Mochammad Wahyudi

Analisis Karakteristik Arus dan Tegangan pada Inisiasi Feroresonansi Transformator Tegangan Rendah

Ferroresonance is an interaction phenomenon between non-linear inductance and capacitance that initiates abnormal waveform of current and voltage. This phenomenon is very sensitive to system parameter and initial condition. In this paper, ferroresonance initiation involved a basic circuit of series ferroresonance with variation of source voltage magnitude on a single phase low voltage transformer. The scheme of experiment was based on the case of transformer energizing. The trends of current and voltage waveform on the primary windings were investigated and transformed by using Fast Fourier Transform (FFT). The harmonics spectrum was then employed to identify the feroresonance mode and calculate the Total Harmonics Distortion (THD) of current and voltage. The experimental results showed that the higher source voltage magnitude caused the ferroresonance responses to be seen more clearly. It was indicated by the more distorted waveform, the higher odd harmonics frequency amplitude especially for 150 Hz, and the greater THD. Based on the harmonics spectrum and wave period, the ferroresonance responses were identified as fundamental mode. The effects of initial conditions, such as residual flux of transformer and capacitor charge, were also seen on the distorted wave peak during transient condition. In addition, the difference of waveform between normal and ferroresonance condition could be more easily observed on the voltage than the current. The waveforms of current and voltage during experiment had been verified by using simulation.

Analysis of low voltage arcing characteristic on direct short circuit through arcing thermal synchronization sensing and short circuit current

Short circuit fault cause arcing fault initiate fire accident. Fire case caused by short circuit fault in low voltage installation is occured every year. Several cases in fire accident at low voltage installation caused by short circuit fault. In this case, protection equipment failed to detect and secure the installation. This experiment investigate short circuit case at low voltage filament conductor cable 1.5 mm2. Short circuit cases variated by filament or strand that experienced contact. When short circuit occurred, arcing is recorded by thermal camera. Moreover, current and voltage arcing will be synchronized with thermal arcing image. The synchronization result is analyzed to obtain the caharacteristics of arcing that consist of value of maximum temperature arcing, sectional area arcing data, and duration of arcing. These characteristics are very useful to design arcing fault detector. The result shows that the arcing temperature, area, and duration respectively are up to 100 °C, 1300 mm2, 10 seconds.

Analysis of physical and electrical characteristics of transformer oil insulation during accelerated thermal aging experiment and its lifetime estimation using arrhenius law and breakdown voltage test

In this paper, the physical and electrical characteristics of accelerated thermal aged transformer oil insulation were investigated. The accelerated thermal aging of commercial transformer oil was conducted by increasing its temperature with different time. They were 100°C for 168 hours, 115°C for 96 hours, and 125°C for 48 hours. The lifetime of the tested oil was then estimated based on Arrhenius law and breakdown voltage test. The result showed that the physical characteristic of the tested oil during accelerated thermal aging could be analyzed based on its color changes, in which the higher level of thermal aging resulted in darker oils color. The electrical characteristic was associated with significant decreasing of breakdown voltage. The lifetime estimation based on Arrhenius law for the tested oil with 100°C, 115°C, and 125°C were about 25663 hours, 4300 hours, and 1408 hours, respectively. The lifetime estimation based on breakdown voltage test for the tested oil with 100°C, 115°C, and 125°C were about 20064 hours, 1526 hours, and 1106 hours, respectively.

Ferroresonance Characteristics on Capacitive Voltage Transformer Under Lightning Impulse Voltage

Nowadays, more papers explain about the occurrence of ferroresonance due to the switching operation. Indeed, the switching operation is more possible to occurr on system respect to other transient disturbances, such as lightning stroke. However, lightning stroke which is always characterized by a high impulse current is also able to initiate the ferroresonance on the system. In this paper, the effect of ferroresonance due to the lightning stroke on capacitive voltage transformer (CVT) is simulated and investigated. The ferroresonance causes an overvoltage as well as on overcurrent on CVT. ATP/EMTP is utilized to simulate and analyze the ferroresonace phenomena. In this study, Heidler’s lightning model is used to describe the lightning condition on the system. Lightning impulse parameters such as its amplitude and duration, including its front time (ts) and tail time (tr) are varied. The effect of these lightning parameters on peak voltage and peak current on the primary side of CVT is investigated. The simulation results show that the peak voltage increases to about 267.5% of its normal peak voltage while peak current increases up to about 266.1% of its normal current. These peak values increase linearly with the amplitude and they increase non-linearly with the duration of the lightning impulse. However, the front time almost does not affect the peak values of voltage and current. Therefore, it can be concluded that lightning impulse characteristics affect the occurrence of ferroresonance on CVT.