Electrical voltage

Voltage
Voltage
	U, V
Dimension	L 2 MT -3 I -1
Units
SI	volt

The electric voltage between points A and B of an electric circuit or an electric field is a physical quantity whose value is equal to the work of an effective electric field (including external fields), which is carried out when a unit test electric charge is transferred from point A to point B ^[1] ^[2] .

Electrical voltage
Amperage
Electric power
Electrical resistance

It is believed that the transfer of the test charge does not change the distribution of charges at the field sources (by definition of the test charge ). The voltage in the general case is formed from the contributions of two works: the work of electric forces $A_{AB}^{el}$ ${\ displaystyle A_ {AB} ^ {el}}$ $A _ {{AB}} ^ {{el}}$ and work of outside forces $A_{AB}^{ex}$ ${\ displaystyle A_ {AB} ^ {ex}}$ ${\ displaystyle A_ {AB} ^ {ex}}$ . If no external forces act on the chain section (i.e. $A_{AB}^{ex}=0$ ${\ displaystyle A_ {AB} ^ {ex} = 0}$ $A _ {{AB}} ^ {{ex}} = 0$ ), the work of moving includes only the work of a potential electric field $A_{AB}^{el}$ ${\ displaystyle A_ {AB} ^ {el}}$ $A _ {{AB}} ^ {{el}}$ (which does not depend on the path along which the charge moves), and the voltage $U_{AB}$ ${\ displaystyle U_ {AB}}$ $U _ {{AB}}$ between points A and B coincides with the potential difference between these points (since $\varphi _{A}-\varphi _{B}=A_{AB}^{el}/q$ ${\ displaystyle \ varphi _ {A} - \ varphi _ {B} = A_ {AB} ^ {el} / q}$ $\ varphi _ {{A}} - \ varphi _ {{B}} = A _ {{AB}} ^ {{el}} / q$ ) In general, the voltage $U_{AB}$ ${\ displaystyle U_ {AB}}$ $U _ {{AB}}$ between points A and B differs from the potential difference between these points ^[3] for the operation of external forces to move a unit positive charge. This work is called electromotive force. ${\mathcal {E}}_{AB}$ ${\ displaystyle {\ mathcal {E}} _ {AB}}$ ${\ mathcal E} _ {{AB}}$ on this section of the chain: ${\mathcal {E}}_{AB}=A_{AB}^{ex}/q.$ ${\ displaystyle {\ mathcal {E}} _ {AB} = A_ {AB} ^ {ex} / q.}$ ${\ displaystyle {\ mathcal {E}} _ {AB} = A_ {AB} ^ {ex} / q.}$

$U_{AB}=\varphi _{A}-\varphi _{B}+{\mathcal {E}}_{AB}.$ ${\ displaystyle U_ {AB} = \ varphi _ {A} - \ varphi _ {B} + {\ mathcal {E}} _ {AB}.}$ $U _ {{AB}} = \ varphi _ {{A}} - \ varphi _ {{B}} + {\ mathcal E} _ {{AB}}.$

The definition of electrical voltage can be written in another form. To do this, submit work $A_{AB}^{ef}$ ${\ displaystyle A_ {AB} ^ {ef}}$ $A _ {{AB}} ^ {{ef}}$ as an integral along the trajectory L laid from point A to point B.

$U_{AB}=\int \limits _{L}{\vec {E}}_{ef}d{\vec {l}}$ ${\ displaystyle U_ {AB} = \ int \ limits _ {L} {\ vec {E}} _ {ef} d {\ vec {l}}}$ $U _ {{AB}} = \ int \ limits _ {L} {\ vec E} _ {{ef}} d {\ vec l}$ - integral of the projection of the effective field strength ${\vec {E}}_{ef}$ ${\ displaystyle {\ vec {E}} _ {ef}}$ ${\ displaystyle {\ vec {E}} _ {ef}}$ (including external fields) to the tangent to the trajectory L , the direction of which at each point of the trajectory coincides with the direction of the vector $d{\vec {l}}$ ${\ displaystyle d {\ vec {l}}}$ ${\ displaystyle d {\ vec {l}}}$ at a given point. In an electrostatic field, when there are no external forces, the value of this integral does not depend on the integration path and coincides with the potential difference.

The dimension of electrical voltage in the International System of Quantities (ISQ ), on which the International System of Units (SI) is based , is L ² MT ^-3 I ^-1 . The unit of measurement of voltage in SI is volt (Russian designation: V ; international: V ).

The concept of voltage was introduced by Georg Ohm in his work in 1827, in which a hydrodynamic model of electric current was proposed to explain Ohm's empirical law discovered in 1826: $U\!=IR$ ${\ displaystyle U \! = IR}$ $U \! = IR$ .

DC Voltage

The voltage in the DC circuit between points A and B is the work that an electric field does when transferring a test positive charge from point A to point B.

