CN115856710A - Main transformer phase failure monitoring method - Google Patents
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Abstract
The invention belongs to the technical field of power system relay protection, and particularly provides a main transformer open-phase monitoring method, which comprises the steps of obtaining a high-voltage side three-phase current, a low-voltage side bushing three-phase current and a high-voltage side three-phase voltage of a main transformer; and judging the phase failure fault condition according to the acquired data information of the main transformer, and when a certain phase reaches the preset phase failure fault condition, generating the phase failure fault of the corresponding phase of the main transformer. According to the method, the obtained data not only comprise the high-voltage side three-phase current, but also comprise the low-voltage side sleeve three-phase current and the high-voltage side three-phase voltage, namely the obtained data are more, and then whether the main transformer has the phase failure or not can be comprehensively analyzed through the obtained data, so that the problem that the phase failure of the high-voltage side is difficult to judge under the low-load operation condition of the main transformer can be solved, and the problem that the main transformer protection is insensitive to the detection of the phase failure is solved.
Description
Technical Field
The invention belongs to the technical field of power system relay protection, and particularly relates to a main transformer phase failure monitoring method.
Background
In 12 months in 2021, the C phase sleeve on the high-voltage side of a Ningxia 750kV Hu transformer No. 3 main transformer breaks down, so that the transformer runs in an open-phase mode, and no protection alarm is given for a long time under the condition of low load. The existing main transformer protection device cannot effectively judge and rapidly remove the main transformer open-phase faults. Monitoring and operating personnel lack accurate warning information prompt, phase failure occurs under the condition of low load operation of a main transformer, and long-time non-warning uploading may occur. The main transformer bushing has phase failure, if the bushing cannot be sensed quickly and necessary processing means are adopted, the risk of main transformer nearby fault caused by the falling of the bushing exists, and permanent damage such as main transformer internal deflagration, insulation breakdown, winding deformation and the like can be caused in serious conditions.
In recent years, certain researches have been made on the open-phase fault of the power transmission line in China, and certain achievements have been achieved. Aiming at the phase failure protection of the transformer, in particular to the phase failure detection of the transformer in a light load or no-load state, a permission group limited company provides an injection type transformer circuit phase failure protection method and a transformer phase failure protection scheme based on an Optical Current Transformer (OCT), and a Nanyun-Rui-Bao electric limited company provides a transformer phase failure protection scheme based on an Optical Current Transformer (OCT). The basic principle of the injection type transformer line open-phase protection is to inject a non-power frequency signal (small signal) into a system through a transformer grounding neutral point, detect the current and the voltage of the injected signal, and adopt comprehensive characteristic criteria to realize the method for judging the open-phase operation condition of the transformer according to the change characteristics of the current and the voltage. The optical current transformer OCT-based transformer open-phase detection method measures three-phase current of a high-voltage side of a transformer through the optical current transformer OCT, and judges whether an open-phase fault occurs according to the current.
However, when the phase failure protection of the circuit of the injection transformer is applied, the neutral point of the high-voltage side of the transformer needs to be directly grounded (the grounding mode of other sides is not limited), the system can be a single or multiple parallel running transformer systems, the main transformer of the 750kV transformer substation is generally a split-phase auto-transformer, and the neutral point grounding mode and the zero-sequence impedance of the system are different from those of the startup and standby transformer of the nuclear power plant, so that the phase failure protection principle of the circuit of the injection transformer is not suitable for the phase failure monitoring of the main transformer. The optical current transformer OCT-based transformer open-phase detection method requires that an OCT primary sensor is manufactured into an optical cable and sleeved on a main transformer high-voltage bushing, the cost of one OCT optical current transformer is about 30 ten thousand yuan, 3 OCT optical current transformers are required, and the cost is relatively high. In the prior art, an alarm signal is given or tripped after long time delay, phase failure occurs inside a main transformer bushing, if the bushing cannot be sensed quickly and necessary processing means are adopted, the risk of main transformer near-region failure caused by the falling of the bushing exists, and the problems of permanent damage such as main transformer internal deflagration, insulation breakdown, winding deformation and the like can be caused in serious cases.
