Electrical Angle Vs Mechanical Angle - Differences?
Sure, let's start with the basic definitions of these two terms and then we will dive into the more technical aspects.
1. Mechanical Angle: This refers to the actual physical rotation of a mechanical component, often expressed in degrees or radians. For instance, when a machine shaft rotates, the rotation is described using mechanical angle.
2. Electrical Angle: This is used to describe the progression of an AC waveform over time. It does not directly refer to a physical rotation, but instead it describes the phase or position of a periodic waveform at a given time. It is also often expressed in degrees or radians.
Now, let's get into more detail.
Mechanical Angle:
The mechanical angle (θ_m) is represented as:
θ_m = ω*tWhere:
- θ_m is the mechanical angle,
- ω is the angular velocity (usually in rad/sec), and
- t is the time (seconds).
The mechanical angle is very important in many different types of machines, for instance, in rotating machines like motors and generators, the mechanical angle directly affects the performance and efficiency of the machine.
Electrical Angle:
The electrical angle (θ_e) is often defined relative to the mechanical angle, especially in the context of rotating machines. This relationship can be represented as:
θ_e = p * θ_mWhere:
- θ_e is the electrical angle,
- p is the number of pole pairs in the machine, and
- θ_m is the mechanical angle.
Note that the number of pole pairs is an integer, and it reflects the basic design of the machine. For a single-phase machine, there's typically one pole pair, for a three-phase machine, three pole pairs, and so on.
It's important to note that the electrical angle doesn't just apply to rotating machines. Any time you have an AC waveform - whether it's coming from a generator, an inverter, or any other source - the electrical angle gives you a way to describe the position or phase of the waveform at any given time.
Difference Between Electrical Angle and Mechanical Angle
Now, the difference between these two angles is in the context of their use.
The mechanical angle is a physical, real-world rotation of a mechanical object. The electrical angle, on the other hand, is a theoretical concept used to represent the phase of an AC waveform, which may or may not correspond to a physical rotation.
Applications:
The concept of electrical and mechanical angle is crucial in many areas of engineering, especially in power systems and control systems.
For example, in a synchronous motor, the rotor and the stator magnetic field rotate synchronously, i.e., at the same speed.
The angle between these two, also known as the torque angle or the power angle, plays a crucial role in the stability of the power system.
In control systems, understanding the relationship between mechanical and electrical angles is crucial for accurate control of motor speed and position.
Examples:
1. In a 2-pole AC motor running at 60 Hz (or 3600 RPM), after one second, the rotor would have completed one revolution. Hence, θ_m = 2π radians or 360°. However, in the same duration, the electrical angle, θ_e = 2 * θ_m = 4π radians or 720°. This shows how the electrical angle could be greater than the mechanical angle in rotating machines.
2. In an electrical circuit with an AC source and a load, at any time 't', the voltage can be described as V = V_max * sin(θ_e), where θ_e = 2πft, f is the frequency, and V_max is the peak voltage. This θ_e is the electrical angle, showing the phase of the voltage waveform at time 't'.
I hope this explanation clarifies your queries about the mechanical and electrical angle. Please let me know if you have any other questions!
Replies
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lalConsider a two pole alternator where poles are on the stator and armature on the rotor.
Assume the coil is exactly midway between the North and South poles. Now the flux linkage is zero and hence the output too. Clearly the rotor has to turn 90 degrees mechanically to bring the coil under the North pole which is positive maximum in the output. Positive maximum is at 90 degrees electrical in the output.
Another 90 degrees turn will bring the coil again exactly midway between the poles. The output turns zero again. That is 180 degrees mechanically and electrically from the initial position. When rotor turns 90 degrees more (270 degrees from initial position), it comes under the south pole. Output is negative maximum in this instant. 90 more degrees mechanical turn will brings the rotor back to initial position completing a cycle. Rotor turned 360 degrees mechanically in total.
In the above case the electrical and mechanical degrees were same.
Consider a 4 pole machine now. The poles will be arranged 360/4 = 90 degrees apart along the stator.
Initial condition be when the coil is exactly midway between a north and south pole where output is zero. The rotor now has to turn only 45 degrees mechanical to come under a north pole. But when the coil is under northpole, output is positive maximum. Positive maximum in output corresponds to 90 degrees electrical, Sin(90). Another 45 degrees brings the coil exactly midway between north and south pole making the output zero again; corresponding to 180 degrees electrical in output though it has mechanically turned only 45 + 45 = 90 degrees. At 135 degrees mechanical, the coil comes under south pole and output becomes negative maximum which corresponds to 270 degrees electrical. 45 more degrees and a cycle is completed in the output.
That is, though the rotor turned only 180 degrees mechanically, the output completed a complete cycle, 360 degrees electrical.
Electrical degrees = Mechanical degrees x P/2
P : Number of poles
Mechanical angle is the angle by which the rotor turns. Electrical angle is related with the output sine waveform. A pair of poles helps cover 360 electrical degrees, but not essentially the same mechanical degrees.
I think I made it a bit complicated 😐 -
Rajasekhar Ramireddythank u friend.....its not complicated....the concept u gave cleared my doubt....its clear for me now....thank u...
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rajeev213Mr.lal, i need some help regarding Ac machine stator winding diagram. i know some data that i have mentioned below:
poles =4, pitch angle=165 electrical degree, breadth between slots =15 electrical degrees. Include enough coils to fill the slots with a double layer winding. please help me to draw the winding diagram.
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