On-Site Lightning Impulse Test and Process Optimization Research on Distribution Network Equipment

Abstract

Lightning impulse tests are conducted on distribution equipment to assess whether the insulation level meets factory standards and to identify potential insulation defects. Such tests enhance the safety and stability of distribution network operation. Firstly, in order to address the issue of complex types and diverse structures of distribution network equipment, by using portable lightning impulse generators and adopting the method of automatically generating test reports, the requirements for test sites and test procedures have been simplified. Secondly, the generation and regulation of standard lightning waveforms were analyzed, and the influencing factors were pointed out. Finally, several distribution equipment such as disconnectors were subject to on-site impulse tests in accordance with the standards, and the general process of on-site standard lightning impulse tests was summarized.

1. Introduction

Lightning is one of the primary external threats to the safe and reliable operation of distribution networks. The resulting lightning overvoltage often leads to equipment insulation breakdown, line tripping, and widespread power outages. Statistics show that insulation damage caused by lightning overvoltage is the most common cause of distribution system operational incidents, severely impacting the continuity and safety of power grids. Lightning impulse testing is widely used to assess the resistance of distribution equipment to lightning. This test simulates the lightning overvoltage process, not only verifying whether the equipment can withstand the effects of lightning overvoltage but also identifying potential insulation defects. Therefore, lightning impulse testing plays an irreplaceable role in the development, type testing, and quality assurance of distribution equipment [1,2,3].

However, with the continuous expansion of distribution networks and the increasing complexity of operating environments, traditional laboratory testing methods are gradually revealing their limitations in practical applications. Firstly, Distribution equipment varies in type—including switchgear, transformers, and vacuum circuit breakers—and their insulation withstand levels differ accordingly. Relying solely on conventional power frequency withstand voltage and impulse tests at the factory stage cannot truly reflect their lightning resistance performance under complex field conditions. Secondly, in recent years, power grid companies have tightened their supervision of the quality of power supplies and gradually implemented a random inspection system for networked equipment. There is an urgent need for a portable on-site lightning impulse test method to determine the insulation withstand capability of distribution network equipment and identify potential fault hazards [4].

The power distribution equipment is complex. Each type of equipment has different lightning impulse withstand levels. In order to verify the impact of lightning impulse on the insulation performance of different power distribution equipment. It is necessary to establish a standard method for lightning impulse testing. Through this test, the insulation performance of distribution network equipment can be evaluated, ensuring its proper insulation level and supporting the safe and stable operation of the distribution system.

Due to the uneven quality levels among power distribution equipment manufacturers, frequent failures in distribution network circuits have seriously affected the reliability of power supply systems. Before the equipment leaves the factory, the manufacturer will conduct a routine withstand voltage test on the distribution network equipment. The test voltage waveform is generally divided into two types: power frequency voltage and impulse voltage. The power frequency voltage impulse test technology is relatively mature, while the impulse voltage test is difficult to complete at the equipment installation site. Therefore, only the conventional withstand voltage impulse test is often used. However, insulation failures caused by lightning strikes may still occur during the use of the distribution network [5,6,7].

Our study employed the standard lightning waveforms defined in IEC 60060-1 [8] to evaluate the insulation performance of various types of distribution equipment. To facilitate the adoption of more rigorous impulse voltage testing methods during manufacturing, storage, transportation, and field operation, a portable lightning impulse voltage test device was used. An impulse test protocol is proposed for distribution equipment, including switchgear, transformers, and circuit breakers.

2. Distribution of Test Sites and Equipment

2.1. Portable Lightning Impulse Generator

The standard lightning impulse is generated by an impulse voltage generator. The impulse voltage generator usually adopts a Marx charge and discharge circuit. A Marx generator is a high-voltage device that uses capacitors to charge in parallel and then discharge in series [9].