Disclosure of Invention
The invention aims to provide a main transformer open-phase monitoring method, which is used for solving the problem that the detection of the open-phase fault of a transformer substation is insensitive in the prior art.
In order to solve the technical problem, the invention provides a main transformer phase failure monitoring method, which comprises the following steps:
1) Acquiring data information of a main transformer; the data information includes: the high-voltage side three-phase current, the low-voltage side bushing three-phase current and the high-voltage side three-phase voltage;
2) Judging the open-phase fault condition according to the acquired data information; the open-phase fault condition includes:
a) The phase current of a certain phase of the high-voltage side is smaller than the set multiple of the minimum load current setting value, and the ratio of the high-voltage side zero-sequence current component to the high-voltage side positive-sequence current component is larger than the zero-sequence current asymmetry setting value or the ratio of the high-voltage side negative-sequence current component to the high-voltage side positive-sequence current component is larger than the negative-sequence current asymmetry setting value;
b) The zero-sequence current component on the low-voltage side is greater than the unbalanced zero-sequence current threshold setting value of the low-voltage side casing;
c) The high-voltage side negative sequence voltage component is greater than the negative sequence voltage setting value or the high-voltage side zero sequence voltage component is greater than the zero sequence voltage setting value or the high-voltage side line voltage is less than the line voltage setting value;
3) If a) and b) are satisfied, and c) is not satisfied, the phase failure of the corresponding phase of the main transformer occurs.
The beneficial effects are as follows: the method comprises the steps of monitoring three-phase current of a high-voltage side of a main transformer in real time, detecting three-phase voltage of the high-voltage side of the main transformer and three-phase current of a sleeve pipe of a low-voltage side of the main transformer, and judging that an open-phase fault occurs when current and voltage criteria meet open-phase conditions. According to the method, the obtained data not only comprise the high-voltage side three-phase current, but also comprise the low-voltage side sleeve three-phase current and the high-voltage side three-phase voltage, namely the obtained data are more, so that whether the main transformer has the phase failure or not can be comprehensively analyzed through the obtained data, and the method can be used for determining which phase has the phase failure, so that the problem that the phase failure at the high-voltage side is difficult to judge under the low-load operation condition of the main transformer can be solved, and the problem that the main transformer protection is insensitive to the detection of the phase failure is solved.
Further, the formula for open-phase fault condition a) is:
wherein, I Φ A certain phase current in three phases A, B and C at the high-voltage side of the main transformer, I p Is a minimum load current setting value, I h0 Is a high-voltage side zero-sequence current component, I h1 Is a high-side positive-sequence current component, I h2 Is a high-side negative-sequence current component, K 0set Is a zero sequence current asymmetry setting value, K 2set The negative sequence current asymmetry setting value is obtained.
Further, the formula for open-phase fault condition b) is:
(I l0 ＞I 0set )；
wherein, I 10 Is a low-voltage side zero-sequence current component, I 0set And setting a zero sequence current threshold value for the unbalance of the low-voltage side sleeve.
Further, the formula for open-phase fault condition c) is:
wherein, U 0 Is a high-side zero-sequence voltage component, U 2 Is a high side negative sequence voltage component, U Line max Is the high side line voltage maximum, U 2set For negative sequence voltage setting value, U 0set Is a zero sequence voltage setting value, U set And setting the line voltage.
Further, in the step 2), the open-phase fault condition is judged through the open-phase monitoring device; the phase failure monitoring device comprises a main transformer high-voltage side phase failure detection module, a main transformer low-voltage side bushing current CT secondary line failure auxiliary module and a high-voltage side voltage non-fault detection module.
The process of judging based on different modules realizes the refined processing of the acquired data, and the judgment process based on the sub-modules shortens the corresponding processing time due to the reduction of the data processed by each module, thereby accelerating the judgment speed, and the error probability of each module is reduced based on the reduction of the processed data, so that the obtained processing result is more reliable.
