A transformer open-phase detection method and protection method

Abstract

This invention discloses a transformer phase loss detection method and protection method, belonging to the field of power system relay protection technology. The method includes: acquiring the transformer high-voltage side voltage, transformer high-voltage side current, transformer high-voltage side neutral point zero-sequence current, and transformer low-voltage side voltage; determining whether a single-phase phase loss has occurred on the high-voltage side; determining whether a two-phase phase loss has occurred on the high-voltage side; determining whether a single-phase phase loss has occurred on the high-voltage side busbar incoming line; and determining whether a two-phase phase loss has occurred on the high-voltage side busbar incoming line. This transformer phase loss detection method and protection method realize the detection of high-voltage side phase loss faults and high-voltage side busbar incoming line open-circuit faults under no-load or light-load conditions. A passive zero-flux high-precision instrument transformer is used to detect the transformer high-voltage side neutral point current, thus realizing the detection of high-voltage side phase loss faults and high-voltage side busbar incoming line open-circuit faults. The high-voltage side neutral point current is activated under no-load or light-load conditions and deactivated under loaded conditions, improving the reliability of the phase loss detection and protection operation.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, specifically relating to a transformer phase loss detection method and protection method. Background Technology

[0002] A broken power line or a phase loss caused by a fault in the power transmission and transformation equipment at a nuclear power plant can lead to motor tripping and reactor shutdown. When a transformer is under no-load or light-load conditions, due to the interconnected magnetic circuits of each phase in a three-phase, three-limb transformer, after a phase on the high-voltage side breaks, the magnetic flux of the broken phase can be synthesized by the magnetic flux of the two intact phases. Therefore, a higher voltage will still be induced at the output terminal of the low-voltage coil corresponding to the fault, preventing the low-voltage busbar on the low-voltage side from issuing a low-voltage alarm. This poses a risk of loss of cooling for the nuclear reactor, adversely affecting the safety of the nuclear power unit. Since auxiliary transformers in nuclear power plants require additional phase loss protection, a new method for detecting and protecting against transformer phase loss needs to be developed to address these existing problems. Summary of the Invention

[0003] The purpose of this invention is to provide a transformer phase loss detection method and protection method to solve the problem of difficulty in detecting phase loss faults in transformers under no-load or light-load conditions.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for collecting transformer high-voltage side voltage, transformer high-voltage side current, transformer high-voltage side neutral point zero-sequence current, and transformer low-voltage side voltage;

[0005] The high-voltage side single-phase phase failure discrimination rules are used to determine whether a single-phase phase failure has occurred on the high-voltage side. The high-voltage side single-phase phase failure selection discrimination rules are used to determine which phase has failed. In other words, the high-voltage side single-phase phase failure selection discrimination rules are used to determine which phase has failed.

[0006] The two-phase phase failure judgment rule of the high-voltage side of the transformer is used to determine whether a two-phase phase failure has occurred on the high-voltage side. The two-phase phase failure selection judgment rule of the high-voltage side is used to determine which two phases have failed, that is, to determine the selected phase or phase of the two phases that have failed on the high-voltage side.

[0007] The single-phase failure of the high-voltage side busbar incoming line is determined by the single-phase failure judgment rule. The single-phase failure of the busbar incoming line is selected by the single-phase failure selection rule.

[0008] The two-phase failure judgment rule of the high-voltage side busbar incoming line is used to determine whether a two-phase failure of the high-voltage side busbar incoming line has occurred. The two-phase failure of the busbar incoming line phase selection judgment rule is used to determine which phase has failed and to determine the selected phase or phase of the two-phase failure of the high-voltage side busbar incoming line.

[0009] If the phase failure detection logic of the protection device determines that a phase failure has occurred, it will trigger an alarm after the first time limit and trip after the second time limit.

[0010] Preferably, the single-phase failure judgment rule on the high-voltage side of the transformer includes: simultaneously satisfying the following conditions;

[0011] The high-voltage side voltage is normal;

[0012] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0013] The low-voltage side voltage is normal;

[0014] The neutral point current on the high-voltage side is greater than the trip setting.

