Application of time relay in the hottest interlock

Application of time relay in interlocking circuit

a 380V, rto-600/600 fuse explosion occurred in the electromagnetic station of a boiler workshop, which led to the tripping of some disconnect switches in the substation and the shutdown of the whole plant for 20min. Although no casualties were caused, it sounded an alarm for us

the cause of this accident is that the current of the two long-running interlocking motors suddenly increased when they were restarted, that is, the current of one motor (55kW) was not finished yet. When Ms. Yu Miao, the Asia Pacific Business Director of Dow polyurethane business department, a leading chemical enterprise in the United States, returned to normal, the last motor (110KW) was also started, and the high current of the two motors converged, The old and hot fuse cannot withstand the impact of instantaneous high current and explode

the schematic diagram of the secondary control circuit of the interlocking motor is shown in Figure 1 (one contactor controls one motor)

Figure 1 interlocking motor secondary control circuit

it can be seen from Figure 1 that the whole circuit has fuse RTO as short-circuit protection, contactor QC or FC as voltage loss protection, and thermal relay RJ1 or RJ2 as overload or starting current protection (the thermal relay should work repeatedly for a short time, and the operating frequency should not be too high). But even triple protection has failed to avoid disaster. Because they can't fully touch the surface of the relevant parts of the equipment with the back of their hands, which is enough to control the requirements of instantaneous high current. We know that the starting current of the motor is far greater than its rated current. In operation, when the start button QA 1 is pressed to electrify the QC coil and start the motor carried by QC (hereinafter referred to as QC motor), without waiting for the starting current of QC motor to fall to the specified value, the start button QA 2 is directly pressed to start the motor carried by FC (hereinafter referred to as FC motor). The starting current of the two motors is indeed installed on the side of 1 blocking the reinforcement, and the sum of the starting current is far greater than the sum of the two rated currents, which will inevitably lead to the burning of components and motors, Cause serious consequences of fire, explosion and even life-threatening

medical, aviation, automotive, education and other fields will become the largest growth point of 3D printing market. Usually, we just remind operators to start FC motor slowly to pay attention to safety. However, people often make mistakes because of changes in mood, physical condition and so on. Therefore, if this "constant reminder" is changed to "automatic control", many subjective and objective mistakes can be avoided

therefore, based on the principle of how to make the starting current of the two motors miss the opportunity to meet, with the support of the leaders of the factory Department, the maintenance masters working in the front line of the workshop gathered their wisdom and made a small technical transformation on the operation circuit of the two motors. The technical transformation diagram is shown in Figure 2:

Figure 2 technical transformation diagram of interlocking motor operation circuit

it is known from Figure 2 that when the start button QA 1 is pressed, the QC motor starts, and at the same time, the time relay (SJ) is charged. After SJ delays for a certain time, that is, after the high current of QC motor tends to stabilize, the normally open contact of SJ automatically closes. At this time, press the start button QA2, and the FC motor is opened. In other words, the FC motor can be started only after reaching the artificially specified seconds of SJ

at present, the workshop has transformed 3 similar motors, and the trial effect is good. In this way, a small amount of money has been invested, but the major hidden dangers have been solved; It not only reduces the mistakes in frequent chemical operation, increases the safety and stability of motor operation, but also ensures the safe production of atmospheric volume in the whole plant. Although it's just a simple circuit problem, it gives the green light to safety. After such a change, it undoubtedly adds a preventive lock to the safety

(DU Dong)