Three point starter and four point starter pdf

In case of an open circuit in the field, there will be no current through the holding coil, and hence, it will be demagnetized, and the spring action returns the arm to the off position. An overload coil is provided to prevent damage to the motor from overload. The contact points of the armature then short-circuit the holding coil and demagnetize it. This type of starter can be used to start both shunt and compound motors.

However, a 3-point starter will be found to be tripping when the motor speed is controlled through the field regulator. The reason could be explained as stated below.

When the speed of a shunt or compound motor is to be increased beyond its rated speed, the resistance is increased in the field regulator to reduce the field current, and thereby, the field flux. While doing so, the holding coil which is in series with the field gets very low current and produces less holding force on the handle armature against the tension of the spiral spring. This is an undesirable effect. To avoid this, the 3-point starter circuit is modified, and the holding coil circuit is made independent of the field circuit.

Such a starter is called a 4-point starter. In applications where many motor speeds are to be increased beyond their rated value, a four-terminal, face plate starter is used with the motor. The four terminal point starter, differs from the three-point starter in that the holding coil is not connected in series with the shunt field.

Instead, it is connected across the supply in series with a resistor. This resistor limits the current in the holding coil to the desired value. The holding coil serves as a no-voltage release rather than as a no-field release. Automated page speed optimizations for fast site performance. Explain Dc motor starters- two point, three point, four point starters.

Dc motor starters- two point, three point, four point starters Explain Dc motor starters- Since the armature is stationary before starting, the back emf which is proportional to speed is zero.

Two-point starter Three-point starter. An amount of resemblance exists between these starters. The three types of starters include a switch namely face plate rotator through an associated set of current limiting transistors. The main and common difference between these point starters is NVC no voltage coil. In a 4 point starter, the no voltage coil is connected directly to the voltage supply. A starter is not necessary for a 6V or 12 V DC motor, and it can be run directly.

A DC motor starter includes external resistance, no-volt release coil, and overload release coil. This article discusses the construction and working principle of a 4 point DC motor starter. The functional characteristics of a 4 point starter are similar to a 3 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. When the value of current increases from the limited value then the OLC closes the contact.

The connection diagram of the three-point starter is shown in the figure below. The construction of the three-point starter is similar to the four-point starter. The only difference in their construction is that the holding coil is disconnected from the field winding and is directly connected to the line terminal along with the current limiting resistor R in series.

The three-point and four-point starter both are similar in construction. But in three-point starter when the speed of the motor varies then the current passes through the field coil and this current affects the no-voltage coil. The four-point starter is designed for reducing the problem.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.

Skip to content The starter is a device which is used to start and run the motor. Key Differences Between the Three-point and Four-point Starter The starter which consists three terminals is known as the three-point starter. The four-point starter consists four terminals and hence called the four-point starter.