Name: rms value for ac power measurement
Uploaded: 2024-07-08T13:19:51.000Z
Duration: 1 min 7 s
Channel: JoVE

Si consideri un circuito CA con una sorgente di tensione periodica collegata a un resistore.
La potenza media erogata al resistore è uguale all'integrale della potenza istantanea su un periodo diviso per il periodo.
Quando questo resistore è collegato a una sorgente CC, la potenza media che assorbe è il prodotto della corrente al quadrato e della sua resistenza.
Considerando che la potenza media erogata da una sorgente CC al resistore è equivalente a quella fornita dalla corrente periodica, la corrente continua è pari al valore effettivo della corrente periodica.
Quindi, il valore effettivo della corrente è la radice quadrata della media dei valori di corrente istantanea al quadrato.
Allo stesso modo, si può ottenere l'espressione per il valore effettivo della tensione.
Per qualsiasi segnale periodico, il valore effettivo, noto anche come valore quadratico medio, è uguale alla radice quadrata della media del quadrato del segnale periodico.
Per una corrente e una tensione sinusoidali, il valore RMS è uguale al valore di picco diviso per la radice quadrata di due.

valore efficace di una forma d'onda periodica

Effective Value of a Periodic Waveform

Il concetto di valore efficace è fondamentale per comprendere i circuiti elettrici e l'erogazione di potenza. Questa idea emerge dalla necessità di misurare l'efficacia di una sorgente di tensione o corrente nel fornire energia ad un carico resistivo.


Il valore efficace di una corrente periodica rappresenta la corrente continua (CC) che trasmette a un resistore la stessa potenza media della corrente periodica stessa. Questo concetto è fondamentale quando si valutano i circuiti CA. Per determinare il valore efficace della corrente, è necessario trovare il valore RMS, che è la radice quadrata della media dei valori di corrente istantanei al quadrato in un periodo. Questo valore RMS corrisponde alla CC che fornisce la stessa potenza media della corrente periodica quando applicata a un resistore.


<img alt="Equation 1" src="/files/ftp_upload/15119/15119_Equation_1.svg" style="height: 60px;">

Il valore efficace della tensione viene si calcola nello stesso modo della corrente. Esso rappresenta la tensione efficace, fondamentale per valutare il consumo energetico negli impianti elettrici.


<img alt="Equation 2" src="/files/ftp_upload/15119/15119_Equation_2.svg" style="height: 60px;">

Il valore efficace è un concetto fondamentale, non limitato ai segnali sinusoidali. Per qualsiasi funzione periodica, il valore RMS viene calcolato trovando il quadrato della funzione, determinando la media dei quadrati e quindi prendendo la radice quadrata di tale media. Nelle applicazioni pratiche, la tensione e la corrente sono spesso espresse in termini di valori efficaci piuttosto che di valori di picco. Questo perché il valore medio di un segnale sinusoidale è zero, rendendo il valore RMS una metrica più utile per l'analisi della potenza. Oltre a ciò, i voltmetri e gli amperometri analogici sono progettati per leggere direttamente i valori efficaci di tensione e corrente, rendendoli strumenti indispensabili nelle misurazioni di potenza.

Valore efficace di una forma d'onda periodica

Si consideri un circuito CA con una sorgente di tensione periodica collegata a un resistore.
La potenza media erogata al resistore è uguale all'integrale del resistore ...

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

AC Steady State Power

Potenza in regime stazionario CA

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

rms value for ac power measurement

The RMS value, or effective value, helps measure how much power a periodic voltage or current can deliver. It is the direct current, or DC, value that gives the same average power to a resistor as the periodic signal does. This idea is especially important in AC circuits.

To find the effective value of current, calculate the root mean square, or RMS, current. First square the instantaneous current values over one period. Then find the mean of those squared values and take the square root. The result is the DC current that would produce the same average power in a resistor.

The same method is used for voltage. The effective value of voltage is the RMS voltage, and it is used to judge power use in electrical systems. The RMS idea also works for any periodic function, not only sinusoidal signals.

For any periodic waveform, the RMS value comes from squaring the function, averaging the squared values, and then taking the square root. In practice, voltage and current are often given as RMS values instead of peak values. That is useful because the average value of a sinusoidal signal is zero, while the RMS value still shows its power effect.

