Annex 1: Mitigating overvoltage from generation at the inverter

55. Distributed generation must be connected to the low voltage network through an inverter that complies with a regulated standard (AS/NZS 4777). These inverters can monitor the local voltage and limit or reduce the generator’s power output when voltage exceeds a threshold.

56. Electricity distributors set technical requirements for connection and operation of generation in their low voltage networks. Some distributors require inverter-based generation to be curtailed, by activating so-called power-quality response modes, when voltage approaches or exceeds the regulated maximum of +6%. Different power-quality response modes can be selected at the inverter when it is installed, or by a technician during a site visit. Power-quality response modes can be set remotely for some inverters.

Regulation 60(2)(f) – Electricity (Safety) Regulations 2010(external link) — New Zealand Legislation

57. The same power-quality response requirements can apply to distributed batteries when discharging into a low voltage network. This includes EV batteries providing a vehicle-to-grid (V2G) service. The rate of electricity discharge can be limited to avoid overvoltage, albeit at an opportunity cost.

58. Batteries can be a valuable source of flexibility to the power system if they are controlled to charge and discharge in a coordinated manner. The coordinated management of distributed batteries could be particularly valuable at times of system stress (such as when total generation on the system is insufficient to meet total demand with an acceptable reserve margin). This value can, in principle, be realised by offering interruptible load into the national instantaneous reserves market. However, this potential value could be limited if battery discharge is limited by power-quality response if the network supply voltage is at or above the allowable voltage when the service is required.

59. More generally, while power-quality response can be an effective way to avoid or minimise overvoltage, it imposes an opportunity cost on the person who would otherwise benefit from using or selling the electricity that is curtailed. The greater the penetration of distributed generation, the greater the curtailment, and the greater the opportunity cost.

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