MPC555LFMZP40 are key devices in electrical protection systems designed to protect circuits from overload conditions. This automatic protection measure is used in a variety of applications to extend the life of electrical equipment by preventing failures caused by overheating.
What Is a Thermal Relay?
MPC555LFMZP40 is a protection device that uses thermal effects to realize circuit control. It is mainly composed of bimetallic strip, heating element and contact system.
Thermal relay is widely used in motors and other electrical equipment for overload protection. This relay has the advantages of simple structure, high reliability and easy maintenance.
Working Principle
MPC555LFMZP40 generate heat by passing current through the heating element, causing the bimetallic strip to deform, thereby driving the contact system to operate. When the deformation reaches a certain distance, the current is too large or the duration is too long, and the heat accumulation causes the bimetallic strip to bend to a certain extent, the contactor loses power, and the main circuit is disconnected, realizing the overload protection of the motor.
Structure
The thermal relay consists of a heating element, a bimetallic strip, contacts and a set of transmission and adjustment mechanisms. The heating element is a resistance wire with a low resistance value, which is connected in series in the main circuit of the motor to be protected. When current passes through, the heating element generates heat and transfers it to the bimetallic strip. The bimetallic strip is composed of two metal strips with different thermal expansion coefficients. The thermal expansion coefficient of the lower metal strip is larger, while the thermal expansion coefficient of the upper metal strip is smaller.
Due to the difference in thermal expansion coefficients, when the bimetallic strip is bent by heat, it will push the contact system to make it operate, thereby cutting off or connecting the circuit to achieve motor protection. The transmission and adjustment mechanism is used to accurately adjust the action time and current range of the thermal relay to meet different protection requirements.
Function
In addition to overload protection, thermal relays also have functions such as delay protection, automatic reset and temperature compensation.
It has a certain delay characteristic, which means it will not act when the motor is overloaded for a short time, but will act when it is overloaded continuously. This delay protection function can prevent the motor from tripping frequently due to instantaneous overload or excessive starting current.
Some thermal relays also have an automatic reset function. When the thermal relay disconnects the circuit due to overload action, the motor cools down, and the thermal relay automatically resets and reconnects the circuit to resume operation of the motor.
Moreover, the thermal relay is protected by the thermal expansion characteristics of the bimetallic strip, and can adapt to changes in ambient temperature and make corresponding adjustments.
How to Install the Thermal Overload Relay?
The direction in which a thermal relay is mounted can significantly affect its performance. If the heating element is located below the bimetallic strip, the strip heats up faster and the relay trips more quickly. Conversely, if the heating element is located next to the strip, the strip heats up more slowly, delaying the relay's response. For this reason, it is usually mounted below other components, at least 50 mm away from them, to avoid thermal interference.
The ambient temperature around the thermal relay is also important. Thermal relays without temperature compensation should be installed in an environment with minimal temperature differences. For relays with temperature compensation, the installation can accommodate some temperature variations, but it is best to minimize the effects of ambient temperature variations.
Also, carefully select the wires that connect the thermal relay. If the wires are too thin, they will heat up and transfer additional heat to the bimetallic strip, causing the relay to trip prematurely. On the other hand, if the wires are too thick, they may not transfer enough heat, delaying the relay's response. It is recommended to use wires with a cross-sectional area as specified in the relay manual or as close as possible.
Maintenance Matters
After tripping, a thermal relay requires a reset period. Automatic reset should complete within 5 minutes, while manual reset should be performed after 2 minutes.
Inspect the heating element and bimetal strip for deformation following a short circuit. Adjust if necessary, but do not remove the components.
Check for overheating, unusual smells, discharge phenomena, loose screws, poor connections, and surface damage every week.
Clean the relay, inspect and repair components, test insulation resistance (should be greater than 1 MΩ), and conduct operational checks. Avoid unnecessary adjustments to screws, except for wiring screws.
Regularly inspect electrical connections for looseness and avoid bending the bimetal strip during maintenance.
FAQs
What factors affect the performance of a thermal relay?
The installation direction, ambient temperature, and the thickness of the connecting wires all affect the performance of a thermal relay.
What materials are typically used in the construction of a thermal relay?
Thermal relays typically use a resistive heating element, a bimetallic strip, and other high thermal expansion materials such as beryllium copper, silver alloys, and gold alloys.