The strength of the struma is 3-phase mesh. Three-phase mesh: tightness analysis, connection scheme
Calculation of the magnitude of total tightness. Rozrahunok of new tension electric lansyug owing to the knowledge of both active and reactive storage, spivvіdnoshennia such a scheme can be described by a tricout of tensions.
For calculation of active (R) that reactive (Q) warehouse 3-phase lancet is carried out summation of their values in the skin phase according to the formulas:
P \u003d R A + R B + R C \u003d U A I A cosφ A + U B I B cosφ B + U C I A Сcosφ C;
Q \u003d Q A + Q B + Q C \u003d U A I A sinφ A + U B I B sinφ B + U Z I A Сsinφ C.
I A , I, I, U A, U, U- Strum vectors and stresses in the phases,
Φ
- Kut zsuvu phase vector_v strumu schodo naprugi.
For symmetrical regime robotic schemes in all phases, the equality of tensions is fixed. Therefore, the magnitude of the tension can be taken by simply multiplying the phase warehouse by the number of phases in the system:
Р=3Р Ф =3U Ф ∙I Ф ∙cosφ;
Q=3Q=3U Ф ∙I Ф ∙sinφ;
S \u003d 3S F \u003d (P2 + Q2) \u003d 3U F I F.
We are working to replace the phase warehouse lines for the їх spіvіdnostnyam for the scheme of the survey: I L \u003d I F, U F \u003d U L / √3.
As a result, we take:
Replace phase warehouses with linear ones for the scheme of the tricutnik for їх spіvіdnostnyam: I Ф \u003d I L / √3, U Ф \u003d U L.
Accounting allowance:
Р=3U Ф ∙I Ф ∙cosφ=(3U L ∙I L /√3)∙cosφ=√3∙U L ∙I L ∙cosφ.
In such a rank, it appeared that the fallowness of the options for the installation of the elements of the lancer by the scheme γ or Δ in a 3-phase symmetrical system the meaning of straining during the day. The stench is calculated for these very formulas:
Р=√3∙U∙I∙cosφ [W];
Q=√3∙U∙I∙sinφ [var];
S \u003d √ (P 2 + Q 2) [VA].
For these viruses, a rule was formed: provide the linear values of the vectors Uі I without assigning any linear indexes.
Ways to overcome tension In the energy sector, there is a constant need for the world electrical quantities. The active storage of total tension is measured with a wattmeter, and the reactive one is measured with a varmeter. The wattmeter works behind the algorithm, we describe it with the formula:
W=U W ∙I W ∙cos(U W ^I W)=Re│U W ∙I W *│.
U W , I W- those vectors, yakі led to the terminal fitting for the control of the active warehouse.
The practice of electrical wiring promotes a few options for connecting to electrical wattmeters. The stink vibirayutsya stalely in the scheme of vikonan commutation navantazhen and її characteristics.
At symmetrical 3 phase system it is enough to turn on one wattmeter in a be-yak phase for a constant wilt active tension with the upcoming construction of the taken result after the algorithm Р=3W=3U Ф ∙I Ф ∙cosφ.
However, this simple method is no longer an orienting estimate of the magnitudes that are frozen, there may be great losses. For this reason, the wine is not very acceptable to the vikonanny of the world, it will require high accuracy from the top commercial enterprises.
Accurate meter of active warehouse for stargazing with a neutral wire ensures the selection of three wattmeters.
Viconation of the skin in the skin phase of vimirovanie may be more accurate. Additional indications of three wattmeters are provided with information about active tension with minimal abductions.
At asymmetric ambition at 3 phase line without neutral dart zastosovuєtsya sposіb vimir two wattmeters.
The peculiarity of the world is in the fact that the linear / phase streams in such an electric lance are mutually related to the 1st law of Kirchhoff, if their sum I A + I B + I C \u003d 0. How to mathematically add up the readings of both wattmeters and describe them by mathematical methods, then we take the following:
As a result, the admission was confirmed that two wattmeters vibrate the active tension of this circuit in case of subsuming these readings. On the indication of the skin of them, the characteristics and magnitude of the need are added.
Looking at the stress vectors and streams on the complex plane for a symmetrical stress, the diagram shows:
For the sake of understanding, for the sake of safety, the readings of wattmeters are vibrated:
W 1 \u003d U L ∙I L ∙cos (φ + 30 °);
W 2 \u003d U L ∙I L ∙cos (φ-30 °).
For the results of the analysis of these formulas, it is not easy to complete the following quilts:
1. When φ=0 equality is created, showing both wattmeters, which is even more typical for pure active quest;
2. Kolya 0≤φ≤90°(a quarter of the active-inductive voltage of the quadrant) the reading of the 2nd wattmeter is higher, lower than the first (W2 > W1). In this quadrant, all indications at the 1st wattmeter gain negative values at values φ>60°;
3. At times 0≥φ≥90°(a quarter of the active-switching voltage of the quadrant) the indication of the 1st wattmeter is greater, lower than the other (W1>W2). For which quadrant the indication of the 2nd wattmeter has a negative value at the values φ.
