how to learn dol electric motor control – a basic motor controller guide for direct on line electrical motor controls
It is the most innovative electrical device to convert electrical energy into mechanical energy, on the contrary, it can also generate electrical energy from mechanical energy or more common generators, power is generated when the motor is coupled with a gas or diesel engine and driven by it.
As the main promoter of machines used in various applications and industries, electric motors are widely used in various applications, such as electric vehicles, electric locomotives, elevators, escalators, water pumps, air compressors, electric fans, hand drills, sewing machines, washing machines, microwave ovens, generators, CD and DVD drives that charge the battery of the car, even the smallest devices such as battery-powered watches, and more other uses and specific applications that we may not even know, but in our daily lives, this is just a common thing we can do.
Depending on the type of application controlled by the motor capacity involved in the mode of operation and driving a specific load, the motor is certainly operated by an electrical activation and control system called the motor controller.
The motor controller is basically the most integral part of the motor and plays an important role in basically providing the right operation of the multiple methods needed to run and stop the motor.
Despite the variety of complex executable methods, this paper aims to cover some of the most basic motor control applications with AC (AC)
Induction motors commonly used in various industries, and the most basic type of motor controller is directly online (DOL)
Direct online motor controller (DOL)
The easiest way to control the motor is directly online (DOL)
The motor controller, which provides the line voltage directly to the motor through a switch or a single unit magnetic contactor.
This type of motor controller is mainly applied to small motors, because small motors do not cause too much load burden, thus adversely affecting the supply voltage from the power grid.
The CAD diagram on the right shows the electrical diagram of the typical method of the 3-phase DOL motor power circuit controller.
The main circuit breaker acts as the main switch that supplies power to the system.
It is also equipped with over current and short circuit protection for automatic trip
Turn off to disconnect the power supply so that the load is disabled when a fault in the load circuit is detected.
The main magnetic contactor acts as the motor operation switch, connecting and disconnecting the supply voltage from the main circuit breaker to the motor.
When the main contactor is off, the supply voltage continues to the motor terminal running the motor.
The thermal overload relay is used to detect the motor overload current, and when this current is detected, it will immediately disconnect the control circuit of the motor controller to stop the operation and prevent the motor from burning.
The DOL control circuit diagram shown on the right shows the typical switching system of the DOL motor controller.
The control circuit becomes complete when the operator presses the run button switch, allowing the power supply to move down to the main contactor coil, which is powered on.
After the main contactor is powered on, its internal three-pole mechanical contacts (
Reference motor control chart)
Connect the supply voltage to the closing device of the motor terminal to run the motor.
Back to the control circuit diagram, since the auxiliary normally open contact of the main contactor parallel on the running button switch is already off after the main contactor coil is activated, even if the operator releases the finger from the running button switch, the power continues to flow to the main contactor coil, a holding contact switch that maintains a complete circuit to run the motor continuously without further human intervention, by running and stopping the button swithces, it provides convenience for the operator to turn on and off the motor.
Two circuits are disconnected in the control system.
In addition to the OFF-button switch, the thermal overload relay is also used as a disconnect switch to make the control circuit disconnected or incomplete, and when the motor overload current is detected, the control circuit deactivates the main contactor to stop the motor.
The forward and reverse selection motor of the motor rotating motor the motor can run forward and reverse depending on the requirements of the application to install the motor, for example, as in the conveyor system, needs to be moved in both directions of the items included in the conveyor table.
When some types of applications require this arrangement, the forward reverse motor controller is applied to the control circuit of the motor to achieve this purpose.
Again, the equipment required for this operational possibility is a magnetic contactor.
The reverse motor rotation of the 3-phase AC induction motor can be achieved by switching the configuration of any two of the three motor terminals U1, V1, W1 relative to the reference supply voltage L1, l2, l3
The following CAD diagram provides an intuitive explanation for this method of operation.
You will notice the magnetic contactor with two units from the motor control diagram above (
Forward contactor and reverse contactor)
Connect parallel to each other.
Please note that the line parameters of these two contactor follow the common connection configuration of the supply voltage L1, L2, L3, and the load parameters of these two contactor have different configurations for the motor terminal U1, v1, t1
The forward contactor is connected to L1, L2 is connected to V1, L3 is connected to W1, which makes the motor run forward.
When the reverse contactor is configured with two terminals in the opposite order, L1 is connected to t1 instead of U1, then L3 is connected to W1 instead of W1, and only L2 is connected to v1.
The forward reverse control circuit diagram shown above shows two DOL control circuits with two magnetic contactor to accommodate forward and reverse motor rotation, however, due to the inclusion of an additional interlock, usually each contactor coil is inserted with a closed contact.
These interlocking contacts are intended as safety precautions to prevent the activation of two contactor coils at the same time, which may damage the motor if not prevented.
When the forward contactor coil is activated, its auxiliary normally closed contact is connected before the reverse contactor coil is opened, thus preventing the reverse button switch from accidentally pressing when the motor is running forward, any power flows to the reverse contactor coil and the positive contactor coil is energized.
Similarly, when the motor is in reverse operation, the reverse contactor coil is energized, and due to the presence of the Open reverse contact switch provided by the powered reverse contactor coil, it is not possible to power the forward contactor coil, so, prevent the motor from running forward when the reverse is active.
Another indispensable electrical control method for AC induction motors is the star delta Motor controller.
The motor controller is also an indispensable part of industrial process automation technology.
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