Showing papers on "Partial discharge published in 1984"

Stochastic Properties of Partial Discharge Phenomena

Abstract: The author presents a bibliography and survey of the literature concerned with theory and measurement of the stochastic behavior of pulsating partial-discharge (PD) phenomena that can occur when insulation is subjected to electrical stress. The types of PD phenomena considered include AC and DC generated electron avalanches, pulsating positive and negative corona in gases, and PD that occur in liquid media and in the presence of solid dielectric surfaces. The basic physical mechanisms of discharge initiation, growth, and memory propagation that determine the probability distributions for pulse occurrence times and pulse amplitudes are discussed. Consideration is also given to special problems associated with the measurement and interpretation of data on the various statistical properties of PD phenomena. >

New theory of electrical discharge and breakdown in low‐mobility condensed insulators

Abstract: Electrical discharge and breakdown in low‐mobility insulating liquids and solids involve the creation of low‐density domains or channels in the bulk by carrier injection from electrical contacts and subsequently dissociative trapping and recombination as a necessary prelude. Internal discharge such as electrical treeing and breakdown are initiated by impact ionization within such low‐density domains or channels and then followed by an indefinite increase in carrier multiplication in the conduction level that extends the channels and finally destroys the material inside them.

Application of Partial Discharge Testing to Hydro Generator Maintenance

Abstract: An improved partial discharge test to ascertain hydraulic generator winding condition, has been in use for the last 7 years. The test, which can be done by generating station staff without disrupting operation, has been applied to about 140 machines in eight North American utilities. Partial discharge testing is one of the main reasons Ontario Hydro has an exceptionally low winding replacement/major repair rate. Examples of results culled from thousands of tests are presented.. The use of the partial discharge test for planning winding maintenanGe and gauging the effectiveness of repairs is discussed.

Partial Discharge Automatic Monitor for Oil-Filled Power Transformer

Abstract: This paper describes a new type of partial discharge (PD) automatic monitor capable of detecting possible troubles caused by PD inside a transformer in the field and preventing the unfavorable phenomenon from expanding.

Combustion initiation system employing hard discharge ignition

Abstract: A system for initiating combustion of fuel, especially for internal combustion engines, employs a very rapid, intense high power electrical breakdown arc to increase the rate of combustion and thereby reduce the need for advanced engine timing The use of a distribution circuit which has exceptionally low inductance and resistance results in the rapid electrical breakdown and coupling of at least 80% of stored pulse energy to the breakdown arc channel within the first half period of the discharge current cycle The resulting arc discharge effects detonation of the fuel mixture through the cooperative effects of photolysis, supersonic hydrodynamic shockwave and high temperature thermal plasma High voltage pulse generation distribution and switching circuits are provided Several discharge electrode geometries and closely coupled pulse forming networks for the discharge device are disclosed

Parameters Affecting the Velocity of Sound in Transformer Oil

Abstract: When attempting to locate partial discharge (Pd) sources in operating transformers, it was found that the speed of the acoustic waves propagating in the transformer oil differed from the value suggested in the literature. Subsequent investigations showed that the sonic velocity in transformer oil was not constant but depended upon a complex relationship which included the temperature of the oil, its gas and moisture content as well as the frequency content of the propagating signal.

V-T Characteristics of Epoxy Mold Insulation for Sustained AC Voltage

Abstract: This paper describes experiments conducted to determine the cause of epoxy mold insulation breakdown under sustained applied AC voltage. It can be readily understood that epoxy mold insulation, widely used as solid insulation in gas-insulated switchgear, is subject to breakdown under sustained applied voltage when the mold insulation contains large voids. However, epoxy mold insulation which is practically void-free also deteriorates under sustained applied voltage. It has been clarified by conducting experiments using various embedded electrode materials that the deterioration of this void-free epoxy mold insulation is primarily caused by an electric field concentration due to micro-protrusions on the embedded electrode surface and a small partial discharge which occurred at minute debonded portions around the micro-protrusions.

Non-destructive detection of voids in plastic materials

Abstract: A sensitive yet non-destructive method and apparatus for detecting the presence of voids contained within dielectric materials is disclosed which comprises applying a voltage across the dielectric material to create an electric field therethrough, increasing this voltage to create a partial electrical discharge and monitoring the field current to detect the voltage at which partial discharge occurs. When the partial discharge is detected, the voltage applied across the test material is recorded. Reference can then be made to mathematical charts and formulas readily available to determine the size and shape of the detected void.