Further, in order to solve the problem of reliability of measured data under the low-load operation condition of the main transformer, in the step 1), high-voltage side three-phase current is obtained through a measurement level CT.
Further, in order to ensure the accuracy of the acquired data, the accurate level of the measurement level CT is 0.5 level or 0.2S level.
Further, in the step 1), the low-voltage side bushing three-phase current is obtained by measuring the internal current of the low-voltage side triangular winding.
Further, the minimum load current setting value range is 2% -5% of secondary rated current, the low-voltage side sleeve unbalanced zero sequence current threshold setting value range is 10 mA-40 mA, the negative sequence voltage setting value range is 2V-6V, the zero sequence voltage setting value range is 4V-8V, and the line voltage setting value range is 60% -70% of secondary rated voltage.
Further, in order to avoid various fault transient interferences of the main transformer and adjacent systems, in step 3), after the main transformer has an open-phase fault, the open-phase protection action of the main transformer is performed after a set delay time.
Drawings
FIG. 1 is a wiring diagram of a typical application of the present invention for an electrical main wiring and a main transformer phase loss monitoring device;
FIG. 2 is a logic diagram of the phase A open-phase fault discrimination of the present invention;
FIG. 3 is a logic diagram of the phase B open phase fault discrimination of the present invention;
fig. 4 is a C-phase open-phase fault discrimination logic diagram of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.
The embodiment of the main transformer phase failure monitoring method comprises the following steps:
in the embodiment, the high-voltage side three-phase current of the main transformer, the high-voltage side three-phase voltage of the main transformer and the low-voltage side sleeve three-phase current of the main transformer are detected, when the detected data meet the phase failure criterion, the phase failure is judged to occur, and an alarm signal or trip is given in a delayed manner. Fig. 1 shows a typical applied electrical main connection used in this embodiment (a specific embodiment of the method is described by taking a main transformer system of a certain 750kV substation as an example), where the main transformer is a three-single-phase three-winding auto-transformer, yn/D-11 connection, the high-voltage side is 750kV 3/2 connection, the low-voltage side is delta-winding connection, the phase failure monitoring device accesses analog quantities including a main transformer high-voltage side three-phase current, a main transformer high-voltage side three-phase voltage, and a main transformer low-voltage side bushing three-phase current, where the main transformer high-voltage side three-phase current is obtained by measuring stage CT, the accurate level of the measurement level CT (current transformer) is 0.5 (as another embodiment, the accurate level may also be 0.2S), for example, the transformation ratio is 1200/2A, the measurement CT only requires to ensure higher accuracy under normal current to ensure accurate measurement, the accuracy level (i.e., the accurate level) generally has 0.1, 0.2, 0.5, 1.0, 3.0 and 5.0 levels, and the larger the value of the accuracy level is, the lower the accuracy is, the accuracy level with S is a special CT, the accuracy is required to be sufficiently high in the range of 1% to 120% of load, and the error of measuring by taking 5 load points is generally smaller than the specified range; the three-phase current of the bushing on the low-voltage side of the main transformer is obtained through a protective stage CT, and the transformation ratio is 2000/1A for example. The specific steps for implementing the phase failure monitoring of the high-voltage side of the main transformer of the transformer substation are as follows:
1) Phase failure monitoring device for acquiring three-phase current (I) of high-voltage side of main transformer in real time A 、I B And I C ) High voltage side zero sequence current component (I) h0 ) High side positive sequence current component (I) h1 ) High side negative sequence current component (I) h2 ) High side three phase voltage (U) A 、U B And U C ) High side three phase line voltage (U) AB 、U BC And U CA ) High side zero sequence voltage component (U) 0 ) High side positive sequence voltage component (U) 1 ) High side negative sequence voltage component (U) 2 ) Three-phase current (I) of main transformer low-voltage side sleeve LA 、I LB And I LC ) And a low-voltage side zero-sequence current component (I) 10 )。
