CN117650479A - Optimization method and device for preventing single-phase grounding protection during parallel operation of multiple pump sets - Google Patents
Optimization method and device for preventing single-phase grounding protection during parallel operation of multiple pump sets Download PDFInfo
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- CN117650479A CN117650479A CN202311682184.XA CN202311682184A CN117650479A CN 117650479 A CN117650479 A CN 117650479A CN 202311682184 A CN202311682184 A CN 202311682184A CN 117650479 A CN117650479 A CN 117650479A
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- 238000000034 method Methods 0.000 title claims abstract description 15
- 238000005457 optimization Methods 0.000 title claims abstract description 15
- 230000007935 neutral effect Effects 0.000 claims abstract description 32
- 230000009466 transformation Effects 0.000 claims description 9
- 238000003825 pressing Methods 0.000 claims description 6
- 238000001514 detection method Methods 0.000 claims description 5
- 238000010586 diagram Methods 0.000 description 5
- 230000035945 sensitivity Effects 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052755 nonmetal Inorganic materials 0.000 description 1
Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/16—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass
- H02H3/162—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass for AC systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Protection Of Generators And Motors (AREA)
Abstract
The invention relates to an optimization method and device for preventing single-phase grounding protection during parallel operation of a plurality of pump sets, wherein the device comprises a first zero-sequence current transformer, a second zero-sequence current transformer and a motor protection device, the first zero-sequence current transformer and the second zero-sequence current transformer are respectively arranged at a motor end and a motor neutral point side, a first zero-sequence current acquisition point of the motor protection device is connected with the first zero-sequence current transformer, a second zero-sequence current acquisition point is connected with the second zero-sequence current transformer, the motor protection device acquires zero-sequence current transformer currents at the motor end and zero-sequence current transformer currents at the motor neutral point side, and the zero-sequence current differences at two sides are calculated and used as logic criteria for single-phase grounding protection. The invention has the characteristics of ensuring the stability of the system operation and has the advantages of high economy and reliability.
Description
Technical Field
The invention relates to the field of relay protection in water conservancy and hydropower engineering, in particular to an optimization method and device for preventing single-phase grounding protection during parallel operation of a plurality of pump sets.
Background
In the field of water conservancy and hydropower diversion water intake engineering, a large pump group is often installed on the same bus, because a 10kV bus connected with a motor can be connected with loads such as a plurality of motors, excitation transformers, station transformers and the like, the probability of single-phase grounding faults of the 10kV bus is high, if the motor protection adopts conventional zero-sequence voltage or neutral point zero-sequence overcurrent protection, the motor protection cannot distinguish whether the single-phase grounding faults occur inside or outside the motor, and as a result, the single-phase grounding faults occurring at any position of 10kV can cause the simultaneous load shedding of all the motors connected with the bus, thereby seriously threatening the safety of a water channel and a unit.
Aiming at the situation that a plurality of motor pump sets are connected into the same section of bus, the conventional scheme and the single-phase grounding fault protection mode are as follows:
(1) According to the number of the pump sets, corresponding high-voltage switch cabinets are added in the high-voltage bus end, corresponding microcomputer motor protection devices are arranged in each circuit of switch cabinets, the motor protection devices are provided with zero sequence voltage or neutral point zero sequence overcurrent protection, and when a single-phase grounding fault occurs in the circuit, the microcomputer motor protection devices output tripping instructions to act on the circuit breaker of the circuit to trip.
(2) The high-voltage bus is provided with a low-current grounding line selection device.
The disadvantage of the above solution is that: in the current grounding line selection device test based on the corresponding theory, the line selection preparation rate reaches more than 90%, but in the field use process of most grounding line selection devices, the line selection rate of the low-current grounding line selection device is not high under the influence of field conditions and operating environment, and the requirement is difficult to meet.