[0015] Among them, the current threshold is relatively conventional, generally ranging from 0.01 to 0.04IN, where IN represents the secondary rated current of the current transformer;

[0016] The rules for determining whether the high-voltage side voltage and the low-voltage side voltage are normal include:

[0017] The high-voltage side three-phase voltage generates a zero-sequence voltage that is less than the zero-sequence voltage threshold and a negative-sequence voltage that is less than the negative-sequence voltage threshold, and all three-phase voltages are greater than 0.9U. N ;

[0018] The low-voltage side three-phase voltage generates a zero-sequence voltage that is less than the zero-sequence voltage threshold and a negative-sequence voltage that is less than the negative-sequence voltage threshold, and all three-phase voltages are greater than 0.9U. N ;

[0019] U N This is the rated secondary voltage of the voltage transformer.

[0020] Preferably, the high-voltage side single-phase phase loss selection rule adopts the cross-virtual power phase selection principle, including:

[0021] The voltage U on the low-voltage side of the transformer ab With the zero-sequence current 3I0 at the neutral point on the high-voltage side h Calculate the virtual power P of phase A crossover. Nab Among them, 3I0 h This represents the zero-sequence current at the neutral point on the high-voltage side.

[0022] The voltage U on the low-voltage side of the transformer bc With the zero-sequence current 3I0 at the neutral point on the high-voltage side h Calculate the virtual power P of phase B crossover. Nbc;

[0023] The voltage U on the low-voltage side of the transformer ca With the zero-sequence current 3I0 at the neutral point on the high-voltage side h Calculate the virtual power P of phase C crossover Nca ;

[0024] Condition 1, C-phase crossover virtual power P Nca Greater than the first cross virtual power threshold a 10 And less than the second cross virtual power threshold a 11 ;

[0025] Condition 2, Phase A crossover virtual power P Nab Greater than the third cross virtual power threshold a 20 And less than the fourth cross virtual power threshold a 21 ;

[0026] Condition 3, Phase B crossover virtual power P Nbc Greater than the fifth cross virtual power threshold a 31 The negative number and less than the sixth cross virtual power threshold a 30 Negative numbers;

[0027] If conditions 1, 2, and 3 are all met simultaneously, it is determined that phase A on the high-voltage side of the transformer is disconnected; condition 4, the virtual power P of phase A. Nab Greater than the first cross virtual power threshold a 10 And less than the second cross virtual power threshold a 11 ;

[0028] Condition 5, Phase B crossover virtual power P Nbc Greater than the third cross virtual power threshold a 20 And less than the fourth cross virtual power threshold a 21 ;

[0029] Condition 6, C-phase crossover virtual power P Nca Greater than the fifth cross virtual power threshold a 31 The negative number and less than the sixth cross virtual power threshold a 30 Negative numbers;

[0030] If conditions 4, 5, and 6 are all met simultaneously, it is determined that phase B on the high-voltage side of the transformer is disconnected; condition 7, the cross-virtual power P of phase B. Nbc Greater than the first cross virtual power threshold a 10 And less than the second cross virtual power threshold a 11 ;

[0031] Condition 8, C-phase crossover virtual power P Nca Greater than the third cross virtual power threshold a 20And less than the fourth cross virtual power threshold a 21 ;

[0032] Condition 9, Phase A crossover virtual power P Nab Greater than the fifth cross virtual power threshold a 31 The negative number and less than the sixth cross virtual power threshold a 30 Negative numbers;

[0033] If conditions 7, 8, and 9 are met simultaneously, it is determined that phase C on the high-voltage side of the transformer is disconnected.

[0034] Fourth cross-virtual power threshold a 21 <First Cross Virtual Power Threshold a 10 <Second Cross Virtual Power Threshold a 11 ;

[0035] 0 < third cross virtual power threshold a 20 <Fourth Cross Virtual Power Threshold a 21 ;

[0036] Second cross-virtual power threshold a 11 <Sixth Cross Virtual Power Threshold a 30 <Fifth Cross Virtual Power Threshold a 31 .

[0037] Preferably, the two-phase loss judgment rule on the high-voltage side of the transformer includes: simultaneously satisfying the following conditions;

[0038] The high-voltage side voltage is normal;

[0039] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0040] The neutral point current on the high-voltage side is greater than the trip setting.