AC Voltage

Do not touch, the housing is live. Prohibition sign , Germany.

The following voltages are used to describe AC circuits :

instantaneous voltage;
the amplitude value of the voltage;
average voltage value;
rms voltage value;
average rectified voltage value.

Instantaneous voltage is the potential difference between two points, measured at a given moment in time. Depends on time (is a function of time):

u=u(t).

{\ displaystyle u = u (t).}

The amplitude value of the voltage is the maximum absolute value of the instantaneous voltage for the entire period of oscillation:

U_{M}=\max(|u(t)|).

{\ displaystyle U_ {M} = \ max (| u (t) |).}

For harmonic (sinusoidal) voltage fluctuations, the instantaneous voltage value is expressed as:

u(t)=U_{M}\sin(\omega t+\phi ).

{\ displaystyle u (t) = U_ {M} \ sin (\ omega t + \ phi).}

For an AC sine wave network with a RMS value of 220 V, the amplitude voltage is approximately 311.127 V.

Amplitude voltage can be measured using an oscilloscope .

The average value of the voltage (constant component of the voltage) is the voltage determined over the entire period of oscillation, as:

U_{m}={\frac {1}{T}}\int _{0}^{T}u(t)dt.

{\ displaystyle U_ {m} = {\ frac {1} {T}} \ int _ {0} ^ {T} u (t) dt.}

For a sinusoid, the average voltage value is zero.

The root-mean-square value of the voltage (outdated names: effective , effective ) is the voltage determined over the entire period of oscillation, as:

U_{q}={\sqrt {{\frac {1}{T}}\int \limits _{0}^{T}u^{2}(t)dt}}.

{\ displaystyle U_ {q} = {\ sqrt {{\ frac {1} {T}} \ int \ limits _ {0} ^ {T} u ^ {2} (t) dt}}.}

The rms voltage value is most convenient for practical calculations, since it does the same job on a linear active load (for example, an incandescent lamp has the same brightness, the heating element emits as much heat) as the constant voltage equal to it.

For sinusoidal voltage, the equality

U_{q}={1 \over {\sqrt {2}}}U_{M}\approx 0,707U_{M};\qquad U_{M}={\sqrt {2}}U_{q}\approx 1,414U_{q}.

{\ displaystyle U_ {q} = {1 \ over {\ sqrt {2}}} U_ {M} \ approx 0.707U_ {M}; \ qquad U_ {M} = {\ sqrt {2}} U_ {q} \ approx 1,414U_ {q}.}

In engineering and everyday life when using alternating current, the term “voltage” refers to the rms value of the voltage, and all voltmeters are calibrated based on its definition. However, constructively, most devices actually measure not the RMS value, but the mean-rectified (see below) voltage value; therefore, for a non-sinusoidal signal their readings may differ from the true value.

The average rectified voltage value is the average value of the voltage module:

U_{m}={\frac {1}{T}}\int \limits _{0}^{T}|u(t)|dt.

{\ displaystyle U_ {m} = {\ frac {1} {T}} \ int \ limits _ {0} ^ {T} | u (t) | dt.}

For sinusoidal voltage, the equality

U_{m}={2 \over \pi }U_{M}(\approx 0,637U_{M})={2{\sqrt {2}} \over \pi }U_{q}(\approx 0,9U_{q}).

{\ displaystyle U_ {m} = {2 \ over \ pi} U_ {M} (\ approx 0.637U_ {M}) = {2 {\ sqrt {2}} \ over \ pi} U_ {q} (\ approx 0.9U_ {q}).}

In practice, it is rarely used, however, most AC voltmeters (those in which the current is rectified before measurement) actually measure this value, although their scale is graduated by rms values.

Three-phase current voltage

In three-phase current circuits , phase and linear voltages are distinguished. Under the phase voltage is understood the rms value of the voltage at each of the phases of the load relative to the neutral, and under the linear - the voltage between the input phase wires. When a load is connected to a triangle, the phase voltage is linear, and when connected to a star (with a symmetrical load or with a grounded neutral), the linear voltage is ${\sqrt {3}}$ ${\ displaystyle {\ sqrt {3}}}$ times more than phase.

In practice, the voltage of a three-phase network is denoted by a fraction, the numerator of which is phase when connected to a star (or, which is the same, the potential of each of the lines relative to the earth), and in the denominator is the linear voltage. So, in Russia, the most common networks with a voltage of 220/380 V ; 127/220 V and 380/660 V networks are also sometimes used.