Voltage Rating Of A Three-Core Power Cable From Considerations Of Discharges In Voids

Abstract: The voltage rating of a three-core belted cable is determined such that it should be above the discharge inception voltage within the cable. The phase voltage is determined as a function of the location of the void within the cable, the diameter of the void, the gas pressure entrained in the void and for spherically and cylindrically shaped voids. It is found that the voltage required to initiate a discharge is a function of the location of the void and it is lowest for voids located in the vicinity of the interface between the conductor and the dielectric. The discharge inception voltage depends on both the dimension and the geometrical shape of the void. The voltage is higher for a spherical than a cylindrical void and decreases with increasing diameter of the void in the range generally found in practical cables.

Equipment for the Energy Measurement of Partial Discharges

Abstract: Unlike apparent charge, energy is an inherent characteristic of partial discharge (DP) and may be used as an objective criterion for their evaluation. Since energy dissipation is responsible for the damaging effect of discharges, the amount of energy liberated in a PD situation is a suitable estimation of the involved risks. Discharge energy measurement was accomplished using a special and readily made metering circuit, including a correlator unit. Good correlations were found to exist between discharge energy and insulation degradation in simple liquid or solid insulating models.

Partial discharge suppression in vapor-mist dielectrics

Abstract: Vapor-mist dielectrics consist of very dense (∼106 droplets/cm3) mists of micron-size liquid droplets suspended in an insulating gas or vapor. They are flameproof and can have several times the uniform field ac electrical strength of SF 6 gas. In recent experiments these dielectrics have been found to also possess remarkable corona or partial discharge (PD) suppression properties. It was found that a brief application of vapor-mist would completely extinguish ac partial discharges at a highly stressed point electrode in atmospheric SF 6 . Furthermore, with the PD suppressed, the applied voltage could then be increased by more than three times without any PD activity. It is believed that the mechanisms by which the PD are suppressed include electron and ion collection by the droplets, absorption of ultraviolet radiation, and the suppression of electron emission from the electrode surface. The experimental results and PD suppression mechanisms are outlined and discussed in this paper.

Insulation measurement of power cable

Abstract: PURPOSE: To enable the detection of the generation of a partial discharge pulse not affected by any high frequency noise, by detecting and integrating the low frequency component alone of the partial discharge pulse, cutting the high frequency one thereof. CONSTITUTION: Any deteriorated part in a power cable 1 causes a partial discharge pulse, which is inputted into a pulse detection circuit. But the high frequency components are blocked from being inputted into an integration circuit 6 with an LPF3 and flows into the ground as intact through a capacitor 2 for charging a low frequency component. On the other hand, the low frequency components are blocked from being inputted into the circuit 6 with the LPF3 but is charged into the capacitor 2 for charging low frequency components. Therefore, as with the capacitor 2, the charged current passes through the LPF3 as DC current and coverted into a voltage with a variable resistor 7, a discharge detection signal having a specified voltage waveform is outputted from the circuit 6. This keeps a high frequency noise from being outputted as detection signal from the circuit 6 thereby enabling the detection of the generation of a partial discharge pulse accurately. COPYRIGHT: (C)1986,JPO&Japio

Electric glow discharge using prepulse and charge storage device

Abstract: A method and apparatus for transferring energy to a gas by means of a glow discharge. A transmission line is charged to a voltage of approximately twice that of the steady-state voltage of the glow discharge. A prepulse voltage source, having a higher voltage sufficient to initiate the glow discharge, is first connected to the discharge electrodes. After the discharge is initiated by the prepulse, the transmission line is connected and transfers its energy to the discharge. In a second embodiment, the transmission line is replaced by a capacitor.

Internal partial discharge monitor for high voltage equipment

Abstract: PURPOSE:To enable the prevention of any erroneous judgement under such a condition that external noises frequently enter by a method wherein a discharge sound pulse is converted into a detection time signal digitized to be memorized into a memory and inspected with a judging section to judge an internal partial discharge. CONSTITUTION:A partial discharge sound pulse generated when a partial discharge occurs in a high voltage equipment 1 is detected with an acoustic detectors 6a-6c and when exceeding the preset threshold, it is inputted into comparators 10. 10a-10c adapted to generate one-shot pulses. One thereof is transmitted into time detecting sections 60. 60a-60c while other one thereof to memory-address counters 21. 21a-21c. Then, they are converted into a time signal corresponding to respective detection times with a pulse converting section and a time detecting section. Taking in of data is stopped temporarily and a control section 100 commands a judging section 90 to read out data memorized from memories 70. 70a-70c. Detection time signals for current pulses or discharge sound pulses failing to meet the requirement are erased from the memory to judge an internal partial discharge.