[0041] The voltage on the low-voltage side is one phase voltage lower than the low-voltage threshold U. Low The other two phase voltages have equal amplitudes but opposite phases.

[0042] Preferably, the high-voltage side two-phase phase loss selection rule includes:

[0043] Phase A voltage is below the low voltage threshold U Low If the voltage amplitudes of phase B and phase C are equal but their phases are opposite, then it is determined that phases A and B are disconnected.

[0044] Phase B voltage is below the low voltage threshold U Low If the voltage of phase C and the voltage of phase A have the same amplitude but opposite phase, then it is determined that phases B and C are disconnected.

[0045] Phase C voltage is below the low voltage threshold U LowIf the voltage amplitudes of phase A and phase B are equal but their phases are opposite, then it is determined that phases C and A are disconnected.

[0046] As a preferred embodiment of the protection method for phase loss detection of unloaded or lightly loaded transformers described in this invention, wherein:

[0047] The neutral point current on the high-voltage side is taken from a passive zero-flux high-precision current transformer installed at the neutral point on the high-voltage side.

[0048] Preferably, the single-phase failure judgment rule of the high-voltage side busbar incoming line of the transformer includes: simultaneously satisfying the following conditions;

[0049] One phase voltage on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of the other two phases are both greater than 0.9U. N ;

[0050] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0051] The low-voltage side voltage is normal.

[0052] Preferably, the single-phase loss phase selection rule for the high-voltage side busbar incoming line of the transformer includes:

[0053] The voltage of phase A on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of both phase B and phase C are greater than 0.9U. N The phase is determined to be A phase failure.

[0054] The voltage of phase B on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of both phase C and phase A are greater than 0.9U. N The phase B was determined to be faulty.

[0055] The voltage of phase C on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of both phase A and phase B are greater than 0.9U. N The phase was determined to be C phase failure.

[0056] Preferably, the two-phase loss judgment rule for the high-voltage side busbar incoming line of the transformer includes:

[0057] Both phase voltages on the high-voltage side are below the low-voltage threshold U. Low The voltage of the other phase is greater than 0.9U. N ;

[0058] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0059] Low-voltage side voltage, one phase voltage is lower than U Low The other two phase voltages have equal amplitudes but opposite phases.

[0060] Preferably, the phase selection rule for two-phase phase loss of the high-voltage side busbar incoming line of the transformer includes:

[0061] The voltages of both phase A and phase B on the high-voltage side are below the low-voltage threshold U. Low The voltage of phase C is greater than 0.9U. N Meanwhile, the voltage of phase A on the low-voltage side is lower than the low-voltage threshold U. Low The voltage amplitudes of phase B and phase C are equal but their phases are opposite, indicating that phases A and B are disconnected.

[0062] The voltages of both phase B and phase C on the high-voltage side are below the low-voltage threshold U. Low Phase A voltage is greater than 0.9U N Meanwhile, the voltage of phase B on the low-voltage side is lower than the low-voltage threshold U. Low Since the voltage amplitudes of phase C and phase A are equal but their phases are opposite, it is determined that phases B and C are disconnected.

[0063] The voltages of both phase C and phase A on the high-voltage side are below the low-voltage threshold U. Low Phase B voltage is greater than 0.9U. N Meanwhile, the voltage of phase C on the low-voltage side is lower than the low-voltage threshold U. Low Since the voltage amplitudes of phase A and phase B are equal but their phases are opposite, it is determined that phases C and A are disconnected.

[0064] The present invention also provides a transformer phase loss protection method, which includes the above-mentioned transformer phase loss detection method, which logically determines that a phase loss has occurred, and then triggers an alarm after a first time limit and trips after a second time limit.