When the internal ground fault occurs in the system, the single-phase ground current of the motor in the loop is possibly smaller than the starting value of the differential protection of the motor when the neutral point of the motor runs through high-impedance ground, and the protection sensitivity is insufficient and does not act. When the system has external ground fault, other motors in the system have zero sequence current and zero sequence voltage, single-phase ground zero sequence protection has no selectivity, other normal operation motors have tripping at intervals, and the power failure range is enlarged.
At present, 90% of motor single-phase grounding protection is arranged at the motor end, the single-phase grounding protection at the neutral point is not included, and once the single-phase grounding protection of the neutral point occurs, the system cannot be protected.
Therefore, the prior art has the problems of low protection sensitivity, poor system operation stability and low economy and reliability.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides an optimization method and device for preventing single-phase grounding protection during parallel operation of a plurality of pump sets.
According to a first aspect of the technical scheme of the invention, an optimization device for preventing single-phase grounding protection during parallel operation of a plurality of pump sets is provided, and the device comprises a first zero-sequence current transformer, a second zero-sequence current transformer and a motor protection device;
the motor protection device is provided with a first zero-sequence current acquisition point which is connected with a first zero-sequence current transformer and used for detecting zero-sequence current of a motor end;
the motor protection device is provided with a second zero-sequence current acquisition point which is connected with a second zero-sequence current transformer and used for detecting zero-sequence current at the neutral point side of the motor;
the first zero sequence current transformer and the second zero sequence current transformer are respectively arranged at the motor end and the motor neutral point side, the zero sequence currents at the two sides are connected into the motor protection device, and the synthesized zero sequence differential current is used as a logic criterion of single-phase grounding protection.
Further, the motor protection device comprises a controller, a switching value output module and an alarm;
the input end of the controller is connected with the output ends of the first zero-sequence current acquisition point and the second zero-sequence current acquisition point and is used for receiving signals output by the controller;
the input end of the switching value output module is connected with the output end of the controller, and the output end of the switching value output module is connected with a tripping circuit of a circuit breaker of the motor circuit and is used for tripping the circuit breaker;
the input end of the alarm is connected with the output end of the controller and is used for positioning the loop number corresponding to the motor interval single-phase grounding fault.
Further, the motor control system also comprises a zero sequence voltage acquisition point, wherein the zero sequence voltage acquisition point is connected with a motor interval zero sequence voltage transformer, and the output end of the zero sequence voltage acquisition point is connected with the input end of the controller and is used for detecting whether a single-phase grounding fault occurs in a motor interval loop.
Further, the motor protection device also comprises a zero sequence protection hard pressing plate used for controlling the switching of the zero sequence protection function.
Further, the model and transformation ratio of the zero sequence current transformer at the motor end and the zero sequence current transformer at the neutral point of the motor are kept consistent.
According to a second aspect of the present invention, there is provided an optimization method for preventing single-phase ground protection when a plurality of pump sets are operated in parallel, comprising the steps of:
s1, setting: a first zero-sequence current transformer and a second zero-sequence current transformer are respectively arranged at the motor end and the neutral point side, and the zero-sequence currents at the two sides are connected into a motor protection device;
s2, detection: detecting whether a single-phase grounding fault occurs in a motor loop or not through a zero-sequence current transformer of a motor end and a neutral point;
s3, judging: when single-phase earth fault occurs, the motor protection device judges whether the zero sequence differential current synthesized at the motor end and at the two sides of the neutral point is larger than a zero sequence differential fixed value;
and S4, protecting that when the synthesized zero sequence differential current is larger than a set value, the motor protection device acts on the circuit breaker of the loop to trip.
Further, the step S2 of detecting further comprises detecting whether a single-phase grounding fault occurs in the motor interval loop through a zero-sequence voltage acquisition point.
Further, the step S3 of judging further includes the step of the motor protection device judging whether the zero sequence voltage in the loop is greater than the zero sequence overvoltage locking fixed value.
