A ring net cabinet current transformer secondary circuit broken line detection method and system

Abstract

The application discloses a ring main unit current transformer secondary circuit disconnection detection method and system, and relates to the field of power distribution network system protection automation. The method comprises the following steps: obtaining a power balance imbalance starting threshold value according to a power sum, judging whether a bus is power imbalanced according to the power balance imbalance starting threshold value, obtaining three-phase currents of incoming lines and outgoing lines of the bus when the bus is power imbalanced, calculating current imbalance degrees of the incoming lines and the outgoing lines of the bus according to the three-phase currents, judging whether a current transformer secondary circuit is abnormal according to the current imbalance degrees, calculating phase sudden change currents according to the obtained three-phase currents of the incoming lines and the outgoing lines of the bus at the same moment when the current transformer secondary circuit is abnormal, judging whether the phase sudden change currents satisfy a third preset condition, and if yes, the current transformer secondary circuit is disconnected. According to the power node power conservation principle, the line current transformer secondary circuit disconnection discrimination accuracy and rapidity are improved under the condition that bus voltages are normal.

Description

Technical Field

[0001] This invention relates to the field of power distribution network system protection automation, and in particular to a method and system for detecting open circuits in the secondary circuit of a current transformer in a ring main unit. Background Technology

[0002] Current transformers are an important piece of equipment in power distribution systems. They convert the large current in the transmission lines of primary equipment into a small current that can be used by secondary equipment for measurement, protection, and automation devices. In actual operation, the secondary circuit of the current transformer may experience line breaks or loose connections due to various reasons. Because of the loose or broken terminals, the current transformer generates overvoltage, causing arcing and burning of the conductors and oxidation of the terminals, which seriously endangers the operation of electrical equipment and personal safety.

[0003] How to accurately detect open circuits in the secondary circuit of current transformers? Currently, all methods for judging open circuits in the secondary circuit of current transformers in low-voltage distribution systems have dead zones and blind zones. How to avoid these dead zones is an urgent problem that needs to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for detecting open circuits in the secondary circuit of a current transformer in a ring main unit, in order to address the shortcomings of the existing technology.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for detecting open circuits in the secondary circuit of a current transformer in a ring main unit includes:

[0007] S1, calculate the total power of the incoming and outgoing lines of the busbar in the ring main unit;

[0008] S2, obtain the power imbalance start-up threshold value based on the total power;

[0009] S3, determine whether the bus is in a power imbalance based on the power imbalance start threshold value;

[0010] S4, when the bus power is unbalanced, obtain the three-phase current of the incoming and outgoing lines of the bus;

[0011] S5, calculate the current imbalance of the incoming and outgoing lines of the busbar based on the three-phase current;

[0012] S6. Determine whether the secondary circuit of the current transformer in the ring main unit is abnormal based on the current imbalance.

[0013] S7. When the secondary circuit of the current transformer is abnormal, calculate the phase change current based on the three-phase currents of the incoming and outgoing lines of the bus obtained at the same time.

[0014] S8, determine whether the phase sudden current meets the third preset condition; if it does, the secondary circuit of the current transformer is disconnected.

[0015] S9 sends the disconnection alarm to cloud operations and maintenance.

[0016] The beneficial effects of this invention are: This solution utilizes the power conservation principle at power nodes to improve the accuracy and speed of identifying open circuits in the secondary circuit of the line current transformer under normal bus voltage conditions.

[0017] Furthermore, the step of determining whether the bus has a power imbalance based on the power imbalance start-up threshold specifically includes:

[0018] Determine whether the power imbalance start threshold value meets the first preset condition; if it does, the bus power is unbalanced.

[0019] Furthermore, the step of determining whether the secondary circuit of the current transformer is abnormal based on the current imbalance specifically includes:

[0020] Determine whether the current imbalance meets the second preset condition; if it does, the secondary circuit of the current transformer is abnormal.

[0021] Furthermore, the first preset condition includes:

[0022] The power imbalance start threshold is equal to the operating power in both the incoming and outgoing power.

[0023] The second preset condition includes:

[0024] The maximum value of the current imbalance is greater than 40%;

[0025] The third preset condition includes:

[0026] The phase change current is a negative change, and the negative change amplitude is greater than the preset amplitude and the current after imbalance is less than the preset current value.

[0027] Furthermore, the following is included before S1:

[0028] Current sensors are installed on the incoming and outgoing lines of the secondary circuit of the ring main unit.

