This reduces inrush currents and protects your drive technology – including modern alternatives!
What is the main purpose of a Star-Delta switch?
The main purpose of a Star-Delta switch is the reduction of the high starting current of three-phase motors to about one third of the direct start current. This protects the electrical network and the mechanical components of the drive train.
When is the use of a Star-Delta switch sensible?
Ein A Star-Delta switch is sensible for motors from about 4 kW that start without high counter-torque, such as with pumps, fans, or conveyor belts with light starting. It represents a cost-effective solution for current limitation.
Which motors are suitable for Star-Delta starting?
Suitable are three-phase motors whose nameplate shows a dual voltage indication where the lower voltage corresponds to the line voltage in delta operation (e.g., 400/690V for a 400V network). Motors with the indication 230/400V are not suitable for Star-Delta starting on a 400V network , as their windings in delta operation are only designed for 230V., da ihre Wicklungen im Dreieckbetrieb nur für 230V ausgelegt sind.
What are the most common problems with Star-Delta circuits?
The most common problem is switching current peaks when transitioning from star to delta operation, which can load relay contacts and trigger protective devices. Another problem is the reduced starting torque (about 1/3 of the rated torque), which is unsuitable for heavy starts.
How can switching current peaks be reduced in Star-Delta switches?
Switching current peaks can be minimized by a correctly set switching pause (typically 50-100 ms) and the use of optimized relay combinations or special winding connections. In critical cases, soft starters or frequency converters are often the better alternatives.
What is the difference between a Star-Delta switch and a soft starter?
Ein A Star-Delta switch reduces the starting current in stages, while a soft starter does this electronically and continuously, allowing for a smoother start and can better match the starting torque to the load. However, soft starters are usually more expensive and complex..
Is a Star-Delta switch suitable for applications with high starting torque?
No, as the starting torque in star connection is reduced to about one third of the rated torque . For applications requiring a high breaking loose or starting torque (e.g., mills, crushers), Star-Delta switches are unsuitable. Here, soft starters or frequency converters alternatives are preferred.
Does ATEK Drive Solutions provide support in selecting the right starting method?
Yes, ATEK Drive Solutions offers as a system provider for the complete industrial drive train comprehensive technical advice. Our experts help you find the optimal starting solution – whether it is a Star-Delta switch, a servomotor controller, or another technology from our portfolio – for your specific application and motors.
Ein A Star-Delta switch reduces the starting current of three-phase motors to about 33% of the direct start value, thus protecting the power grid and can significantly extend the lifespan of mechanical drive components. Despite its cost-effectiveness, the.
Star-Delta starting method has a reduced starting torque reduziertes Anlaufmoment (only about 1/3 of the delta torque) and possible switching current peaks limitations, making it unsuitable for heavy starts.
Modern alternatives such as soft starters and frequency converters often offer superior performance, but the A Star-Delta switch remains a cost-effective and robust solution. ATEK Drive Solutions supports you in choosing the appropriate drive technology..Learn all about Star-Delta switches: Functionality, application areas, advantages and disadvantages, as well as modern alternatives such as frequency converters and soft starters. Optimize your drive technology!
Are you looking for a way to reduce the starting current of your motors and protect your systems? The Star-Delta switch is a proven method. But is it still up to date? Discover the advantages and disadvantages and find the optimal solution for your requirements. Contact us at ATEK Drive Solutions for personalized advice!
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Understand: Master the fundamentals and applications of the Star-Delta circuit
This article addresses A Star-Delta switch the reduction of starting currents and protection of drives. It explains functionality and alternatives for informed decisions to optimize your drive technology, especially when it comes to the use of a Star-Delta switch .
The Star-Delta starting circuit: Fundamentals and applications
Die Star-Delta starting circuit reduces motor starting current (e.g., 22 kW) to about 1/3. Users appreciate this type of motor switch for simplicity/cost, especially without full load starting. Motor start in star (about 58% line voltage, e.g., 230V instead of 400V) reduces current, making the start smoother. See fundamental aspects of three-phase motors.. Voltage reduction protects mechanics/network, a core advantage of the Star-Delta method.
What is a Star-Delta switch?
Ein A Star-Delta switch is an assembly of relays and a time relay. It connects the motor windings first in star connection, then (upon reaching 70-80% of the rated speed) in delta connection. The start thus occurs with reduced current, which is the main function of this switch.
Functionality of the Star-Delta starting circuit
During the starting process with a A Star-Delta switch , the winding ends U2,V2,W2 are short-circuited (star point), while the winding starts U1,V1,W1 are connected to the network. After a preset time (e.g., 5s), switching to delta takes place (U1-W2, V1-U2, W1-V2). A correct setting of the time relay in the Star-Delta switch is crucial for trouble-free operation. See Motor star or delta connection..Analyze: Structure and functionality of Star-Delta switches in detail.
Structure and components of a Star-Delta switch
Ein A Star-Delta switch typically consists of a line contactor, a star contactor, a delta contactor, and a time relay. A mechanical or electrical lock against the simultaneous activation of star and delta contactors is essential for every Star-Delta switch.