[0065] The technical effects and advantages of this invention are as follows: This transformer phase loss detection and protection method realizes the detection of phase loss faults on the high-voltage side and open circuit faults in the high-voltage busbar of a transformer under no-load or light-load conditions. Addressing the difficulty of conventional transformer protection in detecting high-voltage side phase loss faults under no-load or light-load conditions, this invention employs a passive zero-flux high-precision instrument transformer to detect the neutral point current on the high-voltage side of the transformer. Combined with the high-voltage side voltage, high-voltage side current, and low-voltage side voltage, a phase loss detection and protection scheme for no-load or light-load transformers is constructed, realizing the detection of phase loss faults on the high-voltage side and open circuit faults in the high-voltage busbar of the transformer. The high-voltage side neutral point current is activated under no-load or light-load conditions and deactivated under loaded conditions, improving the reliability of the phase loss detection and protection operation. Attached Figure Description

[0066] Figure 1 This is a schematic flowchart of the detection method of the present invention;

[0067] Figure 2 This is a schematic diagram of the three-phase current on the high-voltage side and the zero-sequence current at the neutral point when a single phase is lost on the high-voltage side using the detection method of the present invention.

[0068] Figure 3This is a schematic diagram of the voltage on the high-voltage side and the low-voltage side when a single phase is lost on the high-voltage side in the detection method of the present invention;

[0069] Figure 4 This is a schematic diagram of the three-phase virtual power when phase A on the high-voltage side is disconnected in the detection method of the present invention;

[0070] Figure 5 This is a schematic diagram of the three-phase virtual power when phase B on the high-voltage side is disconnected in the detection method of the present invention;

[0071] Figure 6 This is a schematic diagram of the three-phase virtual power when phase C on the high-voltage side is disconnected in the detection method of the present invention;

[0072] Figure 7 This is a schematic diagram of the three-phase current on the high-voltage side and the zero-sequence current at the neutral point when the two phases A and B on the high-voltage side are disconnected in the detection method of the present invention;

[0073] Figure 8 This is a schematic diagram of the voltage on the high-voltage side and the low-voltage side when the AB phases are disconnected in the detection method of the present invention. Detailed Implementation

[0074] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] This invention provides, for example Figure 1 The transformer phase loss detection method shown is applicable to unloaded or lightly loaded transformers and includes the following steps:

[0076] S1: Collects the high-voltage side voltage, high-voltage side current, zero-sequence current at the neutral point of the high-voltage side, and low-voltage side voltage of the transformer;

[0077] In this embodiment, the high-voltage side voltage is taken from the high-voltage side bus voltage transformer; the high-voltage side current is taken from the high-voltage side ordinary current transformer; the neutral point zero-sequence current is taken from the neutral point passive zero-magnetic flux high-precision current transformer; and the low-voltage side voltage is taken from the low-voltage side bus voltage transformer.

[0078] S2: Use the single-phase phase failure discrimination rules on the high-voltage side of the transformer to determine whether a single-phase phase failure has occurred on the high-voltage side, and use the single-phase phase failure selection discrimination rules on the high-voltage side to determine which phase has failed.

[0079] In this embodiment of the application, the designed single-phase loss detection rule for the high-voltage side of the transformer is as follows:

[0080] The high-voltage side voltage is normal;

[0081] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0082] The low-voltage side voltage is normal;

[0083] The neutral point current on the high-voltage side is greater than the trip setting.

[0084] In this embodiment of the application, the rules for determining whether the high-voltage side voltage is normal and the low-voltage side voltage is normal are designed as follows:

[0085] The high-voltage side three-phase voltage generates a zero-sequence voltage that is less than the zero-sequence voltage threshold and a negative-sequence voltage that is less than the negative-sequence voltage threshold, and all three-phase voltages are greater than 0.9U. N ;

[0086] The low-voltage side three-phase voltage generates a zero-sequence voltage that is less than the zero-sequence voltage threshold and a negative-sequence voltage that is less than the negative-sequence voltage threshold, and all three-phase voltages are greater than 0.9U. N ;

[0087] U N This is the rated secondary voltage of the voltage transformer.

[0088] like Figure 2 and Figure 3 As shown, a phase A disconnection occurs on the high-voltage side, and a zero-sequence current is generated at the neutral point. At the same time, there is no significant change in the voltage on the high-voltage side and the voltage on the low-voltage side.

