Tests on the on-load tap changer (OLTC)

WHY DO WE PERFORM OLTC TEST? The on-load tap changer (OLTC) is the only moving part in a typical power transformer, it permits tap changing and regulating voltage without affecting the network operation. This frequently movements between transformer taps makes the OLTC components the most vulnerable, which implies regular testing and maintenance. On the other hand, by using a conventional static winding resistance measurement, it is hard to detect any anomalies during the switching process because of the fast movements of the OTLC’s switches (40-60 ms). Many mechanical parts are not easily accessible for inspection, and it is recommended to perform additional tests to establish the OLTC condition. Usually, winding resistance measurements are performed on offline power transformers. In [...]

Transformer Vector Group Detection

The three-phase transformer comprises three separate single-phase transformers with shared limbs, each representing a phase consists of primary and secondary windings. The primary or secondary windings are connected in one of several ways. The most common configurations are the star, delta, and Zigzag. The phase angle between the high voltage and the low voltage windings varies between 0o and 360 o. The vector group is the method of categorizing the high voltage HV windings and low voltage LV windings configurations of three phase transformers [1]. The vector group of a transformer is presented as follow: Fig.1. Vector Group Representation THE IMPORTANCE OF THE TRANSFORMERS VECTOR GROUP DETECTION. The transformers vector group identification (Y-Y, Delta-Y, Delta-Delta… etc.) is an essential [...]