System and method for preventing hydraulic steel pulling weakness in a separating roller table

Abstract

The application discloses a method for preventing hydraulic steel pulling from being weak on a steel separating roller, relates to the field of steel separating, and solves the technical problem that sticking of contacts of an existing intermediate relay can cause slow and weak action of a steel pulling claw. The system comprises a control circuit for controlling each intermediate relay and a main circuit for controlling the intermediate relay in an action process according to the corresponding control circuit. The application further discloses a system for preventing hydraulic steel pulling from being weak on a steel separating roller. The application can prevent the sticking of a single contact and the situation that actual action is not completely stopped.

Description

Technical Field

[0001] This invention relates to the field of steel separation, and more specifically, to a system and method for preventing the hydraulic steel pulling process from being ineffective on a steel separation roller conveyor. Background Technology

[0002] like Figure 1 As shown, the existing technical situation is as follows: In existing steel rolling mills, the double-high-speed wire rod separating rollers use a hydraulic system to separate steel. The billets from the single roughing mill line are separated into two lines on the separating rollers. There are a total of four commands: first-line steel-pulling claw rises, first-line steel-pulling claw falls, second-line steel-pulling claw rises, and second-line steel-pulling claw falls. These four commands are controlled by four intermediate relays: the first-line steel-pulling claw rises is controlled by the first-line rise intermediate relay, the first-line steel-pulling claw falls by the first-line fall intermediate relay, the second-line steel-pulling claw rises by the second-line rise intermediate relay, and the second-line steel-pulling claw falls by the second-line fall intermediate relay.

[0003] The power supply to the intermediate relay coil when one wire is pulled up is controlled by the first intermediate relay; the power supply to the intermediate relay coil when one wire is dropped is controlled by the second intermediate relay; the power supply to the intermediate relay coil when two wires are pulled up is controlled by the third intermediate relay; and the power supply to the intermediate relay coil when two wires are dropped is controlled by the fourth intermediate relay.

[0004] Under current technology, after the four actions are commanded, the contacts of the intermediate relays are prone to sticking together, causing the actual action to not be completely stopped. When the valve platform continues to operate in reverse, the valve core's position becomes uncertain under the combined action of both directions, resulting in slow and weak movement of the steel claw. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a system for preventing the hydraulic steel pulling of steel from being weak, which addresses the shortcomings of the existing technology. This system solves the technical problem that the contacts of the existing intermediate relays are prone to sticking, which leads to slow and weak action of the steel pulling claw.

[0006] The present invention discloses a method for preventing the hydraulic steel pulling of a steel separating roller conveyor from being ineffective. The method involves connecting a redundant relay that operates synchronously with the intermediate relay in the control circuit of the first-line steel pulling claw and the second-line steel pulling claw.

[0007] As a further improvement, a freewheeling diode is connected between the two ends of the intermediate relay coil of the main circuit of the first-line steel claw and the second-line steel claw.

[0008] According to the above-mentioned steel separating roller way hydraulic steel pulling powerless prevention system, the system comprises a control circuit and a main circuit, the control circuit comprises a first control sub-circuit, a second control sub-circuit, a third control sub-circuit and a fourth control sub-circuit.

[0009] The main circuit comprises a first sub-circuit, a second sub-circuit, a third sub-circuit and a fourth sub-circuit.

[0010] Further improvement, the first control sub-circuit comprises a first intermediate relay and a fifth intermediate relay, the coil of the first intermediate relay and the coil of the fifth intermediate relay are connected in parallel, and the coil of the first intermediate relay is connected with the controller.

[0011] Further, the first sub-circuit comprises a sixth intermediate relay, a second intermediate relay and a one-line pulling-up intermediate relay, one end of the coil of the one-line pulling-up intermediate relay is connected with the power supply through the normally open contact of the fifth intermediate relay and the normally open contact of the first intermediate relay connected in series, the other end of the coil of the one-line pulling-up intermediate relay is connected with the power supply through the normally closed contact of the sixth intermediate relay and the normally closed contact of the second intermediate relay connected in series, and the two ends of the coil of the one-line pulling-up intermediate relay are connected with a first freewheeling diode.

[0012] Further, the second control sub-circuit comprises a second intermediate relay and a sixth intermediate relay, the coil of the second intermediate relay and the coil of the sixth intermediate relay are connected in parallel, and the coil of the second intermediate relay is connected with the controller.

