Automatic Star Delta Starter with Timer Wiring & Installation Diagram
From the left you have the main contactor with the pneumatic timer because your main contactor is always energized, in the Middle you have the Delta contactor with a thermal overload for motor protection in case the motor exceeds the ampere rating set on the thermal overload, on the right you have the Star contactor which is the first contactor to be energized with the main contactor then when the timer reaches its time limit the Star contactor de-energizes and the Delta contactor energizes and the Motor is running at full load.
Operation & Working of Automatic Star Delta Starter
From L1 The phase current flows to thermal overload contact through fuse, then OFF push button, On push button Interlocking contact 2, and then C3. This way, the circuit is completed, as a result;
- Contactor coil C3 and timer coil (I1) is energized at once and the motor winding then connected in Star. When C3 is energized, its auxiliary open links will be closed and vice versa (i.e. close links would be open). Thus C1 Contactor is also energized and Three Phase Supply will reach to the motor. Since winding is connected in Star, hence each phase will get √3 times less than the line voltage i.e. 230V. Hence Motor starts safely.
- The close contact of C3 in the Delta line opens because of which there would be no chance of activation of contactor 2 (C2) .
- After leaving the push button, Timer coil and coil 3 will receive a supply through Timer contact (Ia) , Holding contact 3 and the close contact 2 of C2.
- When Contactor 1 (C1) is energized, then the two open contact in the line of C1 and C2 will be closed.
- For the specific time (generally 5-10 seconds) in which the motor will be connected in star, after that the Timer contact (Ia) will be open (We may change by rotating the timer knob to adjust the time again) and as a result;
- Contactor 3 (C3) will be off, because of which the open link of C3 will be close (which is in the line of C2) thus C2 will also energize. Similarly, When C3 off, then star connection of winding will also open. And C2 will be closed. Therefore, the motor winding will be connected in Delta. In addition, Contact 2 (which is in the line C3) will open, by which, there would not be any chance of activation of coil 3 (C3)
- Since the motor is connected in Delta now, therefore, each phase of the motor will receive full line voltage (400V) and the motor will start to run in full motion.
Related Post:
- Why We Need to Install a Starter with a Motor?
- Difference between Star and Delta Connections – Comparison Of Y/Δ
Star Delta Starter Power Diagram
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Control Diagram of Star Delta Starter with Timer
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Wiring Diagram of Star Delta Starter with Timer
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Abbreviations: ( FOR Control Wiring of Three Phase Star Delta Starter with Timer)
- R , Y, B = Red, Yellow, Blue ( 3 Phase Lines)
- C.B = General Circuit Breaker
- Main = Main SupplyTwo Speeds One Direction Three Phase Motor Connection Power and Control Diagrams
Disadvantages
- Starting Torque is also reduce to one-third because starter reduce the starting current to one-third of the rated current [as Line voltage also reduced to 57% (1/√3)]
- It required Six leads or terminals Motor (Delta Connected)
- For Delta connection, the supply voltage must be same as the rated motor voltage.
- At switching time (From Star to Delta), if the motor does not reach at least 90% of its rated speed, then the current peak may be equally high as in Direct ON Line starter( D.O.L), thus it may cause harmful effects on the contactors contacts, so it would not be reliable.
- We may not use star delta starter if the required (application or load) torque is more than 50% of the three phase induction motors rated torque
Related Post:
2 Speeds, 2 Directions Multispeed 3-phase Motor Power & Control Diagrams
Characteristics & Features of Star-Delta Starter
- The starting current is 33% of full load current for star delta starter.
- The peak starting torque is 33% of full load torque.
- The peak starting current is 1.3 to 2.6 of full load current.
- Star-Delta Starter can be used only for low to high power three phase induction motors.
- It has reduced starting current and torque.
- The 6 connection cables are needed for motor terminal box.
- In Star Delta starter, Current peak and mechanical load on changeover from star delta
Applications of Star Delta Starter
As we know the main purpose of star delta starter is to start the three phase induction motor in Star Connection while run in Delta Connection.
While keep in mind that Star Delta starter can only be used for low to medium voltage and light starting torque induction motors. In case of direct on line (D.O.L) start, the receiving current at motor is about 33% while the starting torque reduced about 25-30%. This way, Star Delta Starter can be only used for light load during starting the motor. Otherwise, the heavy load motor wont start due to low torque which need to accelerate the motor to rated speed while converting to the Delta connection.
You may also read other power & control diagrams below:
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