Direct Online Starter|direct online starter connection/DOL Starter
In this video, we'll take a detailed look at Direct-On-Line (DOL) starters - a popular method of starting and controlling three-phase induction motors. We'll start with an overview of the starter's operation and its role in motor control. Next, we'll discuss the components of a DOL starter and their functions, as well as the circuit diagram and wiring. We'll also cover some important safety considerations and best practices when working with DOL starters. By the end of this video, you'll have a solid understanding of DOL starters and be able to wire and operate them confidently. Whether you're an electrical engineering student, a professional working in the industry, or just curious about motor control, this video has something for you!
Electrical Engineering by K.M
Different starting methods are employed for starting because Induction Motor draws more starting current during starting. To prevent damage to the windings due to the high starting current flow, we employ different types of starters.
The simplest form of motor starter for the induction motor is the . The Direct On Line Motor Starter (DOL) consists of an MCCB or Circuit Breaker, Contactor and an overload relay for protection. Electromagnetic contactor which can be opened by the thermal overload relay under fault conditions.
Typically, the contactor will be controlled by separate start and stop buttons, and an auxiliary contact on the contactor is used, across the start button, as a hold in contact. I.e. The contactor is electrically latched closed while the motor is operating.
To start, the contactor is closed, applying full line voltage to the windings. The motor will draw a very high inrush current for a very short time, the magnetic field in the iron, and then the current will be limited to the locked rotor current of the motor. The motor will develop Locked Rotor Torque and begin to accelerate towards full speed.
As the motor accelerates, the current will begin to drop, but will not drop significantly until the motor is at a high speed, typically about 85% of synchronous speed. The actual starting current curve is a function of the motor design, the terminal voltage, and is totally independent of the motor load.
The motor load will affect the time taken for the motor to accelerate to full speed and therefore the duration of the high starting current, but not the magnitude of the starting current.
Provided the torque developed by the motor exceeds the load torque at all speeds during the start cycle, the motor will reach full speed. If the torque delivered by the motor is less than the torque of the load at any speed during the start cycle, the motor will stop accelerating. If the starting torque with a DOL starter is insufficient for the load, the motor must be replaced with a motor which can develop a higher starting torque.
The acceleration torque is the torque developed by the motor minus the load torque, and will change as the motor accelerates due to the motor speed torque curve and the load speed torque curve. The start time is dependent on the acceleration torque and the load inertia.
This may cause an electrical problem with the supply, or it may cause a mechanical problem with the driven load. So this will be inconvenient for the users of the supply line who always experience a voltage drop when starting a motor. But if this motor is not a high power one, it does not affect much.
Magnetic motor controllers use electromagnetic energy for closing switches. The electromagnet consists of a coil of wire placed on an iron core. When a current flows through the coil, the iron of the magnet becomes magnetized, attracting an iron bar called the armature. An interruption of the current flow through the coil of wire causes the armature to drop out due to the presence of an air gap in the magnetic circuit.
Line-voltage magnetic motor starters are electromechanical devices that provide a safe, convenient, and economical means of starting and stopping motors, and have the advantage of being controlled remotely. The great bulk of motor controllers sold are of this type.
Contactors are mainly used to control machinery which uses electric motors. It consists of a coil which connects to a voltage source. Very often for single phase motors, 230V coils are used and for three phase motors, 415V coils are used. The contactor has three main NO contacts and lesser power rated contacts named as Auxiliary Contacts [NO and NC] used for the control circuit. A contact is conducting metal parts which complete or interrupt an electrical circuit.
Overload protection for an electric motor is necessary to prevent burnout and to ensure maximum operating life.
Under any condition of overload, a motor draws excessive current that causes overheating. Since motor winding insulation deteriorates due to overheating, there are established limits on motor operating temperatures to protect a motor overheating. Overload relays are employed on a motor control to limit the amount of current drawn.
The ideal and easiest way to overload protection for a motor is an element with current-sensing properties very similar to the heating curve of the motor which would act to open the motor circuit when full-load current is exceeded. The operation of the protective device should be such that the motor is allowed to carry harmless overloads but is quickly removed from the line when an overload has persisted too long.
Normally fuses are not designed to provide overload protection. Fuse is protecting against short circuits (over current protection). Motors draw a high inrush current when starting and conventional fuses have no way of distinguishing between this temporary and harmless inrush current and a damaging overload. Selection of Fuse is dependent on motor full-load current, would “blow” every time the motor is started. On the other hand, if a fuse were chosen large enough to pass the starting or inrush current, it would not protect the motor against small, harmful overloads that might occur later.
The overload relay is the heart of motor protection. It has inverse trip-time characteristics, permitting it to hold in during the accelerating period (when inrush current is drawn), yet providing protection on small overloads above the full-load current when the motor is running. Overload relays are renewable and can withstand repeated trip and reset cycles without the need for replacement. Overload relays cannot, however, take the place of over current protection equipment.
The overload relay consists of a current-sensing unit connected in the line to the motor, plus a mechanism, actuated by the sensing unit, which serves, directly or indirectly, to break the circuit.
