The electric power system is continuously growing in its size, complexity and required reliability. There is an increased risk due to transient overvoltages which can deteriorate the insulation for different power system components. There is a need for monitoring of transient voltages to better monitor the effects due to them on the insulation of the components. It can be achieved using a non-contact voltage measurement technique. The study elucidates the theory and practical application of the non-contact voltage measurements. The measurement of voltage is achieved by utilizing the stray parasitic capacitance between the high voltage conductor and the ground. A metal plate is used as a sensor to detect the voltage, which indirectly acts as a capacitance divider for voltage measurement. The current study uses operational amplifier based differential-integrator circuit topology in order to accurately measure the voltage over a wide bandwidth of 20 Hz - 1 MHz. The measurement technique is used for measurement of three phase voltages and a methodology is proposed for it. The sensor system is also tested in an online test scenario in a substation for monitoring the shunt reactor switching transients.
Partial Discharges (PD) on high-voltage alternating current (HVAC) cables insulated with cross-linked polyethylene (XLPE) has a low occurrence, but consequences are usually severe since PD ultimately results in cable failures. Up until now the only efficient way to monitor HVAC cables for PD has been to install large coupling devices which are able to measure PDs directly from the power cables in order to verify if they are fault-free. These installations, usually of a temporary nature, are troublesome for several reasons like safety issues, measurement uncertainty, labor intensity etc.For the purpose to ultimately create a system that is able to be utilized for PD Detection by means of gas analysis, which is easily applicable in on site, on-line conditions, initial experiments were performed in order to investigate basic material properties of XLPE and to investigate the performance of tin oxide (SnO 2 ) sensors for such an application. For this purpose a specialized test cell was developed in order to be able to investigate different conditions which can be expected in a cable insulation system. It was found from the experiments that surface discharges are detectable by means of gas analysis and that these gases penetrate an XLPE sample. It was also demonstrated that the SnO 2 based sensor system displays a good selectivity to the gases emitted by PD and remain inert towards other gases emitted from XLPE samples.
<p>Condition monitoring of power equipment is a vital step<br />in extending the lifetime of existing equipment and<br />reducing costs for utilities while minimizing the risk of<br />unscheduled outages. Partial discharge (PD) monitoring<br />has evolved as a reliable mean of determining<br />deterioration in insulation systems. Acoustic emission<br />detection techniques are usually utilized for PD<br />detection mainly in oil-filled transformers offering the<br />advantage of being immune to electrical noise and a<br />method to localize PDs. In this work it was attempted to<br />improve the sensitivity of acoustic measurements<br />through wavelet analysis and estimation of the threshold<br />value from actual measurements of the noise, which<br />proved to be more effective compared to other<br />estimation values. The analysis was performed on<br />laboratory measurements from a 36 kV condenser<br />bushing known to exhibit PD activity acquired with a<br />low cost PD acoustic sensor developed at KTH. As a<br />next step the results have to be verified by online<br />measurements, which can result in the addition of an</p><p>Condition monitoring of power equipment is a vital step in extending the lifetime of existing equipment and reducing costs for utilities while minimizing the risk of unscheduled outages. Partial discharge (PD) monitoring has evolved as a reliable mean of determining deterioration in insulation systems. Acoustic emission detection techniques are usually utilized for PD detection mainly in oil-filled transformers offering the advantage of being immune to electrical noise and a method to localize PDs. In this work it was attempted to improve the sensitivity of acoustic measurements through wavelet analysis and estimation of the threshold value from actual measurements of the noise, which proved to be more effective compared to other estimation values. The analysis was performed on laboratory measurements from a 36 kV condenser bushing known to exhibit PD activity acquired with a low cost PD acoustic sensor developed at KTH. As a next step the results have to be verified by online measurements, which can result in the addition of an onboard signal-processing box for improved sensitivity.</p>
Partial discharges (PD) analysis is the common technique for detection and identification of dielectric defects. Certain PD characteristics can be an early sign of degradation. For further understanding, combined voltages can enhance the analysis of PD characteristics in some specific cases. This paper presents an experimental study on the PD appearance under repetitive negative half-sine voltage excitation, as such a combination of AC and DC voltage. Adopting the time-resolved PD pattern technique, PD signals originated from dielectric barrier corona discharge (DBCD) source are recorded in time domain by a DL750 Scope Corder. Preliminary filtered results indicated the strong relationship between surface charge accumulation and back discharge, a time delay movement of back discharge can be clearly observed on the pattern during ‘relaxation time period’ with various insulation materials.
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