Three-phase Electric - is consumed energy metering device. Different from the usual variety of types and functions. This is due to the peculiarities of charging production needs.
From the history of the question
The basis of the three-phase two-phase system laid down Nikola Tesla. Counters are designed in the likeness of the instrument registering a regular alternating current. The scheme depends on the electrical interface. For example, Tesla used switching phases such as applied into the socket pre-war Germany (30th) years. Because of this counter were placed in the gap of each phase, or used double. Likewise arranged three phase counters.
The difference here from the circuit 220 is that the current is able to flow back through the wire an adjacent phase. But to pass a local neutral after entering the building is not possible. Actually, it based on this principle of modern residential meters. At the entrance to the building is worth three phases. The only plant in the apartment because it would take a second to put a separate unit. Therefore, homeowners who have in the territory of the three-phase, three-phase meter is required to deliver.
The first three-phase meters were designed for industrial motors and appeared in the early 90-ies of the XIX century. These products are discussed below, after describing the construction of single-phase meters, similar principles are used.
The need to measure the energy spent arose with the emergence of demand in the 70-ies of the XIX century. Since then, the principle of Electric has changed little. Was consumed energy integration function works voltage at the current at a predetermined interval of time, until incorporated appliances. Name settled immediately. Counters were called:
The latter name is not entirely consistent with purpose, the counter measures the energy, not power. If the voltage is constant, integration relies only current consumption. Such a simplified type of counters was called coulometer or level meter.
If the current variable, you can not use conventional voltmeters, ammeters, to see the value. Arrow galvanometer continuously be tossed at the edges of the scale. However, people have found ways to measure the desired parameter. At the beginning of the XX century used three types of devices:
- Electrolysis counters.
- Motorized counter.
- Time counters.
Electrolysis counter Edison
Historically, this is the first one to use counters, information about the device became known to the public in 1881 by the Paris exhibition. At that time, all used electrical appliances operated by a DC voltage. An incredible number of finished products sold in operation. By the beginning of the XX century, when an alternating current began to take up individual copies remained in circulation. The main advantages of steel simplicity and reliability.
The design shown in the figure, consists of two tanks with copper sulfide, where shipped copper discs reinforced on two shoulders koromyselnogo mechanism. The principle of operation is described by electrolysis. When current flows between the plates, the first partially dissolved at the second precipitate formed from copper. When the shoulder begins to outweigh the mechanism makes the next notch on the consumed energy unit and change through the relay (reminds koromyselny engine Joseph Henry, see. Electromagnetic relays), the direction of current flow.
Thus, swing commit slow oscillations to the right and to the left until the meter readings writes. Alternating current similar device can not be registered. Soon the shortcomings of similar design were identified:
- With increasing temperature, the instrument accuracy swam, he underestimated the testimony.
- A second drawback steel abundance of moving parts and relay contacts.
Improved model (see. photo) did not differ elegance: required to be removed from the solution used wheels, by weight, to determine the amount of energy spent and fresh paste. But eliminated the moving parts, and the current flows in a single direction. Thermal fluctuations are eliminated by adjusting the solution, which changes resistance inversely with copper. As a result, the effect of the two substances are mutually compensated.
AC has been used since 1887 Electrolytic counter Lowry Hall. Measurement was carried out to change the battery plates, included in the lighting circuit. Metal tolerated in a specific direction, by weight accurately determined quantity of consumed energy. The method did not spread and has two distinct disadvantages:
- After light-off battery slowly discharges through spiral bulbs and changed the transferred metal weight.
- It was found that the plate growth conditions show a pronounced frequency dependence, and other factors. It finds it difficult to achieve acceptable accuracy.
The first motorized counter patented in 1882 by Professors Ayrton and Perry, but suffered from mechanical friction. This limitation is overcome in the counter-watt-hours Elihu Thomson. The principle of operation is based on the induction currents (Arago, Foucault). shaft speed of small servo proportional to current consumption. Due to the induction driven in rotation copper disk associated with a countable mechanism. It is noteworthy that due to deliberate design of the direction of movement of the shaft does not depend on the polarity of the voltage, but the device has a lower threshold highest recorded current, for obvious reasons.