[0089] In this embodiment of the application, if a single-phase disconnection is determined to have occurred on the high-voltage side, the single-phase disconnection phase selection discrimination procedure on the high-voltage side is initiated. The procedure employs a cross-virtual power phase selection principle, including:

[0090] The voltage U on the low-voltage side of the transformer ab With the zero-sequence current 3I0 at the neutral point on the high-voltage side h Calculate the virtual power P of phase A crossover. Nab Among them, 3I0 h This represents the zero-sequence current at the neutral point on the high-voltage side.

[0091] The voltage U on the low-voltage side of the transformer bc With the zero-sequence current 3I0 at the neutral point on the high-voltage side h Calculate the virtual power P of phase B crossover. Nbc ;

[0092] The voltage U on the low-voltage side of the transformer ca With the zero-sequence current 3I0 at the neutral point on the high-voltage side h Calculate the virtual power P of phase C crossover Nca ;

[0093] ①C-phase crossover virtual power P Nca Greater than the first cross virtual power threshold a 10 And less than the second cross virtual power threshold a11 ;

[0094] ②A-phase crossover virtual power P Nab Greater than the third cross virtual power threshold a 20 And less than the fourth cross virtual power threshold a 21 ;

[0095] ③P phase crossover virtual power P Nbc Greater than -a 31 And less than -a 30 ;

[0096] a 10 a 11 For the first type of cross-virtual power threshold, satisfying a 21 <a 10 <a 11 ;a 20 a 21 The second type of cross-virtual power threshold satisfies 0 < a 20 <a 21 ;a 30 a 31 For the third type of cross-virtual power threshold, satisfying a 11 <a 30 <a 31 .

[0097] When ①②③ are satisfied simultaneously, it is determined that phase A on the high-voltage side of the transformer is disconnected. Figure 4 As shown;

[0098] ④A-phase crossover virtual power P Nab Greater than the first cross virtual power threshold a 10 And less than the second cross virtual power threshold a 11 ;

[0099] ⑤ Phase B crossover virtual power P Nbc Greater than the third cross virtual power threshold a 20 And less than the fourth cross virtual power threshold a 21 ;

[0100] ⑥C-phase crossover virtual power P Nca Greater than -a 31 And less than -a 30 ;

[0101] When conditions ④, ⑤, and ⑥ are met simultaneously, it is determined that phase B on the high-voltage side of the transformer is disconnected. Figure 5 As shown;

[0102] ⑦ Phase B crossover virtual power P Nbc Greater than the first cross virtual power threshold a 10 And less than the second cross virtual power threshold a11 ;

[0103] ⑧C-phase crossover virtual power P Nca Greater than the third cross virtual power threshold a 20 And less than the fourth cross virtual power threshold a 21 ;

[0104] ⑨ A-phase crossover virtual power P Nab Greater than -a 31 And less than -a 30 ;

[0105] When conditions ⑦, ⑧, and ⑨ are met simultaneously, it is determined that phase C on the high-voltage side of the transformer is disconnected. Figure 6 As shown;

[0106] In this embodiment, the power threshold is taken as follows: first cross-virtual power threshold a 10 =90, second cross virtual power threshold a 11 =100, third cross virtual power threshold a 20 =240, fourth cross virtual power threshold a 21 =260, sixth cross virtual power threshold, sixth cross virtual power threshold a 30 =340, Fifth Cross Virtual Power Threshold a 31 =360.

[0107] S3: If it is not determined that phase A of the high-voltage side voltage has failed, then the two-phase failure discrimination rules for the high-voltage side of the transformer shall be used to determine whether a two-phase failure has occurred on the high-voltage side. If two phases are failed, the two-phase failure selection discrimination rules for the high-voltage side shall be used to determine which two phases have failed.

[0108] In this embodiment of the application, the rule for determining two-phase loss on the high-voltage side of the transformer is as follows:

[0109] The high-voltage side voltage is normal;

[0110] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0111] The neutral point current on the high-voltage side is greater than the trip setting.

[0112] Low-voltage side voltage, one phase voltage is lower than U Low The other two phase voltages have equal amplitudes but opposite phases.

[0113] U Low It has a low voltage threshold.

