As the primary protection of high voltage (HV) and Extra high voltage (EHV) transmission networks, distance protection needs to operate properly under all possible fault conditions. It needs to operate as fast as possible for internal fault, while it also must be able to discriminate between the internal and the external faults to prevent unnecessary trip of the normal system. In real life application, the operational characteristic of commercial distance relays such as operating time and reach accuracy are usually defined using the steady state conditions. This leads to difficulty in understanding the operational characteristic of the relay under the dynamic conditions such as faults. In this thesis, a dynamic test tool based on the latest IEC 60255-121 standard, suitable for performance analysis of distance protection during dynamic condition was developed and validated. The tools are built by using the ATP-EMTP Software and the Omicron secondary injection kit. The test results of two distance relays show that depending on the dynamic conditions, the operational performance of the relay might be affected. In some situations, the operating time of the relays was delayed, while, in other conditions, the accuracy of impedance measurement is affected causing the relay to overreach. Furthermore, this delayed tripping or overreach of distance protection could cause both security and dependability issue in power transmission protection. The dynamic test tool which has been developed can be expanded further to study other dynamic conditions that are not covered in this thesis.