- Main components of a Star-Delta switch: line contactor, star contactor, delta contactor, and time relay.
- Locking between star and delta contactor is mandatory for the safety of the Star-Delta starter..
- Six connections at the motor terminal block (U1,V1,W1; U2,V2,W2) are necessary for operation with a Star-Delta circuit..
- The contactors in the A Star-Delta switch must be dimensioned according to the motor power.
- The starting sequence of a Star-Delta starter includes: starting in star connection (K1+K3), a defined switching pause, then operation in delta connection (K1+K2).
- The switching pause (about 50ms) is used to avoid arcs during the switching operation of the Star-Delta switch.
- Correct wiring of the six motor lines and winding ends is crucial for the function of the entire Star-Delta system..
Components of a typical Star-Delta switch
For the use of a Star-Delta switch the motor terminal block requires 6 connections (U1,V1,W1; U2,V2,W2). The core components are:
- Line contactor (K1): Leads the main current to the motor.
- Star contactor (K3): Forms the star point for the start.
- Delta contactor (K2): Switches the motor to delta for continuous operation.
- Time relay: Controls the duration of the star phase in the A Star-Delta switch.
The contactors of a Star-Delta switch must always be sized according to the motor power (e.g., for 11kW differently than for 4kW).
Procedure of the starting sequence
In starting with a A Star-Delta switch the line contactor (K1) and the star contactor (K3) pull in; the motor starts in star connection. After a set time (e.g., 5-10 seconds), the star contactor K3 drops out. A short switching pause follows (about 50ms). This pause is important to avoid arcs when switching the Star-Delta switch. Then, the delta contactor K2 pulls in, and the motor continues in delta operation.
Important wiring notes
The six motor lines must be connected exactly according to the wiring diagram of the respective Star-Delta switch be connected. Critical is the correct assignment of the winding ends (U1,V1,W1; U2,V2,W2); incorrect connections invariably lead to malfunctions or damages to the motor or the Star-Delta switch. For delta operation: U1 to W2, V1 to U2, W1 to V2.Apply: Recognize sensible areas of application and limits of the Star-Delta starting circuit.
When is the Star-Delta starting circuit sensible?
The use of a Star-Delta starting circuit, realized by a A Star-Delta switch, is particularly sensible for three-phase asynchronous motors (typically in the power range of about 4 kW to 75 kW), which operate in delta and have a low starting torque of the load. The starting torque in star connection is only about one third of the delta torque. This type of starting is used for a gentle start (e.g., with fans, pumps) to protect the mechanics and avoid voltage drops in the grid. See Gear Boxes for three-phase motors..
Suitable motors and voltage networks
For operation with a A Star-Delta switch the nameplate of the motor must have a suitable voltage indication, e.g., 400/690V (meaning Δ400V / Y690V). This allows operation in delta connection on a 400V network and starting in star connection. A motor with the indication 230/400V is unsuitable for Star-Delta starting on a 400V network, as it would be overloaded in delta operation.
Typical application areas
Die Star-Delta circuit. are found in many areas. Typical examples include:
- Fans and ventilators
- Pumps
- Compressors
- Conveyor belts with gentle start-up
- Woodworking machines
By using a star-delta switch, the start-up current is limited, thus increasing the service life of the system.
Restrictions and alternatives
The reduced starting torque is a significant disadvantage of the Star-Delta circuit., especially in applications with high breakaway torque (e.g. crushers, mills). In such cases, soft starters or frequency converters are often a better choice than a conventional star-delta switch.Minimize: Understand and effectively reduce inrush current peaks
The problem of inrush current peaks
During the transition from star to delta configuration, high current peaks can occur. A Star-Delta switch These arise from the phase shift between the residual magnetic field of the motor and the re-applied mains voltage. Such peaks significantly stress the contacts of the star-delta switch and can even exceed the direct starting current (often 10 to 15 times the rated current). The consequences are increased contact wear and unwanted tripping of protective devices. For a detailed analysis see Calculating the current draw of your three-phase motor.
- High current peaks can occur when switching from star to delta operation at a Star-Delta circuit. .
- The main cause is the phase shift between the residual magnetic field of the motor and the applied mains voltage at the moment of switching by the A Star-Delta switch.
- Such current peaks can significantly exceed the normal starting current during direct start (often 10 to 15 times the rated current), which can negate the advantages of the star-delta starting .
- The negative effects include increased wear of the switching contacts in the A Star-Delta switch and unwanted tripping of protective devices.
- The intensity of the current peaks depends on factors such as the duration of the switching pause of the Star-Delta switch and the relative phase position of the rotor to the stator field.
- A correctly set switching pause (typically 50-100 ms) is an important measure to reduce these peaks during Y-Δ start.
- The use of special contactor combinations for A Star-Delta switch can reduce these switching current peaks by up to 50%.
Causes and Effects
The height of the current peaks when switching a Star-Delta switch depends on the duration of the switching pause, the exact timing of the reconnection, and the mechanical coupling of the motor. Especially critical is the phase position of the rotor to the stator field at the moment of switching.