[0029] An anomaly detection was performed on the three-phase voltage circuit of the PT transformer on the busbar of the ring main unit, and the three-phase voltage detection was normal.

[0030] Another technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0031] A circuit break detection system for the secondary circuit of a current transformer in a ring main unit includes: a power calculation module, a start-up threshold calculation module, a first judgment module, a bus current acquisition module, a current imbalance calculation module, a second judgment module, a phase change current calculation module, a third judgment module, and an alarm module.

[0032] The power calculation module is used to calculate the total power of the incoming and outgoing lines of the busbar in the ring main unit;

[0033] The startup threshold calculation module is used to obtain the power imbalance startup threshold value based on the total power.

[0034] The first judgment module is used to determine whether the bus is in a power imbalance based on the power imbalance start threshold value;

[0035] The bus current acquisition module is used to acquire the three-phase current of the incoming and outgoing lines of the bus when the bus power is unbalanced.

[0036] The current imbalance calculation module is used to calculate the current imbalance of the incoming and outgoing lines of the busbar based on the three-phase current.

[0037] The second judgment module is used to determine whether the secondary circuit of the current transformer in the ring main unit is abnormal based on the current imbalance.

[0038] The phase change current calculation module is used to calculate the phase change current based on the three-phase currents of the incoming and outgoing lines of the bus obtained at the same time when the secondary circuit of the current transformer is abnormal.

[0039] The third judgment module is used to determine whether the phase sudden current meets the third preset condition. If it does, the secondary circuit of the current transformer is disconnected.

[0040] The alarm module is used to send disconnection alarms to cloud operations and maintenance.

[0041] The beneficial effects of this invention are: This solution utilizes the power conservation principle at power nodes to improve the accuracy and speed of identifying open circuits in the secondary circuit of the line current transformer under normal bus voltage conditions.

[0042] Furthermore, the first judgment module is specifically used to determine whether the power imbalance start threshold value meets the first preset condition; if it does, the bus power is unbalanced.

[0043] Furthermore, the second judgment module is specifically used to determine whether the current imbalance meets the second preset condition; if it does, the secondary circuit of the current transformer is abnormal.

[0044] Furthermore, the first preset condition includes:

[0045] The power imbalance start threshold is equal to the operating power in both the incoming and outgoing power.

[0046] The second preset condition includes:

[0047] The maximum value of the current imbalance is greater than 40%;

[0048] The third preset condition includes:

[0049] The phase change current is a negative change, and the negative change amplitude is greater than the preset amplitude and the current after imbalance is less than the preset current value.

[0050] Furthermore, it also includes: a pre-configuration module for configuring current sensors on the incoming and outgoing lines of the secondary circuit of the ring main unit;

[0051] An anomaly detection was performed on the three-phase voltage circuit of the PT transformer on the busbar of the ring main unit, and the three-phase voltage detection was normal.

[0052] The advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0053] Figure 1 A flowchart illustrating a method for detecting open circuits in the secondary circuit of a current transformer in a ring main unit, provided as an embodiment of the present invention.

[0054] Figure 2 A structural framework diagram of a circuit break detection system for the secondary circuit of a current transformer in a ring main unit, provided for an embodiment of the present invention;

[0055] Figure 3 Electrical wiring diagrams for online detection methods of open circuits in the secondary circuits of current transformers in distribution network ring main units, provided for other embodiments of the present invention;

[0056] The components represented by each number in the attached diagram are as follows: 1-Bus power node; 2-Gateway; 3-Those with the same shape are sensors; 4-Those with the same shape represent voltage transformers (PT); 5-Those with the same shape represent current transformers (CT); 6-Cloud maintenance master station; 7-Those connected to the sensors are the secondary circuits of the current transformers; 8-Bus. Detailed Implementation

[0057] The principles and features of the present invention are described below with reference to the accompanying drawings. The embodiments described are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0058] like Figure 1 As shown, an embodiment of the present invention provides a method for detecting open circuits in the secondary circuit of a current transformer in a ring main unit, comprising:

[0059] S1. Calculate the total power of the incoming and outgoing lines of bus 8 in the ring main unit.

[0060] It should be noted that the calculation process of the total power can include:

[0061] The total active power of the incoming and outgoing lines on the ring main unit bus 8 is calculated as the operating power |∑Pd|, where the operating power |∑Pd| = |Pk1 + Pk2 + Pk3 + Pk4 + Pk5|, and the sum of the negative powers and the sum of the positive powers with the smallest value is the braking power ∑|Pr|.

