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This paper focuses on studying characteristics of streamers in Exxsol D140. The experiments were carried out with 80 mm point-plane gap under step-voltage up to 540 kV. Inception delay time, stopping time and stopping length of streamers is voltage, polarity and impurity dependent. It is seen how increased voltage changes streamer shape and speed resulting in different propagation modes. Impurities markedly reduce inception, breakdown and acceleration voltage. A low ionization potential additive decelerates the positive streamers and accelerates the negative streamers. In fast mode, positive streamers are approximately 5 times faster than negative streamers, and their velocities can reach the value of 110 km/s and 25 km/s at 540 kV for positive and negative polarities respectively. Besides, positive streamers accelerate at 240 kV, while 420 kV is the value of negative streamers.