[0114] In this embodiment of the application, the phase selection rule for two-phase loss on the high-voltage side is as follows:

[0115] Phase A voltage is below the low voltage threshold U LowIf the voltage amplitudes of phase B and phase C are equal but their phases are opposite, then it is determined that phases A and B are disconnected.

[0116] Phase B voltage is below the low voltage threshold U Low If the voltage of phase C and the voltage of phase A have the same amplitude but opposite phase, then it is determined that phases B and C are disconnected.

[0117] Phase C voltage is below the low voltage threshold U Low If the voltage amplitudes of phase A and phase B are equal but their phases are opposite, then it is determined that phases C and A are disconnected.

[0118] Figure 7 and Figure 8 The figure shows the voltage and current waveforms on the high-voltage side and the low-voltage side when phases A and B on the high-voltage side are disconnected.

[0119] S4: Use the single-phase phase failure judgment rule of the high-voltage side busbar incoming line to determine whether a single-phase phase failure has occurred on the high-voltage side busbar incoming line, and use the single-phase phase failure selection judgment rule of the busbar incoming line to determine which phase has failed;

[0120] In this embodiment of the application, the single-phase loss judgment rule for the high-voltage side busbar incoming line of the transformer is as follows:

[0121] One phase voltage on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of the other two phases are both greater than 0.9U. N ;

[0122] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0123] The low-voltage side voltage is normal.

[0124] In this embodiment of the application, the single-phase loss selection rule for the high-voltage side busbar incoming line of the transformer is as follows:

[0125] The voltage of phase A on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of both phase B and phase C are greater than 0.9U. N The phase is determined to be A phase failure.

[0126] The voltage of phase B on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of both phase C and phase A are greater than 0.9U. N The phase B was determined to be faulty.

[0127] The voltage of phase C on the high-voltage side is lower than the low-voltage threshold U. Low The voltages of both phase A and phase B are greater than 0.9U. N The phase was determined to be C phase failure.

[0128] S5: Use the two-phase phase failure judgment rule of the high-voltage side busbar incoming line of the transformer to determine whether a two-phase phase failure of the high-voltage side busbar incoming line has occurred, and use the two-phase phase failure selection judgment rule of the busbar incoming line to determine which phase has failed;

[0129] In this embodiment of the application, the rule for determining two-phase loss of the high-voltage side busbar incoming line of the transformer is as follows:

[0130] Both phase voltages on the high-voltage side are below the low-voltage threshold U. Low The voltage of the other phase is greater than 0.9U. N ;

[0131] The three-phase currents on the high-voltage side are all less than the current-carrying threshold.

[0132] Low-voltage side voltage, one phase voltage is lower than U Low The other two phase voltages have equal amplitudes but opposite phases.

[0133] In this embodiment of the application, the phase selection rule for two-phase loss of the transformer high-voltage side bus incoming line is as follows:

[0134] The voltages of both phase A and phase B on the high-voltage side are below the low-voltage threshold U. Low The voltage of phase C is greater than 0.9U. N Meanwhile, the voltage of phase A on the low-voltage side is lower than the low-voltage threshold U. Low The voltage amplitudes of phase B and phase C are equal but their phases are opposite, indicating that phases A and B are disconnected.

[0135] The voltages of both phase B and phase C on the high-voltage side are below the low-voltage threshold U. Low Phase A voltage is greater than 0.9U N Meanwhile, the voltage of phase B on the low-voltage side is lower than the low-voltage threshold U. Low Since the voltage amplitudes of phase C and phase A are equal but their phases are opposite, it is determined that phases B and C are disconnected.

[0136] The voltages of both phase C and phase A on the high-voltage side are below the low-voltage threshold U. Low Phase B voltage is greater than 0.9U. N Meanwhile, the voltage of phase C on the low-voltage side is lower than the low-voltage threshold U. Low Since the voltage amplitudes of phase A and phase B are equal but their phases are opposite, it is determined that phase C and phase A are disconnected.

[0137] The present invention also provides a transformer phase loss protection method, which includes the above-mentioned transformer phase loss detection method, which logically determines that a phase loss has occurred, and then triggers an alarm after a first time limit and trips after a second time limit.