[0062] ∑|Pr| = min(∑|P negative|, ∑|P positive|).

[0063] Incoming line power:

[0064] ∑|P negative| = |Pk1|.

[0065] Outgoing line power:

[0066] ∑|P positive| = |Pk2| + |Pk3| + |Pk4| + |Pk5|.

[0067] When calculating the incoming and outgoing line powers on the ring main unit bus 8 without considering the line loss of bus 8, the total active power of all lines:

[0068] ∑|P| = |Pk1| + |Pk2| + |Pk3| + |Pk4| + |Pk5|.

[0069] S2. Obtain the power balance imbalance start threshold value according to the total power.

[0070] It should be noted that the calculation process of the power balance imbalance start threshold value can include:

[0071] △P is the power balance imbalance start threshold value, and △P takes 0.2 times the minimum value of (Pk(1)~Pk(5)), where k = min(∑|P negative|, ∑|P positive|) / max(∑|P negative|, ∑|P positive|); the K value is a real-time dynamic calculation value, and it is approximately = 1 when balanced.

[0072] S3. Judge whether the bus 8 is power imbalanced according to the power balance imbalance start threshold value.

[0073] It should be noted that judging whether there is power imbalance can include:

[0074] If the operating power |∑Pd| < ΔP or the operating power |∑Pd| > ΔP and the braking power ∑|Pr| satisfy not less than K*∑|P|, where K is a coefficient of 0.5, then the power of bus 8 of the ring main unit is considered balanced. Record the three-phase currents (Iah, Ibh, Ich) of sensor 3 for incoming line K1 and outgoing lines (K2, K3, K4, K5). Otherwise, the power of bus 8 of the ring main unit is considered unbalanced. It should be noted that the power imbalance may or may not be defined as ΔP = |∑Pd|. Power imbalance:

[0075] |∑Pd|>△P;∑|Pr| <K*∑|P|。

[0076] S4, when the power of the bus 8 is unbalanced, obtain the three-phase current of the incoming and outgoing lines of the bus 8;

[0077] S5, calculate the current imbalance of the incoming and outgoing lines of the busbar 8 based on the three-phase current;

[0078] S6. Determine whether the secondary circuit 7 of the current transformer in the ring main unit is abnormal based on the current imbalance.

[0079] It should be noted that determining whether the secondary circuit 7 of the current transformer is abnormal may include: calculating the current imbalance ε of the incoming line K1 and the outgoing lines (K2, K3, K4, K5) by using the three-phase currents of the marked lines K1, K2, K3, K4, and K5 after the imbalance is obtained. I2 The maximum current imbalance and the current imbalance ε I2 A current transformer secondary circuit 7 with a current rating greater than 40% is considered abnormal. It should be noted that the input and output power of bus 8 is conserved and should be 0; however, if a phase of a line is disconnected or the reverse calculated power decreases, the input and output power of bus 8 will not be 0.

[0080] S7, When the secondary circuit 7 of the current transformer is abnormal, the phase change current is calculated based on the three-phase currents of the incoming and outgoing lines of the busbar 8 obtained at the same time.

[0081] S8, determine whether the phase sudden current meets the third preset condition; if it does, the secondary circuit 7 of the current transformer is disconnected.

[0082] S9 sends the disconnection alarm to Cloud Operations 6.

[0083] It should be noted that the phase transition current is calculated by subtracting the in-phase unbalanced currents (Ias, Ibs, Ics) of K1, K2, K3, K4, and K5 from the simultaneously acquired balanced three-phase currents (Iah, Ibh, Ich) of K1, K2, K3, K4, and K5.

[0084] △Iφ=|Iφh-Iφs|,

[0085] If the phase current change is negative and the negative change amplitude ΔIφ > 0.1In, and the current after imbalance Iφs < 0.01In, where φ represents any one of the three phases {a, b, c}, the secondary circuit 7 of the current transformer for that phase is determined to be disconnected, and an alarm for the disconnection of the secondary circuit 7 of the current transformer for that phase is sent to the cloud operation and maintenance 6. The third preset condition may include: the phase current change is negative and the negative change amplitude ΔIφ > 0.1In, and the current after imbalance Iφs < 0.01In.

