The Types and Importance of Relays in Electrical Technology

What is Relay? What are the types? The need to transmit electric current over long distances was one of the biggest problems of the 19th century. Because with the use of the telegraph, communication over long distances began. It is obvious that as the transmission distance of electric current increases, power losses occur. Mankind, famous for discovering new inventions in extraordinary situations, invented the relay while looking for a solution to the weakening of telegraph signals. The inventor of the relay is known as Joseph Henry. Henry invented the relay in 1835. People started to use the relay in wider areas over time. So much so that the relay was developed and became the crown jewel of electricity and formed the basis of electronic technology. After telling the relay story, let's come to our topic. This article contains information about the use, connection and types of the relay. What is Relay? It is a switch model that can control the circuit electrically. The biggest reason why relays working with an electromagnetic system are used in electrical and electronic circuits is that high currents can be controlled with low currents. Relay is a passive electrical element. Therefore, it is not active in the circuit when no load falls on it. Another important feature of relays is that they can work with both AC and DC voltage types. Relays have more than one contact structure. Therefore, it can control the simultaneous opening and closing of multiple elements. Since relay contacts can be in both open and closed positions at the same time, the contact connections are expressed as normally open (NO - normal open) or normally closed (NC - normal close).
RELAY STRUCTURE Relays consist of three parts in structure. These; coil, spring and contact. Coil: It is one of the most basic parts in the relay. The function of the coil in the relay is to create a magnetic field inside and change the position of the moving contact inside. It must be used according to the characteristics of the coil inside the relay. One of these features is that it is necessary to know whether the coil operates with DC voltage or AC voltage. It is also necessary to know the operating voltage of the coil. The coil inside the relay is generally operated with voltages such as 5V, 12V, 24V, 120V, 220V. Voltage specifications are printed on the outer casing of the relay. Contact: There is more than one contact in the relay. Contacts are generally expressed as single contact or double contact. While there is one normally open end and one normally closed end in the single contact structure, there are two normally open and two normally closed ends in the double contact structure. The contacts inside the relay can withstand very high voltages and currents. Which of the contacts is open and closed is usually shown at the bottom where the contacts are located. Additionally, the maximum current value it can withstand is indicated on the top of the case. While electronic relay contacts are generally manufactured to withstand currents of 10A or slightly more, relay contacts used in electrical systems can withstand higher current values. The biggest problem with contacts is that the moving contact gets stuck on a fixed contact over time. Spring: The function of the spring in the relay is to ensure that the movable contact returns to its normally closed position after the electrical energy of the coil is cut off. As can be understood from the intended use of the spring, the relay is mechanical rather than electrical. Relay Types Relays are an element that has many varieties in the market. Relays are generally used in control circuits in electrical systems. However, there are also varieties available on electronic cards. Relays are the best elements that can be used in both electrical circuits and electronic circuits to control high-power electric currents. In this part of the article, I will give information about the types of relays available in the industry. GENERAL PURPOSE RELAYS These relays are also known as magnetic relays. All of the information about the relay above describes the magnetic relay. Relays of this type are used to transmit electric current in electrical and electronic applications. Long-distance current transmission is achieved with the help of contact. Because it is impossible for high current to pass through these circuits, the switching feature of the relay, which is a passive control element, is used and the electric current is controlled externally with the help of high current resistant contacts. TIMER Time relay is a special type of relay produced to perform contact control on a timed basis. It opens and closes the time relay contacts with a delay. This delay time is set by us using the system on the time relay. Time relays are produced in two types: direct time relay and reverse time relay. Straight time relay: As soon as the coil of this time relay is energized, its contacts wait for the set time to expire before changing position. Inverse time relay: Unlike the straight time relay, after the coil is de-energized, it waits for the set time to change position before changing position. TIME RELAY CONNECTION The coil ends of the time relay are usually designated A1 and A2. Apart from these, there are points where the phase ends are connected. So there is no need for a separate connection for timing. Adjusting the duration is sufficient for timing. Time relays can be of many types. I shared a time relay picture below. As can be seen from this picture, there is a time indicator and adjustment tip, and the delay time of the time relay is adjusted with the adjustment tip. THERMAL RELAY Another important type of time relay is the thermal relay. Thermal relays are a type of relay that operates sensitively to temperature. Thermal relays' operating logic works by taking advantage of the bimetallic feature, which is the difference in expansion of two different metals. Thermal relays are generally used for phase protection purposes. For example, in cases where devices such as motors are overloaded or run for a long time, the phases may heat up and cause fire or engine failure. In order to prevent such situations, it is used to protect the phases in the circuit against overload. THERMAL RELAY CONNECTION The coil ends of the thermal relay are also designated A1 and A2. The connections of the contact terminals are numbered differently from company to company. However, it is no different from a general purpose relay connection. The only function of the thermal relay is to measure the cable temperature and ensure safety by closing its contacts against overheating. ENGINE PROTECTION RELAY This relay, also known as phase protection relay, has a single function. That is to protect the engine against negativities. The main purpose of the motor protection relay is to prevent damage to the motor by detecting problems occurring in the phases in advance by measuring phase voltages. In 3-phase motors, if there is no voltage coming from one of the phases or if a voltage drop occurs in the phases and there is no motor protection relay in the system, the motor windings will soon become short-circuited due to overheating and the motor will burn out and become unusable. In the motor protection relay connection, the motor protection relay is connected to the R, S, T phase terminals before connecting the phases to the motor. With this connection, control of the phases is ensured. SOLID STATE RELAY (SSR) SSR has two great importance. One of these is that it is a completely electronic relay and the second is that it can withstand very high current values. This durability is provided by the mosfet inside. Although it may vary depending on its structure, it can operate against current values such as 1000-2000 amperes. If mechanical relays were used at these values, the relay contacts would stick after a few openings and closings and become unusable. The control of SSR is provided by an external circuit element, as in other relay types. These external elements are semiconductor products. The contacts of the relay are controlled with the help of an element such as IRLed or triac. SMART RELAY Smart relay is a multifunctional digital relay designed to control a system or system groups from a single point. Smart relays are also known as mini plc. There is a screen on this relay and the contact positions can be checked with the help of this screen. Another reason that makes the smart relay smart is that it has internal counters, timers, registers and operators that can perform arithmetic operations in the input and output units. Due to all these features, they are preferred because they reduce space and cost, especially in complex control circuits. REED RELAY It consists of a contact that inserts inert gas into a glass tube and a coil used to produce a magnetic field. As long as the gas inside the reed relay is maintained, it can be used for many years.