page_title: Leakage inductance
section_title: Applications
hierarchical_section_title: Leakage inductance / Applications
caption_attribution_description: English: Stray field transformer for series connected cold cathode fluorescent lamps, 440 Watt; prim: 220 V 50...60 Hz; sec: 2,5 kV (AC), 50...88 mA Deutsch: Streufeldtransformator 440 VA mit über Stellrad einstellbarem magnetischem Nebenschluss zur Anpassung des Ausgangsstromes (Vorschaltgerät für Leuchtröhren); unten: Primärwicklungen (220 V); oben: Sekundärwicklungen (2,5 kV 50...88 mA); Höhe 215 mm
context_page_description: Leakage inductance derives from the electrical property of an imperfectly-coupled transformer whereby each winding behaves as a self-inductance in series with the winding's respective ohmic resistance constant. These four winding constants also interact with the transformer's mutual inductance. The winding leakage inductance is due to leakage flux not linking with all turns of each imperfectly-coupled winding.
  Leakage reactance is usually the most important element of a power system transformer due to power factor, voltage drop, reactive power consumption and fault current considerations.
  Leakage inductance depends on the geometry of the core and the windings. Voltage drop across the leakage reactance results in often undesirable supply regulation with varying transformer load. But it can also be useful for harmonic isolation of some loads.
  Leakage inductance applies to any imperfectly-coupled magnetic circuit device including motors.
context_section_description: Leakage inductance can be an undesirable property, as it causes the voltage to change with loading.
  In many cases it is useful. Leakage inductance has the useful effect of limiting the current flows in a transformer (and load) without itself dissipating power (excepting the usual non-ideal transformer losses). Transformers are generally designed to have a specific value of leakage inductance such that the leakage reactance created by this inductance is a specific value at the desired frequency of operation. In this case, actually working useful parameter is not the leakage inductance value but the short-circuit inductance value.
  Commercial and distribution transformers rated up to say 2,500 kVA are usually designed with short-circuit impedances of between about 3% and 6% and with a corresponding  ratio (winding reactance/winding resistance ratio) of between about 3 and 6, which defines the percent secondary voltage variation between no-load and full load. Thus for purely resistive loads, such transformers' full-to-no-load voltage regulation will be between about 1% and 2%.
  High leakage reactance transformers are used for some negative resistance applications, such as neon signs, where a voltage amplification (transformer action) is required as well as current limiting. In this case the leakage reactance is usually 100% of full load impedance, so even if the transformer is shorted out it will not be damaged. Without the leakage inductance, the negative resistance characteristic of these gas discharge lamps would cause them to conduct excessive current and be destroyed.
  Transformers with variable leakage inductance are used to control the current in arc welding sets. In these cases, the leakage inductance limits the current flow to the desired magnitude.
  Transformer leakage reactance has a large role in limiting circuit fault current within the maximum allowable value in the power system.
caption: High leakage transformer
exif: {"Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS2 Windows", "Image DateTime": "2009:09:28 23:46:50", "Image ExifOffset": "164", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "302", "Thumbnail JPEGInterchangeFormatLength": "7085", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "639", "EXIF ExifImageLength": "790"}