For the same reason the generator works. The load is applying an opposing force (resistance) that you have to overcome in order to do work. Like trying to start pedaling the wheels of bicycle. It’s easy to pedal if the wheel is up in the air. It’s much more difficult to pedal if the wheel is on the ground and moving the bike.
On a fundamental level: because it has too. Input power always has to equal output power, anything else violates the fundamental laws of thermodynamics. If you increase the electric output power, the mechanical input power must also go up. Since grid generators are held at constant frequency, the only way for this to happen is for the rotor to experience more resistance.
On a more specific level: Because the (increased) flow of current changes the magnetic field around the generator, this change creates a resistance against the generators spin.
Conservation of energy. You gotta do work to create electrical energy, which means applying a force over a distance.
Magnetic force law. If the generator is hooked up to a load, current will flow, so the wires inside the motor coils will experience a magnetic force F = I l x B that you must overcome to keep them moving. If there’s no connection to a load, an open circuit, then no current flows, and no force is needed.
If you want a physical description, then when you are turning a generator, you are either moving coils of wire past permanent magnets, or moving permanent magnets past coils of wire.
A wire passing through a magnetic field generates a current. And this current induces a magnetic field within the coil. So each coil also acts like a magnet.
You know that opposite poles of magnets attract each other, and like poles repel each other.
That means that the magnetic field of each coil could push against the fields from the permanent magnets.
And as a rule, the more electric power the generator is profucing, the more the magnetic fields interfere and push against each other to resist its turning.
In order to get more work out, you have to put more work in, afterall.
Same reason a bicycle pump gets harder to pump when the tire gets more full. The load is providing more resistance. A generator is just pumping electrons instead of air or water.
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For the same reason the generator works. The load is applying an opposing force (resistance) that you have to overcome in order to do work. Like trying to start pedaling the wheels of bicycle. It’s easy to pedal if the wheel is up in the air. It’s much more difficult to pedal if the wheel is on the ground and moving the bike.
On a fundamental level: because it has too. Input power always has to equal output power, anything else violates the fundamental laws of thermodynamics. If you increase the electric output power, the mechanical input power must also go up. Since grid generators are held at constant frequency, the only way for this to happen is for the rotor to experience more resistance.
On a more specific level: Because the (increased) flow of current changes the magnetic field around the generator, this change creates a resistance against the generators spin.
Two ways to understand it.
Conservation of energy. You gotta do work to create electrical energy, which means applying a force over a distance.
Magnetic force law. If the generator is hooked up to a load, current will flow, so the wires inside the motor coils will experience a magnetic force F = I l x B that you must overcome to keep them moving. If there’s no connection to a load, an open circuit, then no current flows, and no force is needed.
If you want a physical description, then when you are turning a generator, you are either moving coils of wire past permanent magnets, or moving permanent magnets past coils of wire.
A wire passing through a magnetic field generates a current. And this current induces a magnetic field within the coil. So each coil also acts like a magnet.
You know that opposite poles of magnets attract each other, and like poles repel each other.
That means that the magnetic field of each coil could push against the fields from the permanent magnets.
And as a rule, the more electric power the generator is profucing, the more the magnetic fields interfere and push against each other to resist its turning.
In order to get more work out, you have to put more work in, afterall.
Same reason a bicycle pump gets harder to pump when the tire gets more full. The load is providing more resistance. A generator is just pumping electrons instead of air or water.
The generator creates power by pushing against a magnetic field.
Applying a load makes the magnetic field stronger, so the generator has to push harder to keep turning.