Partial dischrge measurement of hot cable

Abstract: PURPOSE: To enable the detection of a partial discharge with a high sensitivity as caused in an insulation trouble occurs in a hot cable, by earthing a specified part of a sheath covering a specified length of a hot cable arranged thrugh a parallel resonance circuit. CONSTITUTION: A specified length of a hot cable 1 is arranged from the A end 8 to the B end 9 and the sheathes 3 near the A end 8 and the B end 9 are earthed through LC parallel resonance circuits 5 and 6 as parallel resonance circuit. The LC parallel resonance circuits 5 and 6 has a negligible degree of impedance with respect to commercial frequency, but is resonates to a signal with a single or narrow band specified frequency at about 4,000kHz among discharge pulses accompanying partial discharge generate in the cable. Thus, the discharge pulse is detected with a synchronous amplifier 7 to observe the insulation state of the cable. COPYRIGHT: (C)1986,JPO&Japio

Measuring probe and circuit arrangement for the electrical detection of partial discharges

Abstract: The invention relates to a measuring probe and circuit arrangement for the electrical detection of partial discharges in electrical equipment. It is the aim of the invention to enable partial discharges in electrical equipment to be detected without having to disconnect system components. The invention is based on the object of ensuring a detection of partial discharge signals of equipment under high voltage without high-voltage coupling capacitors. This object is achieved by the measuring probe consisting of a three-electrode system connected to one another via a compensation network, in which system, on the side facing the device under test, a compensation electrode is arranged between a measuring electrode and a reference electrode constructed in the manner of a housing. Within the reference electrode, two differential amplifiers are integrated, the rise time of which is very small compared with the duration of the TE pulses and is within the nanosecond range.

Partial discharge measuring apparatus for stationary electrical appliance

Abstract: PURPOSE:To enable the outputting of information only when an internal discharge is judged by paying attention to the fact that the ratio of both the output pulse peak values at the first and second detector sections varies with an internal discharge pulse and a noise infiltrated through a high voltage bus or the like. CONSTITUTION:An external nozzle pulse N infiltrated into an electric appliance to be measured through a bushing 4 from a high voltage bus 5 is shunted into first and second detection elements Za and Zb through capacitances Ca and Cb, where the value thereof is determined by the ratio of Ca and Cb. On the other hand, when a partial discharge pulse S is generated in a transformer, the peak value thereof is detected in the ratio of (Ce+Cb):Cb, where Cb represents the electrostatic capacitance of the bushing and Ce the electrostatic capacitance which the high voltage bus 5, the bushing 4 and a winding 2 have with respect to the ground. In other words, the ratio between peak values of electrical pulses detected by the first and second detector sections give a value peculiar to an electrical pulse source and hence, determining the ratio enables the discrimination between the internal discharge and noise and only when judged to correspond to the internal discharge or discharge inside the bushing, the output waveform is indicated on a display 20.

Discharge detection and measurement in voids in solid dielectrics

Abstract: Insulating systems invariably contain some cavities or voids entrained within the insulation or at boundaries between dielectric and conductors. The paper presents experimental results obtained in an investigation of the factors affecting the discharge characteristics in voids in solid dielectrics. An E.R.A. discharge detector was used for detection and measurement of discharge magnitudes. The dependency of the discharge magnitude in voids on; the applied voltage, the void dimensions and the duration of the applied voltage was investigated experimentally. Test results also indicate that the discharge magnitude-applied voltage characteristics exhibit same hysterisis. This hysterisis effect is more pronounced for deeper cavities.

Breakdown phenomena in transformer oil subjected to direct voltages with ripple

Abstract: This paper reports the results of experimental investigations on the breakdown phenomenon of transformer oil under inhomogeneous field conditions (rod-plate electrode system) and subjected to DC voltage superimposed on AC voltage. The peak breakdown voltage of transformer oil is found to be decrease with the increasing of ripple content in the applied voltage and gap spacing between electrodes. It has been noticed also that the value of breakdown voltage is lower for positive DC voltage than negative voltage for any particular ripple content.

Internal electric discharge detector of gas insulated hermetic electrical apparatus

Abstract: PURPOSE:To detect internal electric discharge with good sensitivity and to enable location of the position where said discharge arises by providing an electrode for receiving an electromagnetic wave and a photoconductor responding to electric discharge light in the bottom of a hermetic container, and taking out the detection signals thereof via a conducting part to the outside. CONSTITUTION:A gas insulated hermetic container contains gas insulated conductive parts 3 and is connected to an adjacent hermetic vessel via a gas segmenting spacer 5. A transparent protective member 6 which is an insulator, a porous receiving electrode 6, a photoconductor 8, etc. are provided in the longitudinal direction of such vessel 1 in the bottom of said vessel where conductive foreign matter generating partial electric discharge is liable to gather. The electromagnetic wave corresponding to the change in the electric field by the discharge is received and detected by the electrode 6. The photoconductor 8 such as optical fiber responds to the discharge light and the detected outputs thereof are taken out to the outside through the leading-out part of the handwheel 9 of the vessel 1. The internal discharge is thus detected with good sensitivity. The position where the partial discharge arises is located by detecting the discharge in each of the regions segmented by the spacers 5.

