Generator-transformer group CT loop polarity and phase sequence checking method
The reverse flow method detects the wiring accuracy of the CT loop in the power system, and solves the safety hazards caused by the wiring error of the CT loop, and achieves simple and efficient detection and risk reduction effects.
Patent Information
- Application Number
- CN202411645976.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-18
- Publication Date
- 2025-04-11
AI Technical Summary
In power systems, the wiring of the CT loop is complicated, and it is prone to open circuit, short circuit, or polarity, and phase sequence wiring errors, resulting in failure of the protection device, damage to the equipment or fire risk.
The reverse flow method is adopted to introduce an external power supply to the main transformer high voltage side to reverse flow to the CT loop of the generator and transformer group. By measuring the current amplitude and phase, the wiring accuracy of the CT loop is checked.
This method can easily and efficiently detect the wiring accuracy of the CT loop before the unit starts, avoiding the complexity and high risks of traditional methods, reducing labor and time costs, and ensuring the safe operation of the equipment.
Smart Images
Figure CN119805334A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of detection technology of electrical equipment in power systems, and in particular to a method for checking the polarity and phase sequence of a CT (current transformer) circuit of a generator and a transformer group (generator-transformer group). The method can effectively detect the correctness of the wiring of the CT circuit of the generator-transformer group by reverse current flow before the unit is started, so as to ensure the correctness of the polarity and phase sequence of the CT circuit, and prevent safety problems caused by open circuit, short circuit or polarity and phase sequence wiring errors of the CT circuit. Background Art
[0002] In the power system, electrical equipment is mainly divided into primary equipment and secondary equipment. Primary equipment mainly includes generators, transformers, circuit breakers and high-voltage busbars, which are responsible for the production, transmission, distribution and consumption of electric energy. Secondary equipment mainly includes relay protection devices, safety automatic devices and measuring instruments, which are responsible for monitoring, controlling, regulating and protecting primary equipment. Among them, voltage transformers (PT) and current transformers (CT) are key devices connecting primary equipment and secondary equipment, responsible for collecting electrical parameters of primary equipment for real-time monitoring and protection of secondary equipment.
[0003] In power plants, due to the complexity of CT circuit wiring, which involves the connection of many electrical devices, when installing or replacing electrical secondary equipment, especially when the CT secondary circuit changes, it is easy to have CT circuit open circuit, short circuit or polarity and phase sequence wiring errors. These problems may cause:
[0004] The protection device cannot correctly monitor the actual current, resulting in protection failure or malfunction, which may damage the primary equipment in serious cases;
[0005] CT open circuit may cause high voltage in the secondary circuit, which may burn the equipment or cause a fire in serious cases;
[0006] The abnormal situation of the CT circuit was not discovered in time before the unit was started, which affected the normal grid connection and safe operation of the unit.
[0007] The traditional method usually uses a generator short-circuit test to conduct a current flow test to detect the correctness of the CT circuit wiring. However, this method has complex test steps, high risks, and requires a lot of manpower and time costs. In order to solve these problems, the present invention proposes a CT circuit polarity and phase sequence verification method based on reverse current flow, which can be simply and efficiently tested before the unit is started, thereby avoiding many shortcomings of the traditional method. Summary of the invention
[0008] The present invention aims to provide a method for checking the polarity and phase sequence of the CT circuit of a generator-transformer group. The method introduces an external power supply on the high-voltage side of the main transformer to reverse the flow of current in the CT circuits of the main transformer, the generator and the high-voltage transformer, and detects the correctness of the wiring of each CT secondary circuit to ensure the accuracy of the polarity and phase sequence.
[0009] The core of the technical solution
[0010] The present invention adopts the reverse current method, takes the unmodified CT circuit as the reference, measures the current amplitude and phase of other CT circuits, and combines theoretical phase analysis to judge the correctness of CT circuit wiring. The method innovatively introduces 380V AC power supply on the high-voltage side of the main transformer, and through reverse current, energizes the CT secondary circuit of the generator-transformer group, thereby providing conditions for detection before the unit is started.
[0011] Steps for the reverse flow method:
[0012] Safety measures
[0013] Before conducting a reverse current test, it is necessary to complete the restoration of all CT external circuit connections, ensure that the relevant switches are in the disconnected state, and hang a "Do Not Close" warning sign to ensure the safety of personnel and equipment.
[0014] 380V AC power supply access
[0015] Connect the 380V AC power supply without leakage protection function to the lower contact of the primary circuit breaker on the high-voltage side of the main transformer to start the reverse current test. At this time, the current of the 220kV system flows in the reverse direction through the main transformer and generator circuits, thereby energizing the secondary circuits of each CT.
