Power distribution network closed-loop power regulation safety checking method

Abstract

The invention provides a power distribution network closed-loop power regulation safety checking method, and belongs to the field of power distribution networks. The method comprises the following steps: detecting all electrical parameters of a power grid, calculating a voltage difference, a phase difference and impedance, and performing safety check according to steady-state current and impact current analysis, thereby ensuring the accuracy and safety of closed-loop power regulation of the power distribution network. The method comprises the following steps: firstly, detecting all electrical parameters at detection points before and after loop closing, then calculating the voltage difference and phase difference of the parameters, and judging whether the loop closing is reasonable or not. Furthermore, the loop impedance is calculated by measuring the voltage vector difference and predicting the loop closing current. According to the characteristics of the power grid, during each loop closing, the impedance should be updated to keep accuracy. Meanwhile, the impact current and the steady-state current are calculated and analyzed. If the security check of all key nodes is passed and the conditions in the step 2 meet the requirements, a result is obtained, and loop closing can be carried out.

Description

Technical Field

[0001] The present invention belongs to the field of power distribution networks, and more particularly relates to a method for verifying the safety of closed-loop power regulation in a power distribution network. Background Art

[0002] Closed-loop operation of a distribution network refers to the closed-loop operation of a distributed distribution network by closing circuit breakers or switching devices. It is one of the key means of achieving economical and efficient operation of power systems. In this mode of operation, the load of each electrical device is balanced, which helps improve the reliability and flexibility of the power supply, reduce the number of fuse and circuit breaker operations, and extend the service life of distribution equipment. However, closed-loop operation of the distribution network also changes the direction and magnitude of the distribution system current, increases fault current, and complicates the selection and coordination of protective devices, requiring accurate real-time monitoring of the distribution network's operating status.

[0003] Traditional distribution networks mostly operate in a radial fashion. While this approach is simple and straightforward, it also presents challenges such as poor voltage quality and an increasingly unreliable power supply that struggles to meet user needs. With the increasing scale and complexity of distribution networks and the evolving trends in power system development, distribution network operation methods are constantly evolving and improving. Among these, closed-loop operation is a key future trend. However, despite its numerous advantages, achieving closed-loop power regulation safely, accurately, and efficiently remains an unresolved challenge.

[0004] Current methods are primarily limited to simulations, performed blindly without the support of measured data. This lack of real-time performance and accuracy hinders the stable and reliable operation of distribution networks. Therefore, how to achieve closed-loop operation in a safe and efficient manner through real-time monitoring and control of distribution network operating conditions is an important research topic for distribution networks.

[0005] During distribution network operation, closing and opening loops are often necessary to adjust grid operation due to factors such as equipment maintenance, load transfers, and network failures. Due to a lack of effective technical means and equipment, less than 20% of distribution networks currently utilize power outages (small loop networks). Most rely on manual experience, while a smaller number utilize theoretical calculations to guide closing and adjusting loops. Over 80% still utilize power outages (large electromagnetic loop networks). Relying on manual experience without theoretical verification results in highly random loop closing, resulting in a low success rate and significant safety risks. Current theoretical calculations cannot achieve full coverage of the loop network and are not verified, resulting in low reliability. Power outages and adjustment methods suffer from poor reliability, low customer satisfaction, and are not aligned with the future direction of digital and intelligent grid development. Summary of the Invention

[0006] This patent provides a safety verification method for closed-loop power regulation, including measurement, calculation, and verification of the voltage phase sequence, effective value, phase, closed-loop steady-state current, and closed-loop inrush current at both ends of the closed loop. This provides an effective safety verification method for closed-loop power regulation without power outages.

[0007] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: the method comprises:

[0008] Use full-phase measurement devices to detect all electrical quantity parameters, including voltage RMS, phase, current RMS and phase;

[0009] When closing the loop and regulating the power, collect the current voltage, calculate the phase sequence, voltage difference and voltage phase difference before and after closing the loop, and perform verification.

[0010] By measuring the current, the loop impedance is calculated;

[0011] Before each loop closing, update the impedance value;

[0012] Calculate the inrush current and steady-state current during loop closing;

[0013] For lines of key concern, safety verification is carried out, including verification of line rated current and current protection stage I value.

[0014] In one embodiment, the voltage effective value, phase, current effective value and phase parameters collected by the full-phasor measurement device are used to calibrate the voltage of the closed loop to confirm the safety of the closed loop.

[0015] In one embodiment, the method for measuring current includes performing real-time full-phase measurement of current and rapid sampling of current to ensure the accuracy and timeliness of current measurement.

