🔍 Key Concepts

• Synchronizing lamps (sequence method) – how three lamps connected phase-to-phase will brighten in order when there is a phase angle difference between bus and incoming generator. • How the graph in A shows which machine is leading or lagging in phase and whether the incoming generator’s frequency is slightly higher or lower than the bus. • How the direction of phase rotation (ABC vs CBA) and whether the incoming machine is fast or slow determines a clockwise vs counter‑clockwise and fast vs slow lamp sequence.

💭 Think About

• From graph A, is the incoming machine waveform consistently moving ahead of, or falling behind, the bus waveform as phase angle increases? What does that tell you about whether the incoming generator is fast or slow? • Imagine watching one electrical cycle over time: which phase of the incoming generator will reach its voltage peak first compared to the same phase on the bus? How would that affect the order in which the three lamps in circuit B go bright and dark? • If the frequency difference is very small, will the lamps appear to change state quickly or slowly? How does that relate to the exam’s use of the words fast and slow in the choices?

✅ Before You Answer

• Identify clearly from graph A which trace is the bus and which is the incoming machine, and note whether the phase angle error is increasing or decreasing with time. • Determine from the graph whether the incoming generator is running slightly faster or slightly slower than the bus; this directly tells you whether the sequence is labeled fast or slow. • Confirm that the phase rotation of the incoming generator is the same as the bus (ABC to ABC, not reversed); then relate a leading vs lagging incoming voltage to a clockwise vs counter‑clockwise lamp sequence.