CN106371049B - Current transformer secondary open circuit identification method - Google Patents
Current transformer secondary open circuit identification method Download PDFInfo
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- CN106371049B CN106371049B CN201610793873.1A CN201610793873A CN106371049B CN 106371049 B CN106371049 B CN 106371049B CN 201610793873 A CN201610793873 A CN 201610793873A CN 106371049 B CN106371049 B CN 106371049B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/02—Testing or calibrating of apparatus covered by the other groups of this subclass of auxiliary devices, e.g. of instrument transformers according to prescribed transformation ratio, phase angle, or wattage rating
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Abstract
The invention provides a secondary open circuit identification method of a current transformer, which introduces two groups of CT currents and detects open circuit voltages of each phase of the two groups of CT, and if CT saturation does not occur, the method satisfies the formula: i 1φ ‑I 2φ |＞K(|I 1φ |+|I 2φ I) and U 1φ ＞U set Or U (U) 2φ ＞U set And judging the first-path or second-path phi-phase secondary current open circuit after the time delay T1, simultaneously sending a CT open-circuit locking signal to the protection device, shorting the first group or the second group of CT windings by the action of the CT secondary open-circuit device after the time delay T2, and eliminating the CT open-circuit fault. If the conditions are not all satisfied, the return sampling repeats the determination again. The invention combines the two groups of sampling group currents and the secondary open circuit voltage, and can rapidly and correctly judge the CT disconnection fault. The invention belongs to the field of relay protection.
Description
Technical Field
The invention relates to a secondary open circuit identification method for a current transformer, and belongs to the field of relay protection.
Background
The primary winding of the current transformer (CT for short) is connected in series with a high-voltage circuit, and the secondary winding is connected with a measuring instrument and a protection device, so that the accuracy of measurement and metering, the reliability of a relay protection device and the safety of the high-voltage circuit are related. When the CT secondary side is in an approximate short circuit state in normal operation, the output voltage is very low, and thousands of volts or even tens of thousands of volts of overvoltage can be generated on the secondary side if the secondary winding is opened in operation, so that CT is overdriven to burn, the life safety of workers is even endangered, and great economic loss is caused, therefore, the secondary open circuit of the current transformer is prevented, and the research on an effective secondary open circuit identification method of the current transformer has important significance.
The existing secondary open circuit identification method of the current transformer mainly comprises two main types of secondary current and voltage identification methods and overvoltage protection methods.
1. The secondary current and voltage identification method is mainly adopted by relay protection manufacturers, and through carrying out logic discrimination on the secondary side three-phase current and three-phase voltage of a current transformer of an access protection device, the specific criteria of each manufacturer are different, and a discrimination mode with zero sequence current and zero sequence voltage is mainly adopted. When the secondary side of a certain phase of current transformer is out of phase, the phase current disappears, other two phases are normal, zero sequence current can be generated, no ground fault exists at the time, zero sequence voltage is small, and the secondary disconnection of the current transformer is judged by a method with zero sequence current and no zero sequence voltage. The method can not judge the CT secondary open circuit fault when the load current is smaller or the three-phase line is broken, and can not ensure that the CT secondary open circuit requirement can be judged under any condition.
2. The secondary overvoltage detection method mainly utilizes the principle that when the current transformer works normally, the secondary side of the current transformer is in an approximate short circuit state, the output voltage is very low, abnormal peak overvoltage can be generated on the secondary side after the secondary open circuit of the current transformer during operation, whether the CT secondary open circuit occurs or not is judged by detecting the voltage of the CT secondary side, and if the voltage of the secondary side of the current transformer reaches a set value, the overvoltage relay acts, and the CT secondary side is considered to be open circuit. The judging method can produce misjudgment on the lightning overvoltage, and causes misjudgment of the secondary open circuit of the current transformer in normal operation.
Therefore, the existing secondary open circuit identification method of the current transformer has certain limitations, and cannot meet the practical requirements of secondary open circuit real-time detection of the current transformer.
Disclosure of Invention
The invention aims at: the secondary open circuit identification method of the current transformer is provided to solve the problems that the existing secondary open circuit identification methods of the current transformer have certain limitations and cannot meet the real requirement of the secondary open circuit real-time detection of the current transformer, so that the secondary open circuit fault of the current transformer can be effectively detected under any condition.
In order to solve the problems, a secondary open circuit identification method of a current transformer is provided, which comprises the following steps:
(1) The same current transformer is provided with a plurality of groups of secondary windings, secondary currents of two groups of different windings are introduced into the secondary side of the current transformer, A, B, C three-phase currents are simultaneously introduced, and two A, B, C three-phase current sampling groups I can be obtained at the moment 1φ And I 2φ The secondary voltage of each phase of the two windings is measured simultaneously to obtain two A, B, C three-phase voltages by adopting a group U 1φ And U 2φ Wherein I 1 Representing a first set of current samples, I 2 Representing a second set of current samples, U 1φ Representing a first set of open circuit voltage samples, U 2φ Representing a second set of open circuit voltage samples, a surrogate representation of phi A, B, C three phases;
(2) Judgment sampling group I 1φ And I 2φ If CT is saturated, returning to step 1 if CT is saturated, and if CT is not saturated, entering the next step. The sampling value is nonlinear transmission when CT is saturated, and the currents output by different secondary windings are different, so that the CT has no comparability. CT saturation can be determined by using the second and third harmonic content of the secondary current.