Apparatus for diagnosis of interior of enclosed bus bar

Abstract: PURPOSE:To facilitate maintenance and inspection, by detecting the potential of a shield embedded in an insulation spacer as light by a pair of light emitting diodes connected in parallel in positive and negative opposite relationship to make it possible to easily carry out the positional confirmation of the partial discharge place of the insulation spacer. CONSTITUTION:When rated voltage is charged to a bus bar, a current sufficient to emit light from light emitting diodes 5, 6 is not flowed through a circuit constituted from a condenser 8, a resistor 7 and the light emitting diodes 5, 6. On the other hand, when abnormal voltage with positive polarity is generated relative to the bus bar, voltage is generated in a shield and light is emitted from the light emitting diode 5. When abnormal voltage with negative polarity is generated, light is emitted from the light emitting diode 6. Lights from the light emitting diodes 5, 6 are guided to O/E converters 20, 21 through light guides 18, 19 to be converted to electric signals. Respective electric signals are transmitted to a differential amplifier 22 and, by calculating the difference of the respective electric signals, both positive and negative wave forms are measured and an abnormal place can be detected.

Acoustic Emission from Partial Discharge in Encapsulated Voids

Abstract: BACKGROUND The techniques currently used to assess partial discharge activity in power transformers rely on electrical measurements performed at the terminals. Although such measurements can detect aggregate discharge activity, they give little information regarding the location of individual discharge sites and only a crude estimate of the actual discharge activity. In modern encapsulated power transformers, where size and weight limitations lead to stringent requirements of dielectric integrity, such terminal measurements should be supplemented by other techniques in order to provide better quality control of production and better incipient fault detection. An acoustic emission detection system is being developed to locate and evaluate individual partial discharge sites in encapsulated transformers. Experiments in the frequency range of 130 to 170 kHz have been carried out in a specially designed, intFgrated test cell which show the relationship between conventional electrical measurements and acoustic emissions for a range of void sizes. The significance of these two sets of measurements in the evaluation of a practical acoustic emission detection system will be discussed.

Partial discharge characteristics in layered barium titanate structures

Abstract: Pd characteristics for MLC capacitors with different relative permittivities, porosity, and void size distributions were evaluated. The results show that: 1. Pd is a strong function of and increases with the increase of the applied field. 2. Higher dielectric constant, which gives a bigger field enhancement, also enhances the Pd activity. 3. The source of Pd is the ionization discharge across the voids in the bulk as well as those adjacent to the electrodes. Knowing the void size distribution, the Pd characteristics are generally predictable. 4. The cause of low breakdown for a dielectric with high porosity is that the regions of thin dielectric associated with porosity cannot withstand a high field as the voltage across a void drops significantly by the partial discharge.

Electro-optical measurment of pre-breakdown current in dielectric liquids

Abstract: The electrical pre-breakdown current in dielectric liquids under non-uniform field with tungsten tip have been investigated using photo-optical measuing technique and nanosecond rectangular high voltage pulse generator. The streamer propagation velocity is deduced for each dielectrics from the relation curve of gap spacing vs. breakdown time lag. The dependences of the time lag on gap spacing, voltage and temperature are also investigated. The constant streamer propagation velocity between electrodes are unaffected by tip radius and gap spacing at a fixed applied voltage.

Method for measuring partial discharge generating position of cable

Abstract: PURPOSE:To make it possible to measure the partial discharge generating position of a cable regardless of a joint part, by a method wherein the difference in operation start times of each switching clutch elements is measured and the operational order of each elements is determined. CONSTITUTION:When discharge is generated at the point B of a first phase cable 11, it is detected by capacitors C1, C2 and impedances Z1, Z2 attached to a terminal part. In this case, because a partial discharge pulse reaches the terminal of the cable 11 at first, a switching clutch element SCR1 is triggered and operated through an amplifier AMP1 and an absolute value circuit 13 to bring the output IN1 of a gate element EOR to L from H, IN2 to H and output to H and counted by a pulse counter 16 through the driving of an oscillator 15. In the next step, the partial pulse reaches the terminal of a cable 12 and, therefore, the oscillator 15 and the counter 16 are stopped. The calculation value of said counter 16 comes to the difference of partial discharge pulse arrival times between the cables 11, 12. Therefore, the clutch element is operated by the discharge pulse reaching at first and the measurement of time difference is enabled.