in my next post about control circuit of forward reverse for star delta starter…thanks
can anyone tell me about the difference in delta and star connections from the generator?
please post me the book to my email,thank you.
dfghsdhr
in a star delta stater how we can set the timer timing to switch to delta from star according to load characterstics.
it hard to setting the best timing for star delta starter.Typical setting for timer is around 8 until 10 second….
Dear Sir,
We are manufacturer of animal food.it is in pallate fome.and our requirement of Star-Delta Starter for 40HP Motor.so,please give the Quotation for the same.
Kind Regards,
Chandrakant Parekh.
+91 95588 13099
Director
Divine Ani-Food Manufacturing Unit.
Unjha(Mehsana)
Dear Sir
please tell me ,
what will happen if the motor is running and contactornya only 1 ( Delta contactor off )
regards
HF
Hi I am looking for a way to change the rotaion on only delta as motor runs forward in star but tries to reverse rotaion when changing into delta causing fuses to blow.tried to change L1 L3 at motor but motor runs at very high amps
Dear Sir,
Please read my last post : http://www.electricneutron.com/motor-control/how-to-change-rotation-for-star-delta-starter/
Dol starter pump connection
Hi, Can u plis give me control circuit for the compressor of star delta with addition of the solinoid valve and pressure switch
we have supplied dol starter of 10hp motor but it fails because of relay got burnt & after that we once again replaced the relay/contactor it works for 03 days same has repeated & motor winding got burnt.
then we replace the star delta starter found the same has been repeated after 02 days of working condition
kindly inform us the reason for the above if any suggestions.
suresh k g
Please check your actual full load and motor sizing
best information
I need for star Dalta with timer gigram
Please check current rating for your contactor.It should same or high ampere rating from your motor full load ampere.
Sir.. can u kindly help me out as i am confused while connecting my 40hp motor crampton greaves with the starter. Here i will give u the sequences..
Starter.. C1 L1 A1 L2 B1 L3
AO BO CO
Motor… U1 (u ) W2 (k)
V1 (v) U2 (l)
W1 (w) V2 (m)
SO kindly help give me the direction.. waiting for ur anticipation.
How to set a overload relay setting in star as well as in detla connection ??
Very useful
motor in starting come in star connection then after delta. motor burn reason is single phasing check the both contactor continuity that incoming band outgoing connection voltage are ok or not and also check the timer working and thing is o/l relay burn there are three reason
1) bimatlick strip dusty
2) lose connection
3)lower rating
Thanks for your information. Please am a new beginer. Can you please send me a book that contains everything about motor staters method. Again I want to know how the. Star contactor is being connected to the three phase machine. Thanks for your anticipated effort
Sir,
I have a Centrifugal Fan of 150 HP motor which we run with star delta starter with timer and thermal relay base contactors. How much time can be set between star and delta starter ? any thumb rule which depends upon motor HP or any ??
When we are starting the motor it draws 340 amp. it reduce gradually up to 285 amp. and then come in delta in 25 sec. In delta it draws 825 amp. and reduce to 70 amp. with in 2 sec. and again after 2 sec. motor trip. What will be the reason ?? Please help me.
What’s star and delta sent me in email