DC MOTOR STARTERS IN MALAYALAM

Starters for DC Motors
At starting the motor takes large amount of current which is nearly 25 x full load current. This large amount of current can not be allowed to flow in a motor even for a short period of time. This exclusive starting current has to be prevented because
• It cause sudden depression of voltage of supply(large voltage drop occurs) system causing disturbances to other loads connected in the system.
• It would cause heavy sparking at the brushes which may destroy the commutator and brush gear.
• Due to heavy inrush of current at start there is possibility of damage of the motor winding.
Preventing large starting current
A resistance is introduced in series with the armature for very start duration of starting period only, which limits the starting current to a very safe value. This starting resistance is gradually cut out as the motor gains speed and develops the back emf which then regulates the speed of the motor.
Types of starters for DC motor
• Two point Starter
• Three point Starter
• Four point Starter
Two-point Starter
A two-point starter is used for starting dc motor which has the problem of over-speeding due to loss of lod from its shaft. Such a starter is shown in figger.
Here for starting the motor, the control arm is moved clockwise from its OFF position to the ON position against the spring tension. The control arm is held in the ON position by an electromagnet. The hold-on electromagnet is connected in series with the armature circuit. If the motor losses its load, current decreases and hence the strength of the electromagnet also decreases. The control arm returns to the OFF position due to spring tension, this preventing the motor from overspending. The starter arm also returns to the OFF-position when the supply voltage decreases appreciably. L and F are two points of the starter which are connected with the supply and motor terminals.
Three Point Starter
A 3 point starter is a device that helps in the starting and running of a DC shunt motor or compound wound DC motor. The electrical symbols in the diagram below show all the essential parts of a three-point starter.
Construction of 3 Point Starter
Construction wise a starter is a variable resistance, integrated into the number of sections as shown in the figure beside. The contact points of these sections are called studs and are shown separately as OFF, 1, 2, 3, 4, 5, RUN. Other than that there are three main points, referred to as
1. ‘L’ Line terminal (Connected to positive of supply)
2. ‘A’ Armature terminal (Connected to the armaturewinding)
3. ‘F’ Field terminal (Connected to the field winding)
And from there it gets the name 3 point starter. Now studying the construction of 3 point starter in further details reveals that the point ‘L’ is connected to an electromagnet called overload release (OLR) as shown in the figure. The other end of OLR is connected to the lower end of conducting lever of starter handle where spring is also attached with it, and the starter handle also contains a soft iron piece housed on it. This handle is free to move to the other side RUN against the force of the spring. This spring brings back the handle to its original OFF position under the influence of its own force. 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.
Working of Three Point Starter
Having studied its construction, let us now go into the working of the 3 point starter. To start with the handle is in the OFF position when the supply to the DC motor is switched on. Then handle is slowly moved against the spring force to make contact with stud No. 1. 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. While entire starting resistance comes in series with the armature. The high starting armature current thus gets limited .
As the handle is moved further, it goes on making contact with studs 2, 3, 4, etc., thus gradually cutting off the series resistance from the armature circuit as the motor gathers speed. Finally, when the starter handle is in ‘RUN’ position, the entire starting resistance is eliminated, and the motor runs with normal speed.
This is because back emf is developed consequently with speed to counter the supply voltage and reduce the armature current.
So the external electrical resistance is not required anymore and is removed for optimum operation. The handle is moved manually from OFF to the RUN position with the development of speed.

[@yamangaming3914]

Super class very intresting class

[@anaghamp3455]

Doing well🤗

[@nandhukrishnakumar8803]

Good class

[@yamangaming3914]

Thanku

[@nandhakishornk8257]

Super class bro.very useful Tnk U

[@amalp819]

Good class. Tks

[@shiju4721]

Super brooo 😍😍😍

[@അമൽ.എസ്]

DC shund motor field control method അല്ലെ 4point starter ഉപയോഗിക്കുന്നത് sir

[@nature_voice_1999]

👏

[@ajithvs7743]

🔥❤️