A lossless transmission line with 0.6 pu reactance per phase uniformly distributed along the length of the line, connecting a generator bus to a load bus, is protected up to 90% of its length by a distance relay placed at the generator bus. The generator terminal voltage is 1 pu. If no generator is at the load bus, the threshold pu current for operation of distance relay for a solid three-phase to ground fault on the transmission line will be ______