Thermal relays are essential components in various electrical systems as they protect them from overheating and electrical faults. In this article, we will
Electrical systems operate on a specific range of temperatures, and when the temperature exceeds the limit, it can cause damage to the system. Electrical components like motors, transformers, and generators produce heat during their operation. Excess heat can damage the components, causing them to fail. Therefore, it is necessary to protect electrical systems from overheating and electrical faults. Thermal relays are devices that help in preventing such electrical faults.
What are Thermal Relays?
Thermal relays are protective devices used in electrical systems to protect them from overheating and electrical faults. They work on the principle of temperature sensing and act as a switch when the temperature exceeds the predetermined limit. The thermal relay detects the temperature changes in the electrical system and disconnects the power supply to prevent any damage to the components.
How do Thermal Relays Work?
Basic Working Principle
Thermal relays work on the principle of temperature sensing. They consist of a thermal element that detects the temperature changes in the electrical system. When the temperature exceeds the predetermined limit, the thermal element causes the bimetallic strip to bend, which ultimately results in the opening of the contacts of the relay, thereby disconnecting the power supply.
Thermal Element
The thermal element is a device that detects the temperature changes in the electrical system. It is made of materials that have a high coefficient of thermal expansion, such as copper, brass, or aluminum. When the temperature exceeds the predetermined limit, the thermal element expands, causing the bimetallic strip to bend.
Bimetallic Strip
The bimetallic strip is a device made of two different metals that have different coefficients of thermal expansion, such as copper and steel. When the temperature exceeds the predetermined limit, the thermal element causes the bimetallic strip to bend, which ultimately results in the opening of the contacts of the relay, thereby disconnecting the power supply.
Ambient Temperature Compensation
Thermal relays also have an ambient temperature compensation mechanism that helps in adjusting the temperature limits based on the surrounding temperature. The compensation mechanism is essential as the temperature limit of the electrical components depends on the surrounding temperature.
Types of Thermal Relays
There are two types of thermal relays – bi-metallic strip relay and solid-state thermal relay.
Bi-Metallic Strip Relay
The bi-metallic strip relay is the most commonly used type of thermal relay. It consists of a thermal element and a bimetallic strip. When the temperature exceeds the predetermined limit, the thermal element causes the bimetallic strip to bend, which ultimately results in the opening of the contacts of the relay, thereby disconnecting the power supply.
Solid State Thermal Relay
The solid-state thermal relay uses a solid-state sensor instead of a thermal element and a bimetallic strip. The sensor detects the temperature changes in the electrical system and sends a signal to the relay,
Applications of Thermal Relays
Thermal relays are used in various electrical systems, including:
- Motors: Thermal relays protect motors from overheating, which can damage the windings and insulation.
- Transformers: Thermal relays protect transformers from overheating, which can damage the insulation and cause a breakdown.
- Generators: Thermal relays protect generators from overheating, which can cause the winding insulation to fail and lead to a system breakdown.
Advantages and Disadvantages of Thermal Relays
Advantages:
- Thermal relays are cost-effective compared to other protective devices.
- Thermal relays are simple in design and easy to install.
- Thermal relays have a long lifespan and require minimal maintenance.
Disadvantages:
- Thermal relays have a slower response time compared to other protective devices like fuses.
- Thermal relays can be affected by changes in the ambient temperature, which can cause false tripping.
Post time: Mar-31-2023