Phase voltage - a voltage difference between the phase conductor and the neutral.
general information
vector diagrams
In today's networks is dominated by three-phase voltage. Under phase refers to an electrical signal of sinusoidal form. It is described in the vector diagram of a rotating segment. Vector diagrams built to simplify the description of many processes. For example, the capacitor voltage lagging the current, but the human mind to perceive this fact difficult. The chart picture is visible. Vectors are becoming an integral part of electric calculations, when the network becomes more complicated.
To understand the term phase voltage, assumed to represent, as diagrams are constructed. Sinusoid is indicated on it rotates counterclockwise segment. It coincides with the frequency present in the network, but is often used in calculations other parameter. The formulas often contain a certain number of pi. Heaviside once tried to create a rationalized system of measurement, eliminating the mentioned drawback. But removing the number Pi of certain formulas, he always saw him in the other, which is considered a fundamental consequence of the potential fields, which include electric.
Heaviside was not successful, modern physicists use another trick to get rid of unnecessary repetition. The entered concept of circular frequency is constantly applied in the art. A numerical value is equal to the product of twice the number Pi network frequency expressed in Hz. Circular named for its resemblance with the formula for computation of the circumference. Other interpretations of the term is not found.
Sometimes it called a cyclic angular frequency and numerically equal to the angular speed of the rotor of the generator. In the graph the sine wave is based on the angular frequency. Otherwise could not be agreed upon rotation of the vector in such a simple way. 2 Pi - period sinusoid school, familiar from a young age. In order not to break the schedule, it is necessary to add the multiplier. Otherwise moments of passage through zero sine wave do not coincide with the vector diagram.
Settings vector diagrams
Any sinusoidal process on a vector diagram shows the rotating segment having a length and a certain phase. The first physical plane denotes the amplitude (voltage, current), the second - the position in polar coordinates. When audio frequency vectors rotate synchronously but in the reactive elements are shifted. Capacitive impedance causes the current leads the voltage by 90 degrees. Physically, the capacitor begins to empty rapidly charged, the process gradually fades. As a result, voltage delay reaches full value.
Across the inductor current is always behind, unable to gain full value due to the presence of flux linkage between the coils. Tension changes abruptly, and the current gradually reaches the desired value. In industrial networks, it turns out that one parameter is already falling, and the second has not yet reached its peak. This is called a phase shift, which describes the network reactive power. This negative effect, for its elimination inductive and capacitive components are mutually trying to compensate. Parallel running motors are switched capacitor banks.
Vector diagrams used to calculate the complex processes occurring in the circuit. For example, the presence of the transformer in the substation uniquely determines the presence of the reactive component. Current is always lagging behind the phase voltage. But the resistance of the transmission line capacitance, is compensated. It is so strong that to combat the negative effects have to put the reactors - inductive high-voltage resistance. It turns irrational and uneconomic design, but you have to put up with.
Direct current vector diagram is not analyzed. In its reactance circuits do not cause phase shift. The process occurs in the capacitor, it is short-lived. For this reason, a constant current is recommended for transmission over long distances. Disappear radiation losses, reduces the corona effect. As a result, it is possible to transfer more and better. It needs to build transformers at the substation at the consumer, but calculated that the situation is economically viable.
AC parameters Standardization
Phase voltage is a sinusoid on a graph and a rotating vector in the diagram. In the ideal case. In fact, the network parameters are normalized in accordance with GOST 13109, specifying performance requirements. Guided documentation now we need to caution, the government issued a decree passed to phase voltage of 230 V. Now the network is not 380, instead of them - 410 V. Incandescent bulbs produced at 220, are smaller in these conditions. The changes set out in GOST 29322-2014 (IEC 60038-2009).
Simply show the phase voltage on the conventional networks of 220 V. The difference in potential between the wires - the unknown quantity. Phase voltage is measured between the line and the circuit ground. This is the case in an ordinary apartment, but in the production of another. There each phase is considered in conjunction with the other. Sometimes there is no neutral. Then the voltage between phases is called linear. Phase is introduced to recognize the type of network (presence of neutral).
