🔍 Key Concepts

• Ground detection transformer configuration shown in Figure C (note the primary Pa, Pb, Pc connections and the broken-delta secondary Sa, Sb, Sc with the lamp across the opening) • How a single line-to-ground fault on one phase of a 3‑phase system affects the voltages of the other phases to ground • The difference between balanced and unbalanced secondary voltages and how that changes current through lamp L

💭 Think About

• Look at what happens to the primary windings when leg C is accidentally grounded: which primary winding is now effectively tied to ground, and how does that shift the phase voltages? • In a broken‑delta ground‑detection secondary, when the three phase-to-ground voltages are perfectly symmetrical, what is the total voltage around the delta, and what does that mean for the lamp current? • If one phase-to-ground voltage changes because of a fault, what happens to the resultant voltage across the open point of the broken delta where the lamp is connected?

✅ Before You Answer

• Verify whether, with a ground on leg C, the three phase-to-ground voltages remain equal and 120° apart, or whether one of them changes magnitude/angle • Determine if an unbalanced condition in the primary will induce a net voltage around the secondary broken delta (creating voltage across the lamp) or no net voltage (no lamp current) • Check that your final choice correctly matches lamp condition (bright/dark) with balanced vs. unbalanced voltages at the transformer secondary