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Thermal relay works
PUBLISHER:Shanghai Moye Electric Co.,Ltd””RELEASE TIME:2017/7/13
Thermal relay is a very important member of the relay family, the production of the use of more frequent, has a very important significance. Electrician experts will introduce the work of the so-called thermal overload relay
Thermal heaters in the thermal effect of the heating element should be connected in series to the motor circuit, so that the thermal relay can directly reflect the motor overload current. Thermal relay sensing components, the general use of bimetal. The so-called bimetallic, that is, the two linear expansion coefficient of different pieces of metal to mechanical rolling to form a one. Expansion coefficient known as the active layer, the expansion coefficient of small known as the passive layer. The bimetallic sheet is linearly expanded by heat, and since the linear expansion coefficient of the two layers of metal is different and the two layers of metal are closely bonded together, the bimetal is bent toward the side of the passive layer, and the bimetallic sheet is bent The mechanical force will drive contact action. Common JR36 is the use of this principle.
There are four kinds of bimetallic heating methods, namely, direct heating type, indirect heating type, composite heating type and current transformer heating type. Directly heated by the bimetallic as a heating element, so that the current directly through it; indirect heating element from the resistance wire or tape made around the bimetal and bimetallic insulation; composite heating between the above Between the two ways; current transformer heating element is not directly connected to the heating circuit in series, but connected to the secondary side of the current transformer, this method is more used for large motor current occasions to reduce the heat Component current.
Thermal relay with phase protection
Three-phase motor of a wiring loosened or a fuse fuse, is caused by three-phase asynchronous motor burn one of the main reasons. If the motor is protected by the thermal relay, the current of the other two phases increases as the line is de-energized. Since the line current is equal to the phase current, the current flowing through the motor winding and the current flowing through the thermal relay The same proportion, so the ordinary two-phase or three-phase thermal relay can be protected. If the motor is delta-connected, the phase current and the line current are not equal, the current flowing through the motor winding and the proportion of the current flowing through the thermal relay are different, and the heat element is connected in series with the motor Into the line, according to the rated current of the motor that line current to set, set the value of a larger. When the fault line current reaches the rated current, within the motor windings, the current current of the larger phase of the fault current will exceed the rated phase current, there is the risk of overheating. So ”÷ connection must be used with phase protection of the thermal relay.
Thermal relays with phase-breaking protection add a differential mechanism to the general heat relay and compare the three currents. The principle of the differential phase-failure protection device is shown in Fig. The relay of the thermal relay is changed to a differential mechanism consisting of the upper guide plate 1, the lower guide plate 2 and the lever 5, both of which are connected by a rotary shaft.
At this point the three-phase bimetallic are heated to the left bending, but the bending deflection is not enough, so the lower guide to the left to move a short distance, the relay does not move. Figure 3c is the case where the three phases are overloaded at the same time, and the three-phase bimetal is bent at the same time to push the lower guide plate 2 to the left, and the normally closed contact is immediately led by the lever 5.
Thermal heaters in the thermal effect of the heating element should be connected in series to the motor circuit, so that the thermal relay can directly reflect the motor overload current. Thermal relay sensing components, the general use of bimetal. The so-called bimetallic, that is, the two linear expansion coefficient of different pieces of metal to mechanical rolling to form a one. Expansion coefficient known as the active layer, the expansion coefficient of small known as the passive layer. The bimetallic sheet is linearly expanded by heat, and since the linear expansion coefficient of the two layers of metal is different and the two layers of metal are closely bonded together, the bimetal is bent toward the side of the passive layer, and the bimetallic sheet is bent The mechanical force will drive contact action. Common JR36 is the use of this principle.
There are four kinds of bimetallic heating methods, namely, direct heating type, indirect heating type, composite heating type and current transformer heating type. Directly heated by the bimetallic as a heating element, so that the current directly through it; indirect heating element from the resistance wire or tape made around the bimetal and bimetallic insulation; composite heating between the above Between the two ways; current transformer heating element is not directly connected to the heating circuit in series, but connected to the secondary side of the current transformer, this method is more used for large motor current occasions to reduce the heat Component current.
Thermal relay with phase protection
Three-phase motor of a wiring loosened or a fuse fuse, is caused by three-phase asynchronous motor burn one of the main reasons. If the motor is protected by the thermal relay, the current of the other two phases increases as the line is de-energized. Since the line current is equal to the phase current, the current flowing through the motor winding and the current flowing through the thermal relay The same proportion, so the ordinary two-phase or three-phase thermal relay can be protected. If the motor is delta-connected, the phase current and the line current are not equal, the current flowing through the motor winding and the proportion of the current flowing through the thermal relay are different, and the heat element is connected in series with the motor Into the line, according to the rated current of the motor that line current to set, set the value of a larger. When the fault line current reaches the rated current, within the motor windings, the current current of the larger phase of the fault current will exceed the rated phase current, there is the risk of overheating. So ”÷ connection must be used with phase protection of the thermal relay.
Thermal relays with phase-breaking protection add a differential mechanism to the general heat relay and compare the three currents. The principle of the differential phase-failure protection device is shown in Fig. The relay of the thermal relay is changed to a differential mechanism consisting of the upper guide plate 1, the lower guide plate 2 and the lever 5, both of which are connected by a rotary shaft.
At this point the three-phase bimetallic are heated to the left bending, but the bending deflection is not enough, so the lower guide to the left to move a short distance, the relay does not move. Figure 3c is the case where the three phases are overloaded at the same time, and the three-phase bimetal is bent at the same time to push the lower guide plate 2 to the left, and the normally closed contact is immediately led by the lever 5.