Further, the step S1 comprises the selection of the zero-sequence current transformer, and the transformation ratio of the zero-sequence current transformer is selected according to the fault current value calculated by the system when the fault current value is grounded unidirectionally.
Compared with the prior art, the optimization method and the device for preventing single-phase grounding protection during parallel operation of the plurality of pump sets have the following beneficial effects:
the invention respectively installs a first zero sequence current transformer and a second zero sequence current transformer at the motor end and the neutral point side, and the zero sequence currents at the two sides are connected into a motor protection device to synthesize zero sequence differential current. During normal operation, the zero sequence current transformers on the two sides are close to zero, the zero sequence differential current I0cd is zero, and the single-phase grounding protection of the motor can not act. When the motor is externally connected to the single-phase ground (such as a bus is connected to the single-phase ground), the zero-sequence current transformers on two sides have zero-sequence currents, but the zero-sequence differential current I0cd is zero because the zero-sequence current transformers are equal in size and same in direction, and the motor is prevented from being protected from being in single-phase ground. When single-phase grounding occurs in the protection range of the motor, the magnitude and the direction of the zero sequence current at two sides are not the same, and at the moment, the zero sequence differential current I0cd is not zero, and the single-phase grounding protection action of the motor is performed on the interval switch to cut off faults.
Drawings
Fig. 1 is a diagram of a 10kV primary system in an embodiment of the invention.
Fig. 2 is a diagram showing a motor protection function configuration in the embodiment of the present invention.
Fig. 3 is a diagram showing a single-phase ground protection function of the motor according to an embodiment of the present invention.
Fig. 4 is a logic block diagram of single-phase ground protection of zero-sequence differential current of a motor in an embodiment of the invention.
Detailed Description
Specific implementations of the invention are described in detail below in connection with specific embodiments.
As shown in fig. 1, the engineering 10kV system according to the embodiment adopts a single bus segment wiring mode, designs that 3 motors are connected to the section I bus 100, 4 motors are connected to the section II bus 200, and the neutral point of the motors adopts a high-resistance grounding mode.
From the parameters provided by the motor manufacturer, it is known that: the neutral point ground resistance of the motor was 57.7Ω and the single phase ground capacitor current value was 1.924a. Calculating and analyzing the single-phase grounding current of the motor:
1. zero sequence current calculation when internal single phase grounding occurs: when any motor of 10kV is in single-phase grounding, the current flowing through the neutral point of the motor and the zero sequence current transformer at the motor end is as follows: i0 =zero sequence voltage/neutral point ground resistance+motor capacitance current.
(1) If the single camera end metal grounding occurs, the maximum zero sequence current is:
I0＝5.77kV/57.7Ω+1.924A＝101.924A
(2) If the single camera end is in non-metal grounding or the motor stator is in internal grounding, the zero sequence current is as follows: between 0 and 101.924A.
2. When single-phase grounding outside the motor occurs (such as single-phase grounding of a 10kV bus), zero-sequence current calculation is performed:
(1) Maximum ground current: when two sections of buses are operated in parallel, the zero-sequence current of the grounding point is the sum of the zero-sequence currents of all operating motors when single-phase grounding occurs: i0max=7101.924a= 713.468A.
(2) Minimum ground current: when the two bus sections are operated separately, and single-phase grounding occurs, the zero-sequence current of the grounding point is the sum of the zero-sequence currents of all the operating motors on the bus section: i0min=3×101.924a= 305.72a.
According to the calculation, when any motor of 10kV is in single-phase grounding, the single-phase grounding current of the system is overlarge, if a small-current grounding line selection device is arranged on a bus section according to conventional protection configuration, zero-sequence current and zero-sequence voltage can be generated for other motors in the system, the protection is not selective, other normal operation motor intervals can trip, and the power failure range is enlarged.