Characteristic Values and Standards

An object	Voltage type	Value (at customer input)	Value (at source output)
Electrocardiogram	Impulse	1-2 mV	-
Television antenna	High frequency variable	1-100 mV	-
AA type galvanic cell (finger-type)	Constant	1.5 V	-
Lithium cell	Constant	3–3.5 V (in the performance of a finger element, for example, Varta Professional Lithium, AA)	-
Logic signals of computer components	Impulse	3.3 V; 5 v	-
Battery Type 6F22 (Krona)	Constant	9 V	-
Power supply of computer components	Constant	5 V, 12 V	-
Electric equipment of cars	Constant	12/24 V	-
Laptop power supply and LCD monitors	Constant	19 V	-
Network "safe" low voltage for hazardous conditions	Variable	36-42 V	-
The voltage of the most stable burning candles Yablochkova	Constant	55 V	-
Telephone line voltage (off-hook)	Constant	60 v	-
Voltage in Japan	Three phase variable	100/172 V	-
US Home Voltage	Three phase variable	120 V / 240 V ( split phase )	-
Voltage in household electrical networks in Russia	Three phase variable	220/380 V	230/400 V
Stingray discharge	Constant	up to 200-250 V	-
Tram and trolleybus contact network	Constant	550 V	600 V
Electric eel discharge	Constant	up to 650 V	-
Metro Contact Network	Constant	750 V	825 V
Electrified Railway Contact Network (Russia, DC)	Constant	3 kV	3.3 kV
Low power overhead power distribution line	Three phase variable	6-20 kV	6.6-22 kV
Power plant generators, powerful electric motors	Three phase variable	10–35 kV	-
At the anode of the tube	Constant	7-30 kV	-
Static electricity	Constant	1-100 kV	-
On a car spark plug	Impulse	10-25 kV	-
Contact network of an electrified railway (Russia, alternating current)	Variable	25 kV	27.5 kV
Breakdown of air at a distance of 1 cm		10-20 kV	-
Rumkorf Coil	Impulse	up to 50 kV	-
Breakdown of a layer of transformer oil 1 cm thick		100-200 kV	-
High Power Overhead Power Line	Three phase variable	35 kV, 110 kV, 220 kV, 330 kV	38 kV, 120 kV, 240 kV, 360 kV
Electrophore car	Constant	50-500 kV	-
Ultra-high voltage overhead power line (intersystem)	Three phase variable	500 kV, 750 kV, 1150 kV	545 kV, 800 kV, 1250 kV
Tesla Transformer	Pulse high frequency	up to several MV	-
Generator Van de Graaff	Constant	up to 7 MV	-
Thundercloud	Constant	2 to 10 GW	-

Notes

↑ Miller M.A., Permitin G.V. Electric voltage // Physical Encyclopedia / Ch. ed. A.M. Prokhorov . - M .: Great Russian Encyclopedia , 1992. - T. 3. - S. 244-245. - 672 p. - 48,000 copies. - ISBN 5-85270-019-3 .
↑ Electric voltage / Yuryev Yu.V. // Great Russian Encyclopedia : [in 35 t.] / Ch. ed. Yu.S. Osipov . - M .: Great Russian Encyclopedia, 2004—2017.
↑ Detlaf A.A., Yavorsky B.M., Milkovskaya L.B. Physics course. - 1977.- T. 2.

Literature

Miller M.A., Permitin G.V. Electric voltage // Physical Encyclopedia / Ch. ed. A.M. Prokhorov . - M .: Great Russian Encyclopedia , 1992. - T. 3. - S. 244-245. - 672 p. - 48,000 copies. - ISBN 5-85270-019-3 .
Detlaf A.A., Yavorsky B.M., Milkovskaya L.B. Physics course. Electricity and magnetism. - M .: "HIGHER SCHOOL", 1977. - T. 2.

Links

Electrical voltage // Brockhaus and Efron Encyclopedic Dictionary : 86 tons (82 tons and 4 additional). - SPb. , 1890-1907.
About potential difference, electromotive force and voltage
Glossary.ru: Dictionary of Natural Sciences.

[1] Miller M.A., Permitin G.V. Electric voltage // Physical Encyclopedia / Ch. ed. A.M. Prokhorov . - M .: Great Russian Encyclopedia , 1992. - T. 3. - S. 244-245. - 672 p. - 48,000 copies. - ISBN 5-85270-019-3 .

[2] Electric voltage / Yuryev Yu.V. // Great Russian Encyclopedia : [in 35 t.] / Ch. ed. Yu.S. Osipov . - M .: Great Russian Encyclopedia, 2004—2017.

[3] Detlaf A.A., Yavorsky B.M., Milkovskaya L.B. Physics course. - 1977.- T. 2.

Electrical voltage

DC Voltage

AC Voltage

Three-phase current voltage

Characteristic Values and Standards

See also

Notes

Literature

Links

More articles:

Electrical voltage

DC Voltage

AC Voltage

Three-phase current voltage

Characteristic Values ​​and Standards

See also

Notes

Literature

Links

More articles:

Characteristic Values and Standards