Sense of direction (electrical engineering)

In electrical engineering, the sense of direction is understood to be the sign convention of scalar quantities , such as electrical current , electrical voltage or magnetic flux .

A term that contains “direction-” is surprising in connection with scalars, which, unlike vectors, have no direction. In the case of the electrical current intensity, its direction is the direction of movement of positive charge carriers or the direction opposite to the direction of movement of negative charge carriers. In an approximately one-dimensional viewable conductor, z. B. in a cable , so the sign of the current is determined. Electricity is also referred to as the conventional direction of the current or the physical direction of the current .

The scalar quantities, for which a sense of direction is specified in their definition, result from integration over an area from a density vector, from whose direction the sense of direction results. This means that the sense of direction of the electric current results from the direction of the current density vector , the sense of direction of the magnetic flux from the direction of the magnetic flux density, etc.

The withdrawn DIN 5489 uses the term "sense of direction" also in connection with the magnetic flux and the magnetic voltage ; the successor standard DIN EN 60375 speaks simply of the "direction".

Definitions of the sense of direction

size	symbol	SI unit	Application location and direction definition
Electric current	${\ displaystyle i}$	A.	In a conductor cross-sectional area : positive charge carriers in the direction of movement, negative charge carriers in the opposite direction in the case of a flow. Equivalent: in the direction of the surface orientation with a positive flow of the electrical current density , opposite in the case of a negative flow. ${\ displaystyle {\ vec {S}}}$
Electric voltage	${\ displaystyle u}$	V	Between two points: from point 1 to point 2, when the electric field on the carrier of a positive charge led from 1 to 2 performs mechanical work (which is taken from the field energy); in the opposite direction if mechanical work is required to guide the beam (which is stored as field energy). Equivalent: in the direction of the path orientation with a positive line integral of the electric field strength , in the opposite direction with a negative value. Synonymous: from higher to lower electrical potential . With two poles: from the current plus to the minus pole. ${\ displaystyle {\ vec {E}}}$
Electric flow	${\ displaystyle {\ mathit {\ psi}}}$	C.	Through a surface: in the direction of the surface orientation with a positive flow of the electrical flux density , in the opposite direction with a negative flow. ${\ displaystyle {\ vec {D}}}$
Magnetic river	${\ displaystyle {\ mathit {\ phi}}}$	Wb	Through a surface: in the direction of the surface orientation with a positive flow of the magnetic flux density , in the opposite direction with a negative flow. Equivalent: for current-carrying conductor loops and coils , the direction of the magnetic flux is clockwise from that of the generating electrical current (clockwise = in the sense of a right-hand screw = according to the right-hand rule in the sense of the corkscrew rule ). ${\ displaystyle {\ vec {B}}}$
Magnetic tension	${\ displaystyle {\ mathit {v}}}$	A.	Between two points: in the direction of the path orientation with a positive line integral of the magnetic field strength , opposite with a negative value. ${\ displaystyle {\ vec {H}}}$

Equivalent cross-size definition

Flow sizes

The sense of direction of a flow amount ( , or , cf. Table) extending in the same direction with the orientation of a flow equal to the integration area normal and uniformly oriented compared flux density ( , respectively ). ${\ displaystyle i}$ ${\ displaystyle {\ mathit {\ psi}}}$ ${\ displaystyle {\ mathit {\ phi}}}$ ${\ displaystyle {\ vec {S}}}$ ${\ displaystyle {\ vec {D}}}$ ${\ displaystyle {\ vec {B}}}$

Voltage quantities

The sense of direction of a voltage variable ( or ) runs in the same direction as the orientation of a comparative field strength of the same voltage, tangential and uniformly oriented along the integration path ( or ). ${\ displaystyle u}$ ${\ displaystyle v}$ ${\ displaystyle {\ vec {E}}}$ ${\ displaystyle {\ vec {H}}}$

Reference sense and reference arrow

Counting arrows (= reference arrows ) for the current are often entered in circuit diagrams , which indicate the reference sense of electrical or magnetic current or voltage. The direction of the reference arrow can be freely selected. A positive value then means that the sense of direction agrees with the reference sense, and a negative value means that the sense of direction is opposite.

Metrological example

If an ammeter that can display positive and negative values has a positive deflection, the sense of direction of the measured current runs from the plus to the minus terminal of the measuring device, in the case of a negative measured value from the minus to the plus terminal. The operating principle of the measuring device observes the above-explained convention regarding the direction of the electrical current. The freely selectable direction of the reference sense for the current in the calculation model corresponds to the freely selectable polarity of the current-carrying conductor during the measurement.

literature

W. Nerreter: Fundamentals of electrical engineering . Hanser-Verlag, 2011, ISBN 978-3-446-42385-5 .
G. Flegel, K. Birnstiel, W. Nerreter: Electrical engineering for mechanical engineering and mechatronics . Carl Hanser Verlag, 2016, ISBN 978-3-446-44773-8 ( limited preview in Google book search).
H. Eckhardt: Basic features of electrical machines . Springer, 2013, ISBN 978-3-322-94292-0 ( limited preview in Google book search).
A. Prechtl: Lectures on the basics of electrical engineering . Volume 1. Springer, 2013, ISBN 978-3-7091-3833-5 , 6.2 and 6.3 ( limited preview in the Google book search).

References and comments

↑ IEC 60050, see DKE German Commission for Electrical, Electronic and Information Technologies in DIN and VDE: International Electrotechnical Dictionary entry 131-11-29
^ Klaus Lunze : Introduction to electrical engineering . Textbook. 13th edition. Verlag Technik GmbH Berlin, 1991, ISBN 3-341-00980-9 , 0.4, p. 19 : “These are quantities that are linked to the assigned vector by an integral relationship. Correspondingly, the sense of direction of the scalar quantity results from that of the vector. "
^ A. Prechtl: Lectures on the basics of electrical engineering. Volume 2. Springer, 1995, p. 12.
↑ Equal sign of the flow is also sufficient.
↑ Equal sign of the voltage is also sufficient.
↑ DIN EN 60375: 2004-04: Agreements for electrical circuits and magnetic circuits (IEC 60375: 2003); German version EN 60375: 2003.

[IEV-1] IEC 60050, see DKE German Commission for Electrical, Electronic and Information Technologies in DIN and VDE: International Electrotechnical Dictionary entry 131-11-29

[2] Klaus Lunze : Introduction to electrical engineering . Textbook. 13th edition. Verlag Technik GmbH Berlin, 1991, ISBN 3-341-00980-9 , 0.4, p. 19 : “These are quantities that are linked to the assigned vector by an integral relationship. Correspondingly, the sense of direction of the scalar quantity results from that of the vector. "

[3] A. Prechtl: Lectures on the basics of electrical engineering. Volume 2. Springer, 1995, p. 12.

[4] Equal sign of the flow is also sufficient.

[5] Equal sign of the voltage is also sufficient.

[6] DIN EN 60375: 2004-04: Agreements for electrical circuits and magnetic circuits (IEC 60375: 2003); German version EN 60375: 2003.