[0016] In one embodiment, the calculation of the voltage difference and the voltage phase difference includes real-time measurement of the voltages before and after the closing loop, obtaining the effective value and phase of the voltage, and then calculating the voltage difference and the voltage phase difference.

[0017] In one embodiment, the method for calculating loop impedance includes calculating the loop impedance using a formula based on real-time measured values ​​of voltage and current.

[0018] In one solution, before each loop closing, the impedance value needs to be updated, including the average value of each impedance value measured through multiple measurements as the new impedance value.

[0019] In one embodiment, the calculation of the impact current and the steady-state current during the loop closing process includes the current change before and after the loop closing process, so as to calculate the impact current and the steady-state current during the loop closing process.

[0020] In one plan, for lines of key concern, detailed inspection and verification of line rated current and current protection stage I value are included.

[0021] In one solution, during the calibration process, special conditions of the power grid, grid load, grid current and other factors are also considered to ensure the accuracy and comprehensiveness of the calibration.

[0022] Beneficial effects of the present invention:

[0023] This paper proposes a method for calculating the equivalent impedance of a ring network. This method primarily uses historical closed-loop current data to calculate the equivalent impedance of the ring network. This simple and effective method addresses the challenges of long and complex power flow calculations. A method for fusion of impedance data based on the exponentially weighted moving average method is also proposed to ensure that the impedance calculation is more realistic and prevent significant deviations in the results due to outliers.

[0024] A full-phasor measurement device collects voltage and current data at both ends of the closed loop in real time. Based on actual conditions, it can quickly predict the closed loop steady-state current and closed loop inrush current, significantly reducing loop closing preparation time and improving work efficiency. By verifying phase sequence, voltage difference, phase difference, closed loop steady-state current, and closed loop inrush current parameters, the closed loop results are comprehensively determined. Through continuous adjustment and recalibration, 100% non-stop power regulation is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flow chart of the method of the present invention;

[0026] Figure 2 This is a schematic diagram of a 10kV electromagnetic ring network of the present invention;

[0027] Figure 3 This is the principle diagram of the superposition method;

[0028] Figure 4 Equivalent model for calculating closed-loop impulse current. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate exemplary embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those understood by those skilled in the art to which the present invention pertains. The terms used in the present specification are for the purpose of describing specific embodiments only and are not intended to limit the present invention. To facilitate understanding of the present invention, a more comprehensive description of the present invention will be provided below with reference to the accompanying drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0031] like Figure 1 As shown, a method for verifying the safety of closed-loop power regulation in a distribution network includes the following steps:

[0032] Step 1: Use a full-phase measurement device to detect all electrical quantity parameters, including voltage RMS, phase, current RMS and phase.

[0033] In the figure, detection points i and j are full electrical quantity parameter detections completed by the full phasor measurement device, including voltage RMS, phase, current RMS, phase, etc. (a certain phase is used as an example for explanation in this example).

[0034] Step 2: When closing the loop and adjusting the power, collect the current voltage, calculate the phase sequence, voltage difference and voltage phase difference before and after closing the loop, and perform verification.

[0035] When the loop needs to be closed, the full phasor measurement device is used to collect the current voltage. First, the phase sequence on both sides is calculated based on the voltage situation to see if it is consistent (in actual calculation, if the phase sequence is inconsistent, the phase difference between the two ends of the loop must be large, so only the phase difference is calculated). Then the voltage difference and the voltage phase difference are calculated. The voltage is recorded as Then the voltage difference is:

[0036] ΔU=U i -U j (1)

[0037] The voltage phase difference is:

[0038]

[0039] The results of voltage phase sequence, voltage difference, and phase difference calibration are as follows. Assume that the voltage difference threshold is ΔU max , the phase difference threshold is but

[0040]

[0041] When Result is true, it indicates that the voltage phase sequence, voltage difference, and phase difference calibration have passed.

[0042] Step 3: Measure the voltage vector difference and the last closed loop current or the predicted closed loop current to calculate the loop impedance. Assuming that the line has been closed, the current will be obtained by the full phasor measurement device. If the line has not been closed, the line can be closed when the line load is low and safety is ensured, which will also be obtained by the full phase measurement device. If the line has not been closed before and cannot be closed once under safety conditions, the current flow calculation or other methods can be used to obtain The line impedance can be calculated using the following formula:

[0043]

[0044] Step 4: According to the characteristics of the power grid, the impedance changes with time. Therefore, the impedance should be updated every time the loop is closed to maintain accuracy.