Counter (patent US388003 A) Shollenbergera (14 August 1888) is different from a single-phase induction motor cooker hood. Specially designed for the company Westinghouse, which worked Nikola Tesla. The auxiliary coil (not visible in general terms) of the stator arranged at an angle to avoid hanging structure and uniquely specify the direction of shaft rotation. Both are connected in series lead. As Thomson's design, the meter is intended only for AC. For rotation speed limit on the axis end of the blade 4 are fastened, interacting with atmospheric air.
Famed Wikipedia counter Ferranti invented in 1884 and uses a movable contact of metallic mercury, the design resemblance to Faraday first half of XIX century. It is not too secure of the devices. The current entrance in the center of the bowl, placed horizontally between the poles of a permanent magnet, and flowed to the side on the way to the consumer. Due to the interaction of fields discoid mercury and magnet structure rotary shaft countable vane mechanism. Mercury continuous contact maintained due removable metallic ring. With each rotation of the consumer cheat kilowatt-hours. Eyewitnesses claim that the device was used for the AC when needed. Although we believe the hard way.
Counter Perry differs from the previous one - mercury replaced copper cylinder. Current collector in the form of a ring. But mercury is present in the instrument, just to a lesser extent, forming the liquid contact.
The invention relates to the account Aron, in reality it German patent rejected - similar device contained British Patent Senna and Perry. The idea did not practically useful, so consider the first model sample in February 1883 in Mr authorship. Shulberga.
All the counter is not very different from the clocks cuckoo. The top of the pendulum is located between the two electromagnets, the current changing direction causes "watches" go. The resonant system is tuned to properly count the "time" - energy. Structure adapted for AC and DC. Apparently, giving the name of the current measure kilowatt-hours.
Design of the late XIX century,
Produced by the authors search shows that the design of three-phase meters appeared in a few years after a failed attempt Dolivo-Dobrovolsky take out a patent on the use of the three phases. As mentioned in the reviews, the engineer proved that the three-phase AC efficiency of the two. But Nikola Tesla previously proved that it polyphase current invention, and the patent is not given to.
The first three-phase meter
Patent US500868 A taken on multiphase meter. This is the first mention of the three-phase device counts found on the Internet. Based on the foregoing, it is impossible to state with a probability of 100%, which is the first three-phase meter, but is an early example of a device in the present context.
The term multiphase applied not by chance, were previously already in the course of the two-phase counters. In scientific usage, many console - refers to the number of three or more. The term upotreblon in perfect accord with generally accepted standards.
Thomas Duncan got right to the invention July 4, 1893 (Independence Day).
The device is a three-phase meter based on the principle that has been used for a single-phase model, patented by the author a little earlier (US 415 825, 21 December 1891). In fact it is an induction motor, invented by Tesla. The stator has three equidistant from each other on the number of phases of coils (A, B, C), the rotor is made of metallic cylinder. The author writes that come from copper, silver, iron - any metal alloy with high conductivity. The requirement is dictated by the terms of the occurrence of eddy currents.
The cylinder rotates in electromagnet field three phases, connected through the axis with a countable mechanism not shown in the figure. The axes of the stator coils are displaced from the normal to the tangent of the circle that is guaranteed to make a predetermined direction of rotation of the rotor (field directed along the axis beyond the windings of a smooth arc). The principle of operation of the device is different from an induction motor, invented by Nicola Tesla based Arago theory (Foucault experiments):
- The coils effective voltage phase shifted off uniformly 120 degrees.
- The emerging field around the coil induces eddy currents metal cylinder (Arago) direction such that the structures repel each other.
- The stator is fixed and reinforced with tough, rotating the rotor starts.
- Each revolution corresponds to the authors of a particular quantity of energy expended.