The portable impulse generator used in the test features a single-stage tower structure, consisting of a set of parallel-connected high-voltage capacitors for energy storage. The capacitors are charged by a high-voltage DC power supply and discharged in series through a copper ball and a resistor. Appropriate lightning wave head and tail resistors are selected based on the capacitance of the test specimen, and these resistors are easily removable. The main body is made of epoxy material, and the highest-voltage region is protected against aging and corona discharge, ensuring no visible corona occurs during charging. The device is lightweight and can be moved by a single person. Figure 1 illustrates the portable impulse generator, and the corresponding parameters are presented in

Table 1. Partial technical specifications of the portable impulse generator.

Index	Item	Parameter
1	Nominal voltage (kV)	±120
2	Rated voltage (kV)	±120
3	Rated energy (kJ)	11
4	Impulse capacitance (μF)	2
5	Number of stages	1

.

Prior to use, the grounding condition of the portable lightning impulse generator must be verified, and multiple no-load tests should be conducted to compare voltage waveforms and timing parameters, ensuring data accuracy and stability.

2.2. Usability Analysis of the Lightning Impulse Generator

To verify that the standard lightning impulse waveform employed in the tests complies with the requirements for on-site impulse testing. The standard lightning impulse waveform was measured using a STRAUSS impulse measurement system certified by DKD. The usability of the waveform produced by the test generator was evaluated by comparing its measurement results with those obtained from a standard lightning impulse generator.

The STRAUSS impulse measurement system was calibrated in accordance with the requirements for measuring systems specified in IEC 60060-2. Calibration tests included the scale factor calibration, linearity calibration, short-term stability calibration, step response calibration, and temperature effect test. The calibration results were certified by DKD. The peak voltage error was within 1%, the time error within 2%, and the impulse scale factor was ±0.5%.

The wavefront resistance (R_f) and wavetail resistance (R_t) were set as listed in

Table 2. Comparison of waveform parameters and errors between two lightning impulse generators.

Rf (Ω)	Rt (Ω)	A			B			${\mathit{E}}_{{\mathit{T}}_{\mathit{f}}}$/%	${\mathit{E}}_{{\mathit{T}}_{\mathit{t}}}$/%	EU/%
		Tf (μs)	Tt(μs)	Up(kV)	Tf (μs)	Tt(μs)	Up(kV)
860	35	0.86	48.13	30.17	0.85	48.03	30.25	1.18	0.21	0.26
1100		1.05	48.32	30.43	1.07	48.5	30.66	1.87	0.37	0.75
1250		1.22	48.27	30.24	1.21	48.1	30.32	0.83	0.35	0.26
1400		1.36	48.59	30.54	1.37	48.83	30.76	0.73	0.49	0.72
1550		1.51	48.24	30.23	1.5	48.66	30.46	0.67	0.86	0.76

. Using the STRAUSS impulse measurement system, the front time, time to half-value, and peak voltage of the waveforms generated by the portable impulse generator (A) and the standard lightning impulse generator (B) were measured. The front time error was denoted as $E_{T_f}$, the time-to-half-value error as $E_{T_t}$, and the peak voltage error as E_U.

As shown in Table 2, when using the same parameters, the time errors of the waveforms generated by the test lightning impulse generator and the standard lightning impulse generator are both within 2%, and the voltage errors are within 1%. All results meet the requirements for standard lightning impulse waveforms specified in IEC 60060-1 [8]. Therefore, the test equipment used in this study is validated to be effective for on-site impulse testing.

2.3. Distribution of Test Sites

The test site, located in Tangshan, Hebei Province, is 20 m long and 10 m wide. The tests were carried out in a plain region, and no altitude correction was necessary. The experiments were performed under summer conditions, with a temperature of 32 °C and a relative humidity of 44%, which did not require any further environmental adjustments. However, for tests conducted in high-altitude regions or under extreme temperature–humidity conditions, environmental correction factors must be applied to ensure rigorous and accurate results. Round steel is used as the grounding material for the test site grounding system, and the grounding resistance is preferably maintained at approximately 0.5 Ω to prevent the risk of electric shock. During the test, the device housing and portable impulse generator are connected to this grounding point. The equipment under test, the portable lightning impulse generator, and the control console are all located within the site. No other interfering equipment is present. The lightning impulse generator, test product, and control console are positioned within the minimum safe distance for high-voltage testing, and warning signs are posted to prevent unauthorized access. Figure 2 shows the site conditions for the lightning impulse test of power distribution equipment.

