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Partial Discharge Investigation of 22kV Distribution Transformer
(2024-01-01)
Dechothamsathit, Vorawut
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Pannil, Pittaya
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Yamsiri, Thummanoon
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Chumpiboon, Komin
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Jeenmuang, Siwakorn
This paper presents an off-line partial discharge (PD) experiment conducted on a 22 kV/400 V distribution transformer, which was decommissioned after 20 years of service. The study investigates the impact of reduced oil levels within the transformer on PD characteristics that are expected to facilitate PD activity within the transformer. The experiments were performed with reduced oil levels below the top clamp and using both single-phase and three-phase voltage excitations, with PD measurements recorded for each case. The PD signals were measured using High-Frequency Current Transformers (HFCTs) and capturing current pulses of PD in the frequency range of 100 kHz to 20 MHz. Additionally, transformer oil tests were performed, including moisture content, oil breakdown voltage, and oil conductivity. The results of the PD measurements and oil tests are introduced and discussed in this paper.
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Partial Discharge and Dissolved Gas Analysis on 22kV MV Oil-type Transformer - Case Study
(2024-01-01)
Inwanna, Woranan
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Waiwicha, Supisara
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Vanijkirati, Parada
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Monkolsatitpong, Suriya
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Chumpiboon, Komin
Detecting faults leading to potential failure of important power distributing transformers in the power system before an occurrence is an important attribute. Various inspection methods are available, however online PD and oil analysis remain the most preferred method. The methods mentioned do not require equipment shutdown. This paper introduces a case study of the 22kV transformer with online PD and DGA results indicating signs of problems in the insulation. The PD group found initially had an increase in density of signals during the three months and the magnitude shows an upward trend. DGA results found H2 and CH4 gas, the latter is a key gas indicating PD. Results show an increasing trend of almost three times as high during the latter half of the year. In addition, CO, CO2, and C2H6 gases were also found to be higher than average. Virtual inspection was conducted after the transformer was shut down. The surface is found to be uneven around the bus bar, causing high temperatures in the transformer which then impacts the insulation performance.
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The Effect of Surface Leakage Current on Frequency Domain Spectroscopy of 22 kV OIP Bushing
(2024-01-01)
Rojanasunan, Warisanan
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Chumpiboon, Komin
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Udomluksananon, Patt
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Jeenmuang, Siwakorn
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Chancharoensook, Phop
In this paper the dielectric response in frequency domain or frequency domain spectroscopy (FDS) is used to assess the effect of surface leakage current both from high voltage side and ground side on the FDS results of OIP bushings. The test object in this paper is a 22 kV OIP bushing which is out of service. The surface leakage current can be simulated using the copper tape as a bandage around the bushing core in several locations. From the FDS results, several parameters i.e., dissipation factor, capacitance, and capacitance ratio together with frequency scanning of capacitance and dissipation factor from many cases were investigated to get the fundamental knowledge of how to interpret the FDS result of OIP bushing.
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Effect of Sheath Current on the Lead Sheath of 115kV XLPE Underground Cable
(2024-01-01)
Jariyanurat, Kittipod
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Jeenmuang, Siwakorn
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Chumpiboon, Komin
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Kerdmanee, Sittipong
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Lacharochana, Sakda
Currently, underground cable systems are extensively employed in power generation and distribution due to their superior reliability, stability, and safety. Given the significant investment and critical role of these systems, it is essential to rigorously assess their lifetime and performance. Key factors affecting the lifespan and life assessment of underground cables include the insulation system and the physical components of the power cable. Among these, sheath current is a notable factor that contributes to cable deterioration. This paper investigates the impact of prolonged sheath current on XLPE power cables, which have been in operation for approximately 25 years, associated with a 115kV generator unit. Specifically, the study focuses on the degradation of the lead sheath due to sheath current exposure. It was observed that the lead sheath exhibited signs of degradation, including tracking, which affected various layers, such as the lead sheath itself, the semi-conductive tape, and the semi-insulation. The research highlights that while sheath current did lead to observable tracking on the lead sheath, the overall impact on the cable's lifetime was minimal. An analysis of the lead sheath's properties, based on fundamental physical characteristics, revealed that long-term exposure to sheath current primarily caused minor physical tracking on the sheath's surface rather than significantly affecting its lifespan. This finding suggests that although sheath current can induce localized degradation, its effect on the overall functional longevity of the lead sheath is relatively limited.
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Investigation of Dielectric Response in a 22/0.4 kV Distribution Transformer: Effects of Moisture Content
(2024-01-01)
Daengdee, Danaiwat
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Bunlaksananusorn, Chanin
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Suksawat, Dusit
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Chumpiboon, Komin
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Jeenmuang, Siwakorn
Transformers play a crucial role in power systems, ensuring efficient energy transmission and distribution. This research focuses on a 22/0.4 kV transformer decommissioned after over 20 years of service. The study involves draining the transformer oil completely and refilling it with oil characterized by known moisture content and breakdown voltage levels until reaching normal operating conditions. The objective is to study the effects of increased moisture content on the dielectric response within the actual structure of the transformer. Diagnostic measurement techniques, including Frequency Domain Spectroscopy (FDS) and Polarization Depolarization Current (PDC), are utilized to evaluate the insulation condition of the transformer. FDS provides information on the dielectric response over a wide frequency range, while PDC assesses the polarization and depolarization behavior of the insulation material. These techniques offer valuable information on the ageing and moisture content of the insulation. The experimental results will be presented and discussed in this paper.
