Dc offset

BSRIA Power quality guide (AG 2/2000) was written by C C Pearson and V Uthayanan and published by BSRIA in July 2000. It states:

Waveform distortion is defined as a steady state deviation from an ideal sine wave of power frequency, principally characterised by the spectral content of the deviation.

There are five primary types of waveform distortion:

• dc offset
• harmonics
• interharmonics
• notching
• noise

The presence of a dc voltage or current in an ac power system is termed dc offset. This can occur as the result of a geomagnetic disturbance or due to the effect of half-wave rectification. Incandescent light bulb life extenders, for example, may consist of diodes that reduce the rms voltage supplied to the light bulb by half-wave rectification. Direct current in alternating current networks can have a detrimental effect by biasing transformer cores so they saturate in normal operation. This causes additional heating and loss of transformer life. Dc may also cause the electrolytic erosion of earthing electrodes and other connectors.

--BSRIA

[edit] Related articles on Designing Buildings

• Alternating current and direct current
• Ampere.
• BSRIA articles on Designing Buildings.
• BSRIA definitions.
• BSRIA.
• Power.
• Voltage.
• Watt.