Aiming at the technical problem, single-phase grounding protection based on zero sequence differential current is adopted for each motor, and the specific protection scheme is as follows: as shown in fig. 2 and 3, an optimizing device for preventing single-phase grounding protection during parallel operation of a plurality of pump stacks is provided, wherein the device comprises a first zero-sequence current acquisition point 301, a second zero-sequence current acquisition point 302, a first zero-sequence current transformer 303, a second zero-sequence current transformer 304 and a motor protecting device 300; the first zero-sequence current acquisition point 301 is connected with a first zero-sequence current transformer 303 and is used for detecting the zero-sequence current of the motor end; the second zero-sequence current acquisition point 302 is connected with a second zero-sequence current transformer 304 and is used for detecting zero-sequence current at the neutral point side of the motor; the first zero-sequence current transformer 303 and the second zero-sequence current transformer 304 are respectively arranged at the motor end and the motor neutral point side, and the zero-sequence currents at two sides are connected into the motor protection device 300.
During normal operation, the zero sequence current transformers on the two sides are close to zero, the zero sequence differential current I0cd is zero, and the single-phase grounding protection of the motor can not act.
When the motor is externally connected to the single-phase ground (such as a bus is connected to the single-phase ground), the zero-sequence current transformers on two sides have zero-sequence currents, but the zero-sequence differential current I0cd is zero because the zero-sequence current transformers are equal in size and same in direction, and the motor is prevented from being protected from being in single-phase ground.
When the single-phase grounding occurs in the protection range of the motor, the magnitude and the direction of the zero sequence currents on two sides are not the same, at the moment, the zero sequence differential current I0cd is not zero, and the NSP783A motor single-phase grounding protection acts on the interval switch to cut off faults.
Further, the motor protection device 300 includes a controller, a switching value output module, and an alarm; the input end of the controller is connected with the output ends of the first zero-sequence current acquisition point 301 and the second zero-sequence current acquisition point 302 and is used for receiving signals output by the controller; the input end of the switching value output module is connected with the output end of the controller, and the output end of the switching value output module is connected with a tripping circuit of a circuit breaker of the motor circuit and is used for tripping the circuit breaker; the input end of the alarm is connected with the output end of the controller and is used for positioning the loop number corresponding to the motor interval single-phase grounding fault.
Further, the device further comprises a zero sequence voltage acquisition point 307, the zero sequence voltage acquisition point 307 is connected with a motor interval zero sequence voltage transformer 305, an output end is connected with an input end of the controller, and the zero sequence voltage acquisition point 307 is used for detecting whether a single-phase earth fault occurs in a motor interval loop or not so as to improve the protection sensitivity, prevent misoperation caused by zero sequence unbalance, a specific protection logic diagram is shown in fig. 4, a first auxiliary criterion of zero sequence voltage U0 serving as zero sequence differential protection action is added, namely, the zero sequence voltage U0 is larger than a zero sequence overvoltage locking fixed value, and when a zero sequence voltage locking zero-current differential control word is smaller than 1, the zero sequence current differential control setting value of zero sequence voltage locking is set to be larger than or equal to 1, namely, the first auxiliary criterion reaches a starting condition. Further, the motor protection device 300 includes a zero-sequence protection hard pressing plate, which is used for controlling the switching of the zero-sequence protection function, the main criterion of the zero-sequence differential protection action is that the zero-sequence current I0cd is greater than the zero-sequence differential fixed value, and when the system detects that a single-phase earth fault occurs, the zero-sequence protection hard pressing plate is in an unopened state and is ready to be switched to a switching state, and the zero-sequence protection hard pressing plate is used as the second auxiliary criterion of the zero-sequence differential protection action. In addition, the zero-current differential protection soft pressing plate input condition and the zero-current differential protection input control word condition are included to control the zero-current differential protection action, and the zero-current differential protection action is started after the control condition is met at the same time by the fixed value T of the elapsed time.