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Experience in Partial Discharge Investigation of a 155 MVA Air-Cooled Generator
(2024-01-01)
Pathanrat, Khomsan
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Chumpiboon, Komin
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Jeenmuang, Siwakorn
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Worthong, Tehneht
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Pannil, Pittaya
This paper presents the Partial Discharge (PD) and Polarization and Depolarization Current (PDC) investigation for a 155 MVA air-cooled generator. The visual inspection of the stator winding insulation was carried out during the annual preventive maintenance. Several defects in the area of the end winding stator were evidenced. Thereafter, the refurbishment of these problems was performed to improve the stator winding insulation condition, and the offline PD & PDC test was conducted accordingly. Besides, the online PD was continuously monitored, through capacitive PD sensors which have been installed on the terminal of the generator two units per phase. The operating conditions during online PD measurement were also recorded. In this paper, the results from both offline and online PD measurements were presented.
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Off-line and On-line Automatic and Unsupervised Partial Discharge Diagnostics of Electrical Asset Components
(2024-01-01)
Pattanadech, Norasage
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Jeenmuang, Siwakorn
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Udomluksananon, Patt
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Chumpiboon, Komin
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Shafiq, Muhammad
This paper deals with applications of an innovative approach to on-line and off-line partial discharge (PD)-based condition maintenance, where PD detection and analytics are fully automatic and do not require the support of PD experts. PD was measured off-line on a 50 kV A, 22/0.4 kV distribution transformer and on 115 and 230 kV transformer bushings, showing in both cases that PD can be detected and analyzed automatically according to the SID (Separation, Recognition, Identification) procedure. On-line measurements performed on MV generators are also reported and discussed, highlighting that there is potential for on-line MV (and HV) monitoring with automatic and unsupervised noise rejection, and identification of PD phenomena that can feed health assessment software to reach optimized maintenance plans.
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Physical and chemical properties’ comparison of natural ester and palm oil used in a distribution transformer
(2023-03-01)
Kittikhuntharadol, Yannaphol
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Pattanadech, Norasage
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Maneerot, Sakda
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Jongvilaikasem, Korraya
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Jariyanurat, Kittipod
Because of its low cost and suitable qualities, mineral oil (MO) has been commonly employed in transformers. Alternative liquid insulations with great characteristics have recently been presented. Natural ester (NE) and palm oil (PO) are considered alternative liquid insulations. This paper aims to study the physical and chemical properties of NE and PO which were used in a transformer for 21 months. All of the liquid insulation test specimens were sampled every 3 months. Physical properties of the liquid insulation, i.e., interfacial tension (IFT), viscosity, and particles count, were examined. Chemical properties of the liquid insulation, i.e., moisture content, acidity, corrosive sulfur, and furanic compound (2-FAL), were investigated. IFT, particles count, moisture content, acidity, and 2-FAL test results indicated deterioration of liquid insulations of the used liquid insulation; however, there is no observation change for particles amount and acidity of NE. The other test results were not found significantly change.
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Partial Discharge Testing on MV Motor - Case Study
(2023-01-01)
Jeenmuang, Siwakorn
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Rojanasunan, Warisanan
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Dorkmai, Kritsada
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Chumpiboon, Komin
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Udomluksananon, Patt
A failure of a medium voltage (MV) motor during its operation could force an outage of the power plant and also lead to a loss of cost. Hence, the method to ensure the insulation quality of such a motor is needed. Partial discharge (PD) testing is one of the effective methods used to determine the defect and evaluate the integrity of the machine insulation. This paper presents the application of off-line PD testing on MV motors. In the experiment, the PD test instrument conforming to standard IEC 60270 was used as a charge-based measurement. Moreover, during the PD testing, an acoustic imaging camera was employed as an alternative technique for locating the PD sources in the stator winding part. Once PD takes place, it can generate the pressure acoustic wave that propagates surrounding the PD source. Thus, the PD source in the area of endwinding can be located by this technique. From the charge-based PD test results, the phase-resolved PD (PRPD) pattern was considered to identify the type of PD source. It was found that almost MV motors tested have delamination in the bulk insulation. In some cases, the PRPD pattern exhibits the discharge in the area of the overlap region between the semiconductive and stress grading coating in the slot exit, which confirms by using the acoustic technique.
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The Dielectric Properties in Frequency Domain of the 22 kV Underground Cables with Defective Joint
(2023-01-01)
Udomluksananon, Patt
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Jeenmuang, Siwakorn
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Chumpiboon, Komin
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Dorkmai, Kritsada
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Rojanasunan, Warisanan
The failure that occurs in the underground cable systems leads to losses in many aspects, not only in the power system but also in the commercial and business. The most failure location in medium voltage underground cable systems is cable joint and cable termination, where the defects occur from poor workmanship. This paper represents the mean to investigate the dielectric properties of the 22 kV XLPE underground cable system to assess the insulation's integrity of the underground cable system. In the experiments, the underground cable system specimens were prepared by simulating the defects in cable joints, i.e., the iron powder on the XLPE surface and the incision on the XLPE surface; moreover, the underground cable system with the healthy condition joint was prepared to represent the new (or unused) underground cable system. To compare the dielectric properties in the frequency domain of the 22 kV underground cable systems with defective joints and the healthy condition joint, the frequency domain spectroscopy (FDS), the off-line non-destructive test, was performed in this research. From the test results, the dielectric dissipation factor shows a significantly different value in the case of iron powder when compared with the healthy condition joint. It reveals the loss peak on the curve at a frequency of 1 Hz. However, the case of incision on the XLPE surface is almost similar to the healthy condition case. The real part of the complex capacitance of all three cases has a constant value in the measured frequency ranges using the log-log scale. However, the imaginary part capacitance shows the distinct value of all three cases, of which the trends are the same as the dielectric dissipation factor curve.

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