## Power quality metrics

There are various methods for categorizing the severity of power disturbances. The most typical indices for **measuring power quality disturbances** are listed and explained below:

- Distortion factor
- Crest factor
- Notch area
- Recovery time
- Displacement power factor
- Total power factor
- K factor

### 1. Distortion Factor

The ratio of the root square value of the harmonic content to the root square value of the fundamental quantity, expressed as a percentage of the fundamental, also known as total harmonic distortion.

**where:**

**V**is the RMS harmonic voltage (or current) value at a frequency of n times the fundamental frequency_{h}**V**is the RMS fundamental-frequency voltage or current_{1}

These are referred to as **Total Harmonic Distortion (THD _{Vn})** and

**Total Demand Distortion (TDD)**, defined as follows:

**where:**

**V**is the RMS value of the n_{h}^{th}harmonic component of the voltage**V**is the RMS nominal fundamental voltage value_{n}**I**is the RMS value of the n_{h}^{th}harmonic component of the current**I**is the maximum demand load current, typically the average maximum monthly demand over a 12-month period_{L}

### 2. Crest Factor

**The ratio of the peak value of a periodic function to the RMS value, i.e.:**

**where:**

**y**is the peak value of a periodic function_{peak}**y**is the RMS value of the function_{rms}

Because power system voltages and currents are nominally sinusoidal, the nominal crest factor for these would be √2.

### 3. Notch Area

**A notch in the power system voltage (or current) is illustrated in figure 1 below:**

**The notch area for the notch as illustrated in figure above is defined as:**

**where:**

**A**is the notch area in volt-microseconds_{n}**t**is the notch time duration in microseconds**d**is the notch depth in volts

### 4. Recovery time

This is the time needed for the output voltage or current to return to a value within the regulation specification after a step load or line change.

### 5. Displacement Power Factor

The ratio of the active power of the fundamental wave, in watts, to the apparent power of the fundamental wave, in volt-amperes.

**power factor**.

### 6. Total Power Factor

The ratio of the total input power, in watts, to the total volt-ampere input. This includes the effects of harmonics.

### 7. K Factor

**A measure of a transformer’s ability to serve non-sinusoidal loads. The K factor is defined as:**

**where:**

**I**is the harmonic component at h times the fundamental frequency_{h}**h**is the harmonic order of**I**in multiples of the fundamental frequency_{h}**h**is maximum harmonic order present_{max}

**Reference:** Power Quality Considerations- Bill Brown, P.E., Square D Engineering Services

Apolo Fumbuja

If I have not a power analyzer, how can i measure or estimate those parameters?

Jim

Can i ask you something? Why true power doenst change (theoretically speaking right, as long as in actual) and there is a big change in Active energy in the result when i install power quality in the mdp.Thank you and im looking forward for your response.

Emad Eddin

thank you so much for all these useful information , but plz would you like to write some practical examples

thanks

James

I really am interested in that particular section of electrical engineering.

Jimmy Valeriano

Can you discuss how to interpret the grahical test result of power analyzer…