What is direct online motor starting?
What is direct online motor starting?
Direct on line (DOL) motor starting is when a motor is started at full load, with full line voltage applied to motor terminals. As this causes the motor to draw a large amount of current, it is only suitable for motor powers up to 4Kw, with a maximum motor size of 10Kw connected this way.
What is starting torque of a motor?
Starting torque is the torque transferred by the shaft coupling during run-up (see Start-up process). It is calculated based on the ratio of power (P) to angular velocity (ω) and is represented as a rotational speed function.
How do you calculate starting torque?
We know that at the start the rotor speed, N is zero. So, the equation of starting torque is easily obtained by simply putting the value of s = 1 in the equation of torque of the three phase induction motor, The starting torque is also known as standstill torque.
For which type of motors the direct on line starting can be used?
One of the simplest forms of motor starter that is used for induction motors is the Direct On Line starter. It consists of an MCCB or Circuit Breakers, Contactor and an overload relay for protection.
What is a direct online circuit?
The Direct Online or DOL starter employs full voltage or across the line starting technique where the motor is directly connected to full voltage through MCCB or circuit breaker and. This is why such a starter is used with induction motors rated below 5 hp.
What is direct online starter used for?
Direct on line starters are commonly used to start small water pumps, conveyor belts, fans, and compressors. In the case of an asynchronous motor (such as the 3-phase squirrel-cage motor) the motor will draw a high starting current until it has run up to full speed.
Which motors have high starting torque?
The capacitor start motor develops a much higher starting torque of about 3 to 4.5 times of the full load torque.
What is torque in electric motor?
Torque is a rotating force produced by a motor’s crankshaft. The more torque the motor produces, the greater is its ability to perform work. Since torque is a vector acting in a direction it is commonly quantified by the units Nm or pound-feet.
What are the high starting torque IM?
In order to increase the starting torque, extra resistance should be added to the rotor circuit at start and cut out gradually as motor speeds up. The maximum torque is directly proportional to square of rotor induced emf at the standstill. The maximum torque is inversely proportional to rotor reactance.
How do you increase the starting torque of a motor?
There are three ways to improve the starting torque of Single phase induction Motor
- Internal Rotor Resistance. The across the line starting torque at low speed can be increased by increasing the rotor resistance.
- External Rotor Resistance.
- Variable Voltage/Frequency.
What are limitation of direct on line starting of motors?
Disadvantages of DOL Starter It does not reduce the starting current of the motor. High Starting Current: Very High Starting Current (Typically 6 to 8 times the FLC of the motor). Mechanically Harsh: Thermal Stress on the motor, thereby reducing its life.
What are direct online starters used for?
What makes a direct on line motor start?
Fuses are provided in the circuit for short circuit protection. In direct on line starting the starting current may be as large as ten times the full load current, and the starting torque is equal to full load torque. Such a large starting current produces an excessive voltage drop in the line which supplies power to the motor.
What is the starting torque of a motor?
The starting torque is about 25 % of the direct-on-line starting torque. The stress on an application is reduced compared to the direct-on-line starting method. With a variable frequency drive the electrical frequency to the motor is modulated between typical 0-250 Hz. The frequency drive can also be used for soft stops.
What is the starting torque of a DOL motor?
From the above equation we observe that starting torque in DOL or Direct-on-Line Starting is high. The average starting torque is in DOL starting, Torque on starting = 0.5 to 1.5 rated Torque.
How big is the starting current on a direct on line?
In Direct on line starting the starting current may be as large as ten times the full load current, and the starting torque is equal to full load torque. Such a large starting current produces an excessive voltage drop in the line which supplies power to the motor.
