An electrical generator is a machine that changes the form of supplied mechanical energy into electrical energy. The generators are classified into two types based on the output obtained. The output obtained from any machine is alternating current I,e AC whether it is DC or AC generator. So, in DC generator for the transformation of this AC into DC a device is required. This requirement is fulfilled by the usage of a commutator. In this article, we shall discuss what is a commutator segment, its meaning, working, diagram, its usage in DC machine, split ring, and applications.
What is a Commutator?
It is also called a split-ring commutator. The split rings are made of phosphorous bronze and it is a device connected with the armature core. It is used to collect the current from the armature winding. It changes the form of AC to DC or DC to AC depending upon the requirement. The figure that depicts the cross-sectional view is shown below.
It consists of some segments which are arranged in series to which the ends of armature winding are connected. These divided segments are termed as the commutator segments. These segments are laminated by a thin layer of Mica with a thickness of 0.6 to 0.8mm. The dielectric strength of these segments is nearly 30V to 40V. The segments are made of hard drawn copper of high conductivity. Each segment consists of two coil sides (as one coil contains two coil sides).
The number of these segments is equal to the number of coils.
It is attached to the brush which is used to collect the current from the segments. The segments are the rotating part whereas the brushes are the stationary part.
The function of the Commutator Segment
It is a device that converts either AC to DC or DC to AC I,e it can act as both “Rectifier” or as an “Inverter” depending upon the requirement.
In the DC generator, at Θ = 0° the induced emf (Ed ) will be zero, at Θ = 90° the induced emf (Ed ) will be maximum, at Θ = 180° induced emf (Ed )is zero, and at Θ = 270° the induced emf (Ed ) will be maximum.
At Θ = 0°, the coil will be in parallel with the magnetic lines of forces. So, no emf will be induced in the winding.
At Θ = 90°, the coil will be perpendicular to the direction of the magnetic lines of forces. The coil now cuts these lines of forces and an emf will be induced as stated by the faradays law of electromagnetic Induction. The figure which explains the movement of the coil in the magnetic field at Θ = 90° is shown in the figure below.
At Θ = 180°, the coil will be in parallel with the magnetic lines of forces. So, no emf will be induced in the winding.
At Θ = 270°, the coil will be perpendicular to the direction of the magnetic lines of forces. The coil now cuts these lines of forces and an emf will be induced as stated by the faradays law of electromagnetic Induction. The figure which explains the movement of the coil in the magnetic field at Θ = 270° is shown in the figure below.
This process repeats as the coil is rotated inside the magnetic field.
Any machine that is with a heteropolar system generates AC only. AC generator generates AC, DC generator also generates AC. Therefore, any generator with a heteropolar system generates AC only.
Generated emf by any machine initially is shown in the figure below.
So, initially, the generated power will be alternating in any machine that is converted to DC. The waveform after conversion I,e the AC is changed to DC is shown in the figure below.
The generated emf frequency of DC generator or AC generator is given as
f = PN/120
f = frequency of the system,
N = speed in r.p.m, and
P = number of poles.
In the DC generator, the segments convert the generated AC to DC and hence, it acts as a “full-wave uncontrolled mechanical Rectifier”.
In DC Motor, the segments convert the generated DC to AC and hence, it acts as a “full-wave uncontrolled mechanical Inverter”.
Importance of the Commutator
The difference between the AC generator and the DC generator exists in the segments. In the DC machine, the field winding is employed on the stator and armature winding is employed on the rotor to facilitate the commutation process.
In the case of the AC machine, the armature winding is placed on the stator and field winding is placed on the rotor. The stationary armature winding is more advantageous compared to the rotating armature winding. In the DC machine, as the armature winding is placed on the rotor it requires more winding as well as the number of brushes. Due to the increase in the number of brushes, sparking increases at the brushes which decrease efficiency. So, the stationary armature is more advantageous compared to the rotating armature.
The AC generator is comprised of the combination of the slip rings and brush whereas the DC generator is comprised of the combination of the commutator and brush.
- Used in DC generator and motor, Ac generator, and motor, and in universal motors
Thus, in this article, we had an overview of what is a commutator. It consists of some segments that are used for the conversion of AC to DC or DC to AC. Apart from this, we had also studied commutation in DC generators, the importance, methods to improve commutation, and applications. Here is a question for the readers, what is the role of a commutator in a Universal motor?