[0045] Assume that a line is closed n times, is the voltage vector difference between the two ends before the nth loop closing, is the closed-loop current measured after the nth closed-loop, Z ∑ Calculate the impedance when closing the loop for the nth time, then

[0046]

[0047] At the same time, in order to reduce the impedance measurement error, this patent uses the exponentially weighted moving average method to update the impedance. The closer the time, the greater the impedance weight. The impedance calculation formula is as follows:

[0048] Z ∑ (n) = αZ ∑ +(1-α)Z ∑ (n-1) (6)

[0049] Where α is the smoothing factor, when n=1, Z ∑ (n) = Z ∑ .

[0050] Step 5: Calculate the inrush current and steady-state current during the loop closing process.

[0051] The entire loop closing process impacts the distribution network. It undergoes a brief transient transition before returning to steady state, generating both steady-state and surge currents. Closing control alters the network structure, generating circulating currents within the closed loop network and altering the distribution network's power flow. If excessive steady-state and surge currents trigger relay protection, the outage could expand. Therefore, before closing the loop, it's crucial to analyze the closing control conditions that steady-state and surge currents must meet.

[0052] This patent uses the superposition method to calculate the steady-state current and performs the following processing on the closed-loop network:

[0053] The basic principle of superposition method is as follows Figure 3 As shown, Figure (a) is equivalent to the superposition of Figures (b) and (c). Figure (b) retains all power sources and loads in the closed-loop network. Figure (c) removes node loads, ignores power sources and branch lines, and retains only the lines involved in the closed-loop and the equivalent voltage source representing the voltage difference across the tie switch. First, calculate the feeder currents in Figure (b) and the circulating currents in Figure (c), then superimpose them to obtain the steady-state current in Figure (a).

[0054] Assume that in Figure (a) above, the currents in line E and line F are I e and I f , the steady-state current flowing through the closing point is The branch currents in Figure (b) above are I e1 and I f1 , the circulating current in Figure (c) above is The relationship between them is as follows:

[0055]

[0056] from Figure 2 The distribution of node voltage can be obtained from the detection points i and j in , and the voltage difference on both sides of the tie switch before closing the loop control is:

[0057]

[0058] but The calculation formula is:

[0059]

[0060] Among them, Z ∑ It is the equivalent impedance of the additional ring network. By calculating the impedance, the steady-state current of the closed loop can be obtained.

[0061] Due to the presence of inductive components and transformers, the distribution network, after closed-loop control, experiences transient oscillations that decay to a steady state. Although this duration is very short, excessive surge currents can cause significant impacts on lines and equipment, even leading to switch explosions. Therefore, in addition to verifying the steady-state current, it is also necessary to analyze the impact of transient processes and establish a differential equation for the closed-loop network to solve the response.

[0062] Figure 4 In the equation (1), R+jX represents the equivalent impedance after the loop is closed, U is the effective value of the voltage vector difference across the closed-loop switch when the loop is closed, and δ represents the voltage phase angle difference across the switch when the loop is closed.

[0063] After closing the ring, Figure 4The circuit shown has the following differential equation:

[0064]

[0065] The solution of this differential equation is the total current of the closed-loop impulse current, which consists of two parts. The first part is the special solution of this equation, which represents the periodic component i of the impulse circulation current. c , which is the closed-loop steady-state circulation, the second part is called the free component or the non-periodic component, denoted by i ap , which can be solved

[0066]

[0067] In the formula is the effective value of the steady-state circulating current, is the impedance angle of the closed-loop equivalent model. The solution is

[0068] i ap =Cexp(-t / T) (12)

[0069] In the formula, is called the non-periodic component decay time constant, ω=2πf。

[0070] From formulas 11 and 12, the expression of the total current of the closed-loop impact circulating current can be obtained as

[0071]

[0072] Since the current in the inductor cannot change suddenly, the current before the loop is closed should be equal to the current after the loop is closed. It can be seen that the current in the additional network inductor before the loop is closed is 0. When t = 0,

[0073]

[0074] so

[0075] The full current expression of the closed-loop impact current can be further obtained as

[0076]

[0077] In formula 15, the loop impact current is approximately proportional to the voltage amplitude difference between the two points of the loop, and is approximately inversely proportional to the total impedance of the loop network, and is also affected by the phase angle difference of the voltage. When i is 0 or an integer multiple of π, ap =0, that is, it enters the steady state immediately after closing the loop; when When the impact circulation reaches its maximum value, the maximum value is

[0078]

[0079] From the above formula, we can know that when When the current is ±π / 2, the impact circulating current reaches its maximum value. The maximum instantaneous current appears in the second half of the cycle after the closing loop, that is, when t=0.01s. Substituting t=0.01s into the above formula, the maximum value of the closing loop impact circulating current can be calculated as:

[0080]

[0081] In the above formula, is the periodic component, is the non-periodic component, and the two are superimposed to form the maximum value of the impulse current. The above formula can be simplified to

[0082]

[0083] Let K im =1+exp(-0.01 / T), which is called the impact circulation coefficient. Substituting it into the above formula, the maximum value of the closed-loop impact circulation can be calculated.

