Device and method for improving reliability of PLC control system of main cooler

Abstract

The invention relates to the technical field of transformer cooling system control, in particular to a device and method for improving the reliability of a main transformer cooler PLC control system, and the device comprises a first power end, cooler relays KM1, KM2, KM3 and KM4, and cooler motors # 1, # 2, # 3 and # 4; the first power supply end, the cooler relay KM1 and the cooler motor # 1 are connected in sequence, the first power supply end, the cooler relay KM2 and the cooler motor # 2 are connected in sequence, the first power supply end, the cooler relay KM3 and the cooler motor # 3 are connected in sequence, and the first power supply end, the cooler relay KM4 and the cooler motor # 4 are connected in sequence. And a control coil of the cooler relay KM1, a control coil of the cooler relay KM2, a control coil of the cooler relay KM3 and a control coil of the cooler relay KM4 are respectively connected with the PLC control system.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer cooling system control, and in particular to a device and method for improving the reliability of a main transformer cooler PLC control system. Background Art

[0002] Transformers are key electrical equipment responsible for the transmission and distribution of electric energy in power systems, and they play a vital role in ensuring the stable and efficient operation of power systems. At present, large-capacity ultra-high voltage transformers are usually equipped with four cooling oil pumps. The control system of the cooling oil pump is mainly built with PLC as the core. The four cooling oil pumps are the main pump, the first auxiliary pump, the second auxiliary pump, and the standby pump. When the main transformer is put into operation, the main pump is started; when the top oil temperature of the main transformer is greater than the temperature setting 1, the first auxiliary pump is started; when the top oil temperature of the main transformer is greater than the temperature setting 2, the second auxiliary pump is started; when the PLC control system determines that any of the above cooling oil pumps is faulty, the standby pump is started. However, this control method that relies on PLC also has potential risks. If the PLC program fails or the PLC power fails, it is easy to cause all running cooling oil pumps to stop working, causing the cooling system to be completely paralyzed. Summary of the invention

[0003] The purpose of the present invention is to provide a device and method for improving the reliability of the PLC control system of the main transformer cooler. By adding power monitoring and PLC operation monitoring relays, the device can automatically start some coolers when the PLC fails and send out an alarm signal. At the same time, by connecting the auxiliary contacts of the cooler motor relay in series, false tripping is prevented. In addition, a segmented delay design is adopted to provide sufficient time for on-site fault handling. These measures significantly improve the reliability and safety of the main transformer cooling system.

[0004] The embodiments of the present invention are implemented by the following technical solutions:

[0005] A device for improving the reliability of a main transformer cooler PLC control system, comprising: a first power supply end, a cooler relay KM1, a cooler relay KM2, a cooler relay KM3, a cooler relay KM4, a cooler motor #1, a cooler motor #2, a cooler motor #3, and a cooler motor #4; the first power supply end, the cooler relay KM1, and the cooler motor #1 are connected in sequence, the first power supply end, the cooler relay KM2, and the cooler motor #2 are connected in sequence, the first power supply end, the cooler relay KM3, and the cooler motor #3 are connected in sequence, the first power supply end, the cooler relay KM4, and the cooler motor #4 are connected in sequence, wherein the control coil of the cooler relay KM1, the control coil of the cooler relay KM2, the control coil of the cooler relay KM3, and the control coil of the cooler relay KM4 are respectively connected to the PLC control system.

