Leakage inductance

The flux leakage ( engl. magnetic leakage flux ), or magnetic flux leakage with the symbols Φ, is a term used in electrical engineering and describes a part of the magnetic flux which, in an arrangement of two or can occur more conductor loops and their magnetic coupling.

General

By a spatially adjacent arrangement of two or more conductor loops (which are realized in the art, for example in the form of coils, and also referred to as coils ) occur in a circuit loop with respect to the other conductor loop mutual inductances. The time-varying magnetic flux caused - described by the law of induction - in the coils of an electric supply or the closed conductor loops an electric current.

Ideally, the magnetic coupling between the coils is perfect; the entire magnetic flux from the generating conductor loop penetrates all other neighboring conductor loops.

Since the magnetic flux is a source -free vector field ( one expresses this fact by always self-contained flux density of lines ), the magnetic flux is always self-contained, and there are no sources or sinks. In practical applications, it is feasible by this circumstance, and the spatial distance of inevitably needed a plurality of conductive loops to a magnetic flux, which is namely caused by a conductor loop, but does not pass through the other, adjacent conductor ribbons. This takes account of this - known as leakage flux - proportion of non magnetic coupling of the conductor loops with each other in and is therefore to be understood as a kind of " flow - loss ". The leakage flux is schematically sketched in the adjacent figure by the external flux lines thinly drawn, which are generated by loop 1, but not pass through loop 2.

Leakage inductance

The concept of leakage inductance describes those inductivity, which is formed in magnetically coupled systems by the leakage flux. The leakage inductances, commonly referred to as Ls or inductance L, for example, play in the model of the transformer a significant role. The leakage inductance is determined by the same procedures and methods as any other inductor, except that exclusively the leakage flux øs is considered.

Technical application

For transformers of the leakage flux is a key criterion. There, an attempt is by design measures to keep the flux leakage small to maximize the efficiency in power transmission. This requires a spatially close arrangement of the individual windings from each other.

A further technical improvement is achieved by the use of materials with high magnetic conductivity in the so-called core of the transformer: This allows the flow to be largely out selectively in good magnetically conductive core material through the individual windings pass. The leakage flux is thus strongly influenced by the presence of the iron core. The leakage flux is therefore minimized by this measure because most ambient air, similar vacuum, having a relatively poor magnetic conductivity, and thus a large part of the magnetic flux can be guided in the magnetic iron core. The low magnetic permeability of vacuum is also referred to as vacuum permeability and is a natural constant.

Depending on the geometric design of the core and the arrangements to be coupled to the windings of the leakage flux can be kept very small. Toroidal transformers, the leakage flux is only small when all turns of the windings are evenly distributed around the toroidal core.

For very low flux leakage, the windings are bifilar or executed with each layer nested (see also output transformer ). Such transformers possess up to high frequencies, a good transfer performance.

Transformers, which have no core material are also referred to as "air transformer "; they have a relatively high leakage flux. This causes a low efficiency of power transmission, and therefore virtually all of the transformers used for power transmission having the core materials with the highest possible permeability.

For special transformers such as the reactance transformers leakage flux is deliberately increased by the distance between the individual windings to achieve short-circuit resistance and current limit on the output. The bell is used in transformers, welding transformers and upstream transformers for neon sign tubes ( tubes ). Often there is an adjustable magnetic "bypass" in order to regulate the current.

The leakage flux height says something about the level of short-circuit voltage. The greater the stray flux, the higher the short-circuit voltage and the lower the secondary voltage stiffness.