26: What is the most important precaution in any experiment with d.c. shunt motor? Answer: Before switching on d.c. supply, a sufficient resistance should be put in series with the armature of the d.c. shunt motor.
What are the precautions that has to be considered while starting a DC shunt motor?
Never open the shunt field of a motor that is running, the loss of field magnetic strength will cause the armature to pull extremely high current and if the motor is not under load, the lack of counter emf will cause the armature rpm to run away, possibly high enough to cause damage.
What precautions should be taken when working with a DC motor?
Speed regulation in the series motor is quite poor. With the increase in the load speed of the machine decreases. (DC shunt motor maintains almost constant speed from no load to full load). DC series motor should always require to be loaded before starting the motor.
How can you prevent high starting current from flowing through the rotor of a DC motor?
To prevent such an incidence from occurring several starting methods of DC motor has been adopted. The main principal of this being the addition of external electrical resistance Rext to the armature winding, so as to increase the effective resistance to Ra + Rext, thus limiting the armature current to the rated value.
What steps are required in the starting of a DC motor?
So, a DC motor is started by using a starter. There are various types of dc motor starters, such as 3 point starter, 4 point starter, no-load release coil starter, thyristor controller starter etc. The basic concept behind every DC motor starter is adding external resistance to the armature winding during starting.
What should you always do before working on an electric motor?
- You should always keep your work area clean and well lit.
- All motors include many small parts; keep very young children away from your work area.
- Motors spin very fast; always wear safety goggles.
- Super Glue, provided with most of the kits, is “instant bonding”.
What is the need for starter with 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 does insulation type of class refer and how many classes are there?
There are basically four classes of insulation – A, B, F and H – class F being the most commonly used. These insulation classes were established to meet motor temperature requirements found in industrial applications.
Why does a DC motor develop a high starting current when starting?
Answer: The starting current is high as there is no back EMF or counter EMF present in the armature circuit because atstarting counter EMF is zero. … It’s armature has very less resistance due to this it need more current at starting time. Hence DC starters are used to limit the starting current ofmotor.
How can you reduce the torque of a DC motor?
The easiest way is to install some potentiometer (or resistor) between battery and motor. That should decrease the voltage on motor and so RPM. Torque may also a bit decrease.
How do you increase the starting torque of a DC motor?
Any DC motor will experience a decrease in speed when a load is applied, which causes the back EMF to decrease. The reduction in back EMF increases the net voltage, since the supply voltage remains constant. The net voltage increase causes the armature current to increase, which increases the motor torque.
What is a DC shunt motor?
A DC shunt motor (also known as a shunt wound DC motor) is a type of self-excited DC motor where the field windings are shunted to or are connected in parallel to the armature winding of the motor. Since they are connected in parallel, the armature and field windings are exposed to the same supply voltage.
What will happen if DC shunt motor is connected across AC supply?
1. What will happen if DC shunt motor is connected across AC supply? Explanation: In case of parallel field connection, it won’t rotate at all and will start humming and will create vibrations, as a torque produced by positive and negative cycle will cancel out each other. DC motor will be heated up and it may burn.
Which starter is used for DC shunt motor?
A 4 point starter is used to start and control the speed of a Dc shunt motor with field weakening control.