Further, the model and transformation ratio of the first zero-sequence current transformer 303 at the motor end and the second zero-sequence current transformer 304 at the motor neutral point are kept consistent, namely, the transformation ratio of the zero-sequence current transformer at the motor neutral point should correspond to the balance state of the motor end, so that errors in the zero-sequence current detected due to inconsistent transformation ratio of the zero-sequence current transformers are avoided, and normal operation of the system and correct implementation of the protection function are ensured.
According to a second aspect of the present invention, the present invention further provides an optimization method for preventing single-phase grounding protection when a plurality of pump sets are operated in parallel, which adopts the above-mentioned optimization device for preventing single-phase grounding protection when a plurality of pump sets are operated in parallel, and the method comprises the following steps:
s1, setting: a first zero-sequence current transformer 303 and a second zero-sequence current transformer 304 are respectively arranged at the motor end and the neutral point side, and the zero-sequence currents at the two sides are connected into the motor protection device 300;
s2, detection: detecting whether a single-phase grounding fault occurs in a motor loop or not through a zero-sequence current transformer of a motor end and a neutral point;
s3, judging: when a single-phase earth fault occurs, the motor protection device 300 judges whether the zero sequence differential current synthesized at the motor end and at the two sides of the neutral point is larger than a zero sequence differential fixed value;
and S4, protecting that when the synthesized zero sequence differential current is larger than a set value, the motor protection device 300 acts on the circuit breaker of the loop to trip.
The method is characterized in that a first zero-sequence current transformer 303 and a second zero-sequence current transformer 304 are respectively arranged at the motor end and the neutral point side, and the zero-sequence currents at the two sides are connected into a motor protection device 300 after being synthesized into zero-sequence differential currents. During normal operation, the zero sequence current transformers on the two sides are close to zero, the zero sequence differential current I0cd is zero, and the single-phase grounding protection of the motor can not act. When the motor is externally connected to the single-phase ground (such as a bus is connected to the single-phase ground), the zero-sequence current transformers on two sides have zero-sequence currents, but the zero-sequence differential current I0cd is zero because the zero-sequence current transformers are equal in size and same in direction, and the motor is prevented from being protected from being in single-phase ground. When the single-phase grounding occurs in the protection range of the motor, the magnitude and the direction of the zero sequence currents on two sides are not the same, at the moment, the zero sequence differential current I0cd is not zero, and the single-phase grounding protection of the motor acts on the interval switch to cut off faults.
Further, the S2 detection further includes detecting whether the motor interval loop has a single-phase ground fault through the zero sequence voltage acquisition point 307, and improving the sensitivity of protection through detecting whether the motor interval loop has a single-phase ground fault.
Further, the step S3 further includes the step of the motor protection device 300 determining whether the zero-sequence voltage in the loop is greater than the zero-sequence overvoltage locking fixed value, and when the zero-sequence voltage U0 is greater than the zero-sequence overvoltage locking fixed value and the zero-sequence voltage locking zero-current differential control word is less than 1, the zero-sequence current differential control fixed value of the zero-sequence voltage locking is set to be greater than or equal to 1, which is the starting condition of the auxiliary criterion.
Further, the step S1 comprises the selection of the zero-sequence current transformer, and the transformation ratio of the zero-sequence current transformer is selected according to the fault current value calculated by the system when the fault current value is grounded unidirectionally. The magnitude of the fault current is based on the design of the system, and the maximum fault current that can occur when the single phase is grounded can be predicted, and a zero sequence current transformer with a sufficient transformation ratio is selected to ensure that the transformer can accurately detect and transmit signals at the maximum fault current.
Claims (9)
1. An optimizing device for preventing single-phase grounding protection during parallel operation of a plurality of pump sets is characterized by comprising a first zero-sequence current transformer, a second zero-sequence current transformer and a motor protecting device;
the motor protection device is provided with a first zero-sequence current acquisition point which is connected with a first zero-sequence current transformer and used for detecting zero-sequence current of a motor end;
the motor protection device is provided with a second zero-sequence current acquisition point which is connected with a second zero-sequence current transformer and used for detecting zero-sequence current at the neutral point side of the motor;
the first zero sequence current transformer and the second zero sequence current transformer are respectively arranged at the motor end and the motor neutral point side, the zero sequence currents at the two sides are connected into the motor protection device, and the synthesized zero sequence differential current is used as a logic criterion of single-phase grounding protection.