[0006] Optionally, it also includes: cooler power switch QF1, cooler power switch QF2, cooler power switch QF3, cooler power switch QF4; the first power supply end is respectively connected to one end of the cooler power switch QF1, one end of the cooler power switch QF2, one end of the cooler power switch QF3, and one end of the cooler power switch QF4, the other end of the cooler power switch QF1, the cooler relay KM1, and the cooler motor #1 are connected in sequence, the other end of the cooler power switch QF2, the cooler relay KM2, and the cooler motor #2 are connected in sequence, the other end of the cooler power switch QF3, the cooler relay KM3, and the cooler motor #3 are connected in sequence, the other end of the cooler power switch QF4, the cooler relay KM4, and the cooler motor #4 are connected in sequence

[0007] Optionally, the PLC control system includes: a second power supply end, a PLC device, a PLC device power supply monitoring relay KV1, a PLC device operation monitoring relay KP1, a cooler delay start-up relay KY1, and a cooler delay start-up relay KY2; the second power supply end, the PLC device power supply monitoring relay KV1, and the PLC device are connected in sequence, the output end of the PLC device is connected to the control coil of the PLC device operation monitoring relay KP1, the normally open contacts of the PLC device operation monitoring relay KP1 are respectively connected to the control coils of the cooler delay start-up relay KY1 and the control coils of the cooler delay start-up relay KY2, the normally closed contacts of the cooler delay start-up relay KY1 and the normally closed contacts of the cooler delay start-up relay KY2 are respectively connected in parallel with the control circuits of the cooler relay KM1 and the control circuits of the cooler relay KM2.

[0008] Optionally, the PLC control system further includes: a PLC device power circuit breaker 1QF; the second power supply terminal, a PLC device power monitoring relay KV1, a PLC device power circuit breaker 1QF, and a PLC device are connected in sequence.

[0009] A method for improving the reliability of a main transformer cooler PLC control system, which is applied to a device for improving the reliability of a main transformer cooler PLC control system, comprises: a normal operation step, a fault operation step and a full stop protection step, wherein the normal operation step is:

[0010] The second power supply terminal supplies power to the PLC control system;

[0011] The PLC device power supply monitoring relay KV1 and the PLC device operation monitoring relay KP1 remain energized;

[0012] The start and stop of cooler relay KM1, cooler relay KM2, cooler relay KM3 and cooler relay KM4 are controlled through the output end of the PLC device to achieve the normal operation of cooler motor #1, cooler motor #2, cooler motor #3 and cooler motor #4.

[0013] Optionally, the fault operation step includes: a second power supply terminal fault operation sub-step and a PLC device fault operation sub-step; wherein the second power supply terminal fault operation sub-step is:

[0014] The PLC device power supply monitoring relay KV1 loses its magnetism, the normally closed contact of the PLC device power supply monitoring relay KV1 closes, and sends an alarm signal;

[0015] The cooler delay input relay KY1 and the cooler delay input relay KY2 lose magnetism, and the normally closed contacts of the cooler delay input relay KY1 and the cooler delay input relay KY2 are closed and connected in parallel to the control circuits of the cooler relay KM1 and the cooler relay KM2 respectively;

[0016] Cooler #1 starts automatically, and after a delay of the set time, cooler #2 starts automatically. The operator receives the alarm signal and manually starts coolers #3 and #4.

[0017] Optionally, the PLC device fault operation sub-step is:

[0018] The PLC device operation monitoring relay KP1 loses its magnetism, the normally closed contact of the PLC device operation monitoring relay KP1 closes, and sends an alarm signal;

[0019] The cooler delay input relay KY1 and the cooler delay input relay KY2 lose magnetism, and the normally closed contacts of the cooler delay input relay KY1 and the cooler delay input relay KY2 are closed and connected in parallel to the control circuits of the cooler relay KM1 and the cooler relay KM2 respectively;

[0020] Cooler #1 starts automatically, and after a delay of the set time, cooler #2 starts automatically. The operator receives the alarm signal and manually starts coolers #3 and #4.

[0021] Optionally, the full stop protection step is specifically as follows:

[0022] It also includes: full stop alarm, main transformer PLC control system delay relay, full stop trip relay KC2, full stop trip relay KC3 and main transformer non-electrical quantity protection device;

[0023] The PLC device is provided with a full stop alarm and a main transformer PLC control system delay relay; the normally open contact of the full stop trip relay KC2 is connected in series with the normally closed contact of the cooler relay KM1, the normally closed contact of the cooler relay KM2, the normally closed contact of the cooler relay KM3, and the normally closed contact of the cooler relay KM4, and is connected to the input end of the main transformer non-electrical quantity protection device; the normally open contact of the full stop trip relay KC3 is connected in series with the normally closed contact of the cooler relay KM1, the normally closed contact of the cooler relay KM2, the normally closed contact of the cooler relay KM3, and the normally closed contact of the cooler relay KM4, and is connected to the input end of the main transformer non-electrical quantity protection device;

[0024] When the cooler full stop condition is detected, and the main transformer is detected to be in operation, the PLC device executes the first stage of delay timing through the main transformer PLC control system delay relay, and detects the status of each cooler and the main transformer temperature at the same time. The cooler full stop condition is: cooler relay KM1, cooler relay KM2, cooler relay KM3, cooler relay KM4 stop running, and the PLC device controls the full stop alarm to execute the alarm; the first stage of delay timing includes: timing stage 1 and timing stage 2, and the timing stage 1 and timing stage 2 are executed in parallel;

[0025] When the first stage of timing is over, the PLC device controls the full stop trip relay KC2 to be energized, and the delay device of the main transformer non-electrical quantity protection device performs the second stage delay timing for 15 minutes. When the timing is over, the main transformer non-electrical quantity protection device immediately performs the tripping operation;

[0026] When the second stage of timing is over, the PLC device controls the full stop trip relay KC3 to be energized, and at the same time detects whether the upper oil temperature of the main transformer reaches the threshold. If so, the main transformer non-electrical protection device executes the second stage of delay timing. When the timing is over, the main transformer non-electrical protection device immediately performs the tripping operation;

[0027] If the cooler full stop condition is untriggered before the total delay ends, the tripping is cancelled, where the total delay is equal to the sum of the first stage delay timing and the second stage delay timing.

[0028] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0029] The embodiment of the present invention automatically starts some coolers and sends out alarm signals when a PLC fails by adding power monitoring and PLC operation monitoring relays. At the same time, by connecting the auxiliary contacts of the cooler motor relay in series, false tripping is prevented. In addition, a segmented delay design is adopted to provide sufficient time for on-site fault handling. These measures significantly improve the reliability and safety of the main transformer cooling system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A circuit schematic diagram of a device for improving the reliability of a main transformer cooler PLC control system provided by an embodiment of the present invention;

[0031] Figure 2 A circuit schematic diagram of a PLC control system provided by an embodiment of the present invention;

[0032] Figure 3 A logic diagram of a cooler full stop tripping provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0034] like Figure 1 As shown, the present invention provides one of the embodiments: a device for improving the reliability of a main variable temperature cooler PLC control system, comprising: a first power supply end, a cooler relay KM1, a cooler relay KM2, a cooler relay KM3, a cooler relay KM4, a cooler motor #1, a cooler motor #2, a cooler motor #3, and a cooler motor #4; the first power supply end, the cooler relay KM1, and the cooler motor #1 are connected in sequence, the first power supply end, the cooler relay KM2, and the cooler motor #2 are connected in sequence, the first power supply end, the cooler relay KM3, and the cooler motor #3 are connected in sequence, the first power supply end, the cooler relay KM4, and the cooler motor #4 are connected in sequence, wherein the control coil of the cooler relay KM1, the control coil of the cooler relay KM2, the control coil of the cooler relay KM3, and the control coil of the cooler relay KM4 are respectively connected to the PLC control system;

[0035] It also includes: cooler power switch QF1, cooler power switch QF2, cooler power switch QF3, cooler power switch QF4; the first power supply end is respectively connected to one end of the cooler power switch QF1, one end of the cooler power switch QF2, one end of the cooler power switch QF3, and one end of the cooler power switch QF4, the other end of the cooler power switch QF1, the cooler relay KM1, and the cooler motor #1 are connected in sequence, the other end of the cooler power switch QF2, the cooler relay KM2, and the cooler motor #2 are connected in sequence, the other end of the cooler power switch QF3, the cooler relay KM3, and the cooler motor #3 are connected in sequence, and the other end of the cooler power switch QF4, the cooler relay KM4, and the cooler motor #4 are connected in sequence.