2) Determining the minimum load current setting value I according to the main transformer parameters, the measured CT transformation ratio and the accurate level of the high-voltage side measuring level current transformer p ，I p The value range is 2% -5% of secondary rated current, the primary rated current of the transformer in the embodiment is 1132.1A, the CT transformation ratio measured at the high-voltage side is 1200/2A, namely the secondary rated current is 1.887A, and then the 2% rated current is 37.74mA, namely the minimum load current setting value I p The adjustable value is 40mA. Further determining the asymmetry setting value K of the zero-sequence current 0set Negative sequence current asymmetry setting value K 2set Unbalanced zero-sequence current threshold setting value I of low-voltage side casing 0set Negative sequence voltage setting value U 2set Zero sequence voltage setting value U 0set And line voltage setting value U set (ii) a In this example K 0set The value is 0.2, K 2set The value is 0.2,I 0set The general value range is 10 mA-40 mA (the value is 10mA in the embodiment), U 2set The general value range is 2V-6V (4V in this embodiment), U 0set The general value range is 4V-8V (the value of this embodiment is 5V), U set The value range is 60% -70% of the secondary rated voltage (the value of the embodiment is 70V).
3) And the open-phase monitoring device judges the open-phase fault.
The phase failure monitoring device comprises a main transformer high-voltage side phase failure detection module, a main transformer low-voltage side bushing current CT secondary line failure auxiliary module and a high-voltage side voltage non-fault detection module, and the modules are distinguished as follows:
the main transformer high-pressure side open-phase detection module discrimination formula:
the main transformer low-voltage side bushing current CT secondary disconnection auxiliary module discrimination formula:
(I l0 ＞I 0set ) (2)
the high-voltage side voltage non-fault detection module has a discrimination formula:
when the expressions (1) and (2) are satisfied and the expression (3) is not satisfied, the corresponding phase open-phase condition is satisfied, and the corresponding phase open-phase is determined. Wherein I Φ A certain phase current, U, in three phases of A, B and C at the high-voltage side of the main transformer Line max Is the high side line voltage maximum (e.g., when I Φ When phase current is A phase A Then the corresponding U Line max Is a line voltage U AB 、U BC And U CA Maximum value of (1).
4) When the corresponding phase is determined to be out of phase, an out-of-phase alarm or trip signal is sent out after a set time delay (as other real-time modes, the out-of-phase alarm and the trip action can be carried out after the set time delay), the time delay is set for avoiding various fault transient interferences of the main transformer and adjacent systems, and the set value range of the set time delay is 0 s-100 s (the time delay set value of the embodiment is set to be 0.5 s). When a real-time calculated value of a phase current and voltage does not meet the phase failure criterion, the next phase failure judgment and the A, B and C three-phase circulation judgment are carried out, wherein a specific logic diagram of the A phase failure judgment is shown in figure 2, a specific logic diagram of the B phase failure judgment is shown in figure 3, and a specific logic diagram of the C phase failure judgment is shown in figure 4.
By adopting the method of the embodiment, the high-voltage side three-phase current of the main transformer is monitored in real time through the application of the main transformer high-voltage side measurement stage CT, the high-voltage side three-phase voltage of the main transformer and the low-voltage side bushing three-phase current of the main transformer are detected simultaneously, when the current and voltage criteria meet the phase failure criteria, the phase failure fault is determined to occur, and an alarm signal or trip is given out through time delay so as to remind an operator of processing in time. The method of the embodiment can solve the problem that the phase failure fault at the high-voltage side is difficult to distinguish under the low-load operation condition of the main transformer, solve the problem that the main transformer protection is insensitive to the detection of the phase failure fault and is difficult to trip timely, functionally upgrade the existing main transformer protection and facilitate the safe and stable operation of a power grid.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention, the scope of the present invention is defined by the appended claims, and all equivalent structural changes made by using the contents of the specification and the drawings of the present invention should be covered by the scope of the present invention.
