What is a thermal relay and why you need it ?

design

begin with, that will tell you what is in the thermal relay.The basis of Tatarstan laid phenomenon described physical law Joule:

amount of heat in the area of ​​electrical circuit is proportional to the square of the current and the resistance of this area.

This phenomenon has been successfully used in the thermal release.Short circuit section acting as a thermal radiator, coil wound on the insulator.All the current passing through the electrical machine passing through the plot.Directly next to the spiral is bimetallic strip that bends when heated and acts on the contact group.The plate consists of two dissimilar metals having different coefficient of expansion upon heating, combined into one element.

The photo below shows a section of the current machine.Through conductors passes through three phases of power to the electric motor.The winding heating is located on top of a bimetallic plate in order to reduce false alarms from external influence.The plates abut the movable bar which pushes the release mechanism.Above is the spring of the current controller settings to fine-tune the limits of operation, and two groups of contacts (NO open and closed NC).

The principle of

How does the thermal relay, you know, and now we go further and explain how the device works.As we have said earlier, RT protects the motor against continuous overload.

Each motor has a rating plate, which is specified rated operating current.There are mechanisms in which the operating current can be exceeded as during start-up, and in the working process.With long-term impact of such overload, overheat the winding insulation breakdown and failure of the engine.

This thermal overload relay is designed to act on the control circuit by turning off the circuit, contact opening or supply staff on duty warning signal closing the contacts.The device is installed after the start of the contactor in the power circuit to the motor in order to control the current passing.

parameters Installation is made in a big way on the rated motor current, the value of 10-20%, according to the passport data.Machine shutdown does not occur immediately, but after a certain time.It depends on the ambient temperature and overcurrent, and can vary from 5 to 20 minutes.Improperly selected parameter will lead to a false alarm or neglect overloading and equipment failure.

graphical device tag on the scheme in accordance with GOST:

more to learn in detail about the structure of the thermal relay and how it works, you can by viewing this video:

Appointment

Immediately I would say that there are different kinds and types of thermal relays and thus the area of ​​application of each classification of its own.Briefly talk about the appointment of the main varieties of devices.

RTL - three-phase, is designed to protect the motor against overload, phase imbalance, excessive starting or jamming of the rotor.They are attached to the contacts PML starters or as a standalone unit with terminals KRL.

PTT - into three phases, designed to protect the engine from the short-circuited current overload, phase unbalance, rotor jamming and tighten the launch mechanism.It can be attached to the PMA and PME starters, as well as independently installed on the panel.

RTI - protect the motor against overload, phase unbalance, a long start-up and jamming the machine.Three-phase thermal relay, mounted on actuators series KMT and KMI.

TPH - a two-phase relay controls work and start-up mode, a manual reset contacts only, operation of the device is only slightly dependent on the ambient temperature.

three-phase solid-state relays have no moving parts, do not depend on the environment, used in hazardous locations.Monitors load current, acceleration, phase failure, jamming the mechanism.

RTC - control of the temperature probe is happening, located in the electrical cabinet.It is a thermal relay, and controls only one parameter.

RTE - alloy melting relay, electrically conductive wire is made of metal alloy melts at a certain temperature and mechanically breaks the circuit.This thermal switch is integrated directly in the controlled device.

As seen in this article, there are a variety of electrical control of the state, different style and appearance, but equally fulfilling protection of electrical equipment.That's all that I wanted to tell you about the structure, principle of operation and purpose of the thermal relay.We hope the information was useful and interesting for you!

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