Concept 1

Voltage Basics

The first thing to read on any DERMS chart is simple: where voltage sits relative to 1.0 p.u. and whether it crosses the ANSI band.

1.00 p.u. Nominal feeder voltage

1.05 p.u. ANSI Range A upper limit

355 min Baseline overvoltage duration

10-15h Peak violation window during high solar export

How to Read Per-Unit Voltage

1
1.00 p.u. means the feeder is exactly at nominal voltage.
2
1.05 p.u. is the practical ceiling for normal operation.
3
Anything above that red line is a compliance problem, not just a cosmetic bump.

Why Voltage Rises on High-PV Feeders

A
Solar export reverses local power flow and pushes voltage upward near feeder ends.
B
The strongest effect appears around midday, when PV output is highest.
C
Traditional regulation gear reacts slowly compared with solar-driven changes.

Core Visual

Voltage Envelope - Baseline Scenario

The shaded range shows the full spread of bus voltages. Watch the upper edge break through 1.05 p.u. around midday.

Key Insights

Voltage is highest when solar export is strongest, not when customer demand is highest.

The issue persists for hours, which makes it operationally meaningful.

Some buses experience much larger excursions than others, which is why heatmaps matter later.

Next Step

From Symptom to Cause

Now that the voltage envelope is clear, the next concept explains why solar PV changes feeder power flow and creates this midday shape.

Next: PV Integration Challenges