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14 October 2024, 13:43
Thermal relays are circuit elements used to ensure the safe operation of electrical circuits and provide protection against overcurrent.
If overcurrent occurs in electrical circuits, it can damage electrical devices. It may also lead to dangerous situations such as fire.
They are mechanisms developed to eliminate such risks. They are frequently used in motor protection systems and are important components that enhance safety in electrical circuits.
In this article, we will examine in detail what they are, their working principles, types, and where they are used.
A thermal relay is a protective relay that detects overcurrent in electrical circuits and shuts off the circuit. It is commonly used for the protection of motors and other electrical equipment.
Its main function is to prevent electric motors from operating under overcurrent or overload conditions, thereby ensuring the safety of the circuit. Thermal relays operate based on the heat produced as current passes through the circuit. This heat affects a thermal element inside the relay, opening the circuit and providing protection.
These relays offer protection against overloads in many different types of equipment, especially electric motors. When the electric current returns to normal levels, the thermal relay reactivates the circuit, allowing the motor to continue running.
The basic working principle of thermal relays is based on the heat generated by electric current. When electric current passes through a resistor in the circuit, it generates heat.
If the temperature exceeds a certain level, the thermal components heat up and expand. This causes the relay to stop the circuit. This prevents the electrical device from being overloaded and avoids damage to the circuit.
There are two main components: a thermal element and a contact mechanism. The thermal element heats up and expands as electric current passes through it.
If the heating exceeds a specific threshold, the thermal element opens the contact in the circuit and cuts off the electric current. This safely shuts down the circuit, preventing damage to the motor or electrical device due to overcurrent or overload.
There are various types of thermal relays that operate according to different current types and levels. Some thermal relays open the circuit in case of short-term overcurrent. Others only disconnect the circuit during long-term overloads. This difference varies depending on the application and intended use of the thermal relay.
Thermal relays are produced in different types according to usage areas and protection requirements. The most commonly used types of thermal relays are:
Bimetallic: These relays operate based on the expansion properties of two different metals. When electric current passes through, these metals expand at different rates and open the circuit to provide protection.
Electronic: These types of relays detect overcurrent using electronic sensors and microprocessors. They provide more precise protection and are generally used in sensitive devices.
Like every technological device, thermal relays have advantages and some limitations. In this section, we have detailed the strengths and limiting factors of thermal relays.
Effective Protection Against Overload: Thermal relays provide good protection for motors and other electrical devices against overcurrent. When the current in the circuit rises excessively, the relay automatically cuts the circuit to ensure device safety.
Low Cost: Thermal relays, especially bimetallic models, are cost-effective. This makes them common in small to medium-sized businesses and residential applications.
Easy Installation and Use: Installing thermal relays is usually simple and does not require special expertise. This provides an advantage in terms of time and cost during electrical circuit installations.
Slow Response Time: Bimetallic thermal relays may not respond quickly to sudden increases in electric current. This increases the possibility of short-term overcurrent damaging devices.
Provides Only Thermal Protection: Traditional bimetallic thermal relays offer protection only against heat. Therefore, they may be insufficient for some applications. Especially for devices requiring fast response, this type of relay does not provide adequate protection.
The use of thermal relays is widespread and anticipated in almost every sector. Although they are intensively used in industrial environments, they can also be found in many areas ranging from home electricity to automotive.
Industrial Motor Protection: One of the most common areas of use is the protection of industrial motors. Motors used in large factories and production facilities draw high current continuously. These motors are at risk of overload. Thermal relays protect these motors from situations such as overload and short circuits, extending the motor's lifespan.
Automotive Sector: Thermal relays are also used in the automotive industry to protect motors and electrical circuits. The complex electronic systems in modern vehicles are protected against overcurrent and short circuits. This ensures the vehicle operates safely.
Home and Building Electricity: Thermal relays are used in home electrical systems. These relays provide protection against overcurrent and overload situations. Devices with high power consumption, such as air conditioners and refrigerators, can be damaged under overcurrent conditions. Thermal relays are used to ensure these devices operate safely.