New Standard 29322 introduces the concept of networks of 60 Hz. Phases two and three provided. Then specify two digits. For example, 230/400 or 120/240. Is easy to see that the relationship between the numbers in each different pair. Phase voltages are indicated in the first place, line - through fraction. This helps to clarify the topology. Networks vary in structure, phase voltage allows to judge this accurately.
If you specify a pair of 230/400, an electrician can immediately see that the ratio of the numbers equals the square root of three. So, three-phase system. Then look for more information - or isolated neutral gluhozazemlonnaya. Regarding numbers 120/240, specifying the frequency (60 Hz) is possible with certainty say that it is a single-phase network with the topology of the three wires. The phases are fed through a transformer (say) with a common neutral point. A similar scheme was used in pre-war Germany, and in some places still in use. In the latter case, the two-pole machines, if necessary.
In this connection we note that the nominal voltage changed, but GOST 13109 did not realize until the said fact. There is discussed the value of 380 V. The now obsolete However, the parameters of permissible guide for specific cases. GOST 13109 listed as acting parallel introduced additional document - GOST 54149. Document standardizes tolerances as:
- Voltage amplitude deviation - 5 - 10% in each direction depending on the individual case.
- voltage fluctuations.
- Nonsinusoidality.
- Unbalance (for multiphase applications).
- frequency deviation of 0.2 to 0.4 Hz, and so forth.
It is easy to notice that the most stringent requirements for frequency. This is the most important parameter of the phase voltage. The new GOST R 54149 introduces the concept of asynchronous transmission system, where the requirements for frequency noticeably softer. Deviations in the frequencies of 1 Hz to 95% of the time. During the remaining 5% is permitted deviation of 5 Hz in each direction.
These values are probably related to the transmission lines, because today is rare equipment, inability to resist hopping. For example, most of the motors is controlled by voltage. With increasing frequency shifting varies negative reactive impedance network. More precisely - it increases the inductive component and reduced capacitive, aggravating the situation. Inductive part and so eager to make up for the inclusion of capacitor banks to reduce reactive power.
Lowering the frequency looks more advantageous - the imbalance is reduced. But this impairs the transmission voltage across the transformer, in addition, the field - on the motor windings. Perhaps considerations will be taken into account when considering the scientific community the possibility of switching to a higher frequency of power networks. Assume 700 Hz, as proposed by Nikola Tesla. At the end of the XIX century it hindered by the lack of electrical steel for transformers, today, can not be considered such a restriction seriously.
Frequency, amplitude and the RMS value of the phase voltage
Frequency phase voltage discussed above. To construct sinusoids parameter multiplied by 2 pi to cause fluctuations of a physical process to a period of the schedule. Mains frequency depends on the motor speed, but not too much. Now little reason for such strict limitations, the scope will be expanded. For example, an electronic transformer operation is not frequency dependent, while it is set by switching RC-chain and the characteristics of the bipolar transistors.
More specifically, the frequency affects the design of the engine, but less stress. Fringe distinction can be made only specialists. Much more important parameter is considered to be the amplitude of the phase voltage. When the documentation write "220" refers to the current value. In this case a reduction of power produced by the AC to DC. It carries out the procedure according to the law Joule. Located AC power is divided by the current, a certain voltage is obtained which produces an identical thermal effect as a constant current.
All phase voltages are given in current values. Remember when paying isolation. It is known that the arc occurs is a function of current characteristics - AC or DC. In the former case, the amplitude at the same transmit power is higher. The contactors arc ignited at the peak, and goes out spontaneously, when the voltage passes through zero. This important feature is taken into account when designing the relay. Also operates in a similar manner the current being found by calculations.
To find the amplitude of the voltage, you need a valid value multiplied by the square root of two. For networks 220 leaves 311. Such is the amplitude of the phase voltage at the wall outlet before making the decision to raise the government. Now the current value - 230, amplitude - 325. This is taken into account in the design of the input circuits of equipment. Including species:
- transformers;
- condensing units;
- diode bridges and so on.
Phase voltage usually used for unambiguous and shorthand domestic circuits, the line is used in industry. I talk about 220 and 380 often heard V. In this case, there is no doubt about it. But in saying this, people do not suspect that operate phase and line voltage. Readers can now boast the knowledge of what they say.
