current relay. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
Comments on the article
The eternal and old problem: the AC motor burned out. The reason is the work on two phases under load. And why? It is sometimes difficult to give the correct answer.
All sorts of ingenious protections have been invented from this trouble, but the motors still burn, and at the most inconvenient time and in the most inaccessible places. As you know, a three-phase AC electric motor consists of a rotor with a short-circuited winding and a stator, in the grooves of which a system of three coils is laid, shifted relative to each other by 120 ° and connected in a star or triangle (which is much less common). Therefore, consider a system of windings connected in a 380 V star.
From Kirchhoff's law for a branched circuit it follows that the sum of the currents flowing into one point is equal to the sum of the currents flowing from it. In other words, there is no current at the connection point of the three windings, a virtual zero is formed, but relative to the "ground" potential, some potential may be present at this point, so it is isolated.
It is hard to imagine that there are three windings that are completely identical in their parameters, so some equalizing currents flow, but they are insignificant. But if the contact is broken in one of the phases, then the emerging equalizing current finally destroys the formed resistance bridge, the wire burns out, and then the process develops like an avalanche. The equalizing current continues to grow (and the load is not removed!), the motor overheats, smokes and fails.
The electric motor can be protected. If you accurately measure the impedance of its windings before installation and take into account all operating conditions, then you can calculate the fuse parameters (section, length, material). So what is next? Further full self-activity.
And yet there is a protection method that gives a 99% shutdown guarantee (see figure). Let's return to our virtual zero - the point of connection of the windings. When a phase imbalance occurs, a potential arises between the connection point of the phase windings and the common "ground". If the current relay coil is turned on at this point, then the equalizing current, passing through the coil, turns on the relay and breaks the normally closed contacts included in the magnetic starter coil circuit - the electric motor stops.
In three-phase systems with a fourth ground wire, the current relay must be placed in the break of the fourth wire at the point of connection to the ground loop. A current relay can be selected from the range of electrical products, and it does not matter at all if this relay is DC. The relay works for a fraction of a second, and the rest of the time it is de-energized, but due to the conditions of isolation and protection from external influences, it must meet the standards for installations up to 500 V. A wide range of electric motors can be protected with one type of relay.
All of the above applies to AC motors with star windings.
Author: I.P. Semenov
See other articles Section Power Supplies.
Read and write useful comments on this article.
<< Back
Latest news of science and technology, new electronics:
Machine for thinning flowers in gardens
02.05.2024
In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers.
... >>
Advanced Infrared Microscope
02.05.2024
Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>
Air trap for insects
01.05.2024
Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>
| Random news from the Archive Robomobiles for highway construction
30.08.2015
In Florida (USA), it is planned to use innovative equipment for road works - trucks with an autopilot system.
We are talking about special machines equipped with so-called "shock attenuators" (Impact attenuator). These are special devices designed to absorb the impact energy in the event of an accident. Vehicles with "shock absorbers" are installed in the area of roadworks or highway construction to ensure the safety of workers. In addition, such machines can be used to change the trajectory of the crashed vehicle in order to lead it to the safest area.
Robo vehicles with "shock attenuators" were developed by Royal Truck & Equipment as part of a special program supervised by the Ministry of Transport. It is assumed that the autopilot system will avoid injuries and injuries that a truck driver can receive if another car crashes into him at high speed.
There are three ways to control the operation of robotic trucks: using GPS, using a remote control, and also by programming the movement of the vehicle in front.
|
Other interesting news:
▪ New computer memory is 10 times faster than old
▪ The brain predicts the future
▪ Cats are hunting
▪ Profession choice - by genes
▪ Lightyear 0 - solar-powered production car
News feed of science and technology, new electronics
Interesting materials of the Free Technical Library:
▪ Telephony site section. Article selection
▪ article Spaceships. History of invention and production
▪ How Dangerous Are Side Effects of Medicines? Detailed answer
▪ article Deputy director of the school for academic work. Job description
▪ article Metal detector with high sensitivity on microcircuits. Encyclopedia of radio electronics and electrical engineering
▪ article Voltage level deviation LED indicator. Encyclopedia of radio electronics and electrical engineering
Leave your comment on this article:
All languages of this page
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua
2000-2024
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese