Low-voltage pre-magnetizing system and method for marine medium-voltage phase-shifting rectifier transformer

Abstract

The invention discloses a low-voltage pre-magnetizing system and method for a marine medium-voltage phase-shifting rectifier transformer, and the system comprises a first circuit breaker, a first isolation switch and a primary side of the medium-voltage phase-shifting rectifier transformer which are sequentially connected to a three-phase power supply, and is used for providing a power supply for the medium-voltage phase-shifting rectifier transformer; the second circuit breaker, the second isolating switch and the primary side of the low-voltage transformer are sequentially connected to a three-phase power supply and are used for supplying power to the marine distribution board; the third circuit breaker, the main contact of the low-voltage alternating current contactor and the primary side of the pre-magnetizing transformer are connected to the marine distribution board in sequence and provide a power supply for the pre-magnetizing transformer; the secondary side of the pre-magnetizing transformer is connected with the secondary side of the medium-voltage phase-shifting rectifier transformer, and the pre-magnetizing transformer is used for pre-magnetizing the medium-voltage phase-shifting rectifier transformer. According to the system and the method, the surge current during the no-load starting of the transformer is weakened, the stability and the safety of the whole power distribution system during the no-load starting of the transformer are ensured, the anti-risk capability of a medium-voltage system is improved, and the toughness of the whole island microgrid is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas production enhancement operations in oil and gas fields. More specifically, the present invention relates to a low-voltage pre-magnetization system and method for a marine medium-voltage phase-shifting rectifier transformer applicable to marine fracturing operations. Background Art

[0002] Different from the driving forms of diesel engines and internal combustion engines, electric drive has the characteristics of low noise, no oil pollution, and environmental protection. With the continuous advancement of the "3060" goal, oil and gas extraction equipment has gradually shifted to electric operation. The land electric fracturing operation mode in China has achieved large-scale development, effectively increasing production in existing proven and developed oil and gas wells and improving oil and gas extraction efficiency. Different from the land fracturing operation conditions, marine fracturing is in the initial R & D stage. Without a strong power grid as support, the entire ship is constructed with an independent island microgrid consisting only of a medium-voltage generator set, power transmission, medium / low-voltage transformers, and high-power drive loads, and its toughness is not high. Large-capacity electric drive equipment requires large-capacity medium-voltage transformers. To effectively reduce the influence of source-side harmonics, multi-pulse phase-shifting rectifier transformers are often used. Large-capacity phase-shifting transformers have a large excitation current (i.e., inrush current) during no-load startup, which is extremely likely to cause power-on failure accidents, and seriously, it can cause the collapse of the entire island microgrid. Summary of the Invention

[0003] An object of the present invention is to provide a low-voltage pre-magnetization system and method for a marine medium-voltage phase-shifting rectifier transformer, which weaken the inrush current during the no-load startup of the transformer through the system and method, ensure the stability and safety of the entire power distribution system during the no-load startup of the transformer, improve the risk resistance ability of the medium-voltage system, and enhance the toughness of the entire island microgrid.

[0004] To solve the above technical problems, the present invention provides a low-voltage pre-magnetization system for a marine medium-voltage phase-shifting rectifier transformer, including a first circuit breaker, a first disconnecting switch, and the primary side of the medium-voltage phase-shifting rectifier transformer connected in sequence to a three-phase power source, which is a circuit and provides power for the medium-voltage phase-shifting rectifier transformer; it also includes a second circuit breaker, a second disconnecting switch, and the primary side of a low-voltage transformer connected in sequence to the three-phase power source, which provides power for the marine switchboard; it further includes a third circuit breaker, the main contacts of a low-voltage AC contactor, and the primary side of a pre-magnetization transformer connected in sequence to the marine switchboard, which provides power for the pre-magnetization transformer; the secondary side of the pre-magnetization transformer is connected to the secondary side of the medium-voltage phase-shifting rectifier transformer for pre-magnetizing the medium-voltage phase-shifting rectifier transformer.

[0005] Preferably, the primary side voltage phase and phase sequence of the pre-magnetization transformer are consistent with the primary side voltage phase and phase sequence of the low-voltage transformer; the secondary side voltage phase and phase sequence of the pre-magnetization transformer are consistent with the phase and phase sequence of the winding connected to the secondary side of the medium-voltage phase-shifting rectifier transformer.

[0006] Preferably, the pre-charging magnetic control circuit includes a fourth circuit breaker and a fuse connected in sequence to the three-phase power supply of the marine switchboard. The first end of the first auxiliary normally open contact of the low-voltage AC contactor and the first end of the closing self-resetting switch are connected in parallel to the positive pole of the power supply corresponding to the fuse. The second end of the coil of the low-voltage AC contactor and the second end of the green pre-charging magnetic process indicator are connected in parallel to the negative pole of the power supply corresponding to the fuse. The second end of the first auxiliary normally open contact of the low-voltage AC contactor and the second end of the closing self-resetting switch are both connected to the first end of the coil of the low-voltage AC contactor and the first end of the green pre-charging magnetic process indicator.

[0007] Preferably, the first end of the second auxiliary normally open contact of the low-voltage AC contactor and the first end of the normally open contact of the time-delay relay are also connected in parallel to the positive pole of the power supply corresponding to the fuse. The second end of the coil of the time-delay relay, the second end of the coil of the intermediate relay, and the second end of the yellow pre-charging magnetic completion indicator are also connected in parallel to the negative pole of the power supply corresponding to the fuse. The second end of the second auxiliary normally open contact of the low-voltage AC contactor is connected to the first end of the coil of the time-delay relay. The second end of the auxiliary normally open contact of the time-delay relay is connected to the first end of the coil of the intermediate relay and the first end of the yellow pre-charging magnetic completion indicator. The closing control coil of the first circuit breaker is connected in series with the normally open contact of the intermediate relay and controls the electric closing of the first circuit breaker. The closing signal of the first circuit breaker is transmitted to the PLC control system through the normally open contact of the circuit breaker. A normally closed contact of the circuit breaker is also provided between the second end of the first auxiliary normally open contact of the low-voltage AC contactor and the first end of the coil of the low-voltage AC contactor, and it is controlled to be disconnected through the PLC control system.

[0008] Preferably, multiple fuses are provided, and a switching power supply is also provided between the multiple fuses. It is used to step down the voltage provided by the three-phase power supply of the marine switchboard to the voltage required by the pre-charging magnetic control circuit and provide power.

[0009] Preferably, an emergency stop button is also provided between the positive pole of the power supply corresponding to the fuse and the parallel-connected electrical appliances corresponding to it.

[0010] Preferably, the secondary side of the pre-charging magnetic transformer and the access winding of the secondary side of the medium-voltage phase-shifting transformer are any one of the windings of the medium-voltage phase-shifting transformer.

[0011] The present invention also provides a pre-charging magnetic method for a low-voltage pre-charging magnetic system of a marine medium-voltage phase-shifting rectifier transformer, including the following steps: Step 1: The first disconnector, the second disconnector, and the second circuit breaker are all closed to provide power for the marine switchboard; Step 2: The third circuit breaker is closed to provide power for the pre-charging magnetic circuit; Step 3: The fourth circuit breaker is closed to provide power for the pre-charging magnetic control circuit; Step 4: Turn on the closing self-resetting switch. The coil of the low-voltage AC contactor is energized, the main contacts of the low-voltage AC contactor are closed, the pre-charging magnetic circuit is connected, the green pre-charging magnetic process indicator light is energized, and the medium-voltage phase-shifting rectifier transformer starts pre-charging magnetic.

[0012] Preferably, it further includes: Step 5: While the medium-voltage phase-shifting rectifier transformer starts pre-charging magnetic, the second auxiliary normally open contact of the low-voltage AC contactor is closed, the coil of the time-delay relay is energized, and timing starts according to the set time limit; Step 6: After charging magnetic to the set time limit, the auxiliary normally open contact of the time-delay relay is closed, the yellow pre-charging magnetic completion indicator light is energized, indicating the end of the pre-charging magnetic process; meanwhile, the coil of the intermediate relay is energized, the normally open contact of the intermediate relay is closed, and the closing control coil of the first circuit breaker is connected to realize the closing of the first circuit breaker; Step 7: After the closing control coil of the first circuit breaker is connected, the normally open passive contact of the first circuit breaker is closed, feeding back the closing signal of the first circuit breaker to the PLC control system, controlling the normally closed passive contact of the first circuit breaker to disconnect, the coil of the low-voltage AC contactor loses power, the main contacts of the low-voltage AC contactor are separated, the pre-charging magnetic circuit is de-energized, and the medium-voltage phase-shifting rectifier transformer is successfully powered on.

[0013] The present invention has at least the following beneficial effects: 1. The present invention effectively suppresses the no-load exciting current (i.e., inrush current) during the power-on process of the high-power marine medium-voltage phase-shifting rectifier transformer.

[0014] 2. The present invention strengthens the stability and safety of the overall marine medium-voltage system during the power-on process, effectively avoids the power-on failure rate, and the impact on the front-end generator set.

[0015] 3. The low-voltage pre-charging magnetic system of the present invention reduces electrical configurations such as medium-voltage transformers, medium-voltage resistors, and medium-voltage AC contactors that occupy a large space, improving the utilization rate of marine space.

[0016] 4. The low-voltage pre-charging magnetic of the present invention realizes the pre-charging magnetic of the medium-voltage transformer by controlling the 0.4 kV main circuit and the 0.23 kV control circuit, improving the safety of the equipment and the safety of personnel operation.

[0017] Other advantages, objectives, and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the low-voltage pre-charging magnetic circuit of a marine medium-voltage phase-shifting rectifier transformer of the present invention; Figure 2 It is a schematic diagram of the low-voltage pre-charging magnetic control circuit of a marine medium-voltage phase-shifting rectifier transformer of the present invention; Figure 3 Schematic diagram of the operation flow during the pre-magnetization process of the medium-voltage phase-shifting rectifier transformer of the present invention; Figure 4 Schematic diagram of the operation flow after the pre-magnetization of the medium-voltage phase-shifting rectifier transformer of the present invention; Figure 5 Schematic diagram of the pre-magnetization of different-phase windings of the present invention. Detailed implementation manners

[0019] In order to better understand the purpose, structure and function of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0020] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation manners are all conventional methods, and the reagents and materials, unless otherwise specified, can all be obtained from commercial channels; in the description of the present invention, the orientation or positional relationship indicated by the terms "horizontal", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention.

[0021] Such as Figure 1 and Figure 2As shown in the figure, the present invention provides a low-voltage pre-magnetization system for a marine medium-voltage phase-shifting rectifier transformer. The main components of this system circuit include: 4 circuit breakers (QF1, QF2, QF3, QF4 respectively), 2 disconnectors (QS1, QS2 respectively), 3 transformers (T1, T2, T3 respectively), 1 low-voltage AC contactor (KM1), 1 time-delay relay (KT1), 1 intermediate relay (KA1), 1 green pre-magnetization process indicator light (HL1), 1 yellow pre-magnetization completion indicator light (HL2), 1 switching power supply (TC), 1 closing self-resetting switch (SB1), 1 closing control coil (XF) of the QF1 circuit breaker, 1 normally open passive contact (SQ1) of the QF1 circuit breaker, 1 normally closed passive contact (SQ2) of the QF1 circuit breaker, 1 emergency stop button (SB), 4 fuses (FU1, FU2, FU3, FU4 respectively), etc. Among them: The QF1 circuit breaker is connected to the QS1 disconnector and the primary side of the T1 medium-voltage phase-shifting rectifier transformer, mainly providing power for the T1 medium-voltage phase-shifting rectifier transformer; The QF2 circuit breaker is connected to the QS2 disconnector and the primary side of the T2 low-voltage transformer, mainly providing power for the marine 0.4 kV switchboard; The marine 0.4 kV switchboard is connected to the QF3 circuit breaker, the main contacts of the KM1 low-voltage AC contactor, and the primary side of the T3 pre-magnetization transformer, mainly providing power for the T3 pre-magnetization transformer. The secondary side of the T3 pre-magnetization transformer is connected to the secondary side of the T1 medium-voltage phase-shifting rectifier transformer, mainly for pre-magnetizing the T1 medium-voltage phase-shifting rectifier transformer.

[0022] The pre-magnetization process of the entire low-voltage pre-magnetization system includes the following steps: Step S1: Close the QS1 disconnector and the QS2 disconnector; Close the QF2 circuit breaker to provide power for the marine 0.4 kV switchboard; Step S2: Close the QF3 circuit breaker to provide power for the pre-magnetization circuit; Step S3: Close the QF4 circuit breaker to provide power for the pre-magnetization control circuit; Step S4: Press the SB1 closing self-resetting switch, the coil of the KM1 low-voltage AC contactor is energized, the main contacts of the KM1 low-voltage AC contactor are closed, the pre-magnetization circuit is connected, the HL1 green indicator light is energized, and the T1 medium-voltage phase-shifting rectifier transformer starts pre-magnetization. At the same time, the auxiliary normally open contact of the KM1 low-voltage AC contactor is closed, the coil of the KT1 time-delay relay is energized, and the timing starts according to the set time limit.

[0023] Step S5: After reaching the set time limit, the auxiliary normally open contact of the KT1 time-delay relay is closed, the HL2 yellow indicator light is energized, indicating the end of the pre-magnetization process. At the same time, the coil of the KA1 relay is energized, the normally open contact of the KA1 contactor is closed, and the XF closing control coil of the QF1 circuit breaker is connected to realize the closing of the QF1 circuit breaker; Step S6: After the XF closing control coil of the QF1 circuit breaker is energized, the normally open passive contact SQ1 of the QF1 circuit breaker closes, feeding back the closing signal of the QF1 circuit breaker to the PLC control system, the normally closed passive contact SQ2 of the QF1 circuit breaker opens, the coil of the KM1 low-voltage AC contactor loses power, the main contacts of the KM1 low-voltage AC contactor separate, the pre-magnetizing circuit is de-energized, and the T1 medium-voltage phase-shifting rectifier transformer is successfully powered on.

[0024] The present invention utilizes a marine 0.4 kV low-voltage distribution board. Using the T3 pre-magnetizing transformer as a "bridge", after boosting the 0.4 kV voltage to U2, a pre-magnetizing channel for the T1 medium-voltage phase-shifting rectifier transformer is established; the pre-magnetization is mainly controlled by the 0.4 kV main circuit and the 0.23 kV control circuit to achieve the pre-magnetization of the T1 medium-voltage phase-shifting rectifier transformer, which can improve the safety of the equipment and the safety of personnel operation. By controlling the on-off of the primary low-voltage power supply circuit of the T3 pre-magnetizing transformer and the closing time of the QF1 circuit breaker, the automatic control of the pre-magnetization process and the closing process of the QF1 circuit breaker is realized, and the closing signal of the QF1 circuit breaker is uploaded to the PLC system.

[0025] The present invention mainly realizes the establishment of a steady-state magnetic flux approaching the expected value in the iron core of a large-capacity phase-shifting transformer before normal power-on by connecting a small-capacity step-up pre-magnetizing transformer with the same phase and phase sequence as a certain phase of the primary and secondary sides of the large-capacity medium-voltage phase-shifting rectifier transformer in series on the low-voltage side, suppressing the exciting current when the large-capacity phase-shifting transformer starts without load: The primary side winding of the small-capacity step-up T3 pre-magnetizing transformer is connected to the secondary side winding of the T2 low-voltage transformer, and receives the three-phase power supplied by the 400 V, 50 Hz low-voltage distribution network through the QF3 circuit breaker and the main contacts of the KM1 low-voltage AC contactor; the secondary side winding of the small-capacity step-up T3 pre-magnetizing transformer is connected to a certain group of windings on the low-voltage side with the same phase as the T1 medium-voltage phase-shifting rectifier transformer, providing a pre-magnetizing power supply for the T1 medium-voltage phase-shifting rectifier transformer. After the small-capacity step-up T3 pre-magnetizing transformer is energized, it pre-magnetizes the large-capacity T1 medium-voltage phase-shifting rectifier transformer according to the preset pre-magnetizing time, and controls the XF closing control coil of the QF1 circuit breaker in the power supply circuit on the primary side of the T1 medium-voltage phase-shifting rectifier transformer through the KT1 time-delay relay, realizing the automatic closing process of the QF1 circuit breaker, and at the same time automatically disconnecting the main contacts of the KM1 low-voltage AC contactor, realizing the safe and stable no-load power-on process of the T1 medium-voltage phase-shifting rectifier transformer.

[0026] A system and method corresponding to an embodiment of the present application will be described below with reference to the accompanying drawings.

[0027] As shown in the attach Figure 1 ment, it is a schematic diagram of a low-voltage pre-magnetizing circuit for a marine medium-voltage phase-shifting rectifier transformer according to an embodiment of the present invention. The low-voltage pre-magnetizing circuit for the marine medium-voltage phase-shifting rectifier transformer includes: a circuit breaker, a disconnecting switch, a transformer, a low-voltage AC contactor, etc. Among them: Circuit breakers, QF1, QF2 and QF3, where the QF1 circuit breaker provides control and protection for the power supply circuit of the T1 medium-voltage phase-shifting rectifier transformer; the QF2 circuit breaker provides control and protection for the power supply circuit of the T2 low-voltage transformer; the QF3 circuit breaker provides control and protection for the power supply circuit of the T3 pre-magnetizing transformer Isolating switches, QS1 and QS2, where the QS1 isolating switch and the QS2 isolating switch mainly isolate the U1 power supply generated by the generator set during equipment maintenance.

[0028] Transformers T1, T2 and T3, where the T1 medium-voltage phase-shifting rectifier transformer steps down the voltage U1 generated by the generator set to the rated voltage U2 required for voltage driving the skid; the T2 low-voltage transformer steps down the voltage U1 generated by the generator set to the rated voltage 0.4 kV required for marine use; the T3 pre-magnetizing transformer steps up 0.4 kV to the secondary-side rated voltage U2 of the T1 medium-voltage phase-shifting rectifier transformer and ensures that the voltage phase and phase sequence are consistent.

[0029] Low-voltage AC contactor, the main contacts of KM1 mainly control the on and off of the pre-magnetizing circuit. The KM1 AC contactor is selected as a low-voltage AC contactor to reduce the configuration of pre-magnetizing equipment such as medium-voltage resistors and medium-voltage AC contactors that occupy a large space and improve the utilization rate of marine space.

[0030] As shown in the appendix Figure 2 is a schematic diagram of a low-voltage pre-magnetizing control circuit for a marine medium-voltage phase-shifting rectifier transformer according to an embodiment of the present invention. The low-voltage pre-magnetizing control circuit for the marine medium-voltage phase-shifting rectifier transformer includes: circuit breakers, fuses, the closing control coil of the QF1 circuit breaker, the normally open contact of the QF1 circuit breaker, the normally closed contact of the QF1 circuit breaker, a time-delay relay, an intermediate relay, a switching power supply, a low-voltage AC contactor, an indicator light, a closing self-resetting switch, an emergency stop button, etc. Among them: Circuit breaker, QF4 provides control and protection for the pre-magnetizing control circuit.

[0031] Fuses, FU1, FU2, FU3 and FU4 mainly provide overcurrent and short-circuit protection for the pre-magnetizing control circuit.

[0032] The closing control coil of the QF1 circuit breaker, XF is the closing control coil for controlling the electric closing of the QF1 circuit breaker.

[0033] The normally open contact of the QF1 circuit breaker, SQ1 is used to upload the QF1 closing signal to the PLC system.

[0034] The normally closed contact of the QF1 circuit breaker, SQ2 controls the on and off of the KM1 coil and further controls the on and off of the circuit.

[0035] Switching power supply, TC mainly steps down the 0.4 kV voltage to 0.23 kV voltage to provide power for the pre-magnetizing control circuit.

[0036] Indicator lights, HL1 and HL2, where HL1 is the pre-magnetization process indicator light, showing green during normal operation; HL2 is the pre-magnetization completion indicator light, showing yellow during normal operation.

[0037] Closing self-resetting switch, SB1 is the closing button for the circuit breaker's electric operation, mainly realizing the on / off of the control coil of contactor KM1, as well as the on / off of the pre-charge start indicator light HL1.

[0038] Low-voltage AC contactor, KM1 controls the normal on / off of the pre-magnetization circuit, the self-holding function, and the on / off of the control coil of the time-delay relay.

[0039] Time-delay relay, KT1 controls the on / off of the control coil of intermediate relay KA1, as well as the on / off of the pre-magnetization completion indicator light HL2.

[0040] Intermediate relay, KA1 controls the on / off of the closing control coil of circuit breaker QF1.

[0041] Emergency stop button, SB is used to disconnect the entire pre-magnetization process in case of emergency.

[0042] The operating principle of the above marine medium-voltage phase-shifting rectifier transformer low-voltage pre-magnetization system is as follows: Close the QS1 disconnecting switch and the QS2 disconnecting switch, and then close the QF2 circuit breaker and the QF3 circuit breaker in sequence to prepare for the start of 0.4kV low-voltage pre-charge. Press the SB1 closing self-resetting switch, the main contacts of the KM1 low-voltage AC contactor are attracted, and the pre-magnetization process starts. At the same time, the pre-magnetization process indicator light HL1 is energized. At this time, the schematic diagram of the operation flow of the marine medium-voltage phase-shifting rectifier transformer low-voltage pre-magnetization process is as Figure 3 shown.

[0043] When the KT1 time-delay relay meets the preset time limit, the QF1 circuit breaker closes under the control of the XF closing control coil, and uploads the QF1 circuit breaker closing signal to the PLC system. At the same time, the control coil of the KM1 contactor loses power, the pre-magnetization circuit is disconnected, and the pre-magnetization completion indicator light HL2 is energized. At this time, the T1 medium-voltage transformer is successfully powered on safely and stably. The schematic diagram of the operation flow at the end of the marine medium-voltage phase-shifting rectifier transformer low-voltage pre-magnetization is as Figure 4 shown.

[0044] The secondary side of the T3 pre-magnetization transformer and the secondary side access winding of the T1 medium-voltage phase-shifting transformer are not limited to Figures 1 - 4For the +22.5° mode, pre-charging can also be performed from the -22.5°, -7.5°, and +7.5° windings. However, the phase and phase sequence of the primary voltage of the T3 pre-charging magnetic transformer must be consistent with those of the primary voltage of the T2 low-voltage transformer, and the phase and phase sequence of the secondary voltage of the T3 pre-charging magnetic transformer must be consistent with those of the phase and phase sequence of the winding connected to the secondary side of the T1 medium-voltage phase-shifting transformer. As shown in Figure 5 The figure shows a schematic diagram of pre-charging the +7.5° winding.

[0045] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. A low-voltage pre-magnetizing system for a marine medium-voltage phase-shifting rectifier transformer, characterized in that It includes a first circuit breaker, a first disconnecting switch, and the primary side of a medium-voltage phase-shifting rectifier transformer that are sequentially connected to a three-phase power source. This forms a single circuit and supplies power to the medium-voltage phase-shifting rectifier transformer. It also includes a second circuit breaker, a second disconnecting switch, and the primary side of a low-voltage transformer that are sequentially connected to the three-phase power source, which supplies power to the marine switchboard. It further includes a third circuit breaker, the main contacts of a low-voltage AC contactor, and the primary side of a pre-magnetizing transformer that are sequentially connected to the marine switchboard, which supplies power to the pre-magnetizing transformer. The secondary side of the pre-magnetizing transformer is connected to the secondary side of the medium-voltage phase-shifting rectifier transformer and is used to pre-magnetize the medium-voltage phase-shifting rectifier transformer.

2. The low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to claim 1, wherein The phase and phase sequence of the primary side voltage of the pre-magnetizing transformer are consistent with those of the primary side voltage of the low-voltage transformer. The phase and phase sequence of the secondary side voltage of the pre-magnetizing transformer are consistent with those of the phase and phase sequence of the winding connected to the secondary side of the medium-voltage phase-shifting rectifier transformer.

3. The low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to claim 1, characterized in that, The pre-magnetizing control circuit includes a fourth circuit breaker and a fuse that are sequentially connected to the three-phase power source of the marine switchboard. The first end of a first auxiliary normally open contact of the low-voltage AC contactor and the first end of a closing self-resetting switch are connected in parallel to the positive pole of the power source corresponding to the fuse. The second end of the coil of the low-voltage AC contactor and the second end of a green pre-magnetizing process indicator light are connected in parallel to the negative pole of the power source corresponding to the fuse. The second end of the first auxiliary normally open contact of the low-voltage AC contactor and the second end of the closing self-resetting switch are both connected to the first end of the coil of the low-voltage AC contactor and the first end of the green pre-magnetizing process indicator light.

