Differences between a shunt field coil and a series field winding
A shunt field coil is a coil of wire connected in parallel with the armature winding of a DC motor. It is used to create a magnetic field that is constant regardless of the load on the motor. A series field winding is a coil of wire connected in series with the armature winding of a DC motor. It is used to create a magnetic field that is proportional to the load on the motor.
To understand the differences between a shunt field coil and a series field winding, you need to first understand the basic principles of field windings in electrical machines.
Field windings are conductive coils of wire that produce an electromagnetic field in electrical machines, such as motors or generators. This field interacts with the armature or rotor, allowing for the conversion of electrical energy to mechanical energy (in motors) or vice versa (in generators).
Now, let's break down the differences between shunt field coils and series field windings:
1. Connection:
- Shunt field coil: A shunt field coil is connected in parallel with the armature circuit. It receives its power supply directly from the main source of electrical energy.
- Series field winding: A series field winding is connected in series with the armature circuit. The current passing through the armature also flows through the series field winding.
2. Control:
- Shunt field coil: A shunt field coil has a high resistance compared to the armature circuit. This allows for greater control over the field, as the coil can be easily regulated using a variable resistor or rheostat.
- Series field winding: A series field winding has low resistance, meaning that the current flowing through it is directly dependent on the load. As the load increases, the current passing through the series field winding also increases, resulting in a stronger field.
3. Speed regulation:
- Shunt field coil: Shunt field coils provide better speed regulation because their field strength remains relatively constant even with varied armature currents. This is because they have a separate power supply and can maintain a consistent field strength.
- Series field winding: Series field windings do not provide good speed regulation, as their field strength varies with the armature current. As the load increases, the field strength also increases, which can lead to speed changes.
4. Applications:
- Shunt field coil: Shunt field coils are commonly used in applications that require constant speed and precise control, such as in industrial machinery or conveyor systems.
- Series field winding: Series field windings are commonly found in applications where speed regulation is less critical, such as in electric traction systems like locomotives or elevators.
In summary, the main differences between a shunt field coil and a series field winding lie in their connection, control, speed regulation, and applications. Shunt field coils provide constant field strength, better speed regulation, and are suited for applications requiring precise control. In contrast, series field windings vary their field strength with the armature current, have poorer speed regulation, and are used in applications with less strict speed requirements.
1. Configuration:
- Shunt Field Coil: A shunt field coil is connected in parallel with the armature of a DC motor. It has its own separate circuit, and the current flowing through it is a fraction of the total current supplied to the motor.
- Series Field Winding: A series field winding is connected in series with the armature of a DC motor. The same current flowing through the armature also flows through the series field winding.
2. Operating Principle:
- Shunt Field Coil: The shunt field coil is responsible for generating a magnetic field that is relatively constant regardless of the load applied to the motor. It provides motor speed control by regulating the magnetization of the motor.
- Series Field Winding: The series field winding produces a magnetic field that varies with the load on the motor. As the load increases, the current through the series field winding also increases, resulting in a stronger magnetic field and higher torque.
3. Control Characteristics:
- Shunt Field Coil: The shunt field coil provides better speed regulation because its magnetic field remains relatively constant, regardless of the load. It allows for fine control of the motor's speed.
- Series Field Winding: The series field winding offers greater torque at low speeds and weaker torque at high speeds. This makes it suitable for applications requiring high starting torque, such as electric locomotives or elevators.
4. Motor Characteristics:
- Shunt Field Coil: Motors with shunt field coils have a relatively constant speed-torque characteristic, meaning the speed drops slightly as torque increases. They are commonly used in applications that require precise speed control, such as machine tools or conveyor belts.
- Series Field Winding: Motors with series field windings have a non-linear speed-torque characteristic, meaning the speed decreases significantly as torque increases. They are often used in applications that require high starting torque and variable speed, such as electric vehicles or hoists.
5. Safety:
- Shunt Field Coil: Shunt field coils provide better safety compared to series field windings because they are connected in parallel with the armature. If the shunt field coil fails, the motor can still operate, although its speed control may be compromised.
- Series Field Winding: Series field winding failure can lead to complete motor failure. If the series field winding breaks, the armature current is interrupted, resulting in a loss of torque and inability to operate the motor.
Overall, the main difference between a shunt field coil and a series field winding lies in their configuration, control characteristics, motor performance, and safety implications.