In January 2023, in collaboration with our industry partner Transpower Ltd (New Zealand’s national grid operator), a campaign was undertaken to inject large currents into operating high voltage transformers. New Zealand’s high voltage DC (HVDC) link was used to inject current directly into the ground at Haywards substation near Wellington, including into several 216MVA 220 kV / 110 kV autotransformers. Six injection test periods occurred, each lasting 1-2 hours. The peak current injected into the ground was about 621 A, spread across several transformers within the Haywards substation. The injection campaign was undertaken for New Zealand’s Endeavour programme “Solar Tsunamis: Space-Weather Prediction and Risk Mitigation for New Zealand’s Energy Infrastructure”. The technique of substation monitoring using nearby very low frequency (VLF) receivers has been previously reported by the lead author, based on observations of the Halfway Bush substation (HWB) in Dunedin, New Zealand. Evidence of harmonic distortion through enhanced odd and even 50 Hz harmonic amplitudes during geomagnetically induced current (GIC) events of up to 50 A, associated with large geomagnetic storms in 2017 and 2018, have already been observed and analysed in detail. Typically, enhancements in the amplitude of harmonics in the 100 Hz to 600 Hz range have been detected during GIC events. The VLF observations from HWB are consistent with the idea that the local transformers radiate even harmonics of the 50 Hz fundamental mains frequency due to half-cycle saturation driven by additive dc flux induced by GIC. During the Active Injection campaign at Haywards Station, two identical VLF receiving systems were deployed around the substation. Each VLF system comprised a set of orthogonal magnetic field loop aerials. Preliminary results from the VLF harmonic data suggest that observed variations in amplitude in the 100 – 600 Hz frequency range were correlated with temporal variations in the injected ground current, particularly after the current had been applied for more than 20 minutes. Prior to that, a slow increase in harmonic distortion occurred, beginning at the time of the injection onset. For injected substation earth currents ranging from 300 A – 600 A (about 20 A – 35 A for individual autotransformers) even small variations of the order of 10’s of amps appeared to be well correlated with the VLF amplitude variations of even order harmonics. In this study we present the VLF data during the injection events, describing the responses observed from a large, complex substation experiencing geomagnetic storm-like effects.