電気工学英語：必須語彙とフレーズ

"load flow analysis"

A steady-state numerical technique used to determine the voltage, current, and power at every node in an electrical power network under normal operating conditions

"The engineers ran a load flow analysis before commissioning the new substation to ensure voltage levels across the grid remained within acceptable limits."

"short-circuit current"

The abnormally high current that flows when an unintended low-resistance path is created between two conductors, used as the basis for selecting protective equipment ratings

"The relay was sized based on the maximum short-circuit current calculated at the busbar, ensuring it would trip before equipment could be damaged."

"reactive power"

The component of electrical power associated with energy stored and released by inductors and capacitors in an AC circuit, measured in volt-amperes reactive (VAR)

"The utility installed a bank of capacitors at the substation to supply reactive power locally and reduce the reactive current drawn from the transmission line."

"power factor"

The ratio of real power consumed by a load to the apparent power drawn from the supply, expressed as a number between zero and one, with unity indicating a purely resistive load

"The factory's power factor had dropped to 0.72 due to its large induction motors, so the site engineer fitted power factor correction capacitors to bring it back above 0.95."

"busbar"

A rigid metallic conductor — typically copper or aluminium — that connects multiple circuits in a switchboard, substation, or distribution panel, carrying large currents at a common voltage

"A fault on the 11 kV busbar tripped all the feeders connected to it, blacking out an entire industrial estate until the protection system isolated the faulted section."

"voltage regulation"

The percentage change in output voltage from no-load to full-load conditions in a transformer or power line, used as a measure of supply quality

"The voltage regulation of the distribution transformer exceeded 8% under peak demand, causing lamp flicker at the end of the feeder that prompted a complaint from residents."

"earthing system"

The network of conductors and electrodes connecting electrical equipment to the general mass of earth, providing a safe path for fault currents and limiting touch voltages

"The earthing system was tested with a fall-of-potential method, confirming the earth electrode resistance was below 1 Ω as required by the site safety specification."

"islanding"

A condition in which a section of the distribution network continues to be energised by a local generator after the grid connection has been lost, creating a safety hazard for line workers

"The inverter-based solar system was fitted with anti-islanding protection that detected the loss of grid voltage and shut down within 200 milliseconds to prevent islanding."

"operational amplifier"

A high-gain DC-coupled differential voltage amplifier with a very high input impedance and low output impedance, forming the building block of countless analogue circuit designs

"The sensor conditioning circuit used an operational amplifier configured as a non-inverting amplifier with a gain of ten to bring the thermocouple output up to the range accepted by the ADC."

"transistor saturation"

The operating region of a bipolar junction transistor in which both junctions are forward-biased and collector current is limited by external circuit elements rather than base current, making it behave as a closed switch

"The switching circuit relied on driving the transistor into saturation to reduce the collector-emitter voltage drop to below 0.2 V and minimise power dissipation in the on state."

"Kirchhoff's laws"

Two fundamental rules governing the conservation of charge and energy in electrical circuits: the current law states that currents entering a node sum to zero; the voltage law states that voltages around any closed loop sum to zero

"The student applied Kirchhoff's laws to the three-mesh network and obtained a set of simultaneous equations that yielded the branch currents after algebraic solution."

"impedance matching"

The technique of designing source and load impedances to be equal or conjugate so that maximum power is transferred between stages or to minimise signal reflections in high-frequency circuits

"Impedance matching between the 50 Ω RF amplifier output and the antenna feed was achieved using an L-network, maximising the radiated power."

"MOSFET"

Metal-oxide-semiconductor field-effect transistor — a voltage-controlled switching or amplifying device that dominates modern digital logic, power electronics, and analogue integrated circuits

"The buck converter used an n-channel MOSFET with a low on-resistance of 3 mΩ as its main switching element to minimise conduction losses at high output currents."

"Thevenin equivalent"

A simplified model of any linear two-terminal network consisting of a single ideal voltage source in series with a single resistance, making circuit analysis far easier

"Replacing the complex source network with its Thevenin equivalent allowed the team to calculate the load current with a single application of Ohm's law."

"printed circuit board"

A flat board of insulating material with conductive copper tracks laminated onto its surface to mechanically support and electrically interconnect electronic components

"The printed circuit board layout was reviewed carefully to ensure high-frequency signal traces were kept short and surrounded by ground planes to reduce electromagnetic interference."

"gain-bandwidth product"

A constant equal to the product of an amplifier's open-loop gain and the frequency at which that gain applies, which determines the usable bandwidth at any chosen closed-loop gain

"The engineer chose an op-amp with a gain-bandwidth product of 10 MHz so that at a closed-loop gain of 100, the usable bandwidth would still extend to 100 kHz."

"PID controller"

A feedback control algorithm that computes a corrective output from three terms — proportional, integral, and derivative — combined to minimise the error between a setpoint and a measured process variable

"The temperature controller used a PID controller tuned by the Ziegler-Nichols method, achieving a settling time of under 30 seconds with minimal overshoot."

"transfer function"

The ratio of the Laplace transform of a system's output to its input under zero initial conditions, used to characterise the dynamic behaviour of linear time-invariant systems in the frequency domain

"Deriving the transfer function of the servo motor from its electrical and mechanical equations allowed the control designer to predict the closed-loop step response analytically."

"steady-state error"

The difference between the desired output and the actual output of a control system after all transients have died away and the system has reached its final value

"Adding an integrator to the controller eliminated the steady-state error that had caused the robotic arm to stop 2 mm short of its commanded position."

"phase margin"

The additional phase lag required to bring a stable open-loop system to the verge of instability, measured at the gain crossover frequency and used as a stability metric

"The Bode plot showed a phase margin of only 12 degrees, indicating the closed-loop system would exhibit significant overshoot, so the designer added a lead compensator."

"root locus"

A graphical method for analysing how the poles of a closed-loop system move in the complex plane as a parameter — usually the loop gain — is varied

"The root locus plot revealed that increasing the proportional gain beyond 8 would cause two closed-loop poles to cross into the right half-plane, making the system unstable."

"state space representation"

A mathematical framework that describes a dynamic system as a set of first-order differential equations in terms of state variables, inputs, and outputs, enabling modern multi-variable control design

"The multi-axis robotic system was modelled in state space representation to allow the application of linear quadratic regulator theory for optimal trajectory tracking."

"sampling rate"

The frequency at which a continuous analogue signal is measured and converted to digital values in a discrete-time control system, which must exceed twice the highest signal frequency to avoid aliasing

"The digital speed controller used a sampling rate of 10 kHz, well above the bandwidth of the motor dynamics, to ensure the discrete controller behaved almost identically to its analogue equivalent."

"feedforward control"

A control strategy that uses a model of the process to predict and apply the corrective action needed to reject a known disturbance before it affects the output, acting in addition to any feedback loop

"The paper mill added feedforward control based on measured feed moisture content, dramatically reducing moisture variations in the finished sheet compared to feedback alone."

"Fourier transform"

A mathematical operation that decomposes a time-domain signal into its constituent sinusoidal components, expressing