Voltage measurements at different locations describe different electrical boundaries. Before comparing them, identify the node, phase, reference conductor, nominal voltage base, measurement method and time window. A network-wide average cannot replace the individual records needed to evaluate each location. This is a measurement-comparability problem, separate from choosing where a transformer voltage regulator should control.
Define a comparable record
A usable record pairs each value with its phase and connection reference: phase-to-neutral and phase-to-phase voltages are different quantities. Retain sensor location, instrument identity, calibration or uncertainty information and the scaling applied to any voltage-transformer channel. A renamed spreadsheet column does not correct a wrong ratio or reference.
IEC 61000-4-30:2025 addresses in-situ power-quality measurement methods and interpretation for systems with a declared 50 Hz or 60 Hz fundamental frequency. Its public scope includes supply-voltage magnitude. The official page identifies a corrected version incorporating the July 2026 corrigendum. [1] [2] That scope is a method framework, not a universal service-voltage acceptance band; the applicable limits and evaluation rules must be specified separately.
Align time before comparing space
Time aggregation summarizes repeated observations at one defined boundary. Spatial averaging combines different nodes. These operations answer different questions and should not be interchanged. Match timestamps, time zones, sampling or aggregation definitions and any event flags before claiming that two nodes were high or low simultaneously. Missing intervals must remain visible rather than being silently replaced by a smooth trace.
The public standard summary does not supply the detailed aggregation, accuracy or compliance clauses. Specify the method actually used and obtain the necessary full requirements for the project. Do not infer a permitted time window or percentile merely from a meter’s class label.
A spatial mean can conceal both extremes
For an independent synthetic example, assume two simultaneous readings on the same phase-to-neutral base: Node A is 0.93 pu and Node B is 1.07 pu. Assume an example acceptance band of 0.95 to 1.05 pu. Their arithmetic spatial mean is (0.93 + 1.07)/2 = 1.00 pu, although both nodes fall outside the assumed band.
On a declared 230 V base, those readings are 213.9 V and 246.1 V; the assumed bounds are 218.5 V and 241.5 V. These are arithmetic conversions, not legal voltage limits. The mean can describe the dataset, but it cannot demonstrate that either customer location meets its own requirement. Duration, method and the actual governing criterion still matter.
| Record | Per unit | Voltage | Against the example band |
|---|---|---|---|
| Node A | 0.93 pu | 213.9 V | Below |
| Node B | 1.07 pu | 246.1 V | Above |
| Spatial mean | 1.00 pu | 230.0 V | Hides both violations |
Preserve bases and deliver node-level evidence
Do not directly average MV line-to-line values with LV phase-to-neutral readings. Per-unit normalization requires a declared base and reference at each point. A common numerical scale does not remove the transformer connection, tap state or feeder voltage difference. Retain the original units and conversion mapping so the comparison is independently reproducible.
For quasi-static time-series studies, keep calculated values distinct from instrument measurements and preserve the matching topology, load and DER states. Deliver per-node and per-phase records, extrema, relevant durations, missing-data flags and uncertainty. Procurement should identify the measurement channels, timing method and reporting format. The project’s electrical and power-quality specialists determine acceptance; one spatial mean cannot certify the whole supply area.