[0013] Further, the second sub-circuit comprises a fifth intermediate relay, a first intermediate relay and a one-line falling-down intermediate relay, one end of the coil of the one-line falling-down intermediate relay is connected with the power supply through the normally open contact of the sixth intermediate relay and the normally open contact of the second intermediate relay connected in series, the other end of the coil of the one-line falling-down intermediate relay is connected with the power supply through the normally closed contact of the fifth intermediate relay and the normally closed contact of the first intermediate relay connected in series, and the two ends of the coil of the one-line falling-down intermediate relay are connected with a second freewheeling diode.

[0014] Further, the third control sub-circuit comprises a third intermediate relay and a seventh intermediate relay, the coil of the third intermediate relay and the coil of the seventh intermediate relay are connected in parallel, and the coil of the third intermediate relay is connected with the controller.

[0015] Further, the third sub-circuit further comprises an eighth intermediate relay, a fourth intermediate relay and a two-wire pull-up intermediate relay, one end of the coil of the two-wire pull-up intermediate relay is connected with the power supply through the normally open contact of the seventh intermediate relay and the normally open contact of the third intermediate relay connected in series, the other end of the coil of the two-wire pull-up intermediate relay is connected with the power supply through the normally closed contact of the eighth intermediate relay and the normally closed contact of the fourth intermediate relay connected in series, and the two ends of the coil of the two-wire pull-up intermediate relay are connected with a third freewheeling diode.

[0016] Further, the fourth control sub-circuit comprises a fourth intermediate relay and an eighth intermediate relay, the coil of the fourth intermediate relay and the coil of the eighth intermediate relay are connected in parallel, and the coil of the fourth intermediate relay is connected with the controller.

[0017] The fourth sub-circuit comprises a seventh intermediate relay, a third intermediate relay and a two-wire drop intermediate relay, one end of the coil of the two-wire drop intermediate relay is connected with the power supply through the normally open contact of the eighth intermediate relay and the normally open contact of the fourth intermediate relay connected in series, the other end of the coil of the two-wire drop intermediate relay is connected with the power supply through the normally closed contact of the seventh intermediate relay and the normally closed contact of the third intermediate relay connected in series, and the two ends of the coil of the two-wire drop intermediate relay are connected with a fourth freewheeling diode.

[0018] Advantages

[0019] The present application has the advantages that:

[0020] 1. The present application sets control circuit and main circuit, on the basis of the original single intermediate relay and intermediate relay contact control in each action process, adds intermediate relay coil and intermediate relay contact, adopts normally open and normally closed contact interlocking structure, can prevent single contact from sticking, and avoids the situation that actual action is not completely stopped.

[0021] 2. The present application connects a freewheeling diode between the two ends of the coil of the intermediate relay in the main circuit, to protect the contact of the intermediate relay from being burned by electric spark. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is an electrical schematic diagram of the existing control circuit and main circuit;

[0023] Figure 2 It is an electrical schematic diagram of the first control sub-circuit of the present application;

[0024] Figure 3 It is an electrical schematic diagram of the second control sub-circuit of the present application;

[0025] Figure 4 The third control sub-circuit electrical schematic diagram of the present application;

[0026] Figure 5 The fourth control sub-circuit electrical schematic diagram of the present application.

[0027] Wherein: KA1 - one line pull-up intermediate relay, KA2 - one line drop intermediate relay, KA3 - two line pull-up intermediate relay, KA4 - two line drop intermediate relay, KM1 - first intermediate relay, KM2 - second intermediate relay, KM3 - third intermediate relay, KM4 - fourth intermediate relay, KM5 - fifth intermediate relay, KM6 - sixth intermediate relay, KM7 - seventh intermediate relay, KM8 - eighth intermediate relay, D - freewheeling diode. DETAILED DESCRIPTION

[0028] The present application is further described below in conjunction with embodiments, but does not constitute any limitation to the present application, and any limited number of modifications made by anyone within the scope of the claims of the present application is still within the scope of the claims of the present application.

[0029] Reference Figures 2-5 , a steel separator roller prevents hydraulic steel pulling weak system, the system includes control circuit and main circuit, control circuit includes first control sub-circuit, second control sub-circuit, third control sub-circuit and fourth control sub-circuit.