[0016] Current amplitude measurement
[0017] Measure the current amplitude of each CT circuit at the local terminal box to verify the three-phase current balance and the neutral current is zero, so as to check the tightness of the CT circuit wiring.
[0018] Current phase measurement
[0019] At the generator-transformer group protection screen, the current phase on the high-voltage side of the main transformer is measured to lead the current on the generator end by 150°, taking the generator end current as the reference, to verify the correctness of the wiring from the high-voltage side of the main transformer to the generator-transformer group protection screen. Then, the phase to the bus differential protection screen is measured at the CT terminal box on the high-voltage side of the main transformer to ensure that the four groups of protective CT circuits on the CT winding on the high-voltage side of the main transformer are correctly wired.
[0020] Analysis of the relationship between current amplitude and phase
[0021] To ensure the correctness of the CT circuit, accurate analysis of the current amplitude and phase is required.
[0022] Current amplitude: By calculating the impedance of the generator and main transformer winding, the current amplitude is determined to meet the measurement accuracy requirements.
[0023] Phase relationship: Analyze the phase relationship between the high-voltage side and the low-voltage side through the vector diagram. Combined with the Y / △-11 wiring method of the main transformer, confirm the deviation of the current direction during reverse flow, thereby verifying the accuracy of the wiring.
[0024] Inspection after unit connection to the grid
[0025] After the unit is started and connected to the grid, check the normal load current of the CT circuit to verify the sampling values of the protection device and the automatic device. Check that the differential current of the differential protection circuit is zero, and measure the N line and ground line current of the CT secondary circuit to ensure the accuracy of the wiring.
[0026] Beneficial Effects
[0027] The reverse current flow method of the present invention avoids the complexity and high risk of the traditional system short-circuit test. The method can simply and effectively check the polarity and phase sequence of the CT circuit of the generator-transformer group without starting the generator, reducing manpower and time costs, and effectively preventing equipment damage and safety hazards caused by CT circuit wiring errors, and has high practicality and promotion value.
[0028] In summary, the present invention provides an innovative method for checking the polarity and phase sequence of the CT circuit of a generator-transformer group, which ensures the correct wiring of the CT circuit of the generator-transformer group by detecting reverse current flow and current amplitude and phase. The method can be widely used in the installation and maintenance of power plant equipment, thereby improving the safety and reliability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0030] Figure 1 A schematic diagram of the relationship between the primary device and the secondary device of the electrical device according to an embodiment of the present invention;
[0031] Figure 2 This is a schematic diagram of the configuration of the generator-transformer group protection CT according to an embodiment of the present invention;
[0032] Figure 3 Schematic diagram of a reverse flow test method for a generator-transformer group system according to an embodiment of the present invention;
[0033] Figure 4 A schematic diagram of the analysis of the current amplitude and phase relationship of an embodiment of the present invention;
[0034] Figure 5 A schematic diagram of a current vector in a normal state according to an embodiment of the present invention;
[0035] Figure 6 It is a vector diagram of a generator-transformer group in a reverse current flow state according to an embodiment of the present invention;
[0036] Figure 7 A schematic diagram of current phase measurement values of a protection screen of a generator-transformer group according to an embodiment of the present invention;
[0037] Figure 8 It is a schematic diagram of the current phase measurement value of the CT terminal box of the 201 switch according to an embodiment of the present invention. DETAILED DESCRIPTION
[0038] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. At the same time, it is explained here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternatives to implement some known technologies; and the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention.
[0039] It should be noted that the references to "one embodiment", "an embodiment", "an exemplary embodiment", "some embodiments" and the like in the specification indicate that the embodiments described may include specific features, structures or characteristics, but not every embodiment may include the specific features, structures or characteristics. In addition, when a specific feature, structure or characteristic is described in conjunction with an embodiment, it should be within the knowledge of a person skilled in the art to implement such feature, structure or characteristic in conjunction with other embodiments (whether or not explicitly described).
[0040] In general, a term can be understood, at least in part, from its use in context. For example, depending, at least in part, on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense. Additionally, the term "based on" can be understood as not necessarily intended to convey an exclusive set of factors, but can instead, depending, at least in part, on the context, allow for the presence of other factors that are not necessarily explicitly described.
[0041] The present invention relates to a method for checking the polarity and phase sequence of a CT circuit of a generator-transformer group, aiming to detect the correctness of the CT circuit wiring through an innovative method of reverse current flow, thereby avoiding the potential safety hazards caused by incorrect polarity and phase sequence wiring of the CT circuit. The following embodiments describe in detail the operation steps and technical points of the present invention.
