What is frequency and how to calculate?

Do you know the definition of electrical frequency well? This term is widely used by professionals in the field of electrical, mainly with regard to alternating current and analog electronics, but what is this physical concept really, how to really define what is the frequency and its impacts on the circuits? How to calculate this quantity and how to measure it? Do you know the importance of electrical frequency within the concept of electrical machines? If your answer is no or if you have any questions on the subject, come with us to learn a little more. In this article, we will cover what frequency is without mysteries.

What is the frequency?

In a general context when we deal with the physical concept of what frequency is, we have as a definition that frequency is a quantity capable of measuring in a certain period of time, the number of occurrences of an event. This event is repeated in the timeline, which can be oscillations, turns, cycles, magnitude, etc. The number of these repetitions is called frequency.

Another important quantity when it comes to frequency is the period, which is nothing more than the time in which a complete cycle of repetitions is repeated. The mathematical relation of the frequency in relation to the period is given by the following truth, the frequency is the inverse of the period.

Relationship of electrical frequency and wavelength period

Electrical Frequency characteristics

The electrical frequency is a quantity given in Hertz (Hz), in honor of the German physicist Heinrich Rudolf Hertz (1857-1894). It corresponds to the number of oscillations, waves or cycles per second that occurs in the alternating electric current.

This current oscillation is measured in the period of one second, so when we say that we are in a 60Hz network we are saying that the peak value of the network varies between positive peak to negative peak 60 times in one second.

If we have a peak voltage of 127V at a frequency of 60Hz, we understand that in the period of one second, the voltage fluctuated from 127V to -127V, sixty times. The electrical frequency is directly responsible for an effect known as impedance, this effect is not found in direct current circuits where there is no frequency, as the voltage remains constant in the load, therefore, there is only the electrical resistance of the circuit.

In the case of alternating current, where the frequency is present, in addition to the actual resistance of the circuit, we also find the effect of the impedance, which is the electrical resistance, that the frequency imposes the electrical current, in this way we can say that the resistance in a current circuit alternating is resistance (real part) plus impedance (imaginary part).

Alternating current wave and signal oscillation frequency

Electrical frequency is such an important variable within electrical systems that the impacts of frequency fluctuations within electrical power distribution systems and generation facilities cause a huge change in the work performed by electrical equipment, mainly motors and transformers, these oscillations they can generate major disturbances in the network harmonics, due to the variation of the impedance, which also varies with the frequency of the network. Under normal operating conditions and on a permanent basis, the electricity supply in Brazil is standardized to operate within the frequency limits between 59.9 Hz and 60.1 Hz.

The frequency of the electrical network is directly linked to the speed of rotation of the generators, we call this speed of angular speed of the rotor coils. Generally, frequency oscillations outside the determined range are linked to severe faults in the main body of the transmission system, they can cause large load blocks to be shut down (an entire neighborhood, for example) or the fall of generators in some plant, causing a great impact in the energy generation, transmission and distribution system.

Calculation of Frequency

For the calculation of the frequency we have many ways, but we will highlight two ways most used within the area of ​​electrical for frequency calculation.

A very common way to calculate the frequency is through the period or time of a given wave, which represents an electric current. As we have already discussed, frequency is the time of variation of a signal in one second, and the period is the time taken to complete a single complete oscillation, the basic relationship says that the two quantities are inversely proportional. To perform the calculation by this method use the following formula: f = 1 / T .

In this formula, f represents the frequency and T represents the period of time required to complete a single wave oscillation, see the example below:

Mathematical model for calculating frequency as a function of time or period

Another very common way that we use, is the calculation through the angular frequency of generation of the wave. When the angular frequency of generation of a wave is known, for example, we know the angular speed of a small homemade generator, however the output frequency of the generated signal is not known, to perform the calculation of the normal frequency just use the following form f = ω / 2π , note the example:

In this formula, f represents the frequency of the wave and ω represents the angular frequency. As with any mathematical problem, π symbolizes the mathematical constant pi.

Mathematical model for calculating frequency as a function of angular velocity

Understanding the concept of electrical frequency is very important in the context of alternating current circuits, since the variable frequency is responsible for the impedance and distortions in the harmonics of electrical circuits, understanding this concept is the first step to evolve within the theory and important concepts within alternating current. We provide a video to complement your understanding of the subject:

As professionals in the electrical area, we need an understanding of the concepts covered, these concepts become essential for the evolution and for understanding more complex concepts within the electrical area.

The alternating current theme evolves the frequency, which is directly responsible for several phenomena such as the rotation speed of three-phase electric motors, in electrical generation machines it is related to the rotation speed of the winding rotors. Another important phenomenon in AC is the impedance caused by the frequency, the impedance is the frequency opposed to electric current for circuit calculations in alternating current understanding of the concept is fundamental, continue deepening in the subject because the subject is complex and important within the electrical.