[0030] As Figure 2 shown, the first control sub-circuit includes the coil of the first intermediate relay KM1 and the coil of the fifth intermediate relay KM5, the coil of the first intermediate relay KM1 and the coil of the fifth intermediate relay KM5 are connected in parallel, and the coil of the first intermediate relay KM1 is connected with the controller.

[0031] As Figure 3 shown, the second control sub-circuit includes the coil of the second intermediate relay KM2 and the coil of the sixth intermediate relay KM6, the coil of the second intermediate relay KM2 and the coil of the sixth intermediate relay KM6 are connected in parallel, and the coil of the second intermediate relay KM2 is connected with the controller.

[0032] As Figure 4 shown, the third control sub-circuit includes the coil of the third intermediate relay KM3 and the coil of the seventh intermediate relay KM7, the coil of the third intermediate relay KM3 and the coil of the seventh intermediate relay KM7 are connected in parallel, and the coil of the third intermediate relay KM3 is connected with the controller.

[0033] As Figure 5As shown, the fourth control sub-circuit includes the coil of the fourth intermediate relay KM4 and the coil of the eighth intermediate relay KM8. The coils of the fourth intermediate relay KM4 and the eighth intermediate relay KM8 are connected in parallel. The coil of the fourth intermediate relay KM4 is connected to the controller.

[0034] like Figures 2-5 As shown, the main circuit is used to control the intermediate relays during operation according to the corresponding control circuit. The main circuit includes a first sub-circuit, a second sub-circuit, a third sub-circuit, and a fourth sub-circuit.

[0035] like Figure 2 As shown, the first sub-circuit includes the normally open contact of the fifth intermediate relay KM5, the normally open contact of the first intermediate relay KM1, the normally closed contact of the sixth intermediate relay KM6, the normally closed contact of the second intermediate relay KM2, and the coil of the first-line pull-out intermediate relay KA1. One end of the coil of the first-line pull-out intermediate relay KA1 is connected to the power supply through the normally open contacts of the fifth intermediate relay KM5 and the first intermediate relay KM1, which are connected in series. The other end of the coil of the first-line pull-out intermediate relay KA1 is connected to the power supply through the normally closed contacts of the sixth intermediate relay KM6 and the second intermediate relay KM2, which are connected in series. A first freewheeling diode D1 is connected between the two ends of the coil of the first-line pull-out intermediate relay KA1.

[0036] like Figure 3 As shown, the second sub-circuit includes the normally open contact of the sixth intermediate relay KM6, the normally open contact of the second intermediate relay KM2, the normally closed contact of the fifth intermediate relay KM5, the normally closed contact of the first intermediate relay KM1, and the coil of the drop-down intermediate relay KA2. One end of the coil of the drop-down intermediate relay KA2 is connected to the power supply through the normally open contacts of the sixth intermediate relay KM6 and the second intermediate relay KM2, which are connected in series. The other end of the coil of the drop-down intermediate relay KA2 is connected to the power supply through the normally closed contacts of the fifth intermediate relay KM5 and the first intermediate relay KM1, which are connected in series. A second freewheeling diode D2 is connected between the two ends of the coil of the drop-down intermediate relay KA2.

[0037] like Figure 4As shown, the third sub-circuit includes the normally open contact of the seventh intermediate relay KM7, the normally open contact of the third intermediate relay KM3, the normally closed contact of the eighth intermediate relay KM8, the normally closed contact of the fourth intermediate relay KM4, and the coil of the two-wire disconnect intermediate relay KA3. One end of the coil of the two-wire disconnect intermediate relay KA3 is connected to the power supply through the normally open contacts of the seventh intermediate relay KM7 and the third intermediate relay KM3 connected in series. The other end of the coil of the two-wire disconnect intermediate relay KA3 is connected to the power supply through the normally closed contacts of the eighth intermediate relay KM8 and the fourth intermediate relay KM4 connected in series. A third freewheeling diode D3 is connected between the two ends of the coil of the two-wire disconnect intermediate relay KA3.

