Registered Electrical Engineer (G&T) flashcards

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

Per-unit base change

To convert an impedance from one base to another, multiply by the ratio of new to old MVA base and by the square of the old to new voltage base.

Symmetrical components operator a

The operator a equals one at 120 degrees. Positive sequence is a, negative is a squared, and zero sequence is unity; the three sequences sum to zero.

Surge impedance loading

SIL equals line-to-line voltage squared divided by surge impedance. For overhead lines it is roughly the natural loading at which reactive generation equals reactive absorption.

Equal-area criterion

For a single machine against an infinite bus, stability is maintained when the accelerating area equals the decelerating area on the power-angle curve.

Zero-sequence current path

Zero-sequence current flows only when a grounded neutral return path exists. Ungrounded systems have no zero-sequence current, so ground-fault current is limited to capacitive charging.

GMD and GMR

Geometric mean distance is the equivalent spacing between conductors; geometric mean radius is the equivalent conductor radius. Inductance depends on the ratio GMD/GMR.

Subtransient reactance

The subtransient reactance X-double-prime-d determines fault current in the first few cycles after a generator terminal short circuit, when the damper winding is active.

Newton-Raphson load flow

A load-flow method using the Jacobian matrix of power mismatches. It converges quadratically near the solution but requires a good initial guess and matrix inversion.

Slack bus definition

The slack bus fixes voltage magnitude and angle and supplies the difference between total generation and total load plus losses; it is the reference for all bus angles.

Single line-to-ground fault

Fault current equals three times phase voltage divided by the sum of positive, negative, and zero sequence impedances plus three times the fault impedance.

Sequence network connection

Positive, negative, and zero sequence networks connect in series for a line-to-ground fault, in parallel for a line-to-line fault, and in series-parallel for a double line-to-ground fault.

Voltage drop formula

For a lagging load, per-phase voltage drop approximates current times resistance times cosine phi plus current times reactance times sine phi.

Motor starting voltage dip

The voltage dip at the motor terminals during starting equals the motor starting kVA divided by the sum of source short-circuit kVA and motor starting kVA.

Coordination time interval

The minimum time margin between the operating curves of a downstream and an upstream protective device, typically 0.2 to 0.4 seconds, to preserve selectivity.

Arc-flash boundary

The distance from live equipment at which incident energy equals 1.2 calories per square centimeter, the threshold for a second-degree burn without protective equipment.

Cable derating factors

Ampacity is corrected by multiplying ambient temperature, soil thermal resistivity, grouping, and depth factors. Factors are multiplicative, not additive, and apply to tabulated ratings.

TN-S earthing system

A system in which the neutral and protective earth are separate conductors from the source to the installation, so the protective conductor carries no load current.

TT system protection

A system with a local earth electrode at the installation. Earth-fault loop impedance is high, so residual current devices are required for fault disconnection.

RCD sensitivity classes

Thirty milliampere devices protect people against electric shock; three hundred milliampere devices protect against fire; type S devices are time-delayed for selectivity.

Disconnection time TN

For final circuits not exceeding 32 amperes in TN systems, the maximum disconnection time is 0.4 seconds; distribution circuits allow 5 seconds.

Cable sizing inequality

Design current must not exceed the protective device rating, which must not exceed the cable current-carrying capacity, after all derating factors are applied.

Indirect contact condition

Disconnection is achieved when the earth-fault loop impedance does not exceed the nominal line-to-neutral voltage divided by the current that trips the device within the required time.

IP rating digits

The first digit indicates solid-particle protection from zero to six; the second indicates water protection from zero to eight. IP54 is dust-protected and splash-proof.

Insulation resistance test

A 500 volt DC test on low-voltage circuits must give at least one megohm, with values recorded on the installation certificate before energization.

Earned value indices

Cost performance index equals earned value divided by actual cost; schedule performance index equals earned value divided by planned value. Values below one indicate overrun or delay.

Total float definition

The amount of time an activity can slip without delaying the project finish date. Activities with zero total float lie on the critical path.

Risk response hierarchy

Risks are addressed by avoidance, reduction, transfer, or acceptance. Residual risk after treatment must be documented and owned.

Contract type risk

Lump-sum contracts place quantity risk on the contractor; unit-price contracts place it on the owner; cost-plus contracts place cost risk on the owner.

Hold point definition

A stage in the inspection and test plan where work cannot proceed until the client or inspector has been notified and has released the hold.

Resource leveling

A scheduling technique that adjusts activity start and finish dates to resolve resource over-allocation, potentially extending the project finish date.

Sealing engineering work

Only the engineer who prepared or directly supervised the design may seal and sign it; sealing unreviewed work is a professional practice violation.

Conflict of interest duty

An engineer must disclose in writing any financial interest in a supplier, contractor, or specified product before providing a professional opinion.