Transformer winding frequency response curve compensation method considering non-uniform lead impedance

Abstract

The invention discloses a transformer winding frequency response curve compensation method considering non-uniform lead impedance, which comprises the following steps of: calculating a compensation coefficient of a to-be-detected transformer winding frequency response curve according to the length and non-uniform distribution parameters of a lead used for field detection, and further correcting the compensation coefficient. According to the method, errors caused by non-uniform impedance of the lead in the frequency response detection process of the transformer winding can be eliminated, so that the accuracy of fault diagnosis of the transformer winding is ensured.

Description

Technical Field

[0001] The present invention relates to the field of frequency response detection of transformer windings, and particularly to a compensation method for the frequency response curve of a transformer winding considering non-uniform lead impedance. Background Art

[0002] As one of the important devices in the power grid, the safe and stable operation of power transformers directly affects the safety and reliability of power supply. The detection of transformer winding faults is a key link to ensure the safe operation of the power system. Due to its advantages such as high sensitivity and strong anti-interference ability, the frequency response analysis method is widely used to diagnose faults such as winding deformation and inter-turn short circuit. The traditional frequency response analysis technology injects a swept-frequency signal into the transformer winding, obtains its frequency response curve, and judges the fault by comparing the difference between the measured curve and the factory reference curve. The accuracy of the measured frequency response curve directly affects the discrimination of transformer winding faults.

[0003] However, the influence of the difference between the leads used in the detection site and the factory test leads on the frequency response curve has been ignored for a long time, and the problem is particularly prominent in the scenarios of long leads or high-frequency bands. The impedance of the actual lead is affected by factors such as high-frequency skin effect and distribution parameter accumulation, showing non-uniform distribution characteristics. Moreover, the length of the lead used in the detection site is often much greater than that of the factory test lead, resulting in a certain error between the factory standard curve and the measured curve, which may lead to misjudgment of transformer winding faults. Therefore, it is of great significance to correct the frequency response curve of the transformer winding. Summary of the Invention

[0004] The purpose of the present invention is to provide a compensation method for the frequency response curve of a transformer winding considering non-uniform lead impedance, so as to eliminate the error caused by the non-uniform impedance of the lead in the frequency response detection of the transformer winding.

[0005] 1. To achieve the above purpose, the present invention provides the following steps:

[0006] Step 1: Cut off the power supply of the transformer (1) to be measured and use a discharge rod to fully discharge the winding and the bushing. Connect the high-voltage bushing end (3) of the transformer to be measured to the excitation output port (5) of the frequency response tester (4) using a lead (2), and connect the low-voltage bushing end (6) to the signal detection port (7) of the tester. Keep the lengths of the two leads equal and symmetrically distributed, and connect the frequency response tester to the upper computer (8);

[0007] Step 2: By introducing a weight function, improve the ideal uniformly distributed impedance model into a non-uniform model that dynamically adjusts with distance, and calculate the impedance per unit length of the lead according to the following formula:

[0008] Z(x) = a0·f(x) + j·b0·g(x)

[0009] In the formula, x is the distance of a certain point on the lead wire from the transformer end, Z(x) is the impedance per unit length of the lead wire under the non-uniform model, a0 and b0 are the real part and the imaginary part of the original impedance per unit length under the uniform distribution model respectively, and f(x) and g(x) are the distance weight functions of the real part and the imaginary part of the impedance per unit length of the lead wire respectively:

[0010] f(x) = e -0.182x

[0011] g(x) = 1 + 0.05x;

[0012] Step 3: Calculate the total impedance of the lead wire used at the detection site according to the following formula:

[0013]

[0014] In the formula, L is the length of the lead wire used at the detection site, and Z L is the total impedance of the lead wire;

[0015] Step 4: Combine the differences between the lead wire at the measurement site and the standard lead wire, and calculate the frequency response compensation coefficient according to the following formula:

[0016]

[0017] In the formula, α(L) is the frequency response compensation coefficient, Z re is the impedance of the standard lead wire, and L re is the length of the standard lead wire, taking 1 m;

[0018] Step 5: Turn on the frequency response tester (4), inject a swept-frequency signal, record the measured frequency response curve H1(f) and transmit it to the upper computer (8), and use the following formula to correct the measured frequency response curve on site:

[0019] H2(f) = H1(f)·α(L)

[0020] In the formula, H2(f) is the corrected frequency response curve, and compare it with the factory reference curve H re (f) of the transformer to be tested to judge the fault condition of the transformer winding.

[0021] 2. The swept-frequency range of the frequency response tester (4) is set to 1 Hz to 1 MHz, and the number of swept-frequency points N ≥ 1000 points. Description of the Drawings

[0022] Figure 1 is the system installation diagram for compensating the frequency response curve of the transformer winding. Detailed Implementation Modes

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation processes. It should be emphasized that the specific implementation cases described herein are only used to explain the invention patent and are not used to limit the scope of the inventive concept and its claims of the invention patent.

