Question

Q. What is the consequence of open transition in Auto Transformer starting system and why it is not advisable onboard vessels?​

Answer 1

Answer:

                  An Auto transformer Starter is suitable for both star and delta connected motors. In this method, the starting current is limited by using a three-phase auto transformer to reduce the initial stator applied voltage.

           It is provided with a number of tappings. The starter is connected to one particular tapping to obtain the most suitable starting voltage. A double throw switch S is used to connect the auto transformer in the circuit for starting. When the handle H of the switch S in the START position.

• The primary of the auto transformer is connected to the supply line, and the motor is connected to the secondary of the auto transformer.

• When the motor picks up the speed of about 80 percent of its rated value, the handle H is quickly moved to the RUN position. Thus, the auto transformer is disconnected from the circuit, and the motor is directly connected to the line and achieve its full rated voltage.
• The handle is held in the RUN position by the under voltage relay.

• If the supply voltage fails or falls below a certain value, the handle is released and returns to the OFF position. Thermal overload relays provide the overload protection.

DOL ( Direct online Strater ) starters are primarily motors where a high inrush current does not cause excessive voltage drop in the supply circuit (or where this high voltage drop is acceptable).

• Direct on line starters are commonly used to start small water pumps, conveyor belts, fans, and compressors.

For this reason DOLs' are used in-stead of Auto Transformer .

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