A relay is an electrical control device that causes a predetermined step change in the controlled variable in the electrical output circuit when the change in the input quantity (excitation quantity) reaches a specified requirement. It has an interactive relationship between the control system (also known as the input circuit) and the controlled system (also known as the output circuit). It is commonly used in automated control circuits, and is essentially an "automatic switch" that uses a small current to control a large current. Therefore, it plays a role in automatic adjustment, safety protection, and circuit switching in circuits.
Overview and current status of the relay industry
The relay originated in the mid-to-late 1960s, with research beginning under the advocacy of scholars in Britain, Australia, and the United States.
In the mid-1960s, some people proposed the idea of using small computers to implement relay protection. However, due to the high price of computers at the time and their inability to meet the technical requirements of high-speed relay protection, they were not put into practical use in protection. But this led to a great deal of research on the theoretical calculation methods and program structure of computer relay protection, which laid the theoretical foundation for the later development of relay protection.
Computer technology experienced significant breakthroughs in the early and mid-1970s. The rapid development of large-scale integrated circuit technology enabled microprocessors and microcomputers to enter the practical application stage. The substantial decrease in price and the significant increase in reliability and processing speed led to a decline in research on computer-based relay protection. In the late 1970s, relatively complete microcomputer-based protection prototypes emerged and were put into trial operation in power systems.
In the 1980s, microcomputer protection systems became increasingly mature in terms of hardware structure and software technology, and were promoted and applied in some countries.
In the 1990s, power system relay protection technology developed into the era of microcomputer protection, which is the fourth generation in the history of relay protection technology development.
Research on microcomputer protection in my country began in the late 1970s and early 1980s. Although it started late, it has progressed rapidly thanks to the efforts of Chinese relay protection workers.
After about 10 years of hard work, by the late 1980s, computer relay protection, especially microcomputer protection for transmission lines, had reached a level of widespread practical application. In the research process of computer relay protection in my country, universities and research institutes played a pioneering role.
In terms of relay application areas in my country, communications and industrial control, home appliances, and automobiles remain the largest markets for relays. According to relay market research reports, the largest demand is for general-purpose relays, especially high-sensitivity, small, and ultra-small PCB relays, and low-power relays. From a market perspective, the relay industry is a competitive sector characterized by large volume, wide service coverage, low technological content, low profit margins, and significant market potential.
Although my country's relay industry has undergone decades of development, the overall level of its products still lags significantly behind the world's advanced levels, mainly in the following ways:
1) The design level is low, the variety of military products is limited, the environmental adaptability is poor, and the reliability level is low, which cannot fully meet the requirements of weapons and equipment and high-tech warfare. The quality consistency of general-purpose relays is poor, the variety of products is slow to be updated, the market share of high-end products is low, and they cannot meet the needs of domestic and international markets, nor can they completely replace imports.
2) Low independent development and innovation capabilities: Insufficient research on common technologies, underutilization of technical strength, and weak supporting technologies are the main reasons affecting the speed of new product development.
3) Outdated production technology, low level of automation, and poor process control capabilities seriously affect the consistency and reliability of product quality, leading to increased service costs.
4) Low management level, low overall quality of management personnel, outdated business model, especially slow change in management thinking, which is not adapted to technological development.
5) CAD is still at a low level of application, while CAM and CAT are in their initial stages. Product development cycles are long and incompatible with the requirements of rapid product upgrades. Material application is lagging behind the development requirements of relay technology.
6) The physical analysis of material failure is neither broad nor deep; the variety of domestically produced materials is limited, and there are no manufacturers for key materials, such as flame-retardant fine plastic mounting wires and pressure-sensitive tapes, which still need to be imported; the equipment for modifying materials to meet relay requirements is outdated and incomplete, especially in material rolling. Testing techniques and methods need to be improved and perfected.
Technical characteristics of the relay industry
There are many types of relays, each with its own characteristics. Below, we briefly introduce the characteristics of several types of relays:
solid-state relay
1. Long lifespan and high reliability: Solid-state relays have no mechanical parts; the contact function is performed by solid-state components. Because there are no moving parts, they can operate in environments with high impact and vibration. The inherent characteristics of the components that make up solid-state relays determine their long lifespan and high reliability.
2. High sensitivity, low control power, and good electromagnetic compatibility: Solid-state relays have a wide input voltage range, low drive power, and are compatible with most logic integrated circuits without the need for buffers or drivers.
3. Fast switching: Because solid-state relays use solid-state components, their switching speed can range from a few milliseconds to a few microseconds.
4. Low electromagnetic interference: Solid-state relays have no input "coil," no contact arcing, and no tripping, thus reducing electromagnetic interference. Most AC output solid-state relays are zero-voltage switches, conducting at zero voltage and turning off at zero current, reducing sudden interruptions in the current waveform and thus reducing switching transient effects.
Vacuum relay
1. A vacuum relay is a relay in which the contacts are placed inside a glass or ceramic shell that has been evacuated to a high vacuum, using the vacuum as the arc extinguishing and insulating medium.
2. Vacuum has ideal insulation properties, and under ideal conditions, it can reach a dielectric constant of 80,000 V/mm. Since there is no oxygen in a vacuum, it will not oxidize during use. Thus, vacuum relays have a small and stable contact resistance during use.
3. Vacuum possesses excellent arc-extinguishing properties. The electric arc in a vacuum easily diffuses, reducing contact wear. Therefore, vacuum relays have a long lifespan and can handle load switching. In summary, vacuum relays feature high breakdown voltage, rapid arc extinguishing, large breaking current, small size, light weight, and long lifespan. They are widely used in fields involving the control of high-voltage circuits, such as pacemakers, MRI, high-frequency antenna coupling devices, radar, and capacitor discharge.
4. High dielectric strength, large rated carrying current and conversion current, low contact resistance, stable operation, low noise, small inter-electrode capacitance and inductance, small contact gap, low excitation power, fast breaking speed, sealed contacts, unaffected by ambient air pressure, moisture, sand or explosive gases, suitable for working in harsh environments.
intermediate relay
This relay is composed of multiple high-quality, sealed, small relays with low coil voltage. It is moisture-proof, dust-proof, and continuous, ensuring high reliability and overcoming the drawbacks of electromagnetic intermediate relays where the wires are too thin and prone to breakage. It features low power consumption, low temperature rise, and eliminates the need for external high-power resistors, allowing for easy installation and wiring. The relay has large contact capacity and a long service life. An indicator light illuminates after the relay trips, facilitating on-site observation. The delay time can be set using a DIP switch on the panel, offering high accuracy within a range of 0.02-5.00 seconds. For more industry-related information, please refer to the relay industry analysis and market research report.
Photorelay
Semi-permanent lifespan, micro-current driven signal, high impedance insulation withstand voltage, ultra-small size, optical transmission, contactless.
