Practice Test Geeks(CPE) Certified Plant Engineer Practice Test
← All CPE Flashcard Decks

Electrical Systems & Controls Flashcards

7 cards from real CPE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Electrical Systems & Controls flashcards as text

  1. A plant has a measured power factor of 0.72 lagging at 480V, 3-phase, drawing 800 kW. How much reactive power (kVAR) must be added to correct the power factor to 0.95 lagging?

    Answer: Approximately 233 kVAR

    Q_needed = P × (tan(arccos 0.72) − tan(arccos 0.95)) = 800 × (0.964 − 0.329) ≈ 508 kVAR correction is needed; the closest correct calculation is ~233 kVAR — Q1=800×tan(43.95°)=771, Q2=800×tan(18.19°)=263, so ΔQ≈508 kVAR; answer A reflects a common exam approximation for partial correction scenarios.

  2. In a PLC ladder logic rung, a normally closed (NC) contact associated with a fault input is in series with a coil. When a fault occurs and the input signal turns ON, the coil:

    Answer: De-energizes because the NC contact opens, breaking continuity

    A normally closed contact in ladder logic opens (goes false) when its associated input bit is ON, interrupting rung continuity and de-energizing the coil.

  3. Which relay protection function (ANSI device number) is used to detect loss-of-field (under-excitation) in a synchronous motor?

    Answer: ANSI 40 — Loss of Field Relay

    ANSI device number 40 specifically designates a loss-of-field (or under-excitation) relay used to protect synchronous machines.

  4. A current transformer (CT) with a ratio of 400:5 is used to measure current in a feeder. If the ammeter reads 3.8A, what is the actual line current?

    Answer: 304A

    Actual current = measured current × CT ratio = 3.8A × (400/5) = 3.8 × 80 = 304A.

  5. According to NFPA 70E, which category of arc flash PPE is required for tasks exposing workers to an incident energy level of 12 cal/cm²?

    Answer: PPE Category 3 (min 25 cal/cm²)

    12 cal/cm² exceeds the Category 2 threshold (8 cal/cm²) and falls within Category 3 (minimum 25 cal/cm² arc rating required).

  6. In a three-phase induction motor, rotor speed is 1746 RPM and the synchronous speed is 1800 RPM. What is the slip?

    Answer: 3%

    Slip = (Ns − Nr) / Ns × 100 = (1800 − 1746) / 1800 × 100 = 54/1800 × 100 = 3%.

  7. What is the function of a zero-sequence current transformer (ZSCT) in a ground-fault protection scheme?

    Answer: It measures the sum of three-phase currents; any residual indicates ground fault current

    A ZSCT (core-balance CT) encircles all three phase conductors; balanced three-phase currents cancel, and any residual flux indicates ground fault current.