2. An optimizing device for preventing single-phase grounding protection when a plurality of pump sets are operated in parallel as claimed in claim 1, wherein the motor protecting device comprises a controller, a switching value output module and an alarm;
the input end of the controller is connected with the output ends of the first zero-sequence current acquisition point and the second zero-sequence current acquisition point and is used for receiving signals output by the controller;
the input end of the switching value output module is connected with the output end of the controller, and the output end of the switching value output module is connected with a tripping circuit of a circuit breaker of the motor circuit and is used for tripping the circuit breaker;
the input end of the alarm is connected with the output end of the controller and is used for positioning the loop number corresponding to the motor interval single-phase grounding fault.
3. An optimization device for preventing single-phase ground protection during parallel operation of a plurality of pump stacks as claimed in claim 1, further comprising a zero sequence voltage acquisition point, wherein the zero sequence voltage acquisition point is connected with a zero sequence voltage transformer at intervals of the motor, and an output end is connected with an input end of the controller for detecting whether single-phase ground faults occur in an interval loop of the motor.
4. An optimizing device for preventing single-phase grounding protection when a plurality of pump sets are operated in parallel as claimed in claim 1, wherein the motor protecting device further comprises a zero sequence protecting hard pressing plate for controlling the switching of the zero sequence protecting function.
5. An optimizing device for single-phase grounding protection when a plurality of pump sets are operated in parallel according to any one of claims 1 to 4, wherein the model and transformation ratio of the zero sequence current transformer at the motor end and the zero sequence current transformer at the neutral point of the motor are kept consistent.
6. An optimization method for preventing single-phase grounding protection during parallel operation of a plurality of pump sets is characterized by comprising the following steps:
s1, setting: a first zero-sequence current transformer and a second zero-sequence current transformer are respectively arranged at the motor end and the neutral point side, and the zero-sequence currents at the two sides are connected into a motor protection device;
s2, detection: detecting whether a single-phase grounding fault occurs in a motor loop or not through a zero-sequence current transformer of a motor end and a neutral point;
s3, judging: when single-phase earth fault occurs, the motor protection device judges whether the zero sequence differential current synthesized at the motor end and at the two sides of the neutral point is larger than a zero sequence differential fixed value;
and S4, protecting that when the synthesized zero sequence differential current is larger than a set value, the motor protection device acts on the circuit breaker of the loop to trip.
7. An optimization method for preventing single-phase ground protection when multiple pump stacks are operated in parallel as set forth in claim 6, wherein said S2 detection further comprises detecting whether a single-phase ground fault occurs in the motor spacing loop through a zero sequence voltage acquisition point.
8. The optimization method for preventing single-phase ground protection during parallel operation of multiple pump stacks of claim 7, wherein said step S3 judgment further comprises the step of the motor protection device judging whether the zero sequence voltage in the loop is greater than a zero sequence overvoltage lockout constant.
9. An optimization method for preventing single-phase grounding protection during parallel operation of a plurality of pump sets according to any one of claims 6 to 8, wherein S1 comprises selection of zero-sequence current transformers, and the transformation ratio of the zero-sequence current transformers is selected according to the fault current value calculated by the system during single-phase grounding.
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| CN202311682184.XA CN117650479A (en) | 2023-12-08 | 2023-12-08 | Optimization method and device for preventing single-phase grounding protection during parallel operation of multiple pump sets |
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| CN202311682184.XA CN117650479A (en) | 2023-12-08 | 2023-12-08 | Optimization method and device for preventing single-phase grounding protection during parallel operation of multiple pump sets |
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