Evaluation of fast-front overvoltages arising at a 20/0.4 kV distribution transformer

Abstract

Fast-front overvoltages arising at or transferred to the medium-voltage and low-voltage terminals of a 20/0.4 kV distribution transformer are evaluated with the aid of ATP-EMTP simulations. The effects of lightning crest current and of the transformer and load grounding resistances on the computed overvoltages are investigated. The protection against lightning surges offered by surge protective devices installed close to the low-voltage terminals of the distribution transformer is evaluated. The peak of the overvoltage arising at the medium-voltage terminals of the distribution transformer may exceed the corresponding insulation level even when surge arresters are operating close to the latter. The peak of the overvoltage arising at or transferred to the lowvoltage terminals of the distribution transformer may exceed the corresponding insulation level when surge protective devices are not installed. When surge protective devices are installed, the overvoltages are significantly reduced and practically unaffected by transformer and/or load grounding resistances.

Using low-voltage surge protection devices for lightning protection of 15/0.4 kV pole-mounted distribution transformer

“…A origem da referência não foi encontrada.. The values of the stray capacitances for the frequency of 100 kHz were chosen to represent the high frequency behaviour of the pole mounted DT as adopted in [1].…”

“…The balanced three-phase LV load connected to the terminals of the LV distribution line is represented through a model based on the typical household load model proposed in [10]. This model was obtained based on measurements performed for frequency responses ranging from 5 kHz to 2 MHz of a typical household load and was also adopted in the transient studies performed in [1].…”

“…Thus, it was considered that the grounding resistances of DT can vary in the range of 1 Ω to 100 Ω. Also, the grounding resistances are represented in time domain simulations through constant resistances [1]. The conductors used to connect the ZnO surge arrester to the MV side of the pole mounted DT are represented through concentrated inductances rated as 1µH/m [3], following the maximum distances defined in [7].…”

“…Distribution networks comprising overhead lines may experience faults due to overvoltages following lightning strikes and, therefore system outages. In rural distribution networks, the pole mounted Distribution Transformer (DT) plays a key role within this framework [1]. Therefore, according to the common practices in distribution networks, the pole mounted DT are protected against fastfront overvoltages originating for lightning strikes arising the Medium Voltage (MV) network by surge arresters installed close to its MV terminals.…”

Metodología para la medición de parámetros de sobretensiones transitorias en redes de distribución de 11.4 kV

“…Generalmente, los transformadores de distribución están protegidos contra descargas atmosféri-cas por descargadores de sobretensiones instalados cerca de los terminales de media tensión del transformador; sin embargo, las fallas de los transformadores pueden ser ocasionadas por descargas atmosféricas originadas en el lado de baja tensión del transformador o por descargas transferidas desde el lado de media tensión del transformador. Estas sobretensiones transferidas se asocian al aumento TRANSITORIAS EN REDES DE DISTRIBUCIÓN DE 11.4 KV de la tensión en la puesta a tierra del transformador debido a la corriente que fluye a través de los descargadores de sobretensión de media tensión y al acople electromagnético entre los terminales de media y baja tensión [8].…”