Equal value three-phase vanishingє by crossing over the skin phase conductor of the same strum. With any value of the struma strength in the zero conductor, it is equal to zero. The most clear, even phase shifting is manifested in three-phase electric motors. For them, it's a pain reliever phase struma Zdіysnyuєtsya according to the formula P \u003d 3 * Uf * I * cos (φ) \u003d 1.73 Ul * I * cos (φ).
In times of flow in phases of strums, different in magnitude, then Dane's adventurousness bude nerіvnomіrna chi asymmetrical. In such a situation, there is a neutral wire electric struma. At uneven ambition, the appointment of tension will be carried out according to the formula Ptot = Ua * Ia * cos (φ1) + Ub * Ib * cos (φ2) + Uc * Ic * cos (φ3).
Vymіryuvannya sweating with a wattmeter
The vimiryuvannya of the tension of the electric jet is carried out with the help of special vimiryuvalnyh accessories, in the role of which wattmeters play.
Behind the mind of the symmetrical tension, which should be in a three-phase system, it is easy to distinguish between the alternatives of one single-phase wattmeter. In a choti-pipe system, which can have a null wire, the inclusion of the wattmeter's jet winding is carried out in the following way with one of the wires of the phases. For the connection of the voltage winding, the phase and zero wires are switched. This inclusion gives the possibility to determine the intensity of one of the phases (Rf) for an additional wattmeter. Oskіlki equally navantazhenya transmitting the same tension of all three phases, then the total tension of the three-phase system is more advanced: P \u003d 3Rf.
In a system that consists of three wires, the wattmeter windings are switched on up to the wire, and pass through the strum winding line strum. In this way, the indicator of the tightness of the three-phase system immediately shifts the data of the wattmeter Pω, then Р= Рω.
Razrakhanok of tightness of phases with asymmetric navantage
In times of asymmetric tension, the increase in tension of the phase struma, it is practical to carry out the appointment for the help of a large number of wattmeters.
In such a situation, for the purpose of diagnosing the tension of the system with four wires, three wattmeters are required. The winding of the voltage of the skin of them, turns on between zero dart and with the wire of the phase. In this rank, the total tension of the system from three phases is equal to the total tension of the skin of them.
For a three-wire system, two wattmeters are required. Here the voltage windings are connected to the skin wattmeter, the input windings of the strum and the external line wire. The deep tension is formed from the reading of two wattmeters.
At Lanciusi fast strumu the tension is meant to be done simply - tver strumu and tension. The stench does not change at the hour and є with a constant value, it is obvious that the tension is constant, so the system is vrіvnovazhen.
3 meshes variable voltage everything is more complicated. The stench can be single-phase, two-phase, three-phase. Single-phase and three-phase merezhi have the largest width due to their thinness of the smallest vitrates.
A look at the three-phase living system
Such lancers can join in the star or in the trikutnik. For clarity of reading schemes i, in order to avoid pardons of the phase, it is customary to designate U, V, W or A, B, C.
Scheme of z'ednannya zirka:
Scheme of connecting phases at the mirror
For the star, the total voltage at the point N is equal to zero. Tension triphasic struma in this case, it will be a constant value, which means that the three-phase system is vrіvnovazhen, on vіdmіnu vіd single-phase, so it's tightness three-phase mesh fast. Mittevo meaning again triphasic tension there will be one:
IN given type There are two types of voltage present - phase and linear. Phase - ce voltage between phase and zero point N:
Phase voltage in lancius Linear - between phases:
That is why the tightness of the three-phase barrier for this type of plant is more expensive:
Ale oskilki liniyne that phase voltage vіdrіznyayutsya among themselves in, but the sum of phase tensions is also taken into account. When rozrahunku triphasic lanceugs this type is accepted to be koristuvatisya by the formula:
Vidpovidno for active:
For reactive:
Scheme
Like Bachimo with such a look of half, phase that line voltage equal, for which you sing, that the tightness for entering the trikutnik is more expensive:
І vіdpovіdno:
Reducing the pressure
Vimiryuvannya active tension in the laces is carried out with the help of a wattmeter
Depending on the nature of the connection scheme (symmetrical or non-symmetrical), the connection schemes of the accessories can be adjusted. Let's look at the vipadok symmetrical ambitions:
Scheme of turning on the wattmeter with symmetrical input Here the world is carried out only in one phase and then it is possible to multiply by three with the formula. This method allows you to save on attachments and change the dimensions of the vimiruval installation. It will be necessary if the accuracy of the measurement in the skin phase is not required.
Winning with asymmetric vanishing:
Scheme of turning on the wattmeter with asymmetric input This method is more accurate, as it allows you to reduce the tightness of the skin phase, but also requires three accessories, large dimensions of the installation and processing of indications from three accessories.
Vymiryuvannya in lanciug without zero explorer:
Scheme of turning on the wattmeter for the presence of zero drotu This scheme will require two accessories. This method is based on the first law of Kirchhoff showing W 1 less than lower W 2 (W 1
With active and єmnіsnіy (R-C) and W 1\u003e W 2, and with φ<-60 0 показания W 2 <0.