[0036] In implementation, each phase of a large-capacity transformer is equipped with four coolers. During normal operation, the power circuit breakers of the four coolers are closed, and each cooler is started and stopped automatically by the PLC system.

[0037] like Figure 2 As shown, in this embodiment, the PLC control system includes: a second power supply end, a PLC device, a PLC device power supply monitoring relay KV1, a PLC device operation monitoring relay KP1, a cooler delay input relay KY1, and a cooler delay input relay KY2; the second power supply end, the PLC device power supply monitoring relay KV1, and the PLC device are connected in sequence, the output end of the PLC device is connected to the control coil of the PLC device operation monitoring relay KP1, the normally open contact of the PLC device operation monitoring relay KP1 is respectively connected to the control coil of the cooler delay input relay KY1 and the control coil of the cooler delay input relay KY2, the normally closed contact of the cooler delay input relay KY1 and the normally closed contact of the cooler delay input relay KY2 are respectively connected in parallel with the control circuit of the cooler relay KM1 and the control circuit of the cooler relay KM2;

[0038] The PLC control system further includes: a PLC device power supply circuit breaker 1QF; the second power supply end, a PLC device power supply monitoring relay KV1, a PLC device power supply circuit breaker 1QF, and a PLC device are connected in sequence.

[0039] During implementation, there is a risk of main transformer heavy gas misoperation when three or more main transformer coolers are started simultaneously due to a single-phase main transformer cooler control system PLC device failure or power failure. In order to prevent the cooling oil pump from losing control when the PLC program fails or the PLC power fails, causing all running cooling oil pumps to stop and causing the cooling oil pumps to stop and trip, the #1 and #2 coolers are automatically delayed and started intermittently in the event of a PLC program failure or a PLC power failure. At the same time, the main transformer cooler control system PLC device failure and PLC power failure signals are sent to the monitoring system. After the monitoring system receives the PLC device failure or PLC power failure signal, the operating personnel manually start the #3 and #4 coolers on site according to the temperature of the main transformer, and the cooling effect of the main transformer is comprehensively met through automatic and manual methods.

[0040] In the further application of this embodiment, a power monitoring relay KV1 is added before the PLC device power circuit breaker; #1 cooler delayed start relay KY1 and #2 cooler delayed start relay KY2 are installed in the power supply circuit. When the PLC device power fails, #1 cooler delayed start relay KY1 and #2 cooler delayed start relay KY2 lose magnetism, the normally closed contacts of #1 cooler delayed start relay KY1 and #2 cooler delayed start relay KY2 are closed, #1 cooler motor relay KM1 and #2 cooler motor relay KM2 are energized, and #1 and #2 coolers are started in sequence after different delays (to prevent the gas relay from operating when the coolers are started at the same time, the start interval of #1 and #2 coolers of the same phase is greater than 30s); when the PLC device power fails, the normally closed contact of the power monitoring relay KV1 sends an alarm to the monitoring system. After receiving the alarm signal, the on-site operation and maintenance personnel promptly check and handle the PLC power failure problem and manually start #3 and #4 coolers.

[0041] Install PLC operation monitoring relay KP1 on the PLC device. Set in the PLC program that when the PLC device is operating normally, the PLC device monitoring relay KP1 is always energized, and the #1 cooler delay start relay KY1 and #2 cooler delay start relay KY2 are always energized through the normally open contact of relay KP1; when the PLC device fails, relay KP1 loses magnetism, causing the #1 cooler delay start relay KY1 and #2 cooler delay start relay KY2 to lose magnetism, and the result is consistent with the power failure of the PLC device. After different delays, the #1 and #2 coolers are started in sequence, and at the same time, the normally closed contacts of the PLC device monitoring relay KP1 send an alarm to the monitoring system.

