4 Point Starter Pdf
It is so called because it has three terminals L, Z and A. The figure below shows the three-point dc shunt starter. The tapping points of the starting resistance are brought out to a number of studs.
It may be noted that the three point starter also provides protection against an open- field circuit. Because of the three terminals, the starter is named as the three-point starter. The line terminal, cultivez votre charisme pdf field terminal and the armature terminal are the three points of the starter. And the no-load release coil holds the starter arm to run position and the voltage supply lost it leaves the arm.
Note that the only difference between a three-point starter and a four-point starter is the manner in which no-volt release coil is connected. This is because the two circuits are independent of each other. Nowadays automatic push button starters are also used. The four-point starter uses the four terminals for acceleration of motor. One end of the handle is connected to the terminal L through the overload release coil.
To increase the speed of the motor field resistance can be increased. While entire starting resistance comes in series with the armature.
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The holding magnet may release the arm of the starter during the normal operation of the motor and thus disconnect the motor from the line. This is because back emf is developed consequently with speed to counter the supply voltage and reduce the armature current. Thus, the motor is automatically disconnected from the supply. The electrical symbols in the diagram below show all the essential parts of a three-point starter.
The starter consists of starting resistance divided into several sections and connected in series with the armature. This sudden increase in the speed of the motor is known as High-Speed Action of the Motor. If the field winding of the motor gets opened under the running condition, the field current automatically reduces to zero. Thus it also acts as a protective device safeguarding the motor from any kind of abnormality. We can see from the above equation that the current will be dangerously high at starting as the armature resistance R a is small.
Terminals Armature terminal, field terminal and the Line terminal. The three terminals L, Z and A of the starter are connected respectively to the positive line terminal, shunt field terminal and armature terminal. Your email address will not be published. The figure shows the schematic diagram of a three-point starter for a shunt motor with protective devices.
4 Point Starter Working & Construction - Electrical Edition
The armature terminal connected to the armature winding and the field terminal is connected to their field winding. This drawback is overcome in the four point starter. The overvoltage coil consists the armature current. When the current flows through the starter the no voltage coil shown in the figure magnetized.
4 Point Starter Working & Construction
In this starter, we use a microcontroller and thyristors to control the current flows through the motor and manage the speed. If no-volt release coil were not used, then in case of failure of supply, the handle would remain on the final stud.
Therefore, proper speed control can be exercised without affecting the operation of no- volt release coil. And it also makes the starting of Dc motor different from the starting of all other types. Automatic starter circuits have been developed using electromagnetic contactors and time delay relays.
Close by Clicking Below x. Now the no-volt release coil circuit is independent of the shunt field circuit. Leave a Reply Cancel reply Your email address will not be published.
There are also overload release and no volt coil which are protecting devices of the starter. The starter is a device which is used to start and run the motor. The three-point and four-point starter both are similar in construction.
Therefore, the speed of the motor increases drastically, which is dangerous and thus protection is not possible. Field current becomes very low which results in holding electromagnet too weak to overcome the force exerted by the spring. 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. At this point, field winding of the shunt or the compound motor gets supply through the parallel path provided to starting the resistance, through No Voltage Coil. This coil after removing is connected across the line in series with a current limiting resistance R.
The connection diagram of the three-point starter is shown in the figure below. To find the answer to this question let us look into the working of No Voltage Coil. Connects in parallel with the field coil. The above arrangement forms three parallel circuits. The variation in speed of the motor varies their field current.
The starter uses the resistance for limiting the starting current. Electronic Instrumentation. Hence the back emf at the starting of the motor is zero, but it develops gradually as the motor gathers speed. The supply to the field winding is derived through no voltage coil.
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