Measures for reduction
A correctly set switching pause (typically 50-100 ms) is crucial: It must be short enough to prevent a significant drop in motor speed, but long enough for the residual magnetic field to dissipate sufficiently before the A Star-Delta switch switches to delta. Special contactor combinations optimized for star-delta applications can reduce these peaks by up to 50%.Compare: Assess star-delta start against soft starters and frequency converters
Star-delta vs. soft starters and frequency converters
Ein A Star-Delta switch is a cost-effective solution (e.g. for 15 kW often under 200 euros) and known for its robustness. Soft starters and frequency converters, on the other hand, offer better control over the starting process and allow for higher starting torques, but are more expensive than a simple star-delta switch. The choice of starting method heavily depends on the specific application. For more information, see Frequency converters in drive technology.
- Die Star-Delta circuit., realized by a A Star-Delta switch, is a cost-effective and robust method, but reduces the starting torque to about one third and can cause problematic inrush current peaks.
- Soft starters allow for continuous motor start-up with continuous current limitation and are well-suited for applications with sensitive mechanics or high breakaway torque, where a has a is insufficient.
- Frequency converters offer the most comprehensive control over the starting process, torque (often up to 200% of rated torque) and allow for stepless speed regulation, far beyond the capabilities of a Star-Delta switch .
- The selection of the appropriate starting method (A Star-Delta switch, soft starter or frequency converter) is highly application-dependent and considers costs, required starting torque, and the need for control options.
- Significant advantages of the Star-Delta circuit. are their low acquisition costs, the simple and robust design of the Star-Delta switch and the effective reduction of the starting current.
- Disadvantages of a Star-Delta starter. include the reduced starting torque, the occurrence of inrush current peaks, the absence of speed control options, and a fixed preset starting time.
- Despite modern alternatives, the A Star-Delta switch still holds its ground for standard applications (often up to 30 kW), especially when cost is a priority and the starting torque provided by the star-delta method is sufficient.
Advantages and disadvantages of the star-delta starting circuit
The decision for or against a A Star-Delta switch should be made after weighing the pros and cons. Advantages:
- Low acquisition costs of the Star-Delta switch.
- Simple and robust design.
- Reduction of the starting current to about 1/3.
Disadvantages:
- Reduction of starting torque to about 1/3.
- Possible inrush current peaks during the star-delta switching process.
- No possibility for speed control.
- Fixed starting time determined by the time relay.
These aspects should be considered when selecting a starting method if a star-delta switch is being contemplated.
soft starter
Soft starters provide a smooth start, continuous current limitation, and an adjustable current or torque profile. They are ideal for applications with sensitive mechanics or high breakaway torque, where a star-delta switch reaches its limits (often limited to 200% of the rated current).
Frequency converters
Frequency converters allow for full control over the start-up: gentle start, high torque (up to 200% of rated torque), and stepless speed control. Although more expensive to acquire than a star-delta switch, they can often be economically viable through energy savings in operation (e.g. ATEK Servomotor controllers). Sometimes a simple reversing switch for three-phase may be sufficient when no soft start is needed.
Current relevance
For standard applications, often up to a power of 30 kW, the A Star-Delta switch remains an economical solution when cost focus is paramount and the reduced starting torque is sufficient for the application. The simplicity and robustness continue to be clear advantages of this proven starting method.Select: Identify suitable star-delta switches and manufacturers
Available star-delta switches on the market
There is a wide range of star-delta switches, from manual cam switches for smaller powers to completely pre-wired contactor combinations for motors over 100 kW. Important when selecting a star-delta switch are the correct sizing for motor power and the quality of the components. Renowned manufacturers include Schneider Electric, Eaton, Siemens, and Lovato. Prices for star-delta switches vary depending on power, brand, and additional features.
Manufacturers and product examples
Lovato, for example, offers the GSL series for A Star-Delta switch up to 75 kW at 400V, while Eaton has compact solutions up to approx. 15 kW with the MSC series, often including motor protection. Siemens offers a variety of contactors and starters under the SIRIUS series that are suitable for constructing star-delta circuits.
Additional features
Modern A Star-Delta switch or contactor combinations may have additional features such as adjustable time relays for the star phase and the switching pause, integrated overload relays, or connections for external control signals. The Klinger & Born J 400V is an example of a star-delta switch with integrated phase inverter and emergency stop function.
Motor starter J 400V
The motor starter J 400V from Klinger & Born is a complete solution for A Star-Delta switch motors up to 5.5 kW at 400V (protection class IP54). Features of this specific star-delta starter include a main switch, an emergency stop function, adjustable time relays (star phase 0.1-100s, switching pause 0.1-1s), and adjustable overload protection (e.g. 9.5-12.9A). Such complete devices significantly simplify the installation of a star-delta starting .
Der has a, realized by a A Star-Delta switch, remains a cost-effective and reliable method for reducing starting current for many standard applications. The final choice of the starting method always depends on the specific requirements of the application. ATEK Drive Solutions offers individual consulting to find the optimal solution for your drive tasks, whether it’s a A Star-Delta switch or a more advanced alternative.
