The three-phase star-delta starter is the most commonly used type of motor starter. This style of starter is a good choice when there are many phases and common-line loads, such as motors that use 240 volts and 480 volts.
This article will explore the 3-phase star delta starter in detail to help you understand how it works. We will also look at some of the disadvantages and advantages of this type of starter and what to look for when shopping for one.
What is a star-delta motor starter?
A star-delta starter is a type of induction motor starter that changes the current flow in a 3-phase motor circuit. It uses a combination of two different types of starters, known as “star” and “delta” to accomplish this.
A star-connected motor has its three wires connected to form one phase. This means that all three phases share the same current path. The delta-connected motor is connected to create two separate phases, which are then joined by a neutral wire.
What is the purpose of using a star-delta starter?
We normally use a star-delta starter to reduce the starting current for the three-phase motor. With this starter, you will not see the need to introduce any other external device to stir up the motor
as it reduces the starting current; it also does the same on the starting voltage for the motor.
The working principle of a star-delta starter
How does a star-delta starter work? You may ask.
A star-delta starter works in the following way.
When the motor is to be started, the star delta starter sends a control signal to the motor controller (a solid-state device). This device then switches on the power and sends a start command to the motor. The motor then starts running at its set speed. When it reaches this speed, it starts calling for more current.
The star-delta starter then reduces its power supply while increasing its voltage level so that it will not draw more current than necessary.
If required, it can also increase its supply of power and voltage level to support an increase in current flow through the motor. This is done to meet the increasing load of the motor.
This enables the star delta starter to provide a constant voltage to the motor, which is in accordance with its load. This helps in keeping a constant speed of rotation.
In case of an overload, over-temperature, or short circuit, the star delta starter will protect itself and the motor by cutting off the power supply. The off state will allow it to cool down before it can be restarted.
In case of an under-voltage condition, the motor will cut off its power supply until there is enough voltage for it to run again. When the voltage level returns to normal, it will resume its operations from where it left off.
Components of a star-delta starter
We have seen how a star-delta starter works. It is only able to execute the operations above with the help of different key components. These components include:
-Three-pole thermal overcurrent releases
-Fuse elements for the main circuit
-Fuse element for the control circuit
Let’s look at what these components are and the roles played by each of them:
A star delta starter has two main contactors. These are; the star contactor and delta contactor. There work is to connect and disconnect the circuit.
The delta contactor is used to connect the machine motor, and the star contactor is used to connect the incoming source of power.
In order for the machine to work, it should be turned on for a period of time before it can be turned off. A timer or a time relay determines the time required for this running time.
It will send out a signal after the required period of time has elapsed, thus allowing the contactors to switch off or disconnect the power supply from both circuits.
Three pole thermal overload releases
This is another important component of a star-delta starter that protects it from any damage caused by overheating or short-circuiting. The thermal overload releases will turn off the power supply if there is an increase in temperature or if there is an overcurrent condition in either circuit, thus preventing any damage from taking place.
Fuse elements for the main circuit
Also known as automatic cutouts, these are used to protect the main circuit by cutting off supply in case of an overcurrent condition in that particular circuit. They are also used to provide protection against a short-circuit.
Fuse elements for the control circuit
These elements are used to protect the control circuit in case of a fault in that circuit. The fuse elements are used to protect the overload release from damage caused by an overcurrent condition.
Other components of a star-delta starter
Capacitor for the control circuit
The capacitor is used to filter out any high-frequency disturbance that may arise due to the switching of contactors or relays. This will ensure the smooth running of the control circuit.
A voltage transformer is used to convert the incoming power supply from a high voltage to a low voltage. The high voltage from the incoming source of power is sent to the voltage transformer, which then transforms it into a low voltage and sends it to the star-delta starter. The low voltage is then distributed to both circuits via contactors.
Earth leakage circuit breaker
This device will cut off the power supply if there is an earth leakage in either circuit. An earth leakage occurs when there is an electrical connection between two parts of an electrical installation that are at different potentials, thereby creating a possible danger of electric shock.
An earth leakage breaker will prevent any damage caused by this kind of electrical fault and protect against electric shock.
It is usually provided with thermal overload releases that will cut off energy supply if there are any problems with temperature increase or overcurrent in the circuit.