[0042] In another application of this embodiment, Figure 3As shown, in order to prevent the PLC program failure from mistakenly issuing a cooler full stop tripping signal, the normally closed auxiliary contacts of KM1-KM4 of the #1-#4 cooler motor relays are connected in series in the tripping circuit from the main transformer cooler full stop tripping output relay to the main transformer non-electrical quantity, and the contacts of the above 5 relays are connected in series to the main transformer non-electrical quantity protection device using a control cable for cooler full stop tripping.

[0043] Specifically, the full stop protection step is as follows:

[0044] It also includes: full stop alarm, main transformer PLC control system delay relay, full stop trip relay KC2, full stop trip relay KC3 and main transformer non-electrical quantity protection device;

[0045] The PLC device is provided with a full stop alarm and a main transformer PLC control system delay relay; the normally open contact of the full stop trip relay KC2 is connected in series with the normally closed contact of the cooler relay KM1, the normally closed contact of the cooler relay KM2, the normally closed contact of the cooler relay KM3, and the normally closed contact of the cooler relay KM4, and is connected to the input end of the main transformer non-electrical quantity protection device; the normally open contact of the full stop trip relay KC3 is connected in series with the normally closed contact of the cooler relay KM1, the normally closed contact of the cooler relay KM2, the normally closed contact of the cooler relay KM3, and the normally closed contact of the cooler relay KM4, and is connected to the input end of the main transformer non-electrical quantity protection device;

[0046] When the cooler full stop condition is detected, and the main transformer is detected to be in operation, the PLC device executes the first stage of delay timing through the main transformer PLC control system delay relay, and detects the status of each cooler and the main transformer temperature at the same time. The cooler full stop condition is: cooler relay KM1, cooler relay KM2, cooler relay KM3, cooler relay KM4 stop running, and the PLC device controls the full stop alarm to execute the alarm; the first stage of delay timing includes: timing stage 1 and timing stage 2, and the timing stage 1 and timing stage 2 are executed in parallel;

[0047] When the first stage of timing is over, the PLC device controls the full stop trip relay KC2 to be energized, and the delay device of the main transformer non-electrical quantity protection device performs the second stage delay timing for 15 minutes. When the timing is over, the main transformer non-electrical quantity protection device immediately performs the tripping operation;

[0048] When the second stage of timing is over, the PLC device controls the full stop trip relay KC3 to be energized, and at the same time detects whether the upper oil temperature of the main transformer reaches the threshold. If so, the main transformer non-electrical protection device executes the second stage of delay timing. When the timing is over, the main transformer non-electrical protection device immediately performs the tripping operation;

[0049] If the cooler full stop condition is untriggered before the total delay ends, the tripping is cancelled, where the total delay is equal to the sum of the first stage delay timing and the second stage delay timing.