Direct Online Starter|direct online starter connection/DOL Starter
In this video, we'll take a detailed look at Direct-On-Line (DOL) starters - a popular method of starting and controlling three-phase induction motors. We'll start with an overview of the starter's operation and its role in motor control. Next, we'll discuss the components of a DOL starter and their functions, as well as the circuit diagram and wiring. We'll also cover some important safety considerations and best practices when working with DOL starters. By the end of this video, you'll have a solid understanding of DOL starters and be able to wire and operate them confidently. Whether you're an electrical engineering student, a professional working in the industry, or just curious about motor control, this video has something for you!
Electrical Engineering by K.M
Different starting methods are employed for starting because Induction Motor draws more starting current during starting. To prevent damage to the windings due to the high starting current flow, we employ different types of starters.
The simplest form of motor starter for the induction motor is the . The Direct On Line Motor Starter (DOL) consists of an MCCB or Circuit Breaker, Contactor and an overload relay for protection. Electromagnetic contactor which can be opened by the thermal overload relay under fault conditions.
Typically, the contactor will be controlled by separate start and stop buttons, and an auxiliary contact on the contactor is used, across the start button, as a hold in contact. I.e. The contactor is electrically latched closed while the motor is operating.
To start, the contactor is closed, applying full line voltage to the windings. The motor will draw a very high inrush current for a very short time, the magnetic field in the iron, and then the current will be limited to the locked rotor current of the motor. The motor will develop Locked Rotor Torque and begin to accelerate towards full speed.
As the motor accelerates, the current will begin to drop, but will not drop significantly until the motor is at a high speed, typically about 85% of synchronous speed. The actual starting current curve is a function of the motor design, the terminal voltage, and is totally independent of the motor load.
The motor load will affect the time taken for the motor to accelerate to full speed and therefore the duration of the high starting current, but not the magnitude of the starting current.
Provided the torque developed by the motor exceeds the load torque at all speeds during the start cycle, the motor will reach full speed. If the torque delivered by the motor is less than the torque of the load at any speed during the start cycle, the motor will stop accelerating. If the starting torque with a DOL starter is insufficient for the load, the motor must be replaced with a motor which can develop a higher starting torque.
The acceleration torque is the torque developed by the motor minus the load torque, and will change as the motor accelerates due to the motor speed torque curve and the load speed torque curve. The start time is dependent on the acceleration torque and the load inertia.
This may cause an electrical problem with the supply, or it may cause a mechanical problem with the driven load. So this will be inconvenient for the users of the supply line who always experience a voltage drop when starting a motor. But if this motor is not a high power one, it does not affect much.
Magnetic motor controllers use electromagnetic energy for closing switches. The electromagnet consists of a coil of wire placed on an iron core. When a current flows through the coil, the iron of the magnet becomes magnetized, attracting an iron bar called the armature. An interruption of the current flow through the coil of wire causes the armature to drop out due to the presence of an air gap in the magnetic circuit.
Line-voltage magnetic motor starters are electromechanical devices that provide a safe, convenient, and economical means of starting and stopping motors, and have the advantage of being controlled remotely. The great bulk of motor controllers sold are of this type.
Contactors are mainly used to control machinery which uses electric motors. It consists of a coil which connects to a voltage source. Very often for single phase motors, 230V coils are used and for three phase motors, 415V coils are used. The contactor has three main NO contacts and lesser power rated contacts named as Auxiliary Contacts [NO and NC] used for the control circuit. A contact is conducting metal parts which complete or interrupt an electrical circuit.
Overload protection for an electric motor is necessary to prevent burnout and to ensure maximum operating life.
Under any condition of overload, a motor draws excessive current that causes overheating. Since motor winding insulation deteriorates due to overheating, there are established limits on motor operating temperatures to protect a motor overheating. Overload relays are employed on a motor control to limit the amount of current drawn.
The ideal and easiest way to overload protection for a motor is an element with current-sensing properties very similar to the heating curve of the motor which would act to open the motor circuit when full-load current is exceeded. The operation of the protective device should be such that the motor is allowed to carry harmless overloads but is quickly removed from the line when an overload has persisted too long.
Normally fuses are not designed to provide overload protection. Fuse is protecting against short circuits (over current protection). Motors draw a high inrush current when starting and conventional fuses have no way of distinguishing between this temporary and harmless inrush current and a damaging overload. Selection of Fuse is dependent on motor full-load current, would “blow” every time the motor is started. On the other hand, if a fuse were chosen large enough to pass the starting or inrush current, it would not protect the motor against small, harmful overloads that might occur later.
The overload relay is the heart of motor protection. It has inverse trip-time characteristics, permitting it to hold in during the accelerating period (when inrush current is drawn), yet providing protection on small overloads above the full-load current when the motor is running. Overload relays are renewable and can withstand repeated trip and reset cycles without the need for replacement. Overload relays cannot, however, take the place of over current protection equipment.
The overload relay consists of a current-sensing unit connected in the line to the motor, plus a mechanism, actuated by the sensing unit, which serves, directly or indirectly, to break the circuit.
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