The voltage generated in the coil ( anchor ) placed in an extremely rotating magnetic river of a DC generator usually changes. Commutation In a DC machine, or more specifically in a DC generator, commutation is the process in which the alternating current generated by the armature coil of a DC machine is regenerated into direct current, taking into account the commutator and the fixed brushes.
In the case of a DC motor, the input direct current must be regenerated alternately in the armature, which in the case of a DC motor is also done by commutation.
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Separately excited generator
This conversion of current from the rotating coil of a DC machine to the stationary brushes must maintain constantly moving contacts between the commutator segment and the brush. When the armature starts rotating, the coils rotate under a pole (N-pole) between a positive and negative brush, causing the electrical current flowing through this coil to flow in a very short direction within the commutator segment. Now the coil is short-circuited using a brush for a very short fraction of time (1/500th of a second). This is called the switching period. During this short-circuit period, the armature coil rotates under the S pole and rotates between a negative brush and the positive brush that follows it. Now the direction is reversed, i.e. within the opposite direction to the commutator segments. This development of current reversal is called the switching method. We get power from the brush terminals.
Switching is considered optimal when the switching or current reversal process is completed at the end of the short circuit time or switching interval. When the current reversal is completed during the tangential time, sparks occur at the brush contacts and the commutator surface is damaged due to heating and the machine is said to be poorly commutated.
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Classification of DC machines
Switching in DC machines
For the purpose of the switching method, we consider a DC machine with an armature surrounded by a ring winding. Let us additionally consider that the width of the switched rod is equal to the width of the brush and the current flowing through the conductor is I. C.
The brush can move from right to left while the commutator moves from left to right.
In the initial position, the brushes are connected to the commutator bar B, as shown in Fig. a. Then the total current conducted to the brush from commutator bar B is 2I C.
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Classification of DC machines
If the anchor starts moving to the right before the brush contacts rod A. Then the armature current flows through 2 paths and through rods A and B (as shown in Fig. B). The total current (2I C ) remains trapped by the brush.
As the contact space of rod A with the brush increases and the contact space of rod B decreases, the current flow through the rod increases and decreases at the same time. Since the contact space is the same for all commutator bars, the same current flows through all bars (as shown in Fig. C).
When the contact gap between the brush and rod B becomes smaller, the current through coil B changes direction and begins to flow counterclockwise (see Fig. d).
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Armature reaction in DC machine
When the brush passes completely under bar A (see Fig. e) and turns off at bar b, current IC flows counterclockwise through coil B and the short circuit is canceled. This method completes the current reversal or switching process.
Magnetic flux in all electrical machines such as generators, motors and transformers plays a crucial role in the conversion or transmission of energy. The field or magnetization winding of rotating machines generates the flux, while the coil winding provides electrical or mechanical energy. In case of transformers, the primary wing supplies the power requirement of the secondary wing.
The basic plan of an electrical machine includes the orientation of the magnetic circuit, electrical circuit, insulation system, etc. and is determined by applying analytical equations.
A designer is often faced with a variety of problems that may have not just one answer, but multiple solutions. An engineer must ensure that products perform as required, with higher performance, lower material weight for the required performance, lower temperature rise, and lower cost. They also need to be reliable and durable.
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Switching in DC machines
A wise designer must design so that the stock (standard frames, punches, etc.) meets the requirements of the specification. The designer must also find a compromise between perfect design and a design that meets production conditions. An electrical designer must be familiar with the following:
A)National and international standards
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Indian Standard (IS), Bureau of Indian Standard (BIS), India
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British Standard (BS), England
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International Electrotechnical Commission (IEC)
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NEMA (National Electrical Manufacturers Association).
B) Specifications (deals with machine ratings, consumer performance requirements, etc.)
C) materials and labor costs
D) manufacturing limitations, etc.
Because design involves a variety of assumptions and constraints, final design values can only be determined through repeated procedures. The computer plays an important role in determining the final values. The finite element method (FEM) can be used to examine the effect of a parameter on the machine's self-propelled performance. Additionally, some tests that may not even seem possible in a laboratory can be performed using the finite element method.
The design problems to be solved in later posts differ in their nature and the appearance found for each machine. However, these test problems provide sufficient basic design knowledge, which is a sign that the student is incorporating truthful information to inform the overall design.