[0086] This solution utilizes the power conservation principle at power nodes to improve the accuracy and speed of detecting open circuits in the secondary circuit 7 of the line current transformer under normal voltage conditions at bus 8.

[0087] Optionally, in any of the above embodiments, determining whether the bus 8 has a power imbalance based on the power imbalance start-up threshold specifically includes:

[0088] Determine whether the power imbalance start threshold value meets the first preset condition. If it does, then the power of bus 8 is unbalanced.

[0089] Optionally, in any of the above embodiments, the step of determining whether the secondary circuit 7 of the current transformer is abnormal based on the current imbalance specifically includes:

[0090] Determine whether the current imbalance meets the second preset condition. If it does, the secondary circuit 7 of the current transformer is abnormal.

[0091] Optionally, in any of the above embodiments, the first preset condition includes:

[0092] The power imbalance start threshold is equal to the operating power in both the incoming and outgoing power.

[0093] The second preset condition includes:

[0094] The maximum value of the current imbalance is greater than 40%;

[0095] The third preset condition includes:

[0096] The phase change current is a negative change, and the negative change amplitude is greater than the preset amplitude and the current after imbalance is less than the preset current value.

[0097] Optionally, in any of the above embodiments, the method further includes the following step before step S1:

[0098] Current sensors 3 are respectively configured on the incoming and outgoing lines of the secondary circuit 7 of the ring main unit;

[0099] An anomaly detection was performed on the three-phase voltage circuit of the PT transformer on busbar 8 of the ring main unit, and the three-phase voltage detection was normal.

[0100] It should be noted that, in one embodiment, the voltage sensor 3 monitors the three-phase voltage, K1 incoming line, and outgoing line (e.g., the voltage of the PT transformer (4) on the ring main unit bus 8 of the diagram) of the ring main unit. Figure 3 Each of K2, K3, K4, and K5 is equipped with a current sensor 3 to monitor the three-phase current of each line; the gateway 2 is synchronized with the GPS clock, the gateway 2 is synchronized with the sensor 3, and the sensors 3 are synchronized with each other with a synchronization accuracy of less than 10µs. Does the system have power balance calculation capabilities, i.e., the steps S1-S9?

[0101] Gateway 2 first performs anomaly detection on the three-phase voltage circuit of PT voltage transformer 4. Using the real and imaginary parts of the three-phase voltages at the same time, it calculates the negative sequence voltage and the three-phase voltage imbalance ε according to the standard "GBT 19862-2005 General Requirements for Power Quality Monitoring Equipment". U2 If the voltage imbalance is less than 2% of the power quality requirement, the three-phase voltage is considered normal. If the voltage imbalance is not greater than 2%, it means that the three-phase voltage on bus 8 is normal, and power balance calculation can be performed, i.e., steps S1-S9.

[0102] In some embodiments, a method for real-time monitoring of power conservation within a power node and identifying open circuits in the secondary circuit 7 of a current transformer based on sudden changes in current loop sample values ​​is provided. The electrical wiring diagram for the online detection method of open circuits in the secondary circuit 7 of a current transformer in a distribution network ring main unit is shown below. Figure 3 As shown, voltage sensor 3 monitors the three-phase voltage of bus 8, and each incoming and outgoing line is equipped with a current sensor 3 to monitor the three-phase current of the line.

[0103] First, Gateway 2 synchronizes with the GPS. After synchronization, Gateway 2 sends a synchronization command to Sensor 3 within the system. Sensor 3 automatically synchronizes with Gateway 2 upon receiving the synchronization command until the synchronization accuracy is less than 10µs. Once all Sensor 3 is synchronized, it sends a synchronization flag to Gateway 2. Gateway 2 then marks the synchronization status of Sensor 3, and system synchronization is complete. Gateway 2 sends a synchronization command every 1 second to ensure that the synchronization accuracy between Gateway 2 and all Sensor 3 is less than 10µs, and that the synchronization accuracy among all Sensor 3 is less than 10µs. The system can acquire the time-stamped three-phase voltage and three-phase current from all Sensor 3 within the system. Current Sensor 3 sends the time-stamped real and imaginary parts of the three-phase current, and voltage Sensor 3 sends the time-stamped real and imaginary parts of the voltage to Gateway 2. Gateway 2 first performs anomaly detection on the three-phase voltage circuit of the PT cabinet. Using the real and imaginary parts of the voltage at the same time, it calculates the negative sequence voltage and three-phase voltage imbalance ε according to the standard "GBT 19862-2005 General Requirements for Power Quality Monitoring Equipment". U2If the voltage imbalance is less than 2% of the power quality requirement, the three-phase voltage is considered normal. If the voltage imbalance is greater than 4%, the three-phase voltage is abnormal, and no three-phase current anomaly detection is performed by other current sensors 3. After the three-phase voltage is detected as normal, gateway 2 uses the three-phase current of sensor 3 with the same time scale to perform phase sequence anomaly detection.

