The Working Principle of Synchronous and Asynchronous Generators

Synchronous generator circuit, device and principle

What does synchronization mean relative to an electric motor or generator? Simply put, the frequency of communication strictly depends on the speed of the rotor of the electric machine, and vice versa. Therefore, it is relatively easy to control the frequency of communication. Synchronous generators themselves have some advantages, making them the most common. Most importantly, all power plants use synchronous generators.

The driving motor can be any rotating device: an electric motor, a turbine, a windmill impeller, or a water wheel. A generator rotor with excitation windings on the same axis. Apply a constant voltage to the winding and generate a magnetic field around the winding. When the rotor rotates, an electric spark is generated in the stator winding, which is a voltage that has already changed. Its frequency depends on the rotation speed 1 of the rotor n and the number of pole pairs p, which can be calculated using the following formula.

Asynchronous generator circuit, device and principle

Asynchronous generator, which is actually an asynchronous motor. That is to say, any asynchronous motor can enter the power generation mode, and vice versa. Structurally speaking, the device of the generator is completed in a way with good cooling. The editor of Dingbo Electric does not want to delve into the principles of asynchronous machines here, but I would like to briefly introduce why we refer to motors as asynchronous machines.

When applying voltage to the stator winding, a magnetic field is generated, and the three-phase motor is circular and the single-phase motor is elliptical, pursuing a circular shape. The magnetic field begins to cross the stator winding turns. In the short-circuit winding of the rotor, electric sparks, i.e. voltage, are generated. As the winding is short circuited, current begins to flow along it, and the current also generates a magnetic field. The interaction of these magnetic fields drives the rotor to move. What if the rotor speed becomes equal to the magnetic field speed generated by the stator? The correct thing is that the stator magnetic field will stop crossing the rotor winding. This can be compared to two cars traveling at the same speed. The cars seem to be moving, but relative to each other, they seem to be standing in place, just the ground passing under the cars at a fast speed. Therefore, once the rotor speed and stator magnetic field speed are the same, electric sparks are no longer generated in the rotor winding, and the interaction between the stator magnetic field and the rotor magnetic field stops, and the rotor begins to stop. Therefore, the speed of the asynchronous motor rotor is always slightly lower than the speed of the stator magnetic field, and this value is called sliding.

Therefore, in order to make an asynchronous motor a generator, it is necessary to determine sliding and increase the rotor speed by this value. Assuming we have a single pole three-phase asynchronous motor with a shaft speed of 2800 rpm. If this type of engine is synchronous, the speed will be 3000 rpm. The sliding speed is 200 revolutions per minute. This means that if we start rotating the rotor at a speed of 3200 revolutions per minute, the engine will enter power generation mode, no longer consuming, but generating an electric drive system.

This type of generator is difficult to use because it is prone to malfunctions. For example, if an active load (incandescent bulb or heater) is connected, the starting current will be very small. There will be no significant overload and the generator will operate stably. For example, if reactive loads are included, there will be 5-20 times the rated starting current, causing the generator to malfunction, which is to say, causing a voltage drop on the generator winding. After this fault occurs, the asynchronous generator needs to be excited again. So the simplicity of asynchronous generators exceeds a serious drawback.

And a capacitor device is also needed to excite the short-circuit winding of the rotor. If the capacitor capacity is incorrect, the current of the generator will decrease when a fault occurs, and the generator will overheat severely when a fault occurs.

Connecting circuits

In fact, it's not about containing a plan, it's about options. There are generally three types of them:

Automatically turn on. In this case, install a dedicated emergency opening unit. Once the network voltage is disconnected, the unit issues a command to start the generator and switches the network from an external power source to the power generation device.

Manual power on. In this case, the user switches from the external power source to the power generation device and manually starts the generator.

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