Zero-sequence voltage is one of the main quantities that serve as a criterion for detecting earth faults in medium voltage networks. This paper presents a novel but simple method of determining zero-sequence voltage for smart grid protection devices, especially for use in fault current passage indicators. The presented method can also be used to measure zero-sequence voltage in any point of the network, where such values are required and application of other classical measurement methods is not possible. The method is based on continuous measurement of only one phase-to-earth voltage performed by an overhead voltage sensor. Both laboratory and field tests of the proposed method were carried out and their results indicate that the maximum expected relative error in determining the zero-sequence voltage is $\delta U_0=10,15\%$. Taking into account the simplification applied in the method, the obtained measurement results are sufficient to be used in the earth fault detection criteria in fault current passage indicators. The use of the proposed method allows to reduce the installation cost of this type of devices, while maintaining their high efficiency.

零序电压是作为检测中压网络接地故障判据的主要量之一。本文提出了一种新颖但简单的方法来确定智能电网保护装置的零序电压，特别是用于故障电流通过指示器。所提出的方法还可用于测量网络中任何点的零序电压，其中需要此类值并且无法应用其他经典测量方法。该方法基于由架空电压传感器执行的仅一个相对地电压的连续测量。对所提出的方法进行了实验室和现场测试，结果表明确定零序电压的最大预期相对误差为$\delta {你}_0=10,15\%$. 考虑到该方法应用的简化，所获得的测量结果足以用于故障电流通过指标中的接地故障检测标准。使用所提出的方法可以降低此类设备的安装成本，同时保持其高效率。