Communication between the values is obvious. Today, to change the induction motor rotational speed can vary the voltage. This decreases or increases the current, and the voltage becomes a secondary factor. In this case, the voltage is constant and is given by the energy supplier. A consumers included in series with the three coils set current and hence power. From the above it asks the conclusion that the first three-phase counter of inherent disadvantages:
- Firstly, of course, the device makes a reactance inductive reactance in the circuit. This is bad, the motor winding act similarly mutually exacerbating effect. Complementing each other, coils produce a large phase angle, increasing the reactive power. At a certain value of engine power becomes ineffective.
- The second disadvantage is becoming a fact that the author is assumed to be uniform power consumption in all phases. This is obvious, otherwise momentum will stall. Unstable operation of the mechanical part certainly did not contribute to the proper account.
- A third drawback derives from considerations asynchronous motor. To operate the induction currents need arise only if the difference of rotating velocity field (US - 60 Hz) and the stator. The author should make the cylinder in the form of three-pole magnet of the iron ore. The device would be rotated regardless of eddy currents. Complexity remains: the field would tend to reverse it magnetization rotor.
Thomas Duncan, apparently aware of these shortcomings. Writes in the text that stated on the construction drawings are not considered successful implementations of its ideas remain, that are not shown in the sketches - in order to avoid plagiarism and theft of ideas. At the same time Duncan said of the possibility of calculating the rate of four or more phases. Location name derives directly patent.
Single-phase meters Shollenbergera knowingly given up so much attention. Working for a company Westinghouse, inventor inevitably moved to the designs for industrial use: two phases of Nikola Tesla and three - Dolivo-Dobrovolsky. In US531866A patent explicitly states that the procedure is aimed at industry. But at the same time wise inventor states that do not use is prohibited in the home.
Text of the patent published January 1, 1895. The author claimed to have discovered a pattern: if you put a coil fed with alternating current in the other two, the supply voltage same frequency, torque is dependent on a number of variables. This determines the speed or angle of deflection system as a function of the parameters:
- Magnetic field intensity of the coils.
- Sine of the angle difference between the supply voltage phases.
Based on this fact, and built Shollenberger counter. Designed to work in tandem with ac motor Nikola Tesla, but the author quickly found ways to extend the scope of the invention.
On the screen side depicts biphasic counter, the author shows that the stator coil is rotatable in the box and deflected by a certain angle. In the first case it is convenient to use a connected counter mechanism in the second - to use hand and face. That allows you to simultaneously record the process visually and evaluate expended kilowatt-hours.
It should be noted that it is not necessary to use a rotation in structures. Some work on the principle of superposition (vector addition strengths) fields. The figure shows the most options. Fields change synchronously in time, pointer jitter appreciably, and the efficiency of the device greatly depends on the soundness of the design of the mechanical part (inertia of the movable frame). However, similar to say about turnouts pressure sensors of any boiler.
Charles Terry and Wesley Carr testified fact filing patent September 15, 1894, but construction It revealed a serious flaw: the author refuses to accept the fact that the phases of consumption is uneven. However, it took into account Shollenberger in the case of rotary design, which gives future engineers hint of change in the design.
A patent 796 368 was being considered almost 9 years, being declared November 21, 1896. Working in the company of Edison and Thomson, the author was interested vested in DC. The patent is for AC, which is contrary to the interests of the owners of General Electric. Therefore, copyright holders could get in touch with the Bureau and ask to hold publication. When Tesla picked up and began to build a tower Vordenklif, DC became outlive itself. By 1905 it became clear that the world no longer be the same again. Then, patents and published.
Charles Steinmetz design is remarkable, here for the first time introduces the concept of start winding. Alternating counter presented in the figures, is the induction motor with pole reproduction due to phase shift. Reactive element did not start capacitor, as in modern versions, and choke. And the positive and negative voltage change of phase is used to create a rotating magnetic field.
Simply: the capacitor voltage lags the current and inductance at - ahead. Both the phase shift may be used. It turns out that the input values are the same, but artificially divided for the measurement opportunities as a modern single phase compressor refrigerator. So, phase one, supplemented artificially created pseudophase.