[0024] Step 1: Cut off the power supply of the transformer (1) to be tested and use a discharge rod to fully discharge the winding and bushing. As Figure 1 shown, use a lead wire (2) to connect the high-voltage bushing end (3) of the transformer to be tested with the excitation output port (5) of the frequency response tester (4), and connect the low-voltage bushing end (6) to the signal detection port (7) of the tester. The lengths of the two lead wires are kept equal and symmetrically distributed, and the spacing > 0.5 m to reduce mutual inductance interference. Connect the frequency response tester to the host computer (8);

[0025] Step 2: By introducing a weight function, improve the ideal uniformly distributed impedance model into a non-uniform model that dynamically adjusts with distance, and calculate the impedance per unit length of the lead wire according to the following formula:

[0026] Z(x) = a0·f(x) + j·b0·g(x)

[0027] where x is the distance of a certain point on the lead wire from the transformer end, Z(x) is the impedance per unit length of the lead wire under the non-uniform model, a0 and b0 are the real and imaginary parts of the original impedance per unit length under the uniformly distributed model respectively, and f(x) and g(x) are the distance weight functions of the real and imaginary parts of the impedance per unit length of the lead wire:

[0028] f(x) = e -0.182x

[0029] g(x) = 1 + 0.05x;

[0030] Step 3: Calculate the total impedance of the lead wire used at the detection site according to the following formula: <able>

[0031]

[0032] where L is the length of the lead wire used at the detection site, and Z L is the total impedance of the lead wire;

[0033] Step 4: Combine the differences between the lead wire at the measurement site and the standard lead wire, and calculate the frequency response curve compensation coefficient according to the following formula:

[0034]

[0035] where α(L) is the frequency response curve compensation coefficient, Z re is the impedance of the standard lead wire, and L re is the length of the standard lead wire, taking 1 m; <able>

[0036] Step 5: Turn on the frequency response tester (4), set the sweep range to 1 Hz to 1 MHz, the number of sweep points N ≥ 1000 points, inject a sweep signal, record the measured frequency response curve H1(f) and transmit it to the host computer (8), and use the following formula to correct the on-site measured frequency response curve:

[0037] H2(f) = H1(f) · α(L)

[0038] In the formula, H2(f) is the corrected frequency response curve, and compare it with the factory reference curve H re (f) of the transformer to be tested to judge the winding fault condition of the transformer.

Claims

1. A compensation method for the frequency response curve of a transformer winding considering non-uniform lead impedance. According to the length and non-uniform distribution parameters of the leads used on site, the compensation coefficient of the frequency response of the transformer winding to be measured is calculated, and then it is corrected to ensure the accuracy of the fault diagnosis of the transformer winding. It is characterized in that It includes the following steps: Step 1: Cut off the power supply of the transformer under test and use a discharge rod to fully discharge the winding and bushing. Connect the end of the high-voltage bushing of the transformer under test to the excitation output port of the frequency response tester with a lead wire, and connect the end of the low-voltage bushing to the signal detection port of the tester. The lengths of the two lead wires are kept equal and symmetrically distributed. Connect the frequency response tester to the upper computer; Step 2: By introducing a weight function, improve the ideal uniformly distributed impedance model into a non-uniform model that dynamically adjusts with distance, and calculate the impedance per unit length of the lead wire according to the following formula: Z(x) = a0·f(x) + j·b0·g(x) In the formula, x is the distance of a certain point on the lead wire from the transformer end, Z(x) is the impedance per unit length of the lead wire under the non-uniform model, a0 and b0 are the real part and the imaginary part of the original impedance per unit length under the uniformly distributed model respectively, and f(x) and g(x) are the distance weight functions of the real part and the imaginary part of the impedance per unit length of the lead wire respectively: f(x) = e -0.182x g(x) = 1 + 0.05x; Step 3: Calculate the total impedance of the lead wire used at the detection site according to the following formula: Where L is the length of the lead wire used at the detection site, and Z L is the total impedance of the lead wire; Step 4: Combine the differences between the lead wire at the measurement site and the standard lead wire, and calculate the frequency response curve compensation coefficient according to the following formula: where α(L) is the frequency response curve compensation coefficient, Z re is the standard lead impedance, L re is the standard lead length, taken as 1 m; Step 5: Turn on the frequency response tester, inject a swept-frequency signal, record the measured frequency response curve H1(f) and transmit it to the upper computer, and use the following formula to correct the measured frequency response curve on site: H2(f) = H1(f)·α(L) where H2(f) is the corrected frequency response curve, which is compared with the factory reference curve H re (f) of the transformer under test to determine the fault condition of the transformer winding.

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