ABB HCLD flashcards

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

Minimum approach distance

The closest distance a qualified worker may approach an energized conductor, set by voltage class and maximum switching surge per OSHA 1910.269 tables.

Arc flash boundary

The distance from energized equipment at which incident energy equals 1.2 cal/cm2, used to select arc-rated PPE per NFPA 70E.

Step potential

Voltage difference between two points on the earth's surface one step apart, caused by fault current flowing through the ground.

Qualified electrical worker

A worker trained in and familiar with the construction and operation of equipment and the hazards involved, per OSHA 1910.269(a)(2).

NESC Rule 232

The National Electrical Safety Code rule that sets vertical clearance of wires above ground, roads, rails, and water by voltage class.

NESC Grade B construction

A construction grade requiring higher safety factors, typically 4 for pole strength, applied where higher reliability and public safety are needed.

29 CFR 1910.269

OSHA standard covering electric power generation, transmission, and distribution, including approach distances, grounding, and protective equipment testing.

Temporary protective grounds

Grounding cables sized to carry available fault current and installed with a shotgun stick from a safe position to protect workers from induced or backfeed voltage.

Three-phase power formula

P = √3 x VLL x I x power factor, used to compute real power from line-to-line voltage, line current, and power factor.

Per-unit impedance

A normalized impedance value; to convert to ohms, multiply by Z(base) = kV^2/MVA for a three-phase base.

Transformer fault current

Isc ≈ kVA x 1000 / (√3 x VLL x Z%); a 5% impedance transformer produces about 20 times rated current on a bolted fault.

Symmetrical components

A method that resolves unbalanced three-phase quantities into positive, negative, and zero sequence components for fault analysis.

Pole class

ANSI O5.1 classification (Class 1 through 5) specifying the circumference at 6 ft from the butt and rated load at 2 ft from the top.

Ruling span

The equivalent span used to set stringing sag-tension for a line section; individual span sags are adjusted from the ruling span value.

Guy lead angle

The angle between the guy and the pole; a 45-degree guy carries about 1.41 times the horizontal load it resists.

Armor rods

Preformed rods wrapped around a conductor at a support to protect against chafing, bending fatigue, and vibration damage.

Cable pulling tension

The longitudinal force applied during cable installation; limited by conductor strength and by sidewall pressure at bends.

Concentric neutral cable

Underground cable with a neutral conductor wrapped around the insulation; the neutral carries unbalanced and fault current and must be grounded at both ends.

Time-domain reflectometry

A cable test that sends a pulse and measures the reflection time; distance = (velocity of propagation x time)/2 to locate opens and low-resistance faults.

Cable bending radius

The minimum radius to which a cable may be bent without damaging insulation or semicon; typically 8x to 12x the cable diameter for solid dielectric cable.

Open-delta capacity

A bank of two transformers in open delta delivers about 58% of the three-transformer capacity, or √3 times the kVA of one unit.

Subtractive polarity

A transformer polarity where H1 and X1 are adjacent; most distribution transformers are subtractive and must be connected accordingly.

Wye-grounded primary to delta secondary

A connection not permitted on four-wire multi-grounded primary systems because it provides a zero-sequence path and can cause ferroresonance.

Transformer tap changer

A device that changes the number of primary turns to compensate for primary voltage variation, typically in ±5% steps.

Sectionalizer

A device that counts fault-current interruptions and opens on the last count; it has no fault-interrupting rating and must be backed by a recloser.

Recloser fast and delayed curves

A recloser typically uses two fast and two delayed operations; the fast curve saves fuses and the delayed curve lets downstream fuses clear.

Time-current coordination

Selection of protective device settings so that the device nearest the fault operates first and curves do not cross in the fault current range.

Polarization index

The ratio of 10-minute to 1-minute insulation resistance; a value above 2.0 indicates good insulation condition.

Transformer turns ratio test

A test comparing measured winding ratio to nameplate; a deviation greater than 0.5% indicates a winding problem.

Dissolved gas analysis

A transformer oil test that identifies arcing, overheating, and corona by measuring dissolved gases; a rising trend is more significant than a single reading.

Single line-to-ground fault

The most common distribution fault type, accounting for roughly 70% to 80% of faults, often caused by trees, animals, or insulation failure.

Surge generator thumper

A fault-locating tool that applies high-voltage pulses to break down a cable fault, located by acoustic and electromagnetic detection.