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What is the difference between 3point and 4point starters?
The most significant difference between the three point and the four-point starter is that in three-point starter the no voltage coil (NVC) is connected in series with the field winding whereas in four-point starter the NVC is directly connected to the supply voltage.
Why it is called 3 Point starter?
it is called a three-point starter because it has three terminals named L, F, and A. The final connection must then be made from second-line terminals on the main switch to a junction of the remaining two armature and field terminals of motors.
How does a 3 point starter work?
A 3 point starter is a device that helps in the starting and running of a DC shunt motor or compound wound DC motor (similar to a 4 point starter). The back emf develops as the motor armature starts to rotate in presence of the magnetic field, by generating action and counters the supply voltage.
What is 2point starter?
In case of series motors, field and armature are inserted and hence starting resistance is inserted in series with the field and armature. Such a starter used to limit the star4ting current in case of dc series motor is called two point starters. The action of the starter is similar to that of three point starter.
Which is better 3 point starter and 4 point starter?
Four point starter works as a current controlling device in the deficiency of back EMF while starts running of the DC motor. A four-point starter also works as a protecting device. The main difference between a 4 point starter compared to a 3 point starter is, the holding coil is detached from the shunt-field circuit.
Why starters are required in a DC motor?
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.
What is DOL starter with diagram?
The DOL starter consists of two switches namely Green and Red where the green switch is used to start and red switch is used to stop the motor. The DOL starter comprises a circuit breaker (or) MCCB, overload relay & contactor for protecting the motor. The two switches of the motor control the contacts.
What is a 4 point starter?
What is use of 4 Point starter?
A 4 point starter is used to start and control the speed of a Dc shunt motor with field weakening control. High speed protection of DC shunt motor is not provided by 4 point starter.
What are the advantages over 3 point starter?
While starting DC shunt motor it draws huge current from the line which damages the internal parts of the motor. So, a three-point starter helps in limiting the starting current such that the motor begins to attain speed slowly and runs smoothly.
What are the points of a 3 point starter?
The 3 point starter connects the resistance in series with the circuit which reduces the high starting current and hence protects the machines from damage. Mainly there are three main points or terminals in 3 point starter of the DC motor. They are as follows: L is known as the Line terminal, which is connected to the positive supply.
How does the NVC work in a 3 point starter?
The supply to the field winding is derived through no voltage coil. So when field current flows, the NVC is magnetized. Now when the handle is in the ‘RUN’ position, a soft iron piece is connected to the handle and gets attracted by the magnetic force produced by NVC, because of flow of current through it.
How does an overload relay work on a three point starter?
Under overloading conditions handle is moved back to its previous position by means of a relay which is called an overload relay. Three-point starter functions very well, if there is no voltage (power failure occurs) then starter turns OFF. If an overload current is drawn by the machine then the starter comes back to its original position.
What is the starting resistance of a starter?
Another parallel path is derived from the stud ‘1’, given to another electromagnet called No Volt Coil (NVC) which is further connected to terminal ‘F.’ The starting resistance at starting is entirely in series with the armature. The OLR and NVC act as the two protecting devices of the starter.