[0050] In summary, by applying this embodiment, when the PLC program fails or the PLC power fails, the #1 and #2 coolers can be automatically started in sequence, and other coolers can be started on site according to the actual situation based on the fault signal, which can avoid the main transformer cooler from being fully stopped and tripped when the PLC program fails or the PLC power fails. And it can effectively avoid the PLC program failure mistakenly issuing a cooler full stop trip signal to the non-electrical protection device, causing the main transformer to trip. At the same time, the delay of the main transformer cooler full stop trip is divided into two parts: the PLC device delay and the non-electrical protection device delay. After the non-electrical protection device receives the main transformer cooler full stop trip signal, the on-site operating personnel have enough time to check and handle the main transformer cooler accident, start the main transformer cooler in time, and exit the cooler full stop function pressure plate. It can avoid the main transformer cooler from being fully stopped due to other reasons such as power supply failure, causing the main transformer to trip, and the operating personnel can check and restore the power supply of the cooler in time. The optimized main transformer cooler full stop circuit delay setting meets the 60-minute delay tripping of the cooler full stop; the main transformer operation regulations that the main transformer trips when the cooler is fully stopped and the upper oil temperature of the main transformer reaches 75℃ 20 minutes later.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A device for improving the reliability of a main transformer cooler PLC control system, characterized in that: include: The first power supply end, cooler relay KM1, cooler relay KM2, cooler relay KM3, cooler relay KM4, cooler motor #1, cooler motor #2, cooler motor #3, cooler motor #4; the first power supply end, cooler relay KM1, cooler motor #1 are connected in sequence, the first power supply end, cooler relay KM2, cooler motor #2 are connected in sequence, the first power supply end, cooler relay KM3, cooler motor #3 are connected in sequence, the first power supply end, cooler relay KM4, cooler motor #4 are connected in sequence, wherein the control coil of the cooler relay KM1, the control coil of the cooler relay KM2, the control coil of the cooler relay KM3, and the control coil of the cooler relay KM4 are respectively connected to the PLC control system.

2. The device for improving the reliability of the main transformer cooler PLC control system according to claim 1, characterized in that: It also includes: cooler power switch QF1, cooler power switch QF2, cooler power switch QF3, cooler power switch QF4; the first power supply end is respectively connected to one end of the cooler power switch QF1, one end of the cooler power switch QF2, one end of the cooler power switch QF3, and one end of the cooler power switch QF4, the other end of the cooler power switch QF1, the cooler relay KM1, and the cooler motor #1 are connected in sequence, the other end of the cooler power switch QF2, the cooler relay KM2, and the cooler motor #2 are connected in sequence, the other end of the cooler power switch QF3, the cooler relay KM3, and the cooler motor #3 are connected in sequence, and the other end of the cooler power switch QF4, the cooler relay KM4, and the cooler motor #4 are connected in sequence.

3. The device for improving the reliability of the main transformer cooler PLC control system according to claim 2, characterized in that: The PLC control system includes: a second power supply end, a PLC device, a PLC device power supply monitoring relay KV1, a PLC device operation monitoring relay KP1, a cooler delay input relay KY1, and a cooler delay input relay KY2; the second power supply end, the PLC device power supply monitoring relay KV1, and the PLC device are connected in sequence, the output end of the PLC device is connected to the control coil of the PLC device operation monitoring relay KP1, the normally open contact of the PLC device operation monitoring relay KP1 is respectively connected to the control coil of the cooler delay input relay KY1 and the control coil of the cooler delay input relay KY2, the normally closed contact of the cooler delay input relay KY1 and the normally closed contact of the cooler delay input relay KY2 are respectively connected in parallel with the control circuit of the cooler relay KM1 and the control circuit of the cooler relay KM2.

4. The device for improving the reliability of the main transformer cooler PLC control system according to claim 3, characterized in that: The PLC control system further includes: a PLC device power supply circuit breaker 1QF; the second power supply end, a PLC device power supply monitoring relay KV1, a PLC device power supply circuit breaker 1QF, and a PLC device are connected in sequence.

5. A method for improving the reliability of a main transformer cooler PLC control system, which is applied to the device for improving the reliability of a main transformer cooler PLC control system according to any one of claims 1 to 4, characterized in that: include: Normal operation steps, fault operation steps and full stop protection steps, wherein the normal operation steps are: The second power supply terminal supplies power to the PLC control system; The PLC device power supply monitoring relay KV1 and the PLC device operation monitoring relay KP1 remain energized; The start and stop of cooler relay KM1, cooler relay KM2, cooler relay KM3 and cooler relay KM4 are controlled through the output end of the PLC device to achieve the normal operation of cooler motor #1, cooler motor #2, cooler motor #3 and cooler motor #4.

