The control unit calculates total harmonic distortion related to the fundamental value THD, and total harmonic distortion related to RMS values THD-R for voltages and currents.

Displaying the Total Harmonic Distortion

The total harmonic distortion related to the fundamental value THD can be displayed as follows:

oOn the MicroLogic X display screen:

oTHD(I) at Home > Measures > I Harmonics

oTHD(V) at Home > Measures > V Harmonics

oWith EcoStruxure Power Commission software

oWith the EcoStruxure Power Device app

oOn the FDM128 display

oThrough the communication network

The total harmonic distortion related to RMS values THD-R can be displayed as follows:

oWith EcoStruxure Power Commission software

oThrough the communication network

The current THD is a percentage of the RMS value of harmonic currents of ranks greater than 1, in relation to the RMS value of the fundamental current (first order). The control unit calculates the total harmonic current distortion THD up to the fifteenth harmonic:

The current THD can be higher than 100%.

Use the total harmonic distortion THD(I) to assess the distortion of the current wave with a single number. The following table shows the THD limit values.

THD(I) Value |
Comments |
---|---|

THD(I) < 10% |
Low harmonic currents: little risk of disturbance. |

10% < THD(I) < 50% |
Significant harmonic currents: risk of heat rise, oversizing of supplies. |

50% < THD(I) |
High harmonic currents: the risks of disturbance, degradation, and heat rise are almost certain unless the installation is calculated and sized with this restriction in mind. |

Distortion of the current wave created by a nonlinear device with a high THD(I) can lead to distortion of the voltage wave, depending on the level of distortion and the source impedance. This distortion of the voltage wave affects all of the devices powered by the supply. Sensitive devices on the system can therefore be affected. A device with a high THD(I) may not be affected itself but could cause disturbance on other, more sensitive devices on the system.

NOTE: THD(I) measurement is an effective way of determining the potential for problems from the devices on electrical networks.

The voltage THD is the percentage of the RMS value of harmonic voltages of ranks greater than 1, in relation to the RMS value of the fundamental voltage (first order). The control unit calculates the voltage THD up to the fifteenth harmonic:

This factor can in theory be higher than 100% but is in practice rarely higher than 15%.

Use the total harmonic distortion THD(V) to assess the distortion of the voltage wave with a single number. The limit values below are commonly evaluated by energy distribution companies:

THD(V) Value |
Comments |
---|---|

THD(V) < 5% |
Insignificant distortion of the voltage wave: little risk of disturbance. |

5% < THD(V) < 8% |
Significant distortion of the voltage wave: risk of heat rise and disturbance. |

8% < THD(V) |
Significant distortion of the voltage wave: there is a high risk of disturbance unless the installation is calculated and sized based on this distortion. |

Distortion of the voltage wave affects all devices powered by the supply.

NOTE: Use the THD(V) indication to assess the risks of disturbance of sensitive devices supplied with power.

The current THD-R is a percentage of the RMS value of harmonic currents of ranks greater than 1 in relation to the RMS value of the fundamental plus harmonic currents. The control unit calculates the total harmonic current distortion THD-R up to the fifteenth harmonic using the following equation:

The current THD-R cannot be higher than 100%.

Use the total harmonic distortion THD-R(I) to assess the distortion of the current wave with a single number. The following table shows the THD-R limit values.

THD-R(I) Value |
Comments |
---|---|

THD-R(I) < 10% |
Low harmonic currents: little risk of disturbance. |

10% < THD-R(I) < 50% |
Significant harmonic currents: risk of heat rise, oversizing of supplies. |

50% < THD-R(I) |
High harmonic currents: the risks of disturbance, degradation, and heat rise are almost certain unless the installation is calculated and sized with this restriction in mind. |

Distortion of the current wave created by a nonlinear device with a high THD-R(I) can lead to distortion of the voltage wave, depending on the level of distortion and the source impedance. This distortion of the voltage wave affects all of the devices powered by the supply. Sensitive devices on the system can therefore be affected. A device with a high THD-R(I) may not be affected itself but could cause disturbance on other, more sensitive devices on the system.

NOTE: THD-R(I) measurement is an effective way of determining the potential for problems from the devices on electrical networks.

The voltage THD-R is the percentage the RMS value of harmonic voltages greater than 1 in relation to the RMS value of the fundamental plus harmonic voltages. The control unit calculates the total harmonic voltage distortion THD-R up to the fifteenth harmonic using the following equation:

Use the total harmonic distortion THD-R(V) to assess the distortion of the voltage wave with a single number. The limit values below are commonly evaluated by energy distribution companies:

THD-R(V) Value |
Comments |
---|---|

THD-R(V) < 5% |
Insignificant distortion of the voltage wave: little risk of disturbance. |

5% < THD-R(V) < 8% |
Significant distortion of the voltage wave: risk of heat rise and disturbance. |

8% < THD-R(V) |
Significant distortion of the voltage wave: there is a high risk of disturbance unless the installation is calculated and sized based on this distortion. |

Distortion of the voltage wave affects all devices powered by the supply.

NOTE: Use the THD-R(V) indication to assess the risks of disturbance of sensitive devices supplied with power.