[0104] The power direction of the incoming and outgoing lines on busbar 8 is as follows: power flowing towards busbar 8 is negative, and power flowing from busbar 8 to the line is positive. The power loss of busbar 8 in the ring main unit is relatively small and can be ignored. The sum of all active power of the incoming and outgoing lines on busbar 8 of the ring main unit is the operating power |∑Pd|, where |∑Pd|=|Pk1+Pk2+Pk3+Pk4+Pk5|. The minimum sum of negative power and positive power is the braking power ∑|Pr|, where ∑|Pr|=min(∑|Pnegative|, ∑|P Positive|). The incoming line power ∑|Pnegative|=|Pk 1|,Outgoing power ∑|P positive|=|Pk2|+|Pk3|+|Pk4|+|Pk5|. Without considering the line loss of bus 8, the power of incoming and outgoing lines on the ring network cabinet bus 8 is calculated. The total active power of all lines is ∑|P|=|Pk1|+|Pk2|+|Pk3|+|Pk4|+|Pk5|. △P is the threshold value for power imbalance start-up. △P is taken as 0.2 times the minimum value among (Pk(1)~Pk(5)). k is taken as min(∑|P negative|,∑|P positive|) / max(∑|P negative|,∑|P positive|). If the operating power |∑Pd| < ΔP or the operating power |∑Pd| > ΔP and the braking power ∑|Pr| are not less than K*∑|P|, the power of the ring main unit bus 8 is judged to be balanced. The three-phase currents (Iah, Ibh, Ich) of each sensor are recorded respectively. Otherwise, the power of the ring main unit bus 8 is judged to be unbalanced. The three-phase currents (Ias, Ibs, Ics) of each sensor are recorded respectively. The current imbalance degree ε of the incoming and outgoing lines is calculated by using the three-phase currents simultaneously marked after the imbalance. I2 =I2 / I1, the maximum current imbalance and the current imbalance ε I2 If more than 40% of the secondary circuit 7 of the line current transformer is abnormal, subtract the unbalanced current (Ias, Ibs, Ics) of the same phase from the simultaneously acquired balanced three-phase current (Iah, Ibh, Ich) to calculate the phase sudden current ΔIφ = Iφh - Iφs. If the phase sudden current is negative and the negative sudden current amplitude ΔIφ > 0.1In, and the current after imbalance Iφs < 0.01In, where φ represents any phase of the three phases {a, b, c}, it is determined that the secondary circuit 7 of the phase current is disconnected, and an alarm for the secondary circuit 7 of the phase current is sent to the cloud operation and maintenance 6.

[0105] In one embodiment, such as Figure 2As shown, a circuit break detection system for the secondary circuit of a current transformer in a ring main unit includes: a power calculation module 1101, a start-up threshold calculation module 1102, a first judgment module 1103, a bus current acquisition module 1104, a current imbalance calculation module 1105, a second judgment module 1106, a phase change current calculation module 1107, a third judgment module 1108, and an alarm module 1109.

[0106] The power calculation module 1101 is used to calculate the total power of the incoming and outgoing lines of the busbar 8 in the ring main unit;

[0107] The startup threshold calculation module 1102 is used to obtain the power imbalance startup threshold value based on the total power.

[0108] The first judgment module 1103 is used to determine whether the bus 8 is in a power imbalance based on the power imbalance start threshold value;

[0109] The bus current acquisition module 1104 is used to acquire the three-phase current of the incoming and outgoing lines of the bus 8 when the power of the bus 8 is unbalanced.

[0110] The current imbalance calculation module 1105 is used to calculate the current imbalance of the incoming and outgoing lines of the busbar 8 based on the three-phase current.

[0111] The second judgment module 1106 is used to determine whether the secondary circuit 7 of the current transformer in the ring main unit is abnormal based on the current imbalance.

[0112] The phase change current calculation module 1107 is used to calculate the phase change current based on the three-phase currents of the incoming and outgoing lines of the busbar 8 obtained at the same time when the secondary circuit 7 of the current transformer is abnormal.

