The first starter was created by Coleman in 1903 he is an American scientist. Later, in 1911 Kettering and Henry M. Leland further conducted experiments on the starter. In 1911, they invented an electric starter that can be used to start the electric machine. This motor is simply considered as the starter motor which is used to give power to the engines in vehicles. The electric starter finds its application mainly in the case of the automobile industry. But in the case of electricity, the electric starter we use is of different operation. This starter is used to limit the initial current that is carried to the motor. We shall discuss in detail about this topic in this article. In this article, we shall discuss what is a Four-point starter, its principle, construction, operation, and applications.
What is a Four-point Starter?
A question arises what is the need for using a 4-point Starter, it decreases the huge amount of current that occurs during the initiation of any motor. It is a type of starter used for the protection of the device by not allowing excess current to pass the inner parts. Typically it consists of four points this is the reason it is termed as the 4-point starter. These points are L (line), F (field), and A (armature). The Line is used for the giving supply, F is connected to the field, and A to the armature. In addition to these 3 points, there is one more terminal that is neutral (N) linked to the No voltage coil. All these four L, F, A, and N collectively termed as the Four Points.
Principle of Operation
It works on the principle of electromagnetic attraction when current is passed the coil, it gets energized. This coil energized produces a flux that attracts the soft iron piece connected to the handle. When the handle is able to move, we can limit the current by adding additional resistance in series with the circuit. By the addition of this resistance, the current is opposed such that the current is limited.
The Line and the soft iron piece, affixed to an electromagnet and a notch. The line allows the current to pass via the electromagnet. This electromagnet when energized attracts the iron piece as it is of an attracting material. A spring is arranged to reverse the force of attraction from the electromagnet. There are two terminals, one is affixed with the electromagnet and the other with the handle. The former one is the overload coil and the later is theHoldcoil.
The Hold coil is affixed in series with the initial resisting circuit. Apart from this, additional resistance is also connected across the field winding. After energizing the coils, the handle is directed to move over the studs such that resistance is increased. This resistance gets as and when the handle is moved because the resistance gets added due to the movement of handle over the studs. Due to the movement of the handle, the electromagnet also gets energized, which attracts the soft piece.
- Due to the movement of the handle over the studs, the handle gets in contact with the studs imposing the resistance into the circuit. This resistance slowing cuts down slowly as when the handle is moved on to the last stud.
- When the handle is at the first stud, the resistance is high. This way as it has high starting resistance it can oppose the huge current. This helps the motor to avoid high starting current when the resistance is high. As the handle is moved on to the studs further, the resistance gets decreased as it cuts the resistance.
- Due to the decrease in resistance, the current gets picked up slowly because resistance is decreased. Now, the handle moved is at the final position. Basically, there are two forces acting in this operation, one is attraction force and the other is the opposing force. As and when the handle is moved, the handle attached to the notch attracts the electromagnet and the soft iron piece is attracted.
- The opposing force acting due to the spring helps in restraining the handle at its position. For the handle to be at the final position, the attracting force imparted should be greater than the opposing force. By any chance, if the opposing force is greater than the former then the handle returns to the initial position. To maintain proper speed and current limitations always make sure that the attraction force is greater.
- It finds its application in the shunt type of motors where it stops the excess current.
Difference between Three-point and Four-point Starter
- The basic difference between a 3-point and 4-point starter is their terminals.
- The three-point starter has 3 terminals, (line), F (field) and A (armature).
- The four-point starter has 4 terminals, L (line), F (field), A (armature)and neutral (N).
- Hold coil is in series with the field winding in a 3-point starter. But in four-point starter Hold coil (HC) is in parallel with the field coil.
Thus, in this article, we have discussed in detail about the four-point starter that is used mainly for stopping the high current flowing in the machine. Apart from this, we have also discussed the construction, operation, working principle, and applications. We have also seen the difference between the 3-point and 4-point starter. Here is a question for the readers, what is a 3-point starter working principle?