Claims (10)
1. A main transformer phase failure monitoring method is characterized by comprising the following steps:
1) Acquiring data information of a main transformer; the data information includes: the high-voltage side three-phase current, the low-voltage side bushing three-phase current and the high-voltage side three-phase voltage;
2) Judging the open-phase fault condition according to the acquired data information; the open-phase fault condition includes:
a) The phase current of a certain phase of the high-voltage side is smaller than the set multiple of the minimum load current setting value, and the ratio of the high-voltage side zero-sequence current component to the high-voltage side positive-sequence current component is larger than the zero-sequence current asymmetry setting value or the ratio of the high-voltage side negative-sequence current component to the high-voltage side positive-sequence current component is larger than the negative-sequence current asymmetry setting value;
b) The zero-sequence current component on the low-voltage side is greater than the unbalanced zero-sequence current threshold setting value of the low-voltage side casing;
c) The high-voltage side negative sequence voltage component is greater than the negative sequence voltage setting value or the high-voltage side zero sequence voltage component is greater than the zero sequence voltage setting value or the high-voltage side line voltage is less than the line voltage setting value;
3) If a) and b) are satisfied, and c) is not satisfied, the phase failure of the corresponding phase of the main transformer occurs.
2. The method for monitoring phase loss of a main transformer according to claim 1, wherein the formula of the phase loss fault condition a) is as follows:
wherein, I Φ A certain phase current in three phases A, B and C at the high-voltage side of the main transformer, I p Is a minimum load current setting value, I h0 Is a high-voltage side zero-sequence current component, I h1 Is a high-side positive-sequence current component, I h2 Is a high-side negative-sequence current component, K 0set Is a zero sequence current asymmetry setting value, K 2set The negative sequence current asymmetry setting value is obtained.
3. The method for monitoring phase loss of a main transformer according to claim 1, wherein the formula of the phase loss fault condition b) is as follows:
(I l0 ＞I 0set )；
wherein, I 10 Is a low-voltage side zero-sequence current component, I 0set And setting a zero sequence current threshold value for the unbalance of the low-voltage side sleeve.
4. The method for monitoring phase loss of a main transformer according to claim 1, wherein the formula of the phase loss fault condition c) is as follows:
wherein, U 0 Is a high-side zero-sequence voltage component, U 2 Is a high side negative sequence voltage component, U Line max Is the high side line voltage maximum, U 2set Is a negative sequence voltage setting value, U 0set Is a zero sequence voltage setting value, U set And setting the line voltage.
5. The main transformer phase failure monitoring method according to claim 1, wherein in step 2), a phase failure fault condition is judged through a phase failure monitoring device; the phase failure monitoring device comprises a main transformer high-voltage side phase failure detection module, a main transformer low-voltage side bushing current CT secondary line failure auxiliary module and a high-voltage side voltage non-fault detection module.
6. The method for monitoring the phase failure of the main transformer according to claim 1, wherein in the step 1), the high-side three-phase current is obtained through a measurement stage CT.
7. The method for monitoring phase loss of a main transformer according to claim 6, wherein the accurate level of the measurement level CT is 0.5 level or 0.2S level.
8. The method for monitoring the phase failure of the main transformer according to claim 1, wherein in the step 1), the low-voltage side bushing three-phase current is obtained by measuring the internal current of the low-voltage side triangular winding.
9. The method for monitoring the phase failure of the main transformer according to claim 1, wherein the minimum load current setting value ranges from 2% to 5% of the secondary rated current, the unbalanced zero sequence current threshold setting value range of the low-voltage side casing ranges from 10mA to 40mA, the negative sequence voltage setting value ranges from 2V to 6V, the zero sequence voltage setting value ranges from 4V to 8V, and the line voltage setting value ranges from 60% to 70% of the secondary rated voltage.
10. The method for monitoring the phase failure of the main transformer according to claim 1, wherein in step 3), after the phase failure of the main transformer occurs, the phase failure protection action of the main transformer is performed after a set delay time.
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