[0084]

[0085] because Therefore, it can be seen that the impact current is related to the ratio of the reactance and resistance of the closed-loop network.

[0086] Step 6: When performing the "One-Click Ring Closure" power adjustment task, to ensure equipment safety during ring closure, it is necessary to clearly define the ring network topology and perform safety checks on key branches. The safety check is based on two conditions: whether the steady-state current exceeds the line rated current, and whether the inrush current exceeds the current protection level I. If either condition is met, the safety check fails. The following uses the aforementioned ring network as an example to illustrate the principles of safety checks.

[0087] In the above ring network, assuming that line E and line F are weak points and require special attention when closing the ring, these two branches should be checked for safety during the safety check.

[0088] When the loop is closed, the steady-state current of the line where the tie switch is located is The non-periodic component of the closed-loop current is i ap , assuming that the currents of line E and line F before closing are and The steady-state current and impulse current after loop closing are I Eim , I Fim The current after the E and F lines are closed is calculated as follows:

[0089]

[0090] Assume that the rated current and current protection stage I value of line E and line F are I ER , I FR , I EP , I FP , then the judgment logic of the safety check result is as follows:

[0091] Result=(I ER >I EC )∧(I FR >I FC )∧(I EP >I Eim )∧(I FP >I Fim ) (24) When Result is true, it indicates that the safety check has passed.

[0092] Step 7: If the safety checks of all key nodes pass and the conditions in step 2 are met, the results are obtained and the loop can be closed. Otherwise, loop closing is not recommended.

[0093] Step 8: If the loop is closed, the inrush current and steady-state current during the loop closing are detected and stored as data.

[0094] Step 9: If the result is that the loop cannot be closed, adjust the circuit structure according to the actual measurement situation and then judge the loop closing condition again until the loop closing condition is met.

[0095] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware through a computer program. The program can be stored in a computer-readable storage medium, and when executed, the program can include the processes in the above-described method embodiments. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0096] It should be understood that the detailed description of the technical solutions of the present invention using the preferred embodiments above is illustrative and not restrictive. A person skilled in the art, after reading the present specification, may modify the technical solutions described in the embodiments or replace some of the technical features therein with equivalents; such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for verifying the safety of closed-loop power regulation in a distribution network, characterized by: The method includes: Use full-phase measurement devices to detect all electrical quantity parameters, including voltage RMS, phase, current RMS and phase; When closing the loop and regulating the power, collect the current voltage, calculate the phase sequence, voltage difference and voltage phase difference before and after closing the loop, and perform verification. By measuring the current, the loop impedance is calculated; Before each loop closing, update the impedance value; Calculate the inrush current and steady-state current during loop closing; For lines of key concern, safety verification is carried out, including verification of line rated current and current protection stage I value.

2. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: The voltage effective value, phase, current effective value and phase parameters collected by the full-phasor measurement device are used to calibrate the voltage of the closed loop to confirm the safety of the closed loop.

3. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: The current measuring method includes real-time full-phase measurement of the current and rapid sampling of the current to ensure the accuracy and timeliness of the current measurement.

4. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: The calculation of the voltage difference and the voltage phase difference includes measuring the voltages on both sides of the loop in real time, obtaining the effective value and phase of the voltage, and then calculating the voltage difference and the voltage phase difference.

5. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: The method for calculating the loop impedance includes calculating the loop impedance using a formula based on real-time measured values ​​of voltage and current.

6. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: Before each loop closing, the impedance value needs to be updated, including the average value of each measured impedance value obtained through multiple measurements as the new impedance value.

7. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: The calculation of the impact current and the steady-state current during the loop closing process includes the current change before and after the loop closing process, so as to calculate the impact current and the steady-state current during the loop closing process.

8. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: For lines of key concern, detailed inspection and verification of line rated current and current protection stage I value are included.

9. The method for verifying the safety of closed-loop power regulation in a distribution network according to claim 1, characterized in that: During the calibration process, special conditions of the power grid, grid load, and grid flow factors are also taken into consideration to ensure the accuracy and comprehensiveness of the calibration.

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