The characteristic is shown in the following figure. The 12s is a single timing device while the 14s uses two bimetal discs to achieve two independent timings. The 15s consists of one, two or three 12s andor 14s controls mounted on a common plate. Thermal motor protection relays contain three bimetal strips together with a trip mechanism in a housing made of insulating material. The bimetal strips are heated by the motor current, causing them to bend and activating the trip mechanism after a certain travel which depends on the currentsetting of the relay.
A bimetallic overload relay consists of a small heater element wired in series with the motor and a bimetal strip that can be used as a trip lever. A wide variety of bimetal disc and ptc combinations are available to provide a broad range of timings. Ct7n bimetallic overload relays, manual or automatic reset. The labeling field of the overload relay may also be written on by hand. Compensated bimetal overload relays provide a constant trip time in ambient temperatures from 20f to 170f for a given heater rating. In figure 2, representative trip curves illustrate the trip time for overload relays with h, e and k heaters.
Thermal overload relay or a bimetallic relay is a 3 phase motor protection relay which protect the motor during over current flow. Thermal overload relay bimetallic relay working function. Compensated bimetal overload relays provide a constant trip time in. The two metals have different thermal expansion characteristics, so the bimetal strip bends at a given rate when heated. Specification for bimetallic overload relays for ac and dc. The relays shall correctly protect the motors even when they are started 15 times max per hour. Overload relays solid state esp200, class 48, 958, 958l and bimetal general. It is an electronic feature that simulates a bimetal relay based on internal measurements. Overload relays solid state esp200, class 48, 958 and 958l. Motor protection is a central task of electrical equipment for machinery.
The thermal overload relays are three pole relays with bimetal tripping elements 1 per pole. A manual test button is provided to test the operation of the overload relay control contacts. E and k type heater elements are applied to bimetal overload relays. The bimetal strip is made of two dissimilar metals bonded together. The ambient compensated bimetal overload relay heater elements are. These overload relays are designed for the protection of motors. This leads to a release of the relay and a change of the contacts switching position. Bimetal overload relays 3ua and 3uc the 3ua 3uc thermal overload relays are suitable for customers from all industries, who want guaranteed optimum inverse time delayed protection of their electrical loads. Working principle of thermal motor protection relay.
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