3. The Generation Principle of Standard Lightning Impulse

A standard lightning impulse can be generated using a lightning impulse voltage generator. In IEC 60060-1 [8], the standard lightning impulse voltage is defined as a non-periodic transient voltage that rises rapidly to its peak value and then slowly decreases to zero. Three basic parameters are defined to describe the waveform shape: peak voltage, front time and time to half-value. The waveform can be approximated using a double exponential wave: the front time T_f = 1.2 μs ± 30%, and the time to half-value T_t = 50 μs ± 20% [10].

3.1. Principle of Lightning Impulse Generator

According to the basic principle of the impulse voltage generator, it can be represented by the equivalent circuit shown in Figure 3. The charging process can be summarized as follows: the main capacitor C₀ is charged by the rectified power supply, and then it transfers charge to the wavefront capacitor C_f through R_f. To ensure that the voltage on C_f approaches the original voltage of C₀, it is necessary that C₀ ≫ C_f. The discharge process proceeds as follows: C₀, C_f, and the resistor R_f form the wavefront discharge circuit, corresponding to loop 3 in Figure 3. After C₀ and C_f become fully charged, they discharge to ground through R_f, thereby generating the wavefront portion of the impulse. Meanwhile, C₀ in series with R_t and C_f in series with R_t constitute two RC networks, represented by loops 1 and 2 in Figure 3. Through these paths, C₀ and C_f discharge jointly to ground via R_t, producing the wavetail. By appropriately selecting the wavefront and wavetail resistances during the combined discharge of C₀ and C_f, the desired standard lightning impulse waveform can be obtained.

The differential Equation corresponding to the equivalent circuit of the lightning impulse generator in Figure 3 can be formulated as Equation (1).

$$a{\displaystyle \frac{d^{2}u}{d{t}^2}}+b{\displaystyle \frac{du}{dt}}+1=0$$

(1)

where $a=C_0{C}_f{R}_f{R}_t$, $b=C_0{R}_t+C_f(R_t+R_f)$, and in the initial state, the voltage across C₀ is U₀, and the voltage across C_f = 0, so u(0) = 0, ${\displaystyle \frac{du(0)}{dt}}={\displaystyle \frac{U_0}{C_f{R}_f}}$. Solving the differential Equation, the time domain expression is given by (2):

$$u(t)=H\left(e^{-p_{1}t}-e^{-p_{2}t}\right)$$

(2)

where $H={\displaystyle \frac{U_0}{C_f{R}_f(p_2-p_1)}}$, and p₁, p₂ are the two characteristic roots of the differential Equation.

From Equation (2), we can see that the standard lightning waveform is type of double exponential function. Figure 4 shows the standard lightning impulse waveform along with its definition.

3.2. The Influence of Wave Modulation Circuit on Lightning Impulse Waveform

The standard IEC 60060-1 defines the front time T_f as 1/0.6 of the time interval between 30% and 90%. The times corresponding to the 30%, 90% and 50% peaks are recorded as t₁, t₂ and t₅₀, which correspond to points A, B and Q in Figure 4, respectively [11,12,13,14]. The front time can be expressed by (3) as:

$$T_f={\displaystyle \frac{t_2-t_1}{0.6}}$$

(3)

