Voltage drop

In electrical engineering, the voltage drop ( engl. voltage drop or IR -drop) no waste, but a potential difference can be measured between two points of a traversed by the current resistance. Currently, this is preferred, and standard compliant designated according to IEV 151-15-09 60050 as voltage drop. (see eg DIN VDE 0100-520:2013-06 section 525 ).

It is caused by the of a positive charge into an electric field was doing positive shift work, which has an energy drain on. In the opposite case, ie with a power supply, it is called a source voltage. The voltage drop is measured in volts.

It restricts the physical size of voltage from the voltage drop from the following: a general description of the ratio of the voltage available for the displacement of the charge Q and the size of the work load itself to thereby identifying a potential between two points of an electric field independent of the electric current. In contrast, it is called a voltage drop if and only if the time required for separation of two charges with different signs of energy during flow of the stream is free again. Accordingly, there is a voltage, while a voltage drop takes place. The voltage drop is the same direction as the flowing current.

Formulas

From the contexts:

Results in the voltage:

And the potential difference

Capacitive voltage drop

Inductive voltage drop

Voltage drop across a resistor

In practice, the calculation of the voltage drop across the electric field is much more complicated. They charge him for it, if possible, from the contexts of Ohm's law. This is as follows: In a circuit which is driven by the power source voltage counteracts an electrical resistance.

A = cross- section of the conductor, L = length of the conductor, = resistivity of the conductor material

When alternating currents are used for the calculation of the voltage drop the effective value of the current.

For sinusoidal alternating currents with the amplitude of the following applies:

Additional remark: an alternating current flows through a conductor occurs in addition to the ohmic resistance and a capacitive or inductive resistor. These are neglected here. But if you have a wire winding resistance, the inductance is so high that you can not neglect the complex resistance. The same is true in the high-frequency technology.

Voltage drop according to Kirchhoff shear rules

The sum of the voltage drops over the line and the consumption of resources corresponding to the voltage of the voltage source. In a round n partial voltages a DC electric network, the following formula applies:

(Mesh rule from the Kirchhoff's rules )

In AC networks, the sum of the corresponding complex rms values ​​or complex amplitudes of the voltage must be considered.

Voltage drop on the electric lines

In the context of electrical cable systems consistently comes the term voltage drop as defined in IEC 60050 151-15-09 apply. On cables and their connecting points of these should be kept within limits so that the operating voltage of the equipment is sufficiently high and the losses are kept within acceptable limits. A higher voltage drop is allowed in the start of motors and other equipment provided with high inrush currents that move in all cases, the voltage fluctuations within the permissible limits for the resource.

Calculation of the voltage drop on electrical circuits

According to DIN VDE 0100-520:2012-06 Appendix G, the voltage drop can be calculated in electrical wiring according to the following formula:

Here are

  • Voltage drop in volt ...
  • Coefficient ...: in three-phase circuits; for single-phase circuits Note: Three-phase circuits, which are loaded completely unbalanced ( just a phase load) are considered as single-phase circuits.
  • ... Specific electrical resistance of the conductor during normal operation. The value for the presence of the normal operation temperature is used as a resistivity taken, i.e., 1.25 times the resistivity at 20 ° C, or 0.0225 Ω · mm ² / m for copper and 0.036 Ω · mm ² / m for aluminum.
  • Just ... length of wire and cable plant in meters.
  • ... Conductor cross section.
  • Power factor ...; If not known, a value of 0.8 (sin φ = 0.6 ) is assumed.
  • ... Reactance per unit length of the conductor; If not known, a value of 0.08 milliohms / m is assumed.
  • ... Operating current.

The corresponding voltage drop in percent is given by:

It stands for the system voltage in volts.

Note: In low voltage circuits, the limits for the voltage drop must only circuits for lighting ( not eg for bell, control, door opener ) are complied with (assuming that the proper function of this equipment is checked ).

Limits in Germany

  • After the low-voltage terminal Regulation § 13 ( 4 ), formerly the AVBEltV, the voltage drop between the service box and the electricity meter shall be not more than 0.5%.
  • After TAB 2007, the voltage drop between the service connection and meter shall not exceed the following values ​​:
  • According to DIN VDE 0100-520 should be in accordance with Table G.52.1 the voltage drop in consumer equipment between the home port and consumables (sockets or device terminals ) be not more than 3%.
  • According to DIN 18015 Part 1, the voltage drop between the meter and the electrical outlets or equipment terminals should not be more than 3%.

As a basis applies the mains voltage, which is determined according to DIN IEC 38 for Europe at 230/400 V, and the rated current of the overcurrent protective devices, such as 63 A or 16 A.

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