NETA ETT Level 4 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Arc flash boundary

The distance at which incident energy equals 1.2 cal/cm² (5 J/cm²), marking the boundary where PPE is required for arc flash protection.

Limited approach boundary

The shock protection boundary for unqualified persons; for systems below 750 V, it is 1 foot (0.3 m) from exposed energized parts.

Lockout/tagout verification

After locking out, verify absence of voltage with a tester rated for the system, testing on a known live source before and after.

Step potential

Voltage difference between two points on the ground separated by about 0.8 m (one step), caused by fault current flowing through soil.

Thevenin equivalent

A linear circuit reduced to a single voltage source (open-circuit voltage) in series with a resistance (looking back with sources deactivated).

Three-phase power formula

Real power P = √3 × V_L × I_L × cosθ, where V_L is line voltage, I_L is line current, and θ is the power factor angle.

Series resonance

Occurs at f_r = 1/(2π√(LC)) where inductive and capacitive reactances cancel, leaving only resistance and minimum impedance.

Per-unit impedance conversion

Z_new = Z_old × (S_new/S_old) × (V_old/V_new)² converts per-unit impedance from one base to another for power system analysis.

Symmetrical components

A method decomposing unbalanced three-phase currents or voltages into positive, negative, and zero sequence components for fault analysis.

Surge impedance loading

SIL = V² / Z_c, where Z_c = √(L/C) is the surge impedance; it is the power level at which a line produces no reactive power.

Polarization index

Ratio of insulation resistance at 10 minutes to that at 1 minute; a value ≥2.0 is generally acceptable for Class B/F insulation.

Guard terminal

A terminal on an insulation tester that shunts surface leakage current away from the measurement, improving accuracy on contaminated insulation.

Tan delta test

Measures dielectric dissipation factor; increases with moisture, aging, and contamination; typical limit <0.5% for new high-voltage insulation.

Turns ratio test

Verifies transformer voltage ratio against nameplate; deviation >0.5% indicates shorted turns or tap changer problems.

Sweep frequency response analysis

Compares a transformer's impedance fingerprint over frequency to detect winding deformation, displacement, or core issues.

Dissolved gas analysis

Oil test interpreting gases like acetylene (arcing), ethylene (overheating), and hydrogen (partial discharge) to diagnose transformer faults.

Contact resistance test

Micro-ohm measurement across closed breaker contacts; values above manufacturer's limit (e.g., 50 µΩ) indicate pitting or misalignment.

Vacuum bottle integrity test

AC hipot applied across open vacuum interrupter contacts; breakdown or leakage indicates loss of vacuum and need for replacement.

SF6 moisture test

Measures water content in SF6 gas; should be below 500 ppmv for new gas; higher levels reduce dielectric strength and form acids.

CT polarity

Subtractive polarity means current into H1 produces current out of X1; verified by DC kick test to ensure correct relay operation.

Differential protection setting

Pickup set above maximum unbalanced current (e.g., 0.2–0.4 pu) to avoid false trips while detecting internal faults.

Distance relay zones

Zone 1 covers 80% of line, Zone 2 covers 120–150%, Zone 3 provides remote backup; reach settings depend on line impedance.

VLF cable test

Very low frequency (0.1 Hz) AC hipot test for aged cables; test voltage typically 2–3 × U0 for 15–60 minutes, reducing space charge effects.

Time domain reflectometry

Locates cable faults by measuring reflection time; distance = (velocity factor × c × time)/2, where c is speed of light.

Partial discharge test

Detects voids and defects in cable insulation; PD magnitude above 100 pC may require action; inception voltage indicates severity.

Surge comparison test

Applies a surge to each motor phase and compares waveforms; differences indicate turn-to-turn or phase-to-phase insulation faults.

Motor current signature analysis

Analyzes current spectrum to detect broken rotor bars, eccentricity, and load issues in rotating machinery.

Core loss test

Loop test measuring core losses in motors; high losses indicate lamination shorting or core damage.

Fall-of-potential method

Ground resistance measurement using three electrodes; spacing ≥5× electrode depth; typical target <5 Ω for industrial systems.

Touch voltage limit

Per IEEE 80, E_touch = (1000 + 1.5C_s ρ_s) × 0.116/√t, limiting voltage across the body from hand to feet during a fault.

Total harmonic distortion

THD = √(Σ V_h²)/V_1 × 100%; IEEE 519 limits THDv to 5% at the point of common coupling for systems below 69 kV.

Voltage unbalance derating

NEMA MG-1 requires motor derating if voltage unbalance exceeds 1%; unbalance = maximum deviation from average / average × 100%.