UPDA Electrical flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Per-unit base impedance
- Z_base = V_base² / S_base, using line-to-line voltage in kV and three-phase power in MVA; it allows transformer ratios to be eliminated from circuit calculations.
- Symmetrical components
- A method that resolves an unbalanced three-phase system into positive, negative, and zero sequence sets, enabling analysis of unbalanced faults using per-sequence networks.
- Voltage regulation
- The percentage rise in receiving-end voltage when full load is removed, expressed relative to full-load voltage: (V_no-load − V_full-load)/V_full-load × 100.
- Fault level
- The short-circuit apparent power available at a point, equal to √3 × line voltage × fault current; it indicates the duty the protective equipment must withstand.
- Surge impedance loading
- The power a transmission line delivers when its receiving-end load equals its surge impedance √(L/C); at this loading the line has near-flat voltage profile.
- Ferranti effect
- A rise in receiving-end voltage above sending-end voltage on a long, lightly loaded or open-circuit line, caused by the line's capacitive charging current.
- Rankine cycle
- The thermodynamic cycle of steam power plants: heat addition in the boiler, expansion in the turbine, condensation, and pumping back to the boiler.
- Skin effect
- The tendency of alternating current to concentrate near the conductor surface, raising effective AC resistance above the DC value at higher frequencies.
- Transformer EMF equation
- E = 4.44·f·N·Φ_max gives the RMS induced voltage; it shows EMF is proportional to frequency, turns, and peak core flux.
- Induction motor slip
- Slip s = (N_s − N_r)/N_s, the fractional difference between synchronous speed and rotor speed; rotor frequency equals s times supply frequency.
- Synchronous speed
- N_s = 120·f/P rpm, where f is supply frequency in hertz and P is the number of poles; it is the speed of the rotating magnetic field.
- Maximum transformer efficiency
- A transformer reaches maximum efficiency at the load where variable copper loss equals constant core loss, typically below full load.
- Controlled rectifier output
- For a full converter, average DC voltage equals (2·V_m/π)·cos α, where α is the thyristor firing angle measured from the zero crossing.
- Buck chopper
- A DC-DC converter whose average output voltage equals the duty cycle D times the input voltage, always stepping the voltage down.
- V/f control
- A drive strategy that varies motor voltage in proportion to frequency, keeping air-gap flux approximately constant and preserving torque capability.
- Freewheeling diode
- A diode placed across an inductive load or switch to carry current during switch-off, limiting inductive voltage spikes and protecting the switching device.
- Earth fault loop impedance
- The total impedance of the fault current path; it must be low enough for the protective device to disconnect within the required time.
- Diversity factor
- The ratio of the maximum demand of an installation to the sum of individual maximum demands, used to size service and feeder capacity.
- IP code
- An ingress protection rating where the first digit denotes protection against solids and the second against liquids; higher digits mean greater protection.
- IDMT relay
- An inverse definite minimum time overcurrent relay whose operating time decreases as fault current rises, with a time multiplier setting shaping the curve.
- Differential protection
- A scheme that compares currents entering and leaving a protected zone and trips when the difference exceeds a setting, covering faults within the zone only.
- Fall-of-potential method
- An earth resistance test using a current electrode and a potential electrode placed between the earth under test and the current electrode.
- Rolling sphere method
- A lightning protection design technique where a sphere of given radius is rolled over the structure to define the volume protected by air terminations.
- Hazardous area zoning
- Classification of explosive gas atmospheres as Zone 0, 1, or 2 by likelihood of presence, which determines the required equipment protection level.
- Conductor ampacity
- The maximum continuous current a conductor can carry without exceeding its insulation temperature rating under stated installation and ambient conditions.
- Lockout/tagout
- A safety procedure that isolates and locks energy sources and attaches warning tags so equipment cannot be re-energized during maintenance.
- Arc flash boundary
- The distance from an arc source at which incident energy equals the threshold for second-degree burns, defining where protective clothing is required.
- Critical path
- The longest-duration sequence of dependent activities in a project network; it sets the minimum project duration and has zero total float.
- Cost performance index
- CPI = earned value divided by actual cost; a value below one indicates the project is over budget relative to work completed.
- Lump-sum contract
- A fixed-price agreement where the contractor performs the defined scope for a stated total price and bears most quantity and cost risk.
- Betz limit
- The theoretical maximum fraction of wind kinetic energy a turbine can extract, about 59.3%, derived from momentum theory for an ideal rotor.
- PV temperature coefficient
- The rate at which module power changes per degree Celsius of cell temperature, typically negative, so output falls as cells heat up.