Transition Resistors Research Articles

Failure Analysis of OLTC during Transition Resistor Test

Emerging modern technologies and ever-changing demands compete with each other to bring new changes to the sociotechnical life of human beings. OLTC is one such equipment connected as an integral part of the transformer to change the turns ratio while the transformer is in energized condition, to adjust the output voltage. Changing times and technology brought many changes in the OLTC techniques, design and operation. Traditionally OLTC is a complex mechanical device, which has some deficiencies. OLTC design elements are checked during the transition resistor test. Thus, OLTC testing for transition resistors is a method to enhance the reliability of OLTC design. This paper discusses a typical failure case of OLTC during the transition resistor test conducted in CPRI.

Tap Changer Condition Assessment Using Dynamic Resistance Measurement

The DVtest method (Dynamic Resistance Measurement - DRM) is an off-line, non-destructive testing method based on a dc current being injected through a winding and a tap changer as it moves through all of its positions. The test current is recorded with high resolution. Also, an on-load tap changer (OLTC) motor current can be recorded simultaneously with the test current. A high sampling rate is very important due to fast transition processes (transition time of a resistor OLTC type is approximately 50 ms). The DRM method has been proven as a very effective method in the early detection of possible faults on on-load tap-changers (OLTCs). This test may be used to detect problems such as slow transition time, open circuits, problems with contacts, transition resistors, mechanism, motor control, and much more. This paper provides the description of the DVtest method for OLTC analysis. In addition, a few interesting cases about detected tap changer defects and diagnostic analysis are presented, as well.

Fault Line Selection in Distribution Networks Based on Parameter Identification in Frequency Domain

The distribution network is mostly the ungrounded neutral system or the resonant grounded system in many countries. Selecting the fault line as soon as possible is of great significance to power systems. This paper proposes a parameter identification method in frequency domain to solve this problem. By using the matrix pencil method to extract frequency-points and their information in zero-sequence voltage and zero-sequence current, spectral leakage in DFT is avoided. With the estimated frequency points, an equation in frequency domain is established which will help to calculate the capacitance value and thus to identify the fault line. This method requires a low sampling rate and has high accuracy. In addition, the frequency-band in this new method is wider than the SFB's frequency-band. Verified by simulation in ATP-EMTP and data from RTDS, the new method is quite effective in fault line selection with an ability to overcome transition resistor and is immune from the impact of arc-suppression.

New thyristor assisted diverter switch for on load transformer tap changers

Based on a conventional tap changer, a new diverter switch is described which features a single transition resistor and thyristor assisted suppression of arcing at the switch contacts. A simple arrangement of mechanical switch contacts ensures that the thyristor pairs used for arc suppression are only connected and triggered for a short interval of time prior to, during and after the operation of the switch contacts. A thyristor malfunction will not result in damage to the tap selector or transformer.