Analog voltmeters and ammeters are designed to read RMS values directly. That makes them useful tools for measuring voltage and current in power circuits.

RMS Value for AC Power Measurement

instantaneous power

AC Power and Phase Shift

Instantaneous power in an electrical circuit comes from the voltage across an element and the current through it. It is written as p(t) and follows the passive sign convention. For sinusoidal input, this product helps show how power changes at each moment. When instantaneous power is expanded, it has two parts. One part is constant and depends on the phase difference between voltage and current. The other part is a sinusoidal term that varies at twice the frequency of the voltage or current. <br...

average power

Power Consumption in AC Circuits

Power consumption in AC circuits is often described with average power. In practical electrical work, the changing value of instantaneous power is less useful than the average over a time period. Average power is found by integrating instantaneous power over that time and then dividing by the duration. The time-domain expression for average power comes from simplifying the equation for instantaneous power. In that form, one cosine term averages to zero over a complete cycle. The result does...

effective value of a periodic waveform

The RMS value, or effective value, helps measure how much power a periodic voltage or current can deliver. It is the direct current, or DC, value that gives the same average power to a resistor as the periodic signal does. This idea is especially important in AC circuits. To find the effective value of current, calculate the root mean square, or RMS, current. First square the instantaneous current values over one period. Then find the mean of those squared values and take the square root. The...

complex power

Power Triangle in AC Circuits

Power triangle and complex power help describe how an AC load uses energy. Engineers use complex power to capture the combined effect of parallel loads. It gives a full picture of the power consumed by a specific load. Complex power is found by multiplying voltage by the complex conjugate of current. Using rms values, it is written with the rms voltage phasor and the complex conjugate of the rms current phasor. It can also be written in terms of load impedance. The magnitude of complex power...

conservation of ac power

AC Power in Series and Parallel Circuits

AC power in series and parallel circuits follows a power preservation rule. In AC circuits, the complex power, real power, and reactive power produced by the source are equal to the total complex, real, and reactive powers absorbed by the loads. When two load impedances are connected in parallel to an AC source V, the source power can be written as the sum of the complex powers delivered to loads Z1 and Z2. If those same loads are connected in series with the voltage source, the complex power...

power factor

Power Factor and AC Load Behavior

Power factor describes how voltage and current behave in an AC load. It is the ratio of average, or active, power to apparent power. The power factor angle is the phase difference between voltage and current, and the cosine of that angle gives the power factor. It also matches the angle of the load impedance. Power factor shows how much apparent power becomes real, or average, power. Its value ranges from zero to one. When a load is purely resistive, voltage and current are in phase. In that...

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Reducing Reactive Power in AC Loads

Power factor correction helps AC systems use electrical power more efficiently. In a factory circuit, transmitted power includes apparent power, which is made of active power and reactive power. Power factor is the ratio of real power, measured in kW, to apparent power, measured in kVA. It shows how much of the supplied power becomes useful work. A low power factor often happens when an inductive load draws too much reactive power. This creates a lagging power factor. It can also cause large...

the power superposition principle

Power from Multiple AC Sources

Power from multiple AC sources is found by adding the effects of each source separately. In a circuit with two sinusoidal voltage sources, each source acts independently. The superposition principle says the total current is the sum of the currents produced by each source alone. If those currents are labeled i1 and i2, they combine to give the total current. Instantaneous power is the power at one moment in time. In this circuit, it equals the square of the instantaneous current times the...

the maximum power transfer theorem

Matching Load Impedance for Maximum Power

Maximum power transfer in an AC circuit depends on matching the load impedance to the Thevenin equivalent of the source network. The load draws current, and the circuit delivers power to that load. To analyze the current, the voltages, currents, network impedance, and load impedance are written in rectangular form. The average power delivered to the load comes from the square of the current multiplied by the load resistance. To find the condition for maximum power, the power is differentiated...

key terms and concepts

Learn how RMS, or effective value, compares AC voltage and current to DC power in resistive loads, and why it is used in electrical measurements.

RMS Value for AC Power Measurement | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

RMS Value for AC Power Measurement

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