Null Zone

Null Zone was a part of the universe where Time travel is impossible. The said area was generated by a Time Lord technology given by Seratrix to the Daleks. Contained in the Null zone was the group of planets called The Thousand Worlds where the Daleks and Taalyens enslaved the inhabitants to drill to the core of the planets in order to destroy Gallifrey.(AUDIO: The Heart of the Battle)

During the Time War
Time Lord strategist Seratrix was sent by Cardinal Ollistra to the Daleks to give the machine that would generate the Null zone. Later, Ollistra sent a team consisting of the War Doctor, Veklin, Bennus and Arverton to rescue the strategist. In the said mission, the Doctor discovered about the plan of the Daleks to drill into the core of the planets and found that the central control for the operation in the whole Null Zone was in Keska. After stopping the said drills, the Null-zone was deactivated.(AUDIO: The Heart of the Battle)