[0138] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A transformer open-phase detection method, characterized by: include: Collect the high-voltage side voltage, high-voltage side current, zero-sequence current at the neutral point on the high-voltage side of the transformer, and low-voltage side voltage of the transformer; Determine whether a single-phase failure has occurred on the high-voltage side, and select the phase from the single-phase failure on the high-voltage side; Determine whether a two-phase failure has occurred on the high-voltage side, and select the phase from the two phases on the high-voltage side where the failure has occurred; Determine whether a single-phase failure has occurred in the high-voltage side busbar incoming line, and select the appropriate phase if a single-phase failure has occurred in the high-voltage side busbar incoming line. Determine whether a two-phase failure has occurred in the high-voltage side busbar incoming line, and select the appropriate phases if a two-phase failure has occurred in the high-voltage side busbar incoming line. The determination of whether a single-phase failure has occurred on the high-voltage side includes: The high-voltage side voltage is normal; The three-phase currents on the high-voltage side are all less than the current-carrying threshold. The low-voltage side voltage is normal; The zero-sequence current at the neutral point on the high-voltage side is greater than the operating set value. The determination of whether a two-phase failure has occurred on the high-voltage side includes: The high-voltage side voltage is normal; The three-phase currents on the high-voltage side are all less than the current-carrying threshold. The zero-sequence current at the neutral point on the high-voltage side is greater than the operating set value. If the voltage of any phase on the low-voltage side is less than the low-voltage threshold, and the voltages of the other two phases have equal amplitudes but opposite phases; The determination of whether a single-phase failure has occurred in the high-voltage side busbar incoming line includes: Any phase voltage on the high voltage side is less than the low voltage threshold, and the other two phase voltages are both greater than 0.9U N ; The three-phase currents on the high-voltage side are all less than the current-carrying threshold. The low-voltage side voltage is normal; wherein U N represents the secondary rated voltage of the voltage transformer; The determination of whether a two-phase failure has occurred in the high-voltage side busbar incoming line includes: Both of the high-voltage-side two-phase voltages are less than a low-voltage threshold, and the other-phase voltage is greater than 0.9U N ; The three-phase currents on the high-voltage side are all less than the current-carrying threshold. On the low-voltage side, one phase voltage is less than the low-voltage threshold, while the other two phase voltages have equal amplitudes but opposite phases. wherein U N represents the secondary rated voltage of the voltage transformer.

2. The transformer open-phase detection method of claim 1, wherein: The methods for determining whether the high-voltage side voltage is normal include: High voltage side three-phase voltage self-generated zero sequence voltage is less than zero sequence voltage threshold and self-generated negative sequence voltage is less than negative sequence voltage threshold and three-phase voltage is all greater than 0.9U N ; The methods for determining whether the low-voltage side voltage is normal include: Low voltage side three-phase voltage self-generated zero sequence voltage is less than zero sequence voltage threshold and self-generated negative sequence voltage is less than negative sequence voltage threshold and three-phase voltage is all greater than 0.9U N ; wherein U N represents the secondary rated voltage of the voltage transformer.