[0038] like Figure 5 As shown, the fourth sub-circuit includes the normally open contact of the eighth intermediate relay KM8, the normally open contact of the fourth intermediate relay KM4, the normally closed contact of the seventh intermediate relay KM7, the normally closed contact of the third intermediate relay KM3, and the coil of the two-wire drop-down intermediate relay KA4. One end of the coil of the two-wire drop-down intermediate relay KA4 is connected to the power supply through the normally open contacts of the eighth intermediate relay KM8 and the fourth intermediate relay KM4 connected in series. The other end of the coil of the two-wire drop-down intermediate relay KA4 is connected to the power supply through the normally closed contacts of the seventh intermediate relay KM7 and the third intermediate relay KM3 connected in series. A fourth freewheeling diode D4 is connected between the two ends of the coil of the two-wire drop-down intermediate relay KA4. The freewheeling diode is used to protect the intermediate relay contacts from being burned by electric sparks during operation.

[0039] The power supply voltage is 24V.

[0040] A method for preventing insufficient hydraulic steel pulling in a steel separating roller conveyor, as described above.

[0041] Step 1: Identify the reasons for the current lack of power in hydraulic steel pulling.

[0042] By continuously monitoring the operation of the solenoid valve with indicator light plug on the hydraulic valve platform through video surveillance cameras, when the steel pulling claw on the steel separating roller conveyor was unable to pull the steel, the video surveillance of the hydraulic valve platform was reviewed. It was found that before the steel pulling claw was raised, the solenoid valve with indicator light plug on the steel pulling claw was in a slightly energized and lit state when the steel pulling claw was lowered.

[0043] Slightly powered indicator light status: The circuit is not completely disconnected, and the device still has a certain voltage, which is less than the normal operating voltage.

[0044] Step 2: Abnormal operation of the hydraulic valve platform leads to insufficient hydraulic oil flow.

[0045] Through the playback monitoring, it can be found that the double-sided electromagnetic valve coil of the electro-hydraulic reversing valve is electrified, thereby causing the valve core of the hydraulic valve table to be weak in action, and further causing the hydraulic oil flow of the oil way of the steel pulling claw to be small and the pressure to be insufficient, and finally causing the steel pulling action to be slow and weak. Through analysis, the reason for the above situation is that after the two sides of the electro-hydraulic reversing valve are electrified, the valve core is pushed by the opposite electromagnetic force at both ends, causing the valve core to be out of control.

[0046] Electro-hydraulic reversing valve: The electro-hydraulic reversing valve is a common fluid control element, which can change the direction of fluid passing through the valve according to the electric signal, so as to control the flow rate, flow and pressure of the fluid.

[0047] Step three, the double-sided coil of the hydraulic valve table is electrified at the same time, and the position of the valve core of the hydraulic valve table is uncertain.

[0048] The valve core is pushed by the opposite electromagnetic force at both ends, causing the valve core to be out of control, and the position of the valve core of the valve table is uncertain, which finally causes the steel pulling claw of the steel roller to be slow and weak in action.

[0049] Step four, the intermediate relay contact is stuck in the falling of the steel pulling claw.

[0050] When the online coil of the falling intermediate relay KA2 of the steel pulling claw falls down, the normally open contact of the second intermediate relay KM2 will break the circuit and make the falling steel pulling claw fall back. However, due to the electric spark and arc generated during the use of the contact, the contact is ablated and intermittently stuck. After the contact is stuck, the circuit is still conducted, and there may be oxides on the contact, thereby increasing the resistance and conducting part of the voltage, so that the steel pulling claw that has fallen to the bottom is continuously electrified and kept in the falling state. At the same time, the electromagnetic iron in the under-voltage state is easy to cause the coil to heat and burn out.

[0051] Step five, design and draw the circuit.

[0052] According to the requirement of preventing the influence of the mis-conduction caused by the sticking of the contact, the number of normally open contacts of the intermediate relay is increased in the design of the circuit to strengthen the feature, and the normally open and normally closed contacts are interlocked according to the principle of relative action, so as to further enhance the ability to prevent the mis-conduction caused by the sticking of the contact.

[0053] Step six, according to the circuit diagram, four intermediate relays are added.

[0054] Reference Figures 2-5 The installation of the components in the electric cabinet is completed, the new and old intermediate relays are installed side by side on the original relays, the control mode of parallel connection of the coils of the two intermediate relays is adopted, and the synchronous action of the two intermediate relays is controlled by the PLC.

[0055] Step seven, according to the circuit diagram, the wiring is completed.