[0042] Example 1: Reverse flow test method
[0043] Experimental preparation and safety measures
[0044] Before conducting the reverse flow test, all wiring work must be completed and the work ticket must be withdrawn. To ensure the safety of personnel and equipment, the following preparations must be made:
[0045] Restore the CT external circuit connection on the terminal block of the generator-transformer group protection device.
[0046] Check and ensure that the control power supply of 201 circuit breaker, 201-1 and 201-2 isolating switches is disconnected and all switches are in the open position.
[0047] Hang a warning sign "Do not close the switch when someone is working" on the operating handle and control power switch.
[0048] Pull open the grounding switch (201-D2) on the 220kV side, remove the grounding wire of the generator PT primary side and the generator neutral point transformer. Set up a grounding trolley in the 6101 and 6102 switch bays of the #1 machine 6KVIA and IB sections of the 6KV distribution room.
[0049] 380V AC power supply access
[0050] Select a 380V power switch without leakage protection function in the maintenance distribution box of the booster station to avoid the leakage protector tripping due to unbalanced three-phase load.
[0051] Connect the external 380V AC power supply to the lower contact connection of the primary circuit breaker on the high-voltage side of the main transformer (see the position in the figure), and reverse the current to the main transformer and generator from the 220kV system.
[0052] Measure the current amplitude and phase of each CT circuit at the local terminal box, generator-transformer group protection screen, etc.
[0053] Current amplitude measurement at CT local terminal box
[0054] The current amplitude of the high-voltage side CT circuit is measured through the local CT terminal box.
[0055] The transformation ratio of each CT winding is the same, and the current on the secondary side is equal. At this time, the balance state of the three-phase current is tested, and the neutral line current should be 0, which can verify whether the wiring from the CT root to the CT terminal box is tight and not loose.
[0056] Current phase measurement at the protection screen of the generator-transformer group
[0057] After confirming that the CT current amplitude of the modified circuit is correct, current phase measurements are performed on the generator-transformer group protection panel and the main transformer high-voltage side terminal box in turn.
[0058] At the generator-transformer protection panel, the current phase of the main transformer high-voltage side is 150° ahead of the generator-end current (see Figure 7 ). This measurement verifies the correctness of the CT circuit wiring from the high voltage side of the main transformer to the generator-transformer group protection screen.
[0059] Continue at the CT terminal box on the high voltage side of the main transformer, taking the CT of the generator-transformer group protection screen as the reference, and measure the phase relationship of the CT circuit to the bus differential protection screen to be 0° (see Figure 8 ) to verify that the wiring of the four sets of protection CT windings on the high-voltage side of the main transformer is correct.
[0060] Example 2: Analysis of the current amplitude and phase relationship of reverse current
[0061] Analysis of current amplitude
[0062] When the current is reversed, in order to ensure the measurement accuracy, the current generated under the 380V AC voltage must meet the range requirements of the clamp ammeter.
[0063] By calculating the impedance of the generator and main transformer winding, it is found that the secondary induced current of the CT on the high-voltage side of the main transformer is about 20mA, and the secondary induced current of the CT on the low-voltage side of the main transformer is about 16mA, which meets the accuracy requirements. Therefore, using a 380V AC power supply to reversely pass current through the high-voltage side of the main transformer can ensure the accuracy of the amplitude measurement.
[0064] Analysis of phase relationship
[0065] Based on the current vector diagram analysis (see the normal current vector diagram and the reverse current vector diagram), combined with the Y / △-11 wiring method of the main transformer, the phase relationship is confirmed:
[0066] The high voltage side is wired at 180° and the current direction displayed by the protection device is opposite to the actual current.
[0067] The low voltage side is wired at 0°, and the current direction displayed by the protection device is consistent with the actual current.
[0068] When the current is reversed, the phase angles of the currents on the high-voltage side and the low-voltage side of the main transformer are offset by 180°. The current on the low-voltage side of the main transformer at the protection screen lags behind the high-voltage side by 150° (see the vector diagram).
[0069] Example 3: Inspection after unit connection to the grid
[0070] After the unit is started and connected to the grid, the normal load current of each CT circuit is checked by sampling the protection device and the automatic device to further verify the correctness of the CT circuit wiring.
[0071] Check that the differential current value of the differential protection circuit is 0 to ensure that there is no differential current.
[0072] Measure the N-wire and ground-wire currents in the CT secondary circuit. The N-wire and ground-wire currents should be close to 0 to ensure the accuracy of the wiring.
[0073] Example 4: Experimental results data
[0074] In the actual experiment, the current phase data at different measurement positions are recorded, as shown in the table:
[0075] The phase angle data of the current flow test of the protection panel A of the generator-transformer group are: main transformer Ia-machine end Ia is 151.5°, Ib-machine end Ib is 152°, and Ic-machine end Ic is 149.1°.