Earth leakage relays
Earth leakage relays are used to detect any earth leakage in the circuit. They are usually integrated into the control circuit, where they will detect and cut off the power supply if there is an earth leakage in either circuit.
They can also be installed separately from the star delta starter and connected to it via a cable. This is done when there are multiple star-delta starters on one installation, and only one relay is required to control them all.
Circuits of a star delta starter
Other than the components, a star-delta starter comprises of two circuits. These are the power circuit and the control circuit. Let’s have a brief look at each of these circuits.
The power circuit of a delta starter
The power circuit of a delta starter comprises two transformers. These are a primary and a secondary one. The primary one is the primary winding, while the secondary one is the secondary winding. The primary winding is directly linked to the source, while the secondary winding is connected to the load.
The control circuit of a delta starter
The control circuit of a star-delta starter consists of two switches. These are an on-off switch and an on-on switch (i.e., normally closed). When both these switches are in their off positions, there is no current flow from the source to the load (i.e., no current flow through either transformer). When both these switches are in their own positions, there will be current flowing from the source to the load via either transformer.
What kind of motor needs a star-delta starter?
Star delta starters are mainly used on powerful motors. The motor should have more than 10HP. It is also used for large motors, where there are many connections and motors located at a distance from the control device.
Why are star-delta starters preferred for higher HP motors?
Star delta starters are more efficient than the three-phase permanent magnet DC motors. When the motor is operating, its stator winding is energized (and therefore generates a magnetic field) by the excitation winding.
As a result, the motor generates a high torque, making it possible to operate at high speed and with high power output.
In addition, star-delta starters have an extremely high overload capacity and are very reliable in operation.
What are the requirements to install a star-delta starter?
The installation area should be well ventilated. The installation depth should not exceed 6 inches, and it should be installed according to the requirements of UL 1459. The wiring must be installed in accordance with the provisions of NFPA 70 and NFPA 72. The motor must have a voltage rating of at least 110V (the voltage can be reduced to 80V or 60V if necessary).
The motor must have a starting current rating of at least 20 amps (the motor can have a lower current rating if necessary). The starter must have an overload capacity of at least 1,000A (the overload capacity can be reduced to 500A or 300A if necessary). If the starter has more than one phase, then the frequency range must not exceed 50Hz.
Advantages of star-delta starter
Should I buy a star-delta starter? Here are the top advantages that you are likely to gain from using it for your three-phase transformer.
-Simple and smooth operation: A star-delta starter is quite simple to operate. It can be installed easily, and it will not cause any kind of interference with the other electrical devices in your home.
-Reliable: Star delta starters are quite reliable, and they can easily withstand any voltage fluctuations (even during an overload).
-Excellent torque and current performance: Star delta starters can provide excellent torque and current ratings. This is because the motor is able to deliver all its power to the load, and it will not be overloaded.
-High efficiency: Star delta starters have a high-efficiency rating, which means that they can transfer a large amount of power from the source to the load without overheating.
Disadvantages of star-delta starter
While a delta star transformer may be a good choice for your motor, it also has some demerits. They include:
-Break-in supply: While a star-delta starter can be installed quite easily, it can take a while before it starts working properly. This is because the voltage to the starter must be stable during this time.
-Low torque: Star delta starters are not very good at delivering torque, which means that they will not be able to deliver enough power from the source to the load.
-High voltage: Star delta starters have a high voltage rating of around 240 V, which means they do not have much tolerance for voltage fluctuations (i.e., low or high voltages).
What is the difference between the star delta starter and the DOL starter?
DOL starter is another common type of starter used on an induction motor. How is it different from the star delta starter?
The first difference is based on the starting current. With DOL, the motor has a full starting current. On the other hand, the star delta motor reduces the starting current.
The same difference is witnessed when it comes to the voltage. With the DOL, full voltage is applied to the motor at the start. With the star delta starter, the motor is supplied with half voltage at the start.
Their application areas also differ. DOL is perfect for applications that require high starting torque. Star delta starters are not ideal for applications of such a nature.
Now that you have all the vital information about star delta starters, what next? The next step would be to buy one of these starters for your induction motor. You can get them at many online and offline stores. Just make sure that the starter you are buying is right for your application.
And in case you would want to buy a star-delta starter in China, ICRFQ is there for you. We are a reliable sourcing agent for the star delta starters in China.
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