Basic solutions to mitigate harmonics: Difference between revisions
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To limit the propagation of harmonics in the distribution network, different solutions are available and should be taken into account particularly when designing a new installation. | To limit the propagation of harmonics in the distribution network, different solutions are available and should be taken into account particularly when designing a new installation. | ||
== Position the non-linear loads upstream in the system == | |||
Overall harmonic disturbances increase as the short-circuit power decreases.<br>All economic considerations aside, it is preferable to connect the non-linear loads as far upstream as possible (see'''Fig. M16'''). | Overall harmonic disturbances increase as the short-circuit power decreases.<br>All economic considerations aside, it is preferable to connect the non-linear loads as far upstream as possible (see'''Fig. M16'''). | ||
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== Group the non-linear loads''<br>'' === | |||
When preparing the single-line diagram, the non-linear devices should be separated from the others (see '''Fig. M17'''). The two groups of devices should be supplied by different sets of busbars. | When preparing the single-line diagram, the non-linear devices should be separated from the others (see '''Fig. M17'''). The two groups of devices should be supplied by different sets of busbars. | ||
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== Create separate sources == | |||
In attempting to limit harmonics, an additional improvement can be obtained by creating a source via a separate transformer as indicated in the Figure M18.<br>The disadvantage is the increase in the cost of the installation. | In attempting to limit harmonics, an additional improvement can be obtained by creating a source via a separate transformer as indicated in the Figure M18.<br>The disadvantage is the increase in the cost of the installation. | ||
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== Transformers with special connections == | |||
Different transformer connections can eliminate certain harmonic orders, as indicated in the examples below: | Different transformer connections can eliminate certain harmonic orders, as indicated in the examples below: | ||
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== Install reactors == | |||
When variable-speed drives are supplied, it is possible to smooth the current by installing line reactors. By increasing the impedance of the supply circuit, the harmonic current is limited.<br>Installation of harmonic suppression reactors on capacitor banks increases the impedance of the reactor/capacitor combination for high-order harmonics.<br>This avoids resonance and protects the capacitors. | When variable-speed drives are supplied, it is possible to smooth the current by installing line reactors. By increasing the impedance of the supply circuit, the harmonic current is limited.<br>Installation of harmonic suppression reactors on capacitor banks increases the impedance of the reactor/capacitor combination for high-order harmonics.<br>This avoids resonance and protects the capacitors. | ||
== Select the suitable system earthing arrangement == | |||
'''TNC system''' | '''TNC system''' | ||
Revision as of 09:33, 16 June 2011
To limit the propagation of harmonics in the distribution network, different solutions are available and should be taken into account particularly when designing a new installation.
Position the non-linear loads upstream in the system
Overall harmonic disturbances increase as the short-circuit power decreases.
All economic considerations aside, it is preferable to connect the non-linear loads as far upstream as possible (seeFig. M16).
Fig. M16: Non-linear loads positioned as far upstream as possible (recommended layout)
Group the non-linear loads
=
When preparing the single-line diagram, the non-linear devices should be separated from the others (see Fig. M17). The two groups of devices should be supplied by different sets of busbars.
Fig. M17: Grouping of non-linear loads and connection as far upstream as possible (recommended layout)
Create separate sources
In attempting to limit harmonics, an additional improvement can be obtained by creating a source via a separate transformer as indicated in the Figure M18.
The disadvantage is the increase in the cost of the installation.
Fig. M18: Supply of non-linear loads via a separate transformer
Transformers with special connections
Different transformer connections can eliminate certain harmonic orders, as indicated in the examples below:
- A Dyd connection suppresses 5th and 7th harmonics (see Fig. M19)
- A Dy connection suppresses the 3rd harmonic
- A DZ 5 connection suppresses the 5th harmonic
Fig. M19: A Dyd transformer blocks propagation of the 5th and 7th harmonics to the upstream network
Install reactors
When variable-speed drives are supplied, it is possible to smooth the current by installing line reactors. By increasing the impedance of the supply circuit, the harmonic current is limited.
Installation of harmonic suppression reactors on capacitor banks increases the impedance of the reactor/capacitor combination for high-order harmonics.
This avoids resonance and protects the capacitors.
Select the suitable system earthing arrangement
TNC system
In the TNC system, a single conductor (PEN) provides protection in the event of an earth fault and the flow of unbalance currents.
Under steady-state conditions, the harmonic currents flow in the PEN. The latter, however, has a certain impedance with as a result slight differences in potential (a few volts) between devices that can cause electronic equipment to malfunction.
The TNC system must therefore be reserved for the supply of power circuits at the head of the installation and must not be used to supply sensitive loads.
TNS system
This system is recommended if harmonics are present.
The neutral conductor and the protection conductor PE are completely separate and the potential throughout the distribution network is therefore more uniform.