[0076] The phase angle data of the current flow test of the protection screen B of the generator-transformer group are: main transformer Ia-machine end Ia is 148°, Ib-machine end Ib is 152.1°, and Ic-machine end Ic is 151.6°.
[0077] The phase relationship of the busbar protection screen was measured to be 0° at the CT terminal box of the 201 switch, which further verified the correctness of the wiring of all circuits (see Figure 7 and Figure 8 ).
[0078] The phase measurement result from the 201-bay CT to the busbar differential protection screen is shown to be 0°, verifying the accuracy of the CT winding connection.
[0079] Through the above implementation modes, the present invention provides an effective CT circuit wiring detection means before the unit is started, ensures the correctness of the polarity and phase sequence of the generator-transformer group CT, avoids the high risk of the traditional system short-circuit test, and has significant practical value.
[0080] The present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention. In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details. In addition, in order to avoid unnecessary confusion about the essence of the present invention, well-known methods, processes, procedures, components and circuits are not described in detail.
[0081] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A method for checking the polarity and phase sequence of the CT circuit of a generator-transformer group, characterized in that: The reverse current flow method is adopted. By connecting an external power supply to the high-voltage side of the main transformer, the main transformer, generator and high-voltage transformer are driven to flow in reverse, ensuring that each CT secondary circuit is energized. Taking the unchanged CT circuit as the benchmark, the current amplitude and phase of other CT circuits are measured, and then the phase relationship is theoretically analyzed to determine the correctness of the CT circuit wiring.
2. A method for checking polarity and phase sequence of CT circuit of a generator-transformer group according to claim 1, characterized in that: The current amplitude is measured by introducing a 380V AC power supply on the high-voltage side of the main transformer and measuring the induced current on the secondary side of the CT to ensure that the current amplitude meets the instrument measurement accuracy requirements.
3. A method for checking polarity and phase sequence of CT circuit of a generator-transformer group according to claim 1 or 2, characterized in that: When the reverse current is flowing, a 380V AC power supply is connected to the lower contact of the primary circuit breaker on the high-voltage side of the main transformer, and the current amplitude and phase of each CT circuit are measured on the local terminal box and the generator-transformer group protection screen.
4. A method for checking polarity and phase sequence of CT circuit of a generator-transformer group according to claim 3, characterized in that: The analysis of the phase relationship is based on the current vector diagram, by measuring the current phase angle relationship between the high voltage side and the low voltage side, combined with the wiring method of the main transformer (such as Y / △-11 wiring), to ensure that the protection device correctly displays the direction of the current.
5. The method for checking the polarity and phase sequence of the CT circuit of a generator-transformer group according to claim 1 is characterized in that: The following steps are also included: Before reverse current flow, restore the CT external circuit connection on the terminal block of the generator-transformer group protection device, and ensure that the control power supply of the relevant circuit breakers and disconnectors is reliably disconnected and the switches are in the open position.
6. A method for checking polarity and phase sequence of CT circuits of a generator-transformer group according to claim 5, characterized in that: When selecting a power source for reverse current flow, a 380V AC power source without leakage protection function is preferred to prevent the leakage protector from tripping due to unbalanced three-phase load.
7. A method for checking polarity and phase sequence of CT circuits of a generator-transformer group according to claim 1, characterized in that: The amplitude measurement of the CT circuit includes verifying the balance of the three-phase current and the neutral line current is close to zero when the transformation ratio of each CT winding on the high-voltage side is the same, so as to ensure that the wiring from the root of the CT to the CT terminal box is tight and not loose.
8. The method for checking the polarity and phase sequence of the CT circuit of a generator-transformer group according to claim 1 is characterized in that: The CT phase measurement is carried out at the protection screen of the generator-transformer group. The current at the generator end is used as a reference, and the correctness of the loop wiring is verified by measuring the current phase difference between the high-voltage side of the main transformer and the generator end.
9. A method for checking polarity and phase sequence of CT circuits of a generator-transformer group according to claim 8, characterized in that: The phase relationship of the CT circuits at the generator-transformer group protection panel and the bus differential protection panel is verified to ensure that all circuit connections of the CT windings protecting the high-voltage side of the main transformer are correct.
10. A method for checking polarity and phase sequence of CT circuits of a generator-transformer group according to claim 1, characterized in that: After the unit is connected to the grid, the load current of the CT circuit is measured to ensure that the differential current of each differential protection circuit is zero, and the N line and ground line current in the CT secondary circuit are further checked to verify the accuracy of the circuit wiring.