Learning Objectives:
After reading this CONTENT, YOU MUST be able to:
1. Identify the types of Manual Starting of DC Motors.
2. Draw diagrams for Manual Starting of DC Motors.
3. Develop safety awareness in the workplace.
This information sheet will cover the different types of Manual Starting of DC Motors. This will also cover the important details on how to prepare and draw a circuit diagrams for different types of Manual Starting of DC Motors.
Manual DC Motor Starter
The Manual DC Motor Starter module is designed to start the DC Motor/Generator, Model 8501, from a dc power source. The module consists of a manually operated handle, variable-resistance starter. It can be wired as either a 3-or 4-point dc motor starter. When the motor starter is in the full run position, an electromagnet holds the handle in place. If loss of field occurs while the starter is connected in 3-point mode, the holding electromagnet is de-energized and a spring returns the starting handle to the off position. Connections are made through 4 mm color-coded jacks.
Starting Methods Of A DC Motor
By Kiran Daware
In practical DC machines, armature resistance is basically very low, generally about 0.5 Ω. Therefore, a large current flow through the armature during starting. This current is large enough to damage the armature circuit.
Due to this excessive starting current - the fuses may blow out and the armature winding and/or commutator brush arrangement may get damaged. very high starting torque will be produced (as torque is directly proportional to the armature current), and this high starting torque may cause huge centrifugal force which may throw off the armature winding. other loads connected to the same source may experience a dip in the terminal voltage.
A large DC motor will pick up speed rather slowly due to its large rotor inertia. Hence, building up the back emf slowly causing the level of high starting current maintained for quite some time. This may cause severe damage. To avoid this, a suitable DC motor starter must be used. Very small dc motors, however, may be started directly by connecting them to the supply with the help of a contactor or a switch. It does not result in any harm because they gather speed quickly due to small rotor Inertia. In this case, the large starting current will die down quickly because of the fast rise in the back emf.
To avoid the above dangers while starting a DC motor, it is necessary to limit the starting current. 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.