[0113] The third judgment module 1108 is used to determine whether the phase sudden current meets the third preset condition. If it does, the secondary circuit 7 of the current transformer is disconnected.

[0114] The alarm module 1109 is used to send the disconnection alarm to the cloud operation and maintenance 6.

[0115] This solution utilizes the power conservation principle at power nodes to improve the accuracy and speed of detecting open circuits in the secondary circuit 7 of the line current transformer under normal voltage conditions at bus 8.

[0116] Optionally, in some embodiments, the first judgment module 1103 is specifically used to determine whether the power imbalance start threshold value meets the first preset condition, and if it does, the bus 8 is in a power imbalance.

[0117] Optionally, in some embodiments, the second judgment module 1106 is specifically used to determine whether the current imbalance meets the second preset condition; if it does, the secondary circuit 7 of the current transformer is abnormal.

[0118] Optionally, in some embodiments, the first preset condition includes:

[0119] The power imbalance start threshold is equal to the operating power in both the incoming and outgoing power.

[0120] The second preset condition includes:

[0121] The maximum value of the current imbalance is greater than 40%;

[0122] The third preset condition includes:

[0123] The phase change current is a negative change, and the negative change amplitude is greater than the preset amplitude and the current after imbalance is less than the preset current value.

[0124] Optionally, in some embodiments, it further includes: a pre-configuration module for configuring current sensors 3 on the incoming and outgoing lines of the secondary circuit 7 of the ring main unit respectively;

[0125] An anomaly detection was performed on the three-phase voltage circuit of the PT transformer on busbar 8 of the ring main unit, and the three-phase voltage detection was normal.

[0126] It is understood that in some embodiments, some or all of the optional implementations as described in the above embodiments may be included.

[0127] It should be noted that the above embodiments are product embodiments corresponding to the prior method embodiments. For the description of each optional implementation in the product embodiments, please refer to the corresponding description in the above method embodiments, which will not be repeated here.

[0128] In one embodiment, a method for online detection of open circuit in the secondary circuit of a current transformer in a ring main unit includes:

[0129] The first step is to monitor the three-phase voltage of the PT transformer (4) on the busbar 8 by voltage sensor 3, and to configure a current sensor 3 for each of the K1 incoming and outgoing lines (K2, K3, K4, K5) to monitor the three-phase current of each line; the gateway 2 is synchronized with the GPS clock, the gateway 2 is synchronized with the sensor 3, and the sensors 3 are synchronized with each other, with a synchronization accuracy of less than 10us, and the system has power balance calculation.

[0130] The second step involves gateway 2 first performing anomaly detection on the three-phase voltage circuit of PT voltage transformer 4. Using the real and imaginary parts of the three-phase voltages at the same time, it calculates the negative sequence voltage and the three-phase voltage imbalance ε according to the standard "GBT19862-2005 General Requirements for Power Quality Monitoring Equipment".U2 If the voltage imbalance is less than 2% of the power quality requirement, the three-phase voltage is considered normal. If the voltage imbalance is not greater than 2%, it means that the three-phase voltage on bus 8 is normal, and power balance calculation can be performed.

[0131] The third step is to calculate the total active power of all incoming and outgoing lines on busbar 8 of the ring main unit as the operating power |∑Pd|. The operating power |∑Pd|=|Pk1+Pk2+Pk3+Pk4+Pk5|. The minimum sum of negative power and positive power is the braking power ∑|Pr|, ∑|Pr|=min(∑|Pnegative|,∑|Positive|). The incoming line power ∑|Pnegative|=|Pk1|, and the outgoing line power ∑|Ppositive|=|Pk2|+|Pk3|+|Pk4|. |+|Pk5|. Without considering the line loss of bus 8, the power of incoming and outgoing lines on bus 8 of the ring network cabinet is calculated. The total active power of all lines is ∑|P|=|Pk1|+|Pk2|+|Pk3|+|Pk4|+|Pk5|, △P is the threshold value for power imbalance start-up. △P is taken as 0.2 times the minimum value among (Pk(1)~Pk(5)), and k is taken as min(∑|Pnegative|,∑|P Positive|) / max(∑|Pnegative|,∑|P Positive|).

