Voltage bands
The key idea
A voltage band is the rule that turns numbers into verdicts. The study solves the voltages; the band decides which of them count as violations. Same results, different band — different violation list.
The idea
A power flow returns a voltage for every bus: 0.968, 0.945, 0.915... None of these numbers is good or bad on its own. It becomes good or bad when compared against a rule: how far from nominal is acceptable here?
That rule is the voltage band. Two are common:
- ±5% (0.95–1.05 pu). Typical for low-voltage service points, where equipment sits close to the network with nothing downstream to correct the voltage.
- ±10% (0.90–1.10 pu). Often applied on medium-voltage networks, where transformers with tap changers stand between the network and the customer and can correct the remainder.
Standards such as ANSI C84.1 and EN 50160 define bands like these — but which band applies to your network is a matter of the local code, the connection agreements and the equipment installed. It is a decision, not a constant.
Try it
The eight voltages below never change. Switch the rule.
outside ±5%: 3 of 8 buses
The solved voltages are identical under both rules. Switch the band and the violation count changes from three to one. That is why the band is a project decision to make explicitly — not a default to accept.
Why it matters
- The violation list is the study's headline. It is what gets acted on and what gets reported. If the band is wrong, the headline is wrong — over an identical solution.
- Too wide hides real problems; too tight invents them. A ±10% assessment on an LV network passes customers whose equipment is genuinely mistreated. A ±5% assessment on an MV backbone flags "violations" that a downstream tap changer corrects as a matter of routine.
- Set it once, on the project. When the band lives in the project settings, every study and every report judges by the same rule — and the rule is visible, not implicit.
See it in Phasor
Phasor ships ANSI C84.1 and EN 50160 style bands, but the project setting decides which one judges your results. Set it explicitly — the violations list, ordered by severity, is built from that rule.