6. The method for improving the reliability of the main transformer cooler PLC control system according to claim 5, characterized in that: The fault operation step includes: a second power supply end fault operation sub-step and a PLC device fault operation sub-step; wherein the second power supply end fault operation sub-step is: The PLC device power supply monitoring relay KV1 loses its magnetism, the normally closed contact of the PLC device power supply monitoring relay KV1 closes, and sends an alarm signal; The cooler delay input relay KY1 and the cooler delay input relay KY2 lose magnetism, and the normally closed contacts of the cooler delay input relay KY1 and the cooler delay input relay KY2 are closed and connected in parallel to the control circuits of the cooler relay KM1 and the cooler relay KM2 respectively; Cooler #1 starts automatically, and after a delay of the set time, cooler #2 starts automatically. The operator receives the alarm signal and manually starts coolers #3 and #4.

7. The method for improving the reliability of the main transformer cooler PLC control system according to claim 5, characterized in that: The PLC device fault operation sub-steps are: The PLC device operation monitoring relay KP1 loses its magnetism, the normally closed contact of the PLC device operation monitoring relay KP1 closes, and sends an alarm signal; The cooler delay input relay KY1 and the cooler delay input relay KY2 lose magnetism, and the normally closed contacts of the cooler delay input relay KY1 and the cooler delay input relay KY2 are closed and connected in parallel to the control circuits of the cooler relay KM1 and the cooler relay KM2 respectively; Cooler #1 starts automatically, and after a delay of the set time, cooler #2 starts automatically. The operator receives the alarm signal and manually starts coolers #3 and #4.

8. The method for improving the reliability of the main transformer cooler PLC control system according to claim 5, characterized in that: The full stop protection step is specifically as follows: It also includes: full stop alarm, main transformer PLC control system delay relay, full stop trip relay KC2, full stop trip relay KC3 and main transformer non-electrical quantity protection device; The PLC device is provided with a full stop alarm and a main transformer PLC control system delay relay; the normally open contact of the full stop trip relay KC2 is connected in series with the normally closed contact of the cooler relay KM1, the normally closed contact of the cooler relay KM2, the normally closed contact of the cooler relay KM3, and the normally closed contact of the cooler relay KM4, and is connected to the input end of the main transformer non-electrical quantity protection device; the normally open contact of the full stop trip relay KC3 is connected in series with the normally closed contact of the cooler relay KM1, the normally closed contact of the cooler relay KM2, the normally closed contact of the cooler relay KM3, and the normally closed contact of the cooler relay KM4, and is connected to the input end of the main transformer non-electrical quantity protection device; When the cooler full stop condition is detected, and the main transformer is detected to be in operation, the PLC device executes the first stage of delay timing through the main transformer PLC control system delay relay, and detects the status of each cooler and the main transformer temperature at the same time. The cooler full stop condition is: cooler relay KM1, cooler relay KM2, cooler relay KM3, cooler relay KM4 stop running, and the PLC device controls the full stop alarm to execute the alarm; the first stage of delay timing includes: timing stage 1 and timing stage 2, and the timing stage 1 and timing stage 2 are executed in parallel; When the first stage of timing is over, the PLC device controls the full stop trip relay KC2 to be energized, and the delay device of the main transformer non-electrical quantity protection device performs the second stage delay timing for 15 minutes. When the timing is over, the main transformer non-electrical quantity protection device immediately performs the tripping operation; When the second stage of timing is over, the PLC device controls the full stop trip relay KC3 to be energized, and at the same time detects whether the upper oil temperature of the main transformer reaches the threshold. If so, the main transformer non-electrical protection device executes the second stage of delay timing. When the timing is over, the main transformer non-electrical protection device immediately performs the tripping operation; If the cooler full stop condition is untriggered before the total delay ends, the tripping is cancelled, where the total delay is equal to the sum of the first stage delay timing and the second stage delay timing.

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