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Erbrink J.J.,Technical University of Delft | Gulski E.,Technical University of Delft | Smit J.J.,Technical University of Delft | Seitz P.P.,Seitz Instruments AG | And 3 more authors.
IEEE Electrical Insulation Magazine | Year: 2010

On-load tap changers (OLTCs) are designed to change current from one winding tap to another without interrupting the load and without short-circuiting adjacent taps on the transformer windings. Many OLTCs installed in power transmission systems operate on only one or a limited number of tap positions for an extended time period, and this contributes to degradation of the less frequently used contacts. A routine inspection of an OLTC can involve opening the diverter switch compartment, cleaning the soot-covered insulation, and checking the diverter contacts and mechanisms, but it usually does not include inspection of the tap-selector contacts inside the transformer tank. The addition of an important element to OLTC inspection, namely checking the condition of the OLTC contacts without accessing them physically, is discussed below. © 2006 IEEE.


Jongen R.,Seitz Instruments AG | Quak B.,Seitz Instruments AG | Gulski E.,Poznan University of Technology | Cichecki P.,Technical University of Delft | De Vries F.,Alliander
Proceedings of 2012 IEEE International Conference on Condition Monitoring and Diagnosis, CMD 2012 | Year: 2012

Many parameters can influence the quality of the PD measurement and various issues are important during the execution of a PD measurement. In particular when testing long lengths of MV cables the PD detection sensitivity and particularly the PD site location is affected. To increase the measurement sensitivity the measurement system can be extended with an additional PD measuring unit at the far end of the cable. This unit measures PD activity with the conventional standardized PD detection synchronized with the damped AC test voltage. This two sided measurement provides higher detection sensitivity in the case of long cable lengths. Furthermore, when the measurement data of the 2 units at both ends of the cable are combined with each other, further analyses provides the PD site location in case of measured PD activity. In this way it is possible to test and diagnose longer lengths of MV cables. © 2012 IEEE.


Erbrink J.J.,Technical University of Delft | Gulski E.,Technical University of Delft | Smit J.J.,Technical University of Delft | Seitz P.P.,Seitz Instruments AG | And 2 more authors.
IEEE Transactions on Power Delivery | Year: 2010

Due to different degradation mechanisms, onload tap changers (OLTCs) may contribute to power transformer failures. If offline diagnosis is undertaken during functional checks performed during the service life of OLTC devices, some of the degradation effects can be assessed. This paper addresses an OLTC diagnostic method based on the measurement of dynamic resistance. An experimental investigation of the degraded OLTC contacts was used to identify a number of defects revealed by dynamic resistance measurements. © 2010 IEEE.


Erbrink J.J.,Technical University of Delft | Gulski E.,Technical University of Delft | Smit J.J.,Technical University of Delft | Leich R.,Liandon Inc. | And 2 more authors.
IEEE Electrical Insulation Magazine | Year: 2011

On-load tap changers (OLTC) that are in critical condition and require maintenance can be selected on the basis of diagnostic measurement results. Resistance measurements are particularly suitable for assessment of OLTC degradation and to reveal OLTC defects that could lead to failure (see Figure 1). This article discusses dynamic resistance measurements (DRM) on OLTCs. In Part 1 of this series [1], DRM as a diagnostic method for OLTCs was discussed, and a few case studies were presented. In this part the interpretation of the results will be discussed. © 2011 IEEE.


Jongen R.,Seitz Instruments AG | Quak B.,Seitz Instruments AG | Tenbohlen S.,University of Stuttgart | Gulski E.,Poznan University of Technology
Proceedings of 2012 IEEE International Conference on Condition Monitoring and Diagnosis, CMD 2012 | Year: 2012

This contribution presents new developments in the field of on-site (E)HV cable testing, in particular testing of long lengths of power cable. A modern solution is presented for on-site testing and diagnosis of transmission power cables by means of sinusoidal damped AC voltages. With this testing technique on-site voltage testing is performed with additional non-destructive measuring techniques e.g. partial discharges or dissipation factor measurements. To improve the PD detection and particularly the PD location possibilities on long cable lengths an additional range extension measurement system has been developed for PD detection on longer cable lengths. This distributed measurement system can be installed at cable accessories to detect PD signals. © 2012 IEEE.


Houtepen R.,Technical University of Delft | Chmura L.,Technical University of Delft | Smit J.J.,Technical University of Delft | Quak B.,Seitz Instruments AG | And 2 more authors.
IEEE Electrical Insulation Magazine | Year: 2011

The decay of damped ac voltages used for on-site energizing of power cables, and testing generator stator insulation, can be analyzed to estimate the dielectric loss (tan δ) of the insulation. © 2011 IEEE.