[0132] Step 4: If the operating power |∑Pd| < ΔP or the operating power |∑Pd| > ΔP and the braking power ∑|Pr| are not less than K*∑|P|, where K is a coefficient of 0.5, then the power of bus 8 of the ring main unit is considered balanced. Record the three-phase currents (Iah, Ibh, Ich) of sensor 3 for incoming line K1 and outgoing lines (K2, K3, K4, K5). Otherwise, the power of bus 8 of the ring main unit is considered unbalanced. The power imbalance is determined by whether ΔP = |∑Pd|; whether |∑Pd| > ΔP; and whether ∑|Pr| is less than K*∑|P|. <K*∑|P|。

[0133] The fifth step is to use the three-phase currents of the target lines K1, K2, K3, K4, and K5 after the imbalance to calculate the current imbalance ε of the incoming line of K1 and the outgoing lines of (K2, K3, K4, and K5). I2 The maximum current imbalance and the current imbalance ε I2 A current transformer secondary circuit 7 with a current rating greater than 40% is considered abnormal. For bus 8, the input and output power is conserved and should be 0. However, if a phase of a line is disconnected or the reverse calculated power decreases, the input and output power of bus 8 will not be 0.

[0134] Step 6: Subtract the unbalanced currents (Ias, Ibs, Ics) of the same phase of K1, K2, K3, K4, and K5 from the balanced three-phase currents (Iah, Ibh, Ich) acquired at the same time. Calculate the phase change current ΔIφ = |Iφh - Iφs|. If the phase change current is negative and the negative change amplitude ΔIφ > 0.1In, and the unbalanced current Iφs < 0.01In, where φ represents any phase of the three phases {a, b, c}, determine that the secondary circuit 7 of the current transformer in that phase is disconnected, and send an alarm for the disconnection of the secondary circuit 7 of the current transformer in that phase to the cloud operation and maintenance 6.

[0135] Step 7: If the results of steps 2, 3, 4, 5, and 6 are met, the secondary circuit 7 of the current transformer is determined to be disconnected.

[0136] It should be noted that the imaginary and real parts of the three-phase voltage obtained by voltage sensor 3 are used to calculate whether the phase sequence and amplitude meet the requirements for calculating the negative sequence voltage and three-phase voltage imbalance ε according to the standard "GBT 19862-2005 General Requirements for Power Quality Monitoring Equipment". U2 If the voltage imbalance is less than 2% of the power quality requirement, the three-phase voltage is considered normal.

[0137] After the three-phase voltage of bus 8 is normal, the operating power of bus 8 is calculated. If the operating power |∑Pd| < △P or the operating power |∑Pd| > △P and the braking power ∑|Pr| are not less than K*∑|P|, the power of bus 8 of the ring main unit is judged to be balanced; otherwise, the power of bus 8 of the ring main unit is judged to be unbalanced. The criterion for the unbalanced operating zone is that △P is the threshold value for the start of power balance and unbalance. △P is taken as 0.2 times the minimum value among (Pk(1)~Pk(5)), and k is taken as min(∑|Pnegative|,∑|P Positive|) / max(∑|Pnegative|,∑|P Positive|). The operating zone is automatically adjusted according to the calculated operating power △P and the adaptive ratio coefficient K to meet the adaptive operating zone setting of different operating power and braking power of the system.

[0138] Busbar 8 experiences power imbalance. Locate the abnormal line causing the power imbalance and calculate the current imbalance ε of the incoming and outgoing lines using the three-phase currents simultaneously measured after the imbalance. I2 The maximum current imbalance and the current imbalance ε I2 >40% of the secondary circuits of the line current transformers are abnormal;

[0139] The abnormal line causing the power imbalance of busbar 8 is identified. Using the principle of current mutation, a phase is determined to be disconnected. The unbalanced currents (Ias, Ibs, Ics) of the same phase are subtracted from the balanced three-phase currents (Iah, Ibh, Ich) at the same moment to calculate the phase mutation current ΔIφ = |Iφh - Iφs|. The phase mutation current is negative and the negative mutation amplitude ΔIφ > 0.1In, and the current after imbalance Iφs < 0.01In. φ represents any phase of the three phases {a, b, c}. It is determined that the secondary circuit 7 of the current transformer of that phase is disconnected, and an alarm for the secondary circuit 7 of the current transformer of that phase is disconnected is sent to the cloud operation and maintenance 6.

[0140] Readers should understand that in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0141] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the method embodiments described above are merely illustrative. For instance, the division of steps is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple steps may be combined or integrated into another step, or some features may be ignored or not executed.