3. The transformer open-phase detection method of claim 1, wherein: The phase selection for determining the occurrence of a phase failure in a single phase on the high-voltage side includes: Based on the transformer low-voltage side voltage U ab With the high-voltage side neutral point zero sequence current determination A intersection virtual power; Based on the transformer low-voltage side voltage U bc With the high-voltage side neutral point zero sequence current to determine the B phase intersection virtual power; Based on the transformer low-voltage side voltage U ca With the high-voltage side neutral point zero sequence current to determine C intersection virtual power; Condition 1: The virtual power of the C-phase crossover is greater than the first virtual power threshold and less than the second virtual power threshold; Condition 2: The virtual power of phase A crossover is greater than the third crossover virtual power threshold and less than the fourth crossover virtual power threshold; Condition 3: The B-phase cross virtual power is greater than the negative value of the fifth cross virtual power threshold and less than the negative value of the sixth cross virtual power threshold; If conditions 1, 2, and 3 are all met simultaneously, it is determined that phase A on the high-voltage side of the transformer is disconnected. Condition 4: The virtual power of phase A crossover is greater than the first virtual power threshold and less than the second virtual power threshold; Condition 5: The virtual power of phase B crossover is greater than the third virtual power threshold and less than the fourth virtual power threshold; Condition 6: The C-phase cross virtual power is greater than the negative of the fifth cross virtual power threshold and less than the negative of the sixth cross virtual power threshold; If conditions 4, 5, and 6 are met simultaneously, it is determined that phase B on the high-voltage side of the transformer is disconnected. Condition 7: The virtual power of phase B crossover is greater than the first virtual power threshold and less than the second virtual power threshold; Condition 8: The virtual power of the C-phase crossover is greater than the third crossover virtual power threshold and less than the fourth crossover virtual power threshold; Condition 9: The virtual power of phase A is greater than the negative value of the fifth virtual power threshold and less than the negative value of the sixth virtual power threshold; If conditions 7, 8, and 9 are met simultaneously, it is determined that phase C on the high-voltage side of the transformer is disconnected. Among them, the first cross virtual power threshold is greater than the fourth cross virtual power threshold and less than the second cross virtual power threshold; The third cross virtual power threshold is greater than 0 and less than the fourth cross virtual power threshold; The sixth cross-virtual power threshold is greater than the second cross-virtual power threshold but less than the fifth cross-virtual power threshold.

4. The transformer open-phase detection method of claim 1, wherein: The phase selection method for determining the phase failure in the two phases on the high-voltage side includes: If the voltage of phase A is less than the low voltage threshold, and the voltages of phase B and phase C have equal amplitudes but opposite phases, then it is determined that phases A and B are disconnected. If the voltage of phase B is less than the low voltage threshold, and the voltage of phase C is equal in magnitude but opposite in phase to the voltage of phase A, then it is determined that phases B and C are disconnected. If the voltage of phase C is less than the low voltage threshold, and the voltages of phase A and phase B have equal amplitudes but opposite phases, then it is determined that phases C and A are disconnected.

5. The method of claim 1, wherein: The phase selection for determining a single-phase failure in the high-voltage side busbar incoming line includes: The high-voltage-side A-phase voltage is less than a low-voltage threshold, and the B-phase and C-phase voltages are both greater than 0.9U N , and it is determined that the A phase is open-phase. The high-voltage side B-phase voltage is less than a low-voltage threshold, and the C-phase and A-phase voltages are both greater than 0.9U N , and it is determined that the B phase is open-phase. The high-voltage side C-phase voltage is less than a low-voltage threshold, and the A-phase and B-phase voltages are both greater than 0.9U N , and the C-phase is judged to be open-phase. wherein U N represents the secondary rated voltage of the voltage transformer.

6. The transformer open-phase detection method of claim 1, wherein: The phase selection method for determining the occurrence of a two-phase failure in the high-voltage side busbar incoming line includes: The high-voltage-side A-phase and B-phase voltages are both less than the low-voltage threshold, and the C-phase voltage is greater than 0.9U N At the same time, the low-voltage-side A-phase voltage is less than the low-voltage threshold, the B-phase and C-phase voltages have equal amplitudes and opposite phases, and it is judged that the A-phase and B-phase are open-phase. The voltages of phases B and C on the high-voltage side are both below the low-voltage threshold, while the voltage of phase A is greater than 0.9U. N Meanwhile, the voltage of phase B on the low-voltage side is less than the low-voltage threshold, and the voltage amplitudes of phase C and phase A are equal but opposite in phase, indicating that phases B and C are disconnected. On the high-voltage side, the voltages of phases C and A are both below the low-voltage threshold, while the voltage of phase B is greater than 0.9U. N Meanwhile, the voltage of phase C on the low-voltage side is less than the low-voltage threshold, and the voltage amplitudes of phase A and phase B are equal but opposite in phase, indicating that phase C and phase A are disconnected. wherein U N represents the secondary rated voltage of the voltage transformer.

7. A transformer open-phase protection method, characterized by: include: In the transformer phase loss detection method according to any one of claims 1-6, if a phase loss is determined, an alarm is triggered after a first time limit; The circuit breaker tripped after the second time limit.

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