The front time of the lightning impulse waveform, corresponding to 30% and 90% of the voltage peak, can be determined from the time-domain expression of the standard lightning impulse waveform, as shown in Equation (4):

$$\left\{\begin{array}{l}0.3U_m=U_m(1-e^{-t_1/T_2})\\ 0.9U_m=U_m(1-e^{-t_2/T_2})\\ T_2=R_f{\displaystyle \frac{C_0{C}_f}{C_0+C_f}}\\ t_1-t_2=T_2\ln 7\\ T_f={\displaystyle \frac{T_2\ln 7}{0.6}}=3.24{\displaystyle \frac{R_f{C}_0{C}_f}{C_0+C_f}}\end{array}\right.$$

(4)

The time to half-value is the time interval from the apparent origin to the moment when the test voltage reaches half its value. When the voltage peak is 50%, the time to half-value is derived from the time-domain representation of the standard lightning impulse waveform, as given in (5):

$$\left\{\begin{array}{l}1/2U_m=U_m{e}^{-T_1/T_2}\\ T_1=R_t(C_0+C_f)\\ T_t=0.69T_1=0.69R_t(C_0+C_f)\end{array}\right.$$

(5)

According to Equations (4) and (5), the front time of the lightning impulse voltage generated by the impulse generator is proportional to the wavefront resistance R_f, and the time to half-value is proportional to the wavetail resistance R_t.

4. Experimental Determinations

Traditional on-site lightning impulse tests for power distribution equipment usually rely on bulky and complex test equipment, which makes it difficult to meet the withstand voltage verification requirements under on-site conditions. To address this issue, this paper proposes an on-site impulse testing procedure for distribution equipment. A portable lightning impulse generator is used to conduct lightning impulse tests on typical equipment such as transformers, circuit breakers, and disconnectors to evaluate their insulation performance under lightning overvoltage. This paper further establishes a digital test management model to achieve stable data collection, automatic recording and report generation, and effectively reduce the number of high-voltage on-site operators.

4.1. Experimental Simulation Analysis

A set of circuit differential Equations for the lightning impulse generator was established in MATLAB R2022a. This model is based on the theoretical analysis in Section 3.1 and is used to verify the feasibility of the proposed testing scheme. The simulation employed an ordinary differential Equation (ODE) representation of the circuit model, and numerical integration was performed using MATLAB’s built-in adaptive time-step solver ode23. To ensure numerical accuracy, the relative and absolute tolerances were set to RelTol = 10⁻⁶ and AbsTol = 10⁻⁹, respectively, thereby minimizing numerical deviations.

According to the analysis of front time and time to half-value given by Equations (4) and (5) in Section 3.1, these characteristic times depend on the circuit resistance and capacitance [15]. Because distribution equipment exhibits capacitive characteristics that alter the effective circuit capacitance, the resistance values must be adjusted to ensure that the applied impulse waveform complies with the standard lightning impulse specifications defined in IEC 60060-1. The equivalent capacitance of a 10 kV transformer is approximately 2000–4000 pF, that of a 12 kV vacuum circuit breaker is about 100–200 pF, and that of a 10 kV disconnect switch is about 30–70 pF. The wavefront and wavetail resistances listed in

Table 3. Simulation parameters for the test.

Name	Wavefront Resistance (Ω)	Wavetail Resistance (Ω)
Transformer	120	35
Vacuum circuit breaker	1000
Disconnect switch	1000

were selected for lightning impulse tests on different distribution devices. Using these parameter sets, simulations were performed based on the model derived from Equations (4) and (5). The resulting lightning impulse waveforms satisfy the standard waveform parameters specified in IEC 60060-1. The calculated load capacitances for the transformer, vacuum circuit breaker, and disconnect switch are 3500 pF, 112.73 pF, and 48.51 pF, respectively, all of which fall within the expected capacitance ranges of the tested distribution equipment. Using the transformer parameters as an example, the simulation results are shown in Figure 5. The front time of 1.5 μs and the tail time of 47.5 μs satisfy the IEC 60060-1 requirements for standard lightning impulse waveforms.

