Condition Of Stator Winding Insulation Research Articles

Insulation Condition Assessment in Inverter-Fed Motors Using the High-Frequency Common Mode Current: A Case Study

The use of the common mode current for stator winding insulation condition assessment has been extensively studied. Two main approaches have been followed. The first models the electric behavior of ground-wall insulation as an equivalent RC circuit; these methods have been successfully applied to high-voltage high-power machines. The second uses the high frequency of the common mode current which results from the voltage pulses applied by the inverter. This approach has mainly been studied for the case of low-voltage, inverter-fed machines, and has not yet reached the level of maturity of the first. One fact noticed after a literature review is that in most cases, the faults being detected were induced by connecting external elements between winding and stator magnetic core. This paper presents a case study on the use of the high-frequency common mode current to monitor the stator insulation condition. Insulation degradation occurred progressively with the machine operating normally; no exogenous elements were added. Signal processing able to detect the degradation at early stages will be discussed.

A System Based on Artificial Neural Networks for Automatic Classification of Hydro-generator Stator Windings Partial Discharges

Partial discharge (PD) monitoring is widely used in rotating machines to evaluate the condition of stator winding insulation, but its practice on a large scale requires the development of intelligent systems that automatically process these measurement data. In this paper, it is proposed a methodology of automatic PD classification in hydro-generator stator windings using neural networks. The database is formed from online PD measurements in hydro-generators in a real setting. Noise filtering techniques are applied to these data. Then, based on the concept of image projection, novel features are extracted from the filtered samples. These features are used as inputs for training several neural networks. The best performance network, obtained using statistical procedures, presents a recognition rate of 98%.

Investigation of Partial Discharges at the High Voltage Electric Motor Bars

It is well known the use of on-line partial discharge (PD) measurements as an indicator of stator winding insulation condition. The scheduled PD measurements could be used as a test to evaluate the quality of the equipment. The test results could help to diagnose the insulation problems in motors and generators for corresponding action before failure occurs. Although a number of PD measurement methods exists, but the tests results of on operating rotating machines can be influenced by conditions such as humidity, temperature, terminal voltage, and load. This paper describes the development of PD imitation mathematical model in stator insulation. The experimental investigation with physical model was performed for adequacy assessment. The capacitive sensor was used for PD online monitoring. DOI: http://dx.doi.org/10.5755/j01.eie.22.2.6983

13[kV]급 수력발전기 고정자 권선의 운전 및 정지 중 진단시험 현장적용 평가 및 분석

The solid insulation system of stator windings in high voltage rotational machines is usually aging in accordance with long time operation. The partial discharge test have been known to check whether insulation deterioration exist or not, and the PD test can effectively diagnose a solid insulation condition regardless of during operation(on-line) or not(off-line).The on-line PD measurement have proven to be a successful technique in monitoring stator insulation condition nowadays.<BR> This paper describes the characteristics of comparing the on-line PD measurement data using PDMS-HG(Partial Discharge Monitoring System for Hydro-electric Generator) installed in field with the off-line diagnosis measurement data(insulation resistance, winding resistance, PI, Δtanδ and PD) on hydro generator(13[kV]) stator windings. These results make good use of managing rotational machines through evaluating the solid insulation condition of stator windings.

Analysis of Insulation Quality in Large Generator Stator Windings

To evaluate the condition of stator winding insulation in generators that have been operated for a long period of time, diagnostic tests were performed on the stator bars of a 500 MW, 22 kV generator under accelerated thermal and electrical aging procedures. The tests included measurements of AC current (<TEX>${\Delta}I$</TEX>), dissipation factor (<TEX>$tan{\delta}$</TEX>), partial discharge (PD) magnitude, and capacitance (C). In addition, the AC current test was performed on the stator winding of a 350 MW, 24 kV generator under operation to confirm insulation deterioration. The values of <TEX>${\Delta}I$</TEX>, <TEX>${\Delta}tan{\delta}$</TEX>, and PD magnitude in one stator bar indicated serious insulation deterioration. In another stator bar, the <TEX>${\Delta}I$</TEX> measurements showed that the insulation was in good condition, whereas the values of <TEX>${\Delta}tan{\delta}$</TEX> and PD magnitude indicated an incipient stage of insulation deterioration. Measurements of <TEX>${\Delta}I$</TEX> and PD magnitude in all three phases (A, B, C) of the remaining generator stator windings showed that they were in good condition, although the <TEX>${\Delta}tan{\delta}$</TEX> measurements suggested that the condition of the insulation should be monitored carefully. Overall analysis of the results suggested that the generator stator windings were in good condition. The patterns of PD magnitude in all three phases (A, B, C) were attributed to internal discharge.

Novel Sensor for Locating Partial Discharges in High-Voltage Rotating Machines

The online partial discharge (PD) diagnosis has been recently accepted as an effective technique for the evaluation of the insulation condition of stator windings in high-voltage rotating machines. There are several types of sensors used for detecting PD in rotating machines. The so-called capacitive coupler, which is connected to the conductor, has been used most widely. Another sensor, the so-called stator slot coupler (SSC), is used by inserting it between the wedge and the top stator coil. However, these are not economically efficient for small-size rotating machines due to their high installation costs. Also, it takes a long time for insertion to take place and it a difficult process, if the SSC is inserted into small-size rotating machines. In this paper, a novel sensor called the partial discharge locating coupler (PDLC) was developed, which is easily mounted into the small-size rotating machines for the PD measurement, and tested to characterize its detectable frequency band and sensitivity. As a result, it was found that the PDLC has a detection frequency band up to several tens of megahertz, and it detects the induced signals with reasonable sensitivity. The PDLC combined with the digital filtering technique enables us to locate the PD activities. Also, it was found that the radiation or end-winding coupling of the PD signals is initiated >13 MHz.

A Stator Winding Insulation Condition Monitoring Technique for Inverter-Fed Machines

Stator insulation quality assessment is an important issue for pulsewidth modulation inverter-fed machines, since the stator insulation is exposed to increased thermal/electrical stresses. In this paper, a new approach for monitoring the condition of the stator insulation for inverter-fed machines is proposed. The main concept of the proposed approach is to apply various types of test voltages to the motor stator insulation using the inverter, to perform standard offline insulation tests whenever the motor is not operating. Two methods for testing the insulation with modifications to the inverter circuit are proposed and verified experimentally. The results show that the proposed technique provides a simple low cost solution for detecting stator insulation degradation at an early stage for reliable operation of inverter-fed machine systems, since the insulation condition can be monitored frequently. This not only helps prevent forced outages and safety risks due to insulation breakdown, but also helps perform maintenance in an efficient manner since individual motor maintenance can be prioritized and scheduled based on its present condition.

Continuous on-line partial discharge monitoring of generator stator windings

The use of on-line partial discharge (PD) measurements as an indicator of stator winding insulation condition, is well known. Trending results from on-line PD measurements over time, often allows maintenance personnel to become aware of developing stator insulation problems in motors and generators, and take corrective measures before failure occurs. However, partial discharge measurements on operating rotating machines can be influenced by conditions such as humidity, temperature, terminal voltage, and load. Thus, to provide reliable data which can be trended, it is important to take readings under similar machine operating conditions. In remote plants, or on pump storage units which are frequently cycled, it can be both time consuming and costly to ensure that personnel are available to take PD readings under ideal conditions occur. This paper describes the development of an automatic partial discharge monitoring system which is permanently connected to relevant machine sensors and can be configured to collect PD data when suitable conditions are met. The operating principles of the system are described, and some results are presented from data collected to date on 30 hydrogenerators.