PE Power exam formulas cheat sheet basics

These are core relationships to know before you open the reference handbook. NCEES provides its own handbook during the exam, so learn where the full versions live. This sheet is a memory aid, not a substitute.

Three-phase power

• P = √3 × V_LL × I_L × pf
• S = √3 × V_LL × I_L; S = √(P² + Q²); pf = P / S

Power factor correction

• Q_c = P (tan φ₁ − tan φ₂), where φ = arccos(pf)

Per-unit

• Z_base = V_base² / S_base (V_base line-to-line, S_base three-phase)
• I_base = S_base / (√3 × V_base)
• Three-phase fault level ≈ S_base / Z_pu (infinite source)

Machines and transmission

• Synchronous speed N_s = 120 f / p; slip s = (N_s − N) / N_s
• Power transfer P = (V₁ V₂ / X) sin δ for a mostly reactive line

See these used in the free sample questions, then organize your review with the topics overview.

Frequently asked questions

Do I need to memorize these formulas?

NCEES provides a reference handbook during the exam, but knowing the basics cold saves time. Check the NCEES page for current rules.

Is this the complete formula list?

No. It is a short list of fundamentals. Use the NCEES handbook for the full set.

Where do these formulas show up in practice?

Three-phase power, per-unit and fault level appear in the free sample questions linked below.

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