4.2. Experimental Data Management and Automated Test Reporting

In actual lightning impulse tests, the field environment is complex and often accompanied by uncertainties such as temperature fluctuations, electromagnetic interference, and operational complexity. These problems not only affect the integrity and accuracy of data records but also increase the safety risks of personnel approaching high-voltage equipment. To this end, this paper established a test report automatic generation system to improve data reliability and reduce personnel risks [16].

The data management and reporting automation function is developed and implemented based on the Qt platform. By identifying and storing oscilloscope data, the test process data is collected, and data management and reporting are automated. The system can collect key parameters such as impulse peak voltage, front time, and time to half-value in real time. The waveform file is stored in *.DAT format, and the numerical data is saved in Excel format. After the test is completed, the system can automatically generate and save standardized reports, realizing digital management of the entire process from data collection, processing to archiving. Automated recording and remote operation significantly reduce the time personnel stay at the high-voltage site, improving test efficiency while effectively reducing safety risks.

The system consists of a data acquisition module, a real-time data analysis module, a communication module, and a test report generation module. The architecture of the test report automatic generation system is shown in Figure 6.

(1)

Data acquisition module: The voltage signal generated during the test is processed by the signal modulation board, the collected data is cached, the test data is collected through oscilloscope channel 2, and the voltage signal obtained by the oscilloscope is imported into the host computer.

(2)

Real-time data analysis module: This module identifies, stores, and optimizes the acquired data stream. Due to the large data interference in field tests, the acquired data is subject to large noise interference. Therefore, an anti-interference method is introduced to smooth and denoise the pre-processed waveform, identify the processed data, and obtain the peak value, front time, time to half-value and other data required for the test.

(3)

Communication module: The measurement system uses an oscilloscope as the impact test data acquisition device, and a computer as the control platform. The oscilloscope and the computer are connected through the TCP/IP protocol, and the computer is used to control data acquisition and data management.

(4)

Test report generation module: By setting the parameters such as the save data type, save path, format, etc., on the computer, the system will automatically generate the impact test report in sequence according to the test time to facilitate the evaluation and management of the test data results.

4.3. Impulse Test of Common Power Distribution Equipment

To verify the withstand voltage of typical distribution network equipment, this study conducted lightning impulse tests in accordance with relevant standards. Firstly, an insulation impulse test was performed on an on-load tap-changing oil-immersed transformer, model SZ20-M.RL400/10 from Yingda Electric Power Equipment Co., Ltd., Taian China, following IEC60076-3 [17], the test procedure included one full-wave reference impulse at 50–70% of the rated full voltage, followed by three full-wave impulses at 100% of the rated full voltage [18,19,20]. If an external flashover occurred in the line or bushing gap, or if the oscillogram recorded on the specified measurement channel failed, the impulse test was considered invalid and had to be repeated. The test was deemed successful when no significant differences were observed between the voltage and current transient waveforms recorded at reduced voltage and full voltage [21]. Standard lightning full-wave impulses were also applied to vacuum circuit breakers and disconnectors in accordance with IEC62271-1 [22].

Set the impulse test parameters according to the nameplate parameters of the tested equipment. The nameplate parameters of the tested transformer, circuit breaker, and disconnector are shown in

Table 4. Nameplate parameters of the tested transformer.

Rated Capacity (kV·A)	Rated Voltage (kV)	Lightning Impulse Withstand Voltage (kV)	Winding Type
400	10	75	Dyn11

and

Table 5. Nameplate parameters of circuit breakers and disconnect switches.

Name	Rated Voltage (kV)	Lightning Impulse Withstand Voltage (kV)
Vacuum circuit breaker	12	75/85
disconnect switch	10	75/85

, respectively.