Erbrink J.J.,Technical University of Delft | Gulski E.,Technical University of Delft | Smit J.J.,Technical University of Delft | Chmura L.A.,Technical University of Delft | And 3 more authors.
2010 International Conference on High Voltage Engineering and Application, ICHVE 2010 | Year: 2010

Resistance measurements on power transformers are a widely accepted method for finding winding defects. Continuity of the tap changer contacts can also be checked when the on-load tap changer (OLTC) is operated during the resistance measurement. Resistance measurements that also record the resistance during OLTC operation are called dynamic resistance measurements. This off-line diagnostic method can be used during regular maintenance to assess the condition of OLTC parts not accessible for inspection. Besides condition assessment of inaccessible parts of the OLTC, this method can also be used to detect maintenance errors that could lead to failure. In particular, these measurements are very helpful in finding contact discontinuity, mechanical defects that influence the operation of the tap changer contacts, problems with the switch time and the transition resistors and can find contact degradation in an early stage. This paper elaborates on the analysis of service aged power transformers equipped with an OLTC using dynamic resistance measurements. Interpretation of dynamic resistance results is complicated because a large variety of degradation mechanisms act on the OLTC, which can show differently in the dynamic resistance results. A structured procedure for interpreting the dynamic resistance results is presented in this paper. Distinction is made between discontinued tap changer contacts and contacts with increased contact resistance. First, it is discussed how the location of the defect can be determined from deviations in the dynamic resistance. Secondly, the degradation mechanism is determined that underlies the deviating dynamic resistance. Using this information, the importance of the defect or degradation can be determined, this paper gives an example. Finally, condition indexing is discussed and an application example demonstrates how this way of condition assessment can be implemented. ©2010 IEEE.


Erbrink J.J.,Technical University of Delft | Gulski E.,Technical University of Delft | Smit J.J.,Technical University of Delft | Aditya J.,Technical University of Delft | And 4 more authors.
2010 International Conference on High Voltage Engineering and Application, ICHVE 2010 | Year: 2010

Resistance measurements on power transformers are offline diagnostic methods that are performed without opening the transformer main tank. In case the power transformer is equipped with an on-load tap changer (OLTC), this resistance measurement can be used to find degradation and defects inside the OLTC. Many OLTC defects as well as contact degradation can be measured by means of dynamic resistance measurements, which is a resistance test during OLTC operation. A low (DC) test current through the on-load tap changer is used during dynamic resistance measurements. This method is in particular sensitive to maintenance errors, contact degradation and contact timing problems. In general, distinction can be made between defects that interrupt the current through the OLTC, defects that affect the timing of the OLTC contacts and contact degradation resulting in abnormal contact resistance. Firstly, this paper evaluates two ways to perform dynamic resistance measurements on OLTCs: 1) a direct measurement of the OLTC resistance by measuring the current through the OLTC and the voltage of the corresponding transformer terminals and 2) an indirect measurement of the induced voltage on the (secondary) windings without OLTC when the OLTC switches a DC current. The measurement procedure for the direct method is discussed for condition diagnosis of in-tank high-speed resistor tap changers. Secondly, the effect of the test circuit and test parameters on the measurement results is discussed. This influences the readings directly, in particular at service-aged contacts. Current amplitude, the secondary short-circuit and circuit resistance are considered. Simulation results and experimental data are presented to demonstrate those effects and to select an optimal test setup. ©2010 IEEE.


Patent
Seitz Instruments AG | Date: 2016-12-21

A novel method and system for partial discharge (PD) measurement on power cable (PC) is described, which comprises connecting at two measurement locations a capacitor (Ck) to the high-voltage conductor (C) of the cable (PC) and connecting to the low-voltage end of each capacitor (Ck) a communication coupling device (CCD), measurement coupling device (CD), a communication coupling device (CCD) and a communication device (CS). High voltage signals are provided to the high-voltage conductor (C) of the cable (PC) and a partial discharge signal is measured at each measurement location by means of measurement instruments (MI). Measurement results of the partial discharge signals received at one measurement location are transmitted via the high-voltage conductor of the cable to the other measurement location and the location of the partial discharge is calculated. The method utilizes the high-voltage conductor for transmittal of the partial discharge signal and communication between the measurement instruments.


Patent
Seitz Instruments AG | Date: 2014-08-13

A novel device for testing of insulation of capacitive electric components (26) having a metallic core and an outer insulation is described, which comprises a power supply (15), a solid-state switch (20) for short-circuiting the power supply (15) and an inductor (21), wherein the inductor (21) and the capacitance of the capacitive electric component (26) provide an LC circuit. The solid-state switch (20) is additionally designed for opening when the LC circuit is charged by electrical energy.

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