4. The low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to claim 3, wherein, The first end of a second auxiliary normally open contact of the low-voltage AC contactor and the first end of a normally open contact of a time-delay relay are also connected in parallel to the positive pole of the power source corresponding to the fuse. The second end of the coil of the time-delay relay, the second end of the coil of an intermediate relay, and the second end of a yellow pre-magnetizing completion indicator light are also connected in parallel to the negative pole of the power source corresponding to the fuse. The second end of the second auxiliary normally open contact of the low-voltage AC contactor is connected to the first end of the coil of the time-delay relay. The second end of the auxiliary normally open contact of the time-delay relay is connected to the first end of the coil of the intermediate relay and the first end of the yellow pre-magnetizing completion indicator light. The closing control coil of the first circuit breaker is connected in series with the auxiliary normally open contact of the intermediate relay and controls the electric closing of the first circuit breaker. The closing signal of the first circuit breaker is transmitted to the PLC control system through a normally open contact of the circuit breaker without power. A normally closed contact of the circuit breaker without power is also provided between the second end of the first auxiliary normally open contact of the low-voltage AC contactor and the first end of the coil of the low-voltage AC contactor, and its disconnection is controlled by the PLC control system.

5. The low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to claim 3, characterized in that Multiple fuses are provided, and a switching power supply is also provided between the multiple fuses. It is used to step down the voltage provided by the three-phase power source of the marine switchboard to the voltage required by the pre-magnetizing control circuit and supply power.

6. The low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to claim 4, characterized in that, An emergency stop button is also provided between the positive pole of the power source corresponding to the fuse and the parallel-connected electrical appliances corresponding to it.

7. The low-voltage pre-magnetizing system of the marine medium-voltage phase-shifting rectifier transformer according to claim 1, characterized in that, The secondary side of the pre-magnetizing transformer and the winding connected to the secondary side of the medium-voltage phase-shifting transformer are any one of the windings of the medium-voltage phase-shifting transformer.

8. The pre-magnetization method of the low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to any one of claims 1 to 7, characterized in that, It includes the following steps: Step 1: Close the first disconnecting switch, the second disconnecting switch, and the second circuit breaker to supply power to the marine switchboard. Step 2: Close the third circuit breaker to supply power to the pre-magnetizing circuit; Step 3: Close the fourth circuit breaker to supply power to the pre-magnetizing control circuit; Step 4: Turn on the closing self-resetting switch. The coil of the low-voltage AC contactor is energized, the main contacts of the low-voltage AC contactor are closed, the pre-magnetizing circuit is connected, the green pre-magnetizing process indicator light is energized, and the medium-voltage phase-shifting rectifier transformer starts pre-magnetizing.

9. The pre-magnetization method of the low-voltage pre-magnetization system of the marine medium-voltage phase-shifting rectifier transformer according to claim 8, characterized in that, It also includes: Step 5: While the medium-voltage phase-shifting rectifier transformer starts pre-magnetizing, the second auxiliary normally open contact of the low-voltage AC contactor is closed, the coil of the time-delay relay is energized, and timing starts according to the set time limit; Step 6: After magnetizing to the set time limit, the auxiliary normally open contact of the time-delay relay is closed, the yellow pre-magnetizing completion indicator light is energized, indicating the end of the pre-magnetizing process; at the same time, the coil of the intermediate relay is energized, the normally open contact of the intermediate relay is closed, and the closing control coil of the first circuit breaker is connected to achieve the closing of the first circuit breaker; Step 7: After the closing control coil of the first circuit breaker is connected, the normally open passive contact of the first circuit breaker is closed, feeding back the closing signal of the first circuit breaker to the PLC control system, controlling the normally closed passive contact of the first circuit breaker to open, the coil of the low-voltage AC contactor loses power, the main contacts of the low-voltage AC contactor are separated, the pre-magnetizing circuit is de-energized, and the medium-voltage phase-shifting rectifier transformer is successfully powered on.

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