Table of Contents
What is a high starting torque for a motor?
DC motor has high starting torque.In a series motor the same current flows through the armature and the field winding. The torque is therefore proportional to the square of the current.
What is a starting torque?
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.
What is meant by low starting torque?
AT starting Torque is directly proportional to RESISTANCE of windings of rotor of wound type induction motor. SO to increase torque during starting ,resistance is increased by external connection,which leads to low starting current as it is inversly proportional to resistance.
Why is starting torque important?
Starting torque is the amount required to overcome the inertia of a standstill. Pull-up torque is the minimum torque generated by a motor as it accelerates from standstill to operating speed. If a motor’s pull-up torque is less than that required by its application load, the motor will overheat and eventually stall.
Which motor has high starting torque and high starting current?
Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor? DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load.
Why do series motor have high starting torque?
Torque. Series motors have the characteristic of developing very high starting torques. The reason for this is the same current that passes through the armature also passes through the field windings.
Which applications require high starting torque?
Applications of DC series motor: As It has a very high starting torque, it is used for heavy-duty applications such as electric railways, mine hoists, continuous conveyors cranes, rolling mills, metallurgical works etc.
How do you increase starting torque?
There are four ways to improve the starting torque of an induction motor.
- Internal Rotor Resistance.
- External Rotor Resistance.
- Double Cage Rotor Design.
- Variable voltage & Variable Frequency.
Should torque be high or low?
“Higher torque at lower r.p.m. means you have a lot more horsepower at lower r.p.m., which makes it easier to tow things from a standstill. That’s usually how trucks are geared,” Murray said. “High torque at higher r.p.m. means more power while you’re already underway, which usually results in higher top speed.
Why motor takes high starting current?
At start, the reactance of the rotor is high because the slip of the motor is equal to unity. The value of Rr/s increase as the slip gets decrease. When the induction motor is started the rotor reactance is more than the rotor resistance and because of the large Xr/Rr ratio the motor takes large inductive current.
Which type of motor has low starting torque?
Large single-phase motors (15-50 hp) have been developed. These are capacitor start-capacitor run squirrel-cage induction motors. They are designed with very low inrush current and have low starting torque.
Why do DC motors have high torque?
The field windings are thicker diameter, with fewer turns than in a DC shunt motor, so the resistance of the windings is lower. This allows the series motor to draw a large amount of current and produce a high amount of torque.
Why are starters used with DC motors?
Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.
Which DC motor is preferred for elevator?
DC cumulative compound motor having high starting torque up to 450% depending upon the degree of compounding. The speed regulation is varying up to 25 ~ 30%. That’s why these motors are used in elevators.
How is starting torque of induction motor increased?
Starting torque of induction motor can be increased by increasing the rotor resistance. This can be done by reducing cross sectional area of rotor bars and by changing the conductor material. However, This will reduce the efficiency of motor.
How do you overcome low starting torque?
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 is the benefit of higher torque?
An engine’s power is the product of force and the speed with which this force acts. Engine power and torque are both indicators that depend on the engine speed. A high torque enables efficient and energy-saving driving. A high engine power enables a car to accelerate quickly and reach a high top speed.
Does induction motor have high starting torque?
A high starting torque induction motor with simultaneously reduced starting current adapted to be associated with a drive having a high load torque on starting that includes a stator, a rotor, a first end ring fixed on said rotor, a second movable end ring associated with said rotor and having a lower electrical …
Why do induction motors have low starting torque?
The large rotor reactance at the start makes the starting torque of the motor poor. The motor draws about 5 to 6 times the current of its full load current and produces very less torque. Most of the current is reactive in nature and does not contribute to the production of torque.
What are the applications of high starting torque?
Examples of high starting torque applications are rotary kiln, bucket elevator, railway traction, etc. The DC series motor is the best motor for high starting torque to drive high inertia loads.
What happens if the start-up torque of a motor is too high?
If the start-up torque of your motor is not greater than the start-up torque of your mechanical system, then the motor will not be able to get the system moving. The image below shows the torque curve for a typical AC motor.
Which motor produces the highest starting torque?
The DC series motor produces the highest torque among all kinds of motors.The DC series motor produces high starting torque as compared to starting torque of the separately excited DC shunt motor and the DC shunt motor. The DC series motor is used for driving the high inertia loads which demand higher starting torque,
What is the meaning of high torque?
Coming to the High part, it means a motor or engine is capable of turning a big block of disc rather than a small one you usally see in bikes. Best example = A bulldozer or excavator has high starting and operating torque. Also slow speed diesel engines produce high torques, like a locomotive based diesel engine.