[0056] Referring to Figures 2-5 After the installation of the components in the electrical cabinet is completed, wiring is performed, and during the operation process, one output terminal of the intermediate relay is connected in series with two normally open contacts, and the other output terminal is connected in series with two normally closed contacts for interlocking, and a continuous current diode D is connected in parallel with the electromagnetic valve coil at the output terminal for protecting the intermediate relay contacts from being burned by electric sparks.

[0057] Step eight, test completion, trial run is normal.

[0058] After the equipment modification is completed, the steel roll separating roll way puller hydraulic station needs to be started, and the starting authority is punched to the local mode, and the operation is completed on site:

[0059] When the one-line puller lifting action is needed, the coil of the first intermediate relay KM1 and the coil of the fifth intermediate relay KM5 are energized;

[0060] After the coil of the first intermediate relay KM1 and the coil of the fifth intermediate relay KM5 are energized, the normally open contact of the fifth intermediate relay KM5 and the normally open contact of the first intermediate relay KM1 are closed at the same time, and the normally closed contact of the fifth intermediate relay KM5 and the normally closed contact of the first intermediate relay KM1 are opened at the same time, the coil of the one-line puller lifting intermediate relay KA1 is energized, and the one-line puller lifting action is started.

[0061] When the one-line puller lowering action is needed, the coil of the second intermediate relay KM2 and the coil of the sixth intermediate relay KM6 are energized;

[0062] After the coil of the second intermediate relay KM2 and the coil of the sixth intermediate relay KM6 are energized, the normally open contact of the second intermediate relay KM2 and the normally open contact of the sixth intermediate relay KM6 are closed at the same time, and the normally closed contact of the second intermediate relay KM2 and the normally closed contact of the sixth intermediate relay KM6 are opened at the same time, the coil of the one-line puller lowering intermediate relay KA2 is energized, and the one-line puller lowering action is started.

[0063] When the two-line puller lifting action is needed, the coil of the third intermediate relay KM3 and the coil of the seventh intermediate relay KM7 are energized;

[0064] After the coil of the third intermediate relay KM3 and the coil of the seventh intermediate relay KM7 are energized, the normally open contact of the third intermediate relay KM3 and the normally open contact of the seventh intermediate relay KM7 are closed at the same time, and the normally closed contact of the third intermediate relay KM3 and the normally closed contact of the seventh intermediate relay KM7 are opened at the same time, the coil of the two-line puller lifting intermediate relay KA3 is energized, and the two-line puller lifting action is started.

[0065] When the second line puller pawl falling action is needed, the coil of the fourth intermediate relay KM4 and the coil of the eighth intermediate relay KM8 are energized;

[0066] When the coil of the fourth intermediate relay KM4 and the coil of the eighth intermediate relay KM8 are energized, the normally open contact of the fourth intermediate relay KM4 and the normally open contact of the eighth intermediate relay KM8 are closed at the same time, the normally closed contact of the fourth intermediate relay KM4 and the normally closed contact of the eighth intermediate relay KM8 are opened at the same time, the coil of the second line falling intermediate relay KA4 is energized, and the second line puller pawl falling action is started.

[0067] Finally, it is tested whether the puller pawl of the first line and the puller pawl of the second line are normally pulled up and fallen down, and whether the intermediate relay contact produces obvious electric spark and other arc phenomena.

[0068] The above only describes the preferred embodiments of the present application. It should be noted that for those skilled in the art, without departing from the structure of the present application, several modifications and improvements can be made, which will not affect the effect of the present application and the practicality of the patent.