[0142] If the above methods are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0143] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for detecting open circuits in the secondary circuit of a current transformer in a ring main unit, characterized in that, include: S1, calculate the total power of the incoming and outgoing lines of the busbar in the ring main unit; S2, obtain the power imbalance start-up threshold value based on the total power; S3, determine whether the bus is in a power imbalance based on the power imbalance start threshold value; S4, when the bus power is unbalanced, obtain the three-phase current of the incoming and outgoing lines of the bus; S5, calculate the current imbalance of the incoming and outgoing lines of the busbar based on the three-phase current; S6. Determine whether the secondary circuit of the current transformer in the ring main unit is abnormal based on the current imbalance. S7. When the secondary circuit of the current transformer is abnormal, calculate the phase change current based on the three-phase currents of the incoming and outgoing lines of the bus obtained at the same time. S8, determine whether the phase sudden current meets the third preset condition; if it does, the secondary circuit of the current transformer is disconnected. S9 sends the disconnection alarm to cloud operations and maintenance; The step of determining whether the bus has a power imbalance based on the power imbalance start-up threshold specifically includes: Determine whether the power imbalance start threshold value meets the first preset condition; if it does, the bus power is unbalanced. The step of determining whether the secondary circuit of the current transformer is abnormal based on the current imbalance specifically includes: Determine whether the current imbalance meets the second preset condition; if it does, the secondary circuit of the current transformer is abnormal. The first preset conditions include: The power imbalance start threshold is equal to the operating power in both the incoming and outgoing power. The second preset condition includes: The maximum value of the current imbalance is greater than 40%; The third preset condition includes: The phase change current is a negative change, and the negative change amplitude is greater than the preset amplitude and the current after imbalance is less than the preset current value.

2. The method for detecting open circuits in the secondary circuit of a current transformer in a ring main unit according to claim 1, characterized in that, Before S1, the following also applies: Current sensors are installed on the incoming and outgoing lines of the secondary circuit of the ring main unit. An anomaly detection was performed on the three-phase voltage circuit of the PT transformer on the busbar of the ring main unit, and the three-phase voltage detection was normal.

3. A system for detecting open circuits in the secondary circuit of a current transformer in a ring main unit, characterized in that, include: The system includes a power calculation module, a start-up threshold calculation module, a first judgment module, a bus current acquisition module, a current imbalance calculation module, a second judgment module, a phase change current calculation module, a third judgment module, and an alarm module. The power calculation module is used to calculate the total power of the incoming and outgoing lines of the busbar in the ring main unit; The startup threshold calculation module is used to obtain the power imbalance startup threshold value based on the total power. The first judgment module is used to determine whether the bus is in a power imbalance based on the power imbalance start threshold value; The bus current acquisition module is used to acquire the three-phase current of the incoming and outgoing lines of the bus when the bus power is unbalanced. The current imbalance calculation module is used to calculate the current imbalance of the incoming and outgoing lines of the busbar based on the three-phase current. The second judgment module is used to determine whether the secondary circuit of the current transformer in the ring main unit is abnormal based on the current imbalance. The phase change current calculation module is used to calculate the phase change current based on the three-phase currents of the incoming and outgoing lines of the bus obtained at the same time when the secondary circuit of the current transformer is abnormal. The third judgment module is used to determine whether the phase sudden current meets the third preset condition. If it does, the secondary circuit of the current transformer is disconnected. The alarm module is used to send disconnection alarms to cloud operations and maintenance. The first judgment module is specifically used to determine whether the power imbalance start threshold value meets the first preset condition; if it does, the bus power is unbalanced. The second judgment module is specifically used to determine whether the current imbalance meets the second preset condition. If it does, the secondary circuit of the current transformer is abnormal. The first preset conditions include: The power imbalance start threshold is equal to the operating power in both the incoming and outgoing power. The second preset condition includes: The maximum value of the current imbalance is greater than 40%; The third preset condition includes: The phase change current is a negative change, and the negative change amplitude is greater than the preset amplitude and the current after imbalance is less than the preset current value.

4. The open circuit detection system for the secondary circuit of a current transformer in a ring main unit according to claim 3, characterized in that, Also includes: A pre-configured module is used to configure current sensors on the incoming and outgoing lines of the secondary circuit of the ring main unit. An anomaly detection was performed on the three-phase voltage circuit of the PT transformer on the busbar of the ring main unit, and the three-phase voltage detection was normal.

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