How does a thermal relay work, with circuit schematic diagrams, please

Thermal relay is an electrical protection element. It is the use of the thermal effect of the current to promote the action mechanism to make the contacts closed or disconnected protection appliances, mainly used for motor overload protection, phase protection, current imbalance protection, and other electrical equipment when the heat state control.

The working principle of the thermal relay

The thermal element made of resistance wire, its resistance value is small, it will be connected in series in the main circuit of the motor, the resistance wire around the bimetal is made of two pieces of different coefficients of linear expansion of the metal sheet pressed together, the left end of the shell with the fixed. When the current through the thermal element exceeds its rated value and overheating, due to the bimetal sheet of the upper layer of the coefficient of thermal expansion is small, while the following large, so that the bimetal sheet is heated upward bending, resulting in buckling plate debuckling, buckling plate in the spring under the tension will be normally closed contacts disconnected. The contacts are connected in series in the motor's control circuit, causing the action coil of the contactor in the control circuit to be de-energized, thus cutting off the motor's main circuit.

The basic structure of a thermal relay

Includes a heating element, a main bimetal, an action mechanism and contact system, and a temperature compensation element.

Types of thermal relays

There are many types of thermal relays, commonly used JR0, JR16, JR16B, JRS and T series.