4.3.1. Transformer On-Site Lightning Impulse Test

The transformer withstand voltage test is carried out using a full-wave lightning voltage of 75 kV. The transformer has two internal winding configurations: a delta connection on the high-voltage side and a Y connection on the low-voltage side. Considering the internal winding arrangement, a standard full-wave lightning impulse is sequentially applied to phases A, B, and C on the high-voltage side [23]. The wiring diagram of the test transformer is shown in Figure 7. Taking the phase A test as an example, phase A is connected to the lightning impulse generator output terminal, while all remaining terminals are grounded.

According to the lightning impulse withstand voltage information on the transformer nameplate, one impulse at 60% of the rated full voltage and three impulses at 100% of the rated full voltage were applied sequentially to the three high-voltage terminals of the transformer. To ensure the rigor of the test, both positive and negative lightning impulses were applied. The specific application parameters for each terminal are listed in

Table 6. Transformer lightning impulse test application parameters.

Lightning Waveform	A (kV)	B (kV)	C (kV)
1.2/50 μs (60%)	45	45	45
1.2/50 μs (100%)	75	75	75
1.2/50 μs (100%)	75	75	75
1.2/50 μs (100%)	75	75	75

.

Table 7. Transformer lightning impulse test results.

Index	Polarity	Front Time (μs)	Time to Half-Value (μs)	Peak Voltage (kV)
1	Positive	1.55	48.67	46.74
	Negative	1.51	47.17	−49.68
2	Positive	1.51	47.42	77.25
	Negative	1.53	47.64	−77.88
3	Positive	1.53	47.01	76.95
	Negative	1.52	48.32	−77.33
4	Positive	1.54	47.01	77.54
	Negative	1.48	47.50	−77.00

shows that the lightning impulses applied to the transformer conformed to the standard lightning impulse waveform. The measured results are in good agreement with the simulation results shown in Figure 5. No abnormal discharge or flashover was observed during the test, and no odor was detected. The waveform record at the rated full voltage is shown in Figure 8. The test waveform exhibited no distortion, and the overshoot amplitude remained within the standard range. Therefore, the transformer was deemed to have passed the standard lightning impulse test.

4.3.2. Lightning Impulse Test for Switchgear

According to IEC 62271-1 and the nameplate parameters, standard lightning impulses with the specified polarity were applied to the test piece [24,25,26]. If no more than two destructive discharges occurred on the self-recovering insulation and no insulation damage was observed, the vacuum circuit breaker and disconnector were deemed to have passed the lightning impulse withstand voltage test. The test parameters are listed in

Table 8. Lightning impulse test parameters for different switchgear.

Name	Rated Voltage (kV)	General (kV)	Between Fractures (kV)
Vacuum circuit breaker	12	75	85
Disconnect switch	10	75	85

.

Impulse tests were carried out on the vacuum circuit breaker and disconnector in both open and closed states, as well as between phases and ground. No abnormal discharge or smell was observed during the tests. The test data are summarized in

Table 9. Lightning impulse test results of different switchgear.

Name	Positive	Front Time (μs)	Time to Half-Value (μs)	Peak Voltage (kV)
Vacuum Circuit breaker	Positive	1.25	48.95	76.91
	Negative	1.24	50.11	−76.68
Disconnect switch	Positive	1.11	48.30	75.55
	Negative	1.08	49.09	−76.40

, and the waveforms recorded for the vacuum circuit breaker and disconnector are shown in Figure 9 and Figure 10, respectively.

Based on the measured front time and time to half-value, the applied impulses were confirmed to conform to the standard lightning impulse waveform. The peak voltages satisfied the insulation withstand requirements specified in the nameplate parameters of the circuit breaker and disconnector in Table 9, and the corresponding output waveforms exhibited no distortion. Throughout the test, no flashover or other abnormal discharge phenomena were observed. Therefore, both the circuit breaker and the disconnector are considered to have successfully passed the lightning impulse test.

