Power line tower grounding grid impulse grounding impedance measuring instrument

The invention discloses a power line tower grounding grid impulse grounding impedance measuring instrument and a measuring method. The measuring instrument consists of an impulse current generator, an impulse current collector and an impulse voltage collector; the impulse voltage collector has a three route peak voltage synchronous measurement function; a measuring return circuit consists of a current testing return circuit and a three route electric potential testing return circuit; the current testing return circuit consists of the impulse current generator, a grounding device, the impulse current collector, a current electrode, a connecting line and earth; the three route electric potential testing return circuit consists of the grounding device, the impulse voltage collector, three voltage electrodes, connecting lines and earth; the measuring method comprises the following steps: the current electrode is arranged at a distance of dGC from a grounding grid, the distance of dGC is five times as much as a ma