The results of investigation of flashovers and damages of power line insulators due to high voltage pulses with power on and power off have shown that joint action of a pulse disturbance and operating voltage of a power line can lead to catastrophic phenomena in power supply systems. High-voltage transformers are much more important and expensive elements of such systems. A set of ways of transformers tests to joint action of pulse disturbance and operating voltage of a high-voltage power line is presented in this article.