4.4. Analysis of Test Data Errors

Repeated withstand voltage tests were performed on transformers, circuit breakers, and disconnectors to assess the reliability of the test parameters. The variances of the wavefront time and the half-peak time were calculated to evaluate the data fluctuation. The variance of the wavefront time is denoted as ${\sigma }_{T_f}^2$, and the variance of the half-peak time is denoted as ${\sigma }_{T_t}^2$. The peak voltage was configured via the control system. During the test, both the measured and set peak voltages were recorded. The reliability of the peak voltage was assessed using the difference ratio U_e = (U_m − U_set)/U_set, where U_set denotes the set peak voltage and U_m denotes the measured peak voltage.

Based on the test data in

Table 10. Reliability analysis of lightning impulse front time and time to half-value.

Name	Front Time (μs)	Time to Half-Value (μs)	$\mathbf{Variance} \mathbf{of} \mathbf{Front} \mathbf{Time} \left({\mathsf{\sigma }}_{{\mathit{T}}_{\mathit{f}}}^2\right)$	$\mathbf{Variance} \mathbf{of} \mathbf{Time} \mathbf{to} \mathbf{Half}\text{-}\mathbf{Value} \left({\mathsf{\sigma }}_{{\mathit{T}}_{\mathit{t}}}^2\right)$
Transformer	1.51	47.42	8.0 × 10−5	0.06
	1.53	47.00	8.0 × 10−5	0.06
	1.52	47.00	8.0 × 10−5	0.06
	1.51	47.17	8.0 × 10−5	0.06
	1.53	47.64	8.0 × 10−5	0.06
Vacuum Circuit breaker	1.25	48.73	6.4 × 10−5	0.08
	1.25	49.43	6.4 × 10−5	0.08
	1.27	48.84	6.4 × 10−5	0.08
	1.25	48.94	6.4 × 10−5	0.08
	1.26	49.36	6.4 × 10−5	0.08
Disconnect switch	1.07	48.53	6.4 × 10−5	0.02
	1.08	48.25	6.4 × 10−5	0.02
	1.07	48.50	6.4 × 10−5	0.02
	1.09	48.53	6.4 × 10−5	0.02
	1.07	48.26	6.4 × 10−5	0.02

and

Table 11. Reliability analysis of lightning impulse peak voltage data.

Name	Peak Voltage (Um/kV)	Set Value (Uset/kV)	Error Rate (Ue/%)
Transformer	77.25	75	3.00
	76.95	75	2.60
	76.47	75	1.96
	76.85	75	2.47
	76.76	75	2.35
Vacuum circuit breaker	76.85	75	2.47
	76.78	75	2.37
	76.78	75	2.37
	76.66	75	2.21
	76.83	75	2.44
Disconnect switch	75.46	75	0.61
	75.63	75	0.84
	75.36	75	0.48
	75.42	75	0.56
	75.50	75	0.67

, the wavefront time and half-peak time satisfy T_f = 1.2 μs ± 30%, T_t = 50 μs ± 20%. The permissible error range of the peak voltage is ±3%. The variances of the wavefront time are nearly the same for all types of power distribution equipment, and the same trend is observed for the half-peak time. The difference between the maximum measured and set peak voltages is within 3%. These results indicate that the applied lightning impulses meet the standard requirements. The data show uniform distribution and high reliability, supporting their use in on-site impulse tests of power distribution equipment.

5. Conclusions

This paper establishes an on-site lightning impulse test method for distribution equipment and conducts standard lightning impulse tests on typical devices, including transformers, vacuum circuit breakers, and disconnectors. The generation principle of the standard lightning impulse waveform is described, and the effects of front and tail resistances on the impulse waveform are analyzed. On this basis, an on-site lightning impulse testing procedure for distribution network equipment is developed using a portable lightning impulse generator. The feasibility of the parameter settings is verified through both simulation and on-site tests. This study provides an effective on-site impulse testing scheme for distribution equipment, expands the available locations for material sampling tests, and overcomes the limitation that distribution equipment must be transported to test halls for impulse testing.