Fault analysis and treatment of the coil of the ho

Fault analysis and treatment of non release of relay coil

overview

the 2200 cubic meter blast furnace 1nba slag treatment system in iron making plant is an important part of blast furnace production. It turns the fire slag analyzed by the error source of electronic testing machine generated by iron making into water slag, which is transferred to the main slag belt through the transfer station and transported to the slag yard. There are four rubber belts transported as water slag. The following is an example of the non release fault of the relay coil in the electrical control system of the belt conveyor motor

1. The electrical control system of slag and debris left in the jaw of the belt conveyor should be cleared in time

1.1 the principle of the electrical control system of the belt conveyor

the electrical control schematic diagram of the belt conveyor is shown in Figure 1:

Figure 1 the electrical control schematic diagram of the belt conveyor

it can be seen from the schematic diagram: when the coil of relay k12.k13 is closed, the coil of the main contactor K1L of the belt motor can be pulled in, and the belt operates. On the contrary, when the coil of relay K12 or K13 is released, The K1L coil of the main contactor of the belt motor loses power and is released, and the belt stops

1.2 electrical control working condition of belt conveyor

a belt conveyor is about 80 meters long, and a pull rope switch is installed on the left and right of the belt every 20 meters, which is used by the operator to stop the belt operation in time in case of emergency. The emergency stop switch, rope pull switches b11-b18, emergency switches S11 and S12 in Figure 1 are installed in the transfer station at both ends of the site belt, and the other components are installed in the control cabinet of the main control building, with an interval of about 350 meters between the production site and the control cabinet. The coil working voltage of contactor and relay is AC 220V. Relay K12 and K13 coil control live wire uses three cables of a kvvr4 * 1.5 control cable to take the power L (i.e. control live wire) from the control cabinet, which is connected to K12 and K13 coils through the on-site rope pull switch b11-b18 and emergency switch. The power n of relay K12 and K13 coils is taken from the automatic control cabinet

2. Fault phenomenon

when the belt conveyor is running, disconnect the on-site emergency switch S11 or S12, release the coils of relays K12 and K13, release the coil of belt main contactor K1L, and stop the belt. However, when relays K12 and K13 are powered on and closed at the same time, disconnect any one of the pull rope switches b11-b14 on the left side of the site belt, and the coil of relay K12 cannot be released, or disconnect any one of the pull rope switches b15-b18 on the right side of the site belt, and the coil of relay K13 cannot be released, resulting in the coil of belt main contactor K1L cannot be released, and the belt cannot be stopped, which obviously does not meet the requirements of safe production, Without breaking the pull rope switch in case of emergency, the belt will stop quickly to avoid sudden safety and equipment accidents, so as to achieve the purpose of ensuring personal and equipment safety

3. Cause analysis and judgment

3.1 cause of induced voltage

according to the electrical control schematic diagram before the transformation, one end of the coils of relays K12 and K13 is connected to the neutral line (and connected to the zero line of the control cabinet), and the other end is connected to the live wire of the control cabinet through the on-site rope pull switch, and the emergency switch is connected to the live wire of the control cabinet, and the coils of relays K12 and K13 are always closed during normal operation. Because the relay K12 and K13 coil control live wire use the same common control cable, only one cross current power supply is connected to the multi-core cable, and the cable cores are arranged in parallel to produce capacitance effect, it is easy to generate induced voltage on the uncharged core, and the longer the cable length, or the greater the power supply current, the higher the induced voltage will be generated. Because the cable of the belt conveyor control relay is too long, the influence of induced electricity is considered. Relays K12 and K13 adopt miniature relays, which have small tension of release spring and low maintenance voltage after coil is pulled in

the presence of induced voltage can usually be judged by measurement. Disconnect the left pull cord switch. Theoretically, under the condition of confirming that the cable insulation is normal. Use a multimeter to measure both ends of relay K12 coil, and the voltage should be 0V. For example, relay K12 establishes an industrial alliance for intelligent manufacturing standardization in the tire industry. There is voltage at both ends of the coil, so it can be judged that the measured voltage value is caused by induction. During actual operation, after disconnecting the left pull cord switch, 150V voltage was measured at both ends of relay K12 coil. The technical parameters of the relay used indicate that the release voltage of the relay is less than 30% of the rated voltage of the coil, and the rated voltage of the coil is 220V, so the relay will release when the voltage is less than 66.6v. Similarly, when relays K12 and K13 are pulled in, disconnect the right pull cord switch. Measure the voltage at both ends of relay K13 coil to reach about 150V. The coil will still not release

3.2 the cause of transient voltage

is due to the inductive element coil. It is an energy storage element. According to lengzi's law. When the coil changes from one state to another. It always tries to maintain its original state and hinder the increase or decrease of current. The coils of relays K12 and K13 have certain inductance. At the moment of breaking the pull cord switch, the sudden change current in the coil will produce a large back EMF transient voltage. When the transient voltage value is greater than the release voltage of the relay, the coil cannot be released normally

4. Elimination measures

4.1 elimination of induced voltage

aiming at the actual situation of induced voltage on site. We can take the following measures: first. Twisted pair cables can be used for control circuit cables to avoid parallel arrangement of cables, so as to eliminate induced voltage, but the price of twisted pair cables is 2-4 times that of ordinary control cables. Second: when designing electrical control wiring, make the current direction in the cable core different in the same cable. To counteract the induction; Or design the current of different phase sequence to be wired in the same cable from none to one to eliminate the induced voltage. Third: connect a suitable resistance in parallel on the relay coil, usually 2-4 times of the coil resistance value, to absorb the induced voltage. The wiring method is shown in Figure 2 (a)

Figure 2 wiring diagram of energy release circuit

4.2 elimination of transient voltage

generation of transient voltage. Measures can be taken to suppress it. K12 and K13 coils can be provided with an energy release path respectively, so that the stored energy can be consumed in the release circuit. The energy release circuit can be composed of resistance and capacitance. The specific implementation can be slightly different according to different situations. The wiring method is shown in Figure 2 (a) (b). During normal operation, the resistance R consumes a certain power, and the component parameters of R and C can be selected through simple calculation

in addition, the method of shunt varistors at both ends of the coil can also be adopted. Because when the varistor works normally, the resistance is very large and the power consumption is almost zero. When the circuit is disconnected. It can also limit the overvoltage to a safe range. The wiring mode is shown in Figure 3. When selecting a varistor, pay attention to selecting the voltage value and rated power of the varistor

Figure 3 varistor wiring diagram

5. Conclusion

to sum up, the simplest way is to connect a resistor R in parallel at both ends of relay K12 and K13 coils. That is, it can eliminate induced electricity. It can also suppress transient voltage. This method is used in the actual treatment of the non release fault of the relay of the belt conveyor, and satisfactory results are obtained. It can be seen from the analysis. In the power system, reasonable equipment selection and correct wiring are very important. It is hereby sorted out and summarized to provide some successful experience for the improvement of similar equipment. (end)