(3) According to the formula: i 1φ -I 2φ |>K(|I 1φ |+|I 2φ I) to go to the next step if the formula is established, and to return to step 1 if not. Wherein K is a reliability coefficient, and is 0.6-0.8.
(4) According to the formula: u (U) 1φ >U set Or U (U) 2φ >U set Make a judgment if U 1φ >U set If so, judging that the first phi-phase secondary current is open after delaying for a period of time T1, simultaneously sending a CT open-close signal to the protection device A, and shorting the first group of CT windings by the action of the CT secondary open-circuit device after delaying for a period of time T2. If U 2φ >U set If so, judging that the second phi-phase secondary current is open after delaying for a period of time T1, simultaneously sending a CT open-close signal to the protection device B, and shorting the second group of CT windings by the action of the CT secondary open-circuit device after delaying for a period of time T2. If the two formulas are not established, returning to the step 1. U in set For the secondary open circuit voltage setting value, the delay time T1 is between 0 and 600 volts, the delay time T2 is between 0 and 30 seconds, and the delay time T2 is between 0 and 5 seconds.
Compared with the prior art, the method combines the current differences of different windings of the current transformer with the secondary side open circuit voltage criterion, solves the problems that the current load is small, three-phase simultaneous disconnection cannot be effectively judged and lightning overvoltage misjudgment is caused by the conventional secondary open circuit judgment method, and provides a new reliable judgment method for secondary open circuit of the current transformer.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a secondary open circuit detection device of a current transformer;
fig. 2 is a flowchart of a method for identifying a secondary open circuit of a current transformer according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below,
examples:
the overall structure of the secondary open circuit detection device of the current transformer shown in fig. 1 is that the CT secondary open circuit detection device 1 is installed between the CT secondary winding and the protection device, and two groups of secondary currents of different windings are introduced at the secondary side of the same current transformer, wherein the a-phase secondary winding 7, the B-phase secondary winding 8 and the C-phase secondary winding 9 form a first group of secondary currents, the a-phase secondary winding 4, the B-phase secondary winding 5 and the C-phase secondary winding 6 form a second group of secondary currents, the two groups of secondary currents respectively flow into the protection device A2 and the protection device B3 through the CT secondary open circuit detection device 1, and the CT secondary open circuit detection device 1 monitors the overvoltage of each secondary winding at the same time when monitoring the current of the CT secondary winding, for example, monitors the overvoltage between 1SA and 1SAN at two sides of the a-phase primary winding 7, so as to judge the step 4 in the scheme.
Fig. 2 is a flowchart representation of a current transformer secondary open circuit identification method of the present invention, comprising the steps of:
(1) The same current transformer is provided with a plurality of groups of secondary windings, secondary currents of two groups of different windings are introduced into the secondary side of the current transformer, A, B, C three-phase currents are simultaneously introduced, and two A, B, C three-phase current sampling groups I can be obtained at the moment 1φ And I 2φ The secondary voltage of each phase of the two windings is measured simultaneously to obtain two A, B, C three-phase voltages by adopting a group U 1φ And U 2φ Wherein I 1 Representing a first set of current samples, I 2 Representing a second set of current samples, U 1φ Representing a first set of open circuit voltage samples, U 2φ A second set of open circuit voltage samples is represented, phi being an alternate representation of A, B, C three phases.
(2) Judgment sampling group I 1φ And I 2φ If CT is saturated, returning to step 1 if CT is saturated, and if CT is not saturated, entering the next step. The sampling value is nonlinear transmission when CT is saturated, and the currents output by different secondary windings are different, so that the CT has no comparability. CT saturation can be determined by using the second and third harmonic content of the secondary current.
(3) According to the formula: i 1φ -I 2φ |>K(|I 1φ |+|I 2φ I) to go to the next step if the formula is established, and to return to step 1 if not. Wherein K is a reliability coefficient, and is 0.6-0.8, and K is 0.6 in specific implementation.
(4) According to the formula: u (U) 1φ >U set Or U (U) 2φ >U set Make a judgment if U 1φ >U set If so, judging that the first phi-phase secondary current is open after delaying for a period of time T1, simultaneously sending a CT open-close signal to the protection device A, and shorting the first group of CT windings by the action of the CT secondary open-circuit device after delaying for a period of time T2. If U 2φ >U set If so, judging that the second phi-phase secondary current is open after delaying for a period of time T1, simultaneously sending a CT open-close signal to the protection device B, and shorting the second group of CT windings by the action of the CT secondary open-circuit device after delaying for a period of time T2. If the two formulas are not established, returning to the step 1. U in set For the secondary open circuit voltage setting value, the delay time T1 is between 0 and 600 volts, the delay time T2 is between 0 and 30 seconds, and the delay time T2 is between 0 and 5 seconds. U during specific implementation set 300 volts was taken, T1 was taken as 0.2S, and T2 was taken as 0.1 seconds.