For the daily development of technology, digital wattmeters appeared. The stench is on the vіdmіnu vіd analog smaller in size, richly lighter and less dimensional. More than that, digital wattmeters can fix the strum, voltage, change the cosφ in a measure or something else. The stench is allowed in the real time mode, depending on the difference in magnitude and to see the advance at the time of rest. It’s more convenient and not necessary to carry out vimiryuvannya struma, tension, and then mathematically all virakhovuvat. The digital wattmeter is attached to the case and is connected (for the use of buttocks) in the main way - as the main stop - the plug is built into the socket.
Zmist:The pressure of a constant stream in an electric lance is determined in a simple way by the path of the multiplier of the stream's strength and voltage. The value of the magnitude is constant and not shilln to change at the hour, so the value of tension will be constant, the whole system will be in a leveled state.
Changed strum for all parameters changes in a constant, especially the number of phases. Even more often, situations are blamed, if it is necessary to overcome the tension of the triphasic strum, in order to correctly determine the characteristics of the tension that is being connected. Carrying out such surveys will require special knowledge about the operation of a three-phase living system. Three-phase lines, in order of single-phase ones, had a wide width at the link with low material strength and durability of operation.
Characteristics of a three-phase system
Triphasic lancers sound like two main ways - with a star (Fig. 1) and a tricot, which will be looked down below. On all diagrams, for a good alignment, the phases are denoted by the symbols A, B, Z or U, V, W.
With the alternative scheme "zirka" (Fig. 1), the value of the total voltage at the point of the phase transition N is equal to zero. In this depression, in pairs with single-phase, there will be constant tension. The position indicates the importance of the triphasic system, and the mitteva tension will be shown in the following formula:
The latter are characterized by two species (Fig. 3). In the first wave, the voltage is shown between one of the phases and the zero exact span N. The linear voltage is shown by the voltage, which is between the phases themselves.
In this rank, the meaning of the new tension for the day with a star is shown by the following formula:
However, the next step is to balance the difference between the linear and phase voltage, which becomes √3. Therefore, it is necessary to rahuvati the sum of the tightness of all phases. The formula P \u003d 3 x U f x I f x cos φ , and for reactive- P \u003d √3 x U l x I f x cos φ .
The "trikutnik" is used in the most expanded way of phase control.
Danish view of the transmission of the same value of the phase (U f) and linear (U l) voltage. Spivvіdnenja between phasic and linear strumas depends on the formula I = √3 x I f the value of the phase stream becomestime I f \u003d I x √3.
In this way, the tightness of the linear values with this method of z'ednannya turns behind the help of offensive formulas:
- External tension: S \u003d 3 x S f \u003d √3 x U x I;
- Active tension: Р = √3 x U x I x cosφ;
- Reactive pressure: Q = √3 x U x I x sinφ.
At a glance, the formulas for skin tightness are similar in appearance. For the presence of sufficient knowledge, that knowledge can lead to incorrect vysnovkіv. To avoid similar pardons, look at the butt of a typical rozrahunka.
- The end of the electric motor is vikonano at the sight of the tricutnik, the voltage in the string is 380 V, the power of the stream is 10 A. Therefore, the value of the total tension will come: S \u003d 1.73 x 380 x 10 \u003d 6574 V x A.
- Dali tsey elektrodvigun buv z'ednany zirkoy. In this case, the voltage on the skin winding of the phase became 1.73 times lower, lower when connected with a tricot, although the voltage of the wire was too large. Obviously, the strength of the struma in the windings also changed by 1.73 times. There is one more important moment: when the line strum was connected by a tricoutnik, having overshot the phase by 1.73 times, then farther, if the scheme changed to a star, its value became equal. As a result, the change in the linear struma folded: 1.73 x 1.73 = 3 times.
- In this way, in the same formula, there are different values: S = 1.73 x 380 x 10/3 = 2191 V x A, also when the electric motor is switched on from the circuit of the tricutnik to the star, the tension is reduced by 3 times.
Vymіryuvannya sweating with a wattmeter
In electric laces, the mitigation of tension is controlled by a special device - a wattmeter. Connection schemes can be different, depending on the connection of the same characteristics. In the case of a symmetrical experiment (Fig. 1), only one phase is used to conduct the winnowing, and the results, then, are multiplied by three. This way is the most economical, allowing you to reduce the size of the wintry fitting. Vіn vikoristovuєtsya in quiet moods, if there is no need in obtaining accurate data on the skin phase.
In times of asymmetric vanishing (Fig. 2), the metrics will be more accurate. However, to reduce the tightness of the skin phase, three accessories with large dimensions are required. You can also complete the display with three accessories.
The rise in tension of the triphasic strumum and її wimming can be overcome in the electric lance due to the presence of the zero conductor (Fig. 3). In such a scheme, two accessories are installed, and the first Kirchhoff's law is applied for the expansion of vicor: I A + I B + I C \u003d 0. In this way, the indication of two wattmeters in the sum gives the value of the three-phase pressure for a given lance.
