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Re: Liquid Rotor Starter
A variant of the induction motor, is the slip ring, or wound rotor motor.
The induction motor has a "squirrel cage" rotor which is in effect a short circuited winding in the rotor. The start and run characteristics are influenced by the resistance and inductance of the rotor circuit. One of the problems of the induction motor, is that the start current is very high (600 - 900%) and the start torque is relatively low (120 - 200%) compared to the start current drawn. The induction motor has a speed at which maximum torque is produced and this is very close to full speed.
By altering the resistance in the rotor design, we can alter the speed at which maximum torque is produced. Below this speed, the current goes high and the torque goes down. Above this speed, the current drops with the torque.
The wound rotor motor, has a winding on the rotor that is not short circuited, but is brought out to slip rings. This enables the effective rotor resistance to be altered.
By varying the rotor resistance while the motor starts, we can cause the speed of maximum torque to shift from zero speed up to very close to full speed in a number of steps. The big advantage of this, is that the motor is able to provide a high start torque (around 200%) and a low start current (around 200%) from zero speed to full speed. This is very god for starting high inertia and difficult start loads on relatively weak supplies.
The rotor resistors can be cast resistors, wound resistors, or liquid resistors. With standard resistors, the stages are switched in and out by contactors to alter the resistance. With liquid resistors, the resistance can be varied by varying the immersion of probes in the electrolyte. This can be achieved by raising and lowering the probes, or the liquid level.
What else can I help you with?
What is the total copper loss when rotor is standstill?
It is the supply voltage divided by the rotor resistance including the resistance of the brushes.
What is the function of liquid in liquid resistance starter?
Combination of water and caustic soda for improving the resistance in starter, that's called Liquid Resistancestarter.If any slip ring Induction motor, at the time of startinggiven the external resistance required to rotor side, why because starting current and starting torque is very high.So we are using resistance starter depend on motor capacity , at that place using Liquid resistance starter.Liquid resistance starter (LRS) ,IN which externalresistance is liquid media which is use for the startingmethod of slip ring motor. For starting of slip ring motor external resistance arerequired so that we use liquid (addition of some causticsoda)as resistance so that is called as LRS.
What will happen to speed-torque characteristics of an induction motor is the rotor resistance is increased?
If Rotor resistance is increased torque is increased
What is double cage rotor and deep bar cage rotor?
deep bars in the rotor that result in higher rotor resistance at low speeds thus resulting in larger starting torques. The higher resistance is due to the skin effect.
Why rotor contactor in external resistance of slipring motor connected in delta?
rotor contactor are used to cut the resistance in slip-ring motor connected through resistance box. resistance is proportional to torque. so by controlling rotor contactor resistance can be controlled and hence torque can be controlled. for more information check torque and speed characteristic of wound motor.
Why will the rotor of a wound-rotor motor not turn if the rotor circuit is left open with no resistance connected to it?
Because there is no current flowing in the rotor, and thus there is no magnetic field in the rotor, and thus there is no torque between the rotor and the field.
The resistance of a liquid to following is its?
the resistance of liquid to following is its viscosity.
What happen if the field of the DC motor is opened?
Assuming a shunt-fed motor, it means the rotor would stop generating a back-emf and it would also stop generating any torque. The current would rise until limited by the resistance of the rotor, but before that the circuit-breaker would operate.
Can a liquid offer resistance to stress?
yes.due to the surface tension ,there is liquid offer resistance.
What will happen if the field of dc motor motor is opened?
Assuming a shunt-fed motor, it means the rotor would stop generating a back-emf and it would also stop generating any torque. The current would rise until limited by the resistance of the rotor, but before that the circuit-breaker would operate.
What do you mean by Rotor resistance?
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How a slip ring motor work?
The stator coil is exactly the same as a 3 phase induction motor. The difference being the rotar which has 3 phase wiring in star point or delta connection and also has the sliprings connected to the wiring of the rotor. Brushes are use for the contact between the surpply and the rotor. By controling the current we can control the torgue and speed of the motor. This is done with resistance. Resistance can be greated by means of a resistance bank, liquid resistance or a variable resistance. The basic Idee is: The higher the resistance, low starting current, high torque, high % slip. Motor runs slowlyLow resistance , Higher starting current, lower torgue, lower % slip Motor runs faster.Thus by varing the rotor resistance the motor can be adapted for a spesific load.The motor Are mainly used for Overhead cranes, Elevators in buldings, Pumps under pressure and large fans