An example of use is given below, taking the first set of phase a CT breaks, the others are normal, no saturation occurs, and the fault persists for 0.4 seconds. Sampling the first and second groups of current and voltage to obtain I 1A 、I 2A 、U 1A 、U 2A 。
In the case of a broken line of the first group A and other normal conditions, I 1A =0, detect U 1A And its value is greater than U set ，I 2A Normal U 2A =0. From fig. 2, step 3 is entered in case no CT saturation occurs, the formula is evident: i 1A -I 2A |>0.6(|I 1A |+|I 2A I) is true. Step 4, when the first group of current transformersWhen the phase A breaks, a high voltage, namely U, is generated on the secondary side 1A >U set The method is characterized in that the method comprises the steps of judging that a first-path A-phase secondary current is open-circuited by 0.2 seconds of delay, sending a CT open-circuit locking signal to a protection device A, locking the protection device to avoid misoperation, and shorting a first group of CT windings by the action of a CT secondary open-circuit device by 0.1 seconds of delay, wherein a CT open-circuit fault disappears.
Finally, it should be noted that the above description is only a preferred embodiment of the present invention, and that many similar changes can be made by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (7)
1. The secondary open circuit identification method for the current transformer is characterized by comprising the following steps of:
(1) The same current transformer is provided with a plurality of groups of secondary windings, secondary currents of two groups of different windings are introduced into the secondary side of the current transformer, A, B, C three-phase currents are simultaneously introduced, and two A, B, C three-phase current sampling groups I can be obtained at the moment 1φ And I 2φ The secondary voltage of each phase of the two windings is measured simultaneously to obtain two A, B, C three-phase voltage sampling groups U 1φ And U 2φ Wherein I 1φ Representing a first set of current samples, I 2φ Representing a second set of current samples, U 1φ Representing a first set of open circuit voltage samples, U 2φ Representing a second set of open circuit voltage samples, a surrogate representation of phi A, B, C three phases;
(2) Judgment sampling group I 1φ And I 2φ If the CT is saturated, returning to the step 1, if the CT is not saturated, entering the next step, and judging the CT saturation by the contents of secondary and third harmonic waves in the secondary current;
(3) According to the formula: i 1φ -I 2φ |>K(|I 1φ |+|I 2φ I) judging, if the formula is established, entering the next step, and if the formula is not established, returning to the step 1, wherein K is a reliability coefficient;
(4) According to the formula: u (U) 1φ >U set Or U (U) 2φ >U set Make a judgment if U 1φ >U set If so, judging that the first phi-phase secondary current is open after delaying for a period of time T1, simultaneously sending a CT open-close signal to the protection device A, and shorting the first group of CT windings by the action of the CT secondary open-circuit device after delaying for a period of time T2; if U 2φ >U set If yes, judging that a second phi phase secondary current is open after delaying for a period of time T1, simultaneously sending a CT open-close signal to a protection device B, shorting a second group of CT windings by the action of a CT secondary open-close device after delaying for a period of time T2, and returning to the step 1 if the two formulas are not met, wherein U is as follows set Is the secondary open circuit voltage set point.
2. The method for identifying the secondary open circuit of the current transformer according to claim 1, wherein the method comprises the following steps: k is 0.6-0.8.
3. The method for identifying the secondary open circuit of the current transformer according to claim 2, wherein the method comprises the following steps of: k is taken to be 0.6.
4. The method for identifying the secondary open circuit of the current transformer according to claim 1, wherein the method comprises the following steps: u (U) set The time delay time T1 is between 0 and 600 volts, the time delay time T2 is between 0 and 5 seconds, and the time delay time T1 is between 0 and 30 seconds.
5. The method for identifying the secondary open circuit of the current transformer according to claim 4, wherein the method comprises the following steps: u (U) set 300 volts was taken.
6. The method for identifying the secondary open circuit of the current transformer according to claim 4, wherein the method comprises the following steps: t1 is taken for 0.2 seconds.
7. The method for identifying the secondary open circuit of the current transformer according to claim 4, wherein the method comprises the following steps: t2 is taken for 0.1 seconds.
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| CN106877285B (en) * | 2017-03-24 | 2018-10-02 | 山东中实易通集团有限公司 | The station-service subsidiary engine CT thread-breakage protectings and relay system of differential protection is not configured |
| CN109932676A (en) * | 2019-03-27 | 2019-06-25 | 国家电网有限公司 | The method for detecting abnormality of voltage transformer circuit |
| CN109932675A (en) * | 2019-03-27 | 2019-06-25 | 国家电网有限公司 | The method for detecting abnormality of current transformer loop |
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