Claims

1. A system for preventing hydraulic steel pulling weakness in a separate roller table, characterized by A redundant relay is connected in parallel with the intermediate relay of the control circuit of the one-line and two-line draw-off claws and is synchronous with the intermediate relay; A freewheeling diode is connected between the two ends of the coil of the intermediate relay of the main circuit of the one-line and two-line draw-off claws; The system comprises a control circuit and a main circuit, the control circuit comprises a first control sub-circuit, a second control sub-circuit, a third control sub-circuit and a fourth control sub-circuit; The main circuit comprises a first sub-circuit, a second sub-circuit, a third sub-circuit and a fourth sub-circuit; The first control sub-circuit comprises a first intermediate relay (KM1) and a fifth intermediate relay (KM5), the coil of the first intermediate relay (KM1) and the coil of the fifth intermediate relay (KM5) are connected in parallel, and the coil of the first intermediate relay (KM1) is connected with the controller. The first sub-circuit comprises a sixth intermediate relay (KM6), a second intermediate relay (KM2) and a one-line draw-off intermediate relay (KA1), one end of the coil of the one-line draw-off intermediate relay (KA1) is connected with the power supply through the normally open contact of the fifth intermediate relay (KM5) and the normally open contact of the first intermediate relay (KM1) connected in series, the other end of the coil of the one-line draw-off intermediate relay (KA1) is connected with the power supply through the normally closed contact of the sixth intermediate relay (KM6) and the normally closed contact of the second intermediate relay (KM2) connected in series, and a first freewheeling diode (D1) is connected between the two ends of the coil of the one-line draw-off intermediate relay (KA1).

2. The system for preventing hydraulic steel pulling forcelessness of a steel separating roller bed according to claim 1, characterized in that, The second control sub-circuit comprises a second intermediate relay (KM2) and a sixth intermediate relay, the coil of the second intermediate relay (KM2) and the coil of the sixth intermediate relay (KM6) are connected in parallel, and the coil of the second intermediate relay (KM2) is connected with the controller.

3. The system for preventing hydraulic steel pulling forcelessness of a steel separating roller bed according to claim 2, characterized in that, The second sub-circuit comprises a fifth intermediate relay (KM5), a first intermediate relay (KM1) and a one-line drop intermediate relay (KA2), one end of the coil of the one-line drop intermediate relay (KA2) is connected with the power supply through the normally open contact of the sixth intermediate relay (KM6) and the normally open contact of the second intermediate relay (KM2) connected in series, the other end of the coil of the one-line drop intermediate relay (KA2) is connected with the power supply through the normally closed contact of the fifth intermediate relay (KM5) and the normally closed contact of the first intermediate relay (KM1) connected in series, and a second freewheeling diode (D2) is connected between the two ends of the coil of the one-line drop intermediate relay (KA2).

4. The system for preventing hydraulic steel pulling forcelessness of a steel separating roller bed according to claim 1, wherein The third control sub-circuit comprises a third intermediate relay (KM3) and a seventh intermediate relay (KM7), the coil of the third intermediate relay (KM3) and the coil of the seventh intermediate relay (KM7) are connected in parallel, and the coil of the third intermediate relay (KM3) is connected with the controller.

5. The system for preventing hydraulic steel pulling forcelessness of a steel separating roller bed according to claim 4, wherein The third sub-circuit includes eighth intermediate relay (KM8), fourth intermediate relay (KM4) and two-wire pull-up intermediate relay (KA3), one end of the coil of the two-wire pull-up intermediate relay (KA3) is connected with the power supply through the normally open contact of the seventh intermediate relay (KM7) and the normally open contact of the third intermediate relay (KM3) connected in series, the other end of the coil of the two-wire pull-up intermediate relay (KA3) is connected with the power supply through the normally closed contact of the eighth intermediate relay (KM8) and the normally closed contact of the fourth intermediate relay (KM4) connected in series, and the both ends of the coil of the two-wire pull-up intermediate relay (KA3) are connected with the third freewheeling diode (D3).

6. A system for preventing hydraulic steel pulling weakness in a separating roller bed according to claim 1, characterized in that, The fourth control sub-circuit includes fourth intermediate relay (KM4) and eighth intermediate relay (KM8), the coil of the fourth intermediate relay (KM4) and the coil of the eighth intermediate relay (KM8) are connected in parallel, and the coil of the fourth intermediate relay (KM4) is connected with the controller; The fourth sub-circuit includes seventh intermediate relay (KM7), third intermediate relay (KM3) and two-wire drop intermediate relay (KA4), one end of the coil of the two-wire drop intermediate relay (KA4) is connected with the power supply through the normally open contact of the eighth intermediate relay (KM8) and the normally open contact of the fourth intermediate relay (KM4) connected in series, the other end of the coil of the two-wire drop intermediate relay (KA4) is connected with the power supply through the normally closed contact of the seventh intermediate relay (KM7) and the normally closed contact of the third intermediate relay (KM3) connected in series, and the both ends of the coil of the two-wire drop intermediate relay (KA4) are connected with the fourth freewheeling diode (D4).

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