Fundamentals of Electric Power

Electromagnetism

Electromagnetism is a phenomenon that allows magnetic fields to generate electric currents. By moving a conductor through a magnetic field, it is possible to generate both voltage and current in the conductor.

A magnetic field, called a flux, exists around the north and south poles of a magnet. When a conductor cuts through this flux, voltage is created on the conductor. If there is a complete circuit for current to flow through, then current is also generated.

The amount of voltage and current produced by electromagnetism is influenced by the strength of the magnetic field and the speed and direction of the conductor moving through the field. For example, only motion cutting through the flux generates voltage. If a conductor moves parallel to the flux, then no voltage is created in the conductor.

The reverse of this phenomenon is also true - a current flowing through a conductor creates a magnetic field which is emitted from the conductor in circles. This phenomenon is the basis for electromagnets. However, the magnetic force of a straight conductor is very weak.

To increase the strength of the magnetic field, we can wind our conductor into a coil. Each loop in the coil is called a turn and the magnetic field at the center of the coil is strengthened by each turn of the coil.

The magnetic field between coils are of equal strength, moving in opposite directions and cancel each other out. Because of this cancellation, we are left with a magnetic field oriented in one direction inside the coil and in the opposite direction outside of the coil.

Building a Generator

So, how can we leverage the phenomenon of electromagnetism to generate electricity?

To generate enough electricity to do a significant amount of work, we will need a way to pass the conductor through the flux repeatedly. We could do this by bending the conductor into a loop and adding a hand crank to rotate the conductor through the flux manually. As the conductor loop rotates through the flux, the conductor cuts the flux repeatedly - first in one direction and then in the opposite direction.

As the loop conductor rotates, voltage is generated. To create a complete circuit and access the generated electricity, we can add a slip ring to each end of the loop. This slip ring rotates against a metal brush, which has wires attached to it. The wires are connected to the load we want to power, such as a light.

Now there is a complete circuit, so when the loop conductor rotates through the flux, voltage is created and since there is a complete circuit, current flows through the circuit and powers the load.

Generated Voltage

The magnitude of the voltage that we are generating changes based on the movement of the conductor through the flux. Let's look at the magnitude of the voltage as the loop conductor moves through a full rotation.

Initially, the conductor loop is parallel to the flux. Since it is not cutting through the flux, the voltage generated is 0 volts.

As the coil moves, it begins to closer to right angles through the flux. At this point, more voltage is generated.

When the coil cuts right angles through the flux, the amount of voltage generated peaks.

After the peak, the amount of voltage generated decreases since the loop is cutting farther from right angles through the flux. Eventually, the amount of voltage generated returns to 0 when the loop reaches point A.

Now the loop cuts through the flux in the opposite direction. This creates voltage of equal magnitude in the negative range.

Finally, the loop moves back to A and the voltage generated returns to 0.

This pattern repeats as the loop continues to turn in the flux. This graph is a typical representation of AC voltage.

A Three Phase Generator

Three phase power is popular in industry.

We could modify our generator to generate three phase power by adding two more loops to our generator, separated and spaced evenly apart, and two more slip rings to access the voltage generator by the additional loops.

Most three phases generators are a modified version of this concept. In a modified three phase generator, the loops are stationary and the magnetic field rotates. This is a more popular construction because it eliminates the need for slip rings while still producing the same three phase power.

Each phase adds voltage to the system, so the voltage generated looks like this:

Why Use Three Phase Power?

Industries tend to use three phase power for a number of reasons.

To start with, three phase motors tend to be easier to work with.

Three phase motors have better starting torque when compared to equivalent single phase motors.

It is also possible to change the direction of rotation of a three phase motor by changing the input sequence of two of the three phases. This is generally not possible on a single phase motor, unless they were specifically designed to be reversing motors.

The amount of current required to drive a single phase motor is typically 70% higher than what is required to drive an equivalent three phase motor. Because of this, smaller wires can be used with a three phase motor. These smaller wires are cheaper and easier to work with.

Conclusion

In this post, we learned the fundamentals of electric power. Specifically, we learned how electromagnetism is used to create electricity and how single phase and three phase voltages are generated. We also learned why three phase power is preferred in industry.

In the next part of the series, we will learn how power plants generate electricity and deliver that electricity to end user factories.