The disadvantages apparent: passing a similar construction, the current diverges to the voltage at decent angle. Power factor is far from ideal. A modern version of a capacitor is much better, but venture to suggest that the subject remains unexplored at the time of filing of the patent. In 1896, there were no other capacitors, except for Leyden jars. Other designs were not available to inventors in mass. Tesla Coil with pronounced capacitive characteristics serve only to compensate for the self-inductance of the properties that are not suited to the needs of this class of devices.
Describe the principle of operation is not necessary, it is common scheme. Instead of the capacitor to start the induction motor used inductance (to create a phase shift). Let us add that after the shaft acceleration normally start winding switched off so as not to make the reactive component in consumption. In 1896, it seemed impossible for obvious reasons: puskozaschitnoy relay is not used in large quantities, it appears difficult to set them so low-power design specific purpose.
George Hummel construction of two water droplets resembles a modern meter staging ideas. US Patent No. 633 695 A shows that even at the end of 1897 the creator knew the uneven consumption in three phases. The construction of the first to use an asymmetrical switching circuit: current transformers take interphase for evaluation.
This scheme isolated neutral, the counter works well. Attention is drawn to the executive part of the mechanism. This engine with implicit poles formed by the laminated core of the magnetic circuit. For rotating phases (!) Using one of the two windings (see. previous subtitle). As a result, single phase creates a rotating magnetic field and allows the meter to wind kilowatt-hours.
The circuit material removal signal is given in the figure showing the identity of the idea of the modern versions. And three-phase precursor is believed wattmeter where voltage coil perpendicular to the coil current, and the values are removed by means of transformers. The fundamental difference between - Hummel operates linear values and modern meters - phase (to neutral).
Small nuances are indicated in the text accompanying the patent. For example, it is written that the phase shift of the winding is not 90, but only 30 degrees. Therefore, the poles are located, respectively. Small phase shift due to the presence of relatively large active winding resistance and the difficulty of obtaining high inductance.
There is no more sense to touch patents, energy consumption measurement bases are set forth. It only remains to see how the three-phase Electric modern type.
Electronic three-phase counters
Today, electronic counter controlled by a microcontroller. On the Internet, distributed switching circuit MSP430F449 chip. It is easy to notice - it is counter-clockwise with a crystal on 32.768 kHz. While ticks "mechanism", the analog-to-digital converter takes readings of three current transformers and detects the voltage of each phase. For supporting the conclusion is neutral, not shown in the figure.
Binary information is provided to the microcontroller, which produces the multiplication of variables and their time integration using the frequency of the quartz resonator. The smaller the sampling interval of the electronic circuit, the more accurate readings. In this case, the error is much less than one hundredth of a percent, which is enough for typical applications. Presented counter easily calculates the active and reactive power, producing the Fourier transformation, or using other algorithms.
The second factor affecting the accuracy is bit analog-to-digital converter. The higher it is, the less errors and more high-speed equipment expected. Because the principle of digitizing usually enclosed in a gradual increase of the voltage comparator and comparing it with the input value. The waveform resembles a ladder terminating step where the comparator decides that has reached the required level.
electronics advantage in the possibility of digital processing, which depends solely on the speed of clock frequency and performance microcontroller. This first bit kernel, which is now fighting for the operating systems in the world, the second - a circuit diagram of the processor architecture.
From this it must be inferred that the principle of capacity calculation is not too much has changed over the past 150 years from the time of challenges for engineers (primarily Edison). Modern systems are more accurate, the very first model only takes into account current, we do not engage in multiplication. And if you charge a 12-volt battery through the first power meters may get a fantastic figure.
This applies to types of devices discussed above. They use magnetic flux or rate of electrolysis, depending only on the current value. Advanced ADC is easier to measure the voltage. In particular, current inputs are high-resistance voltage divider. That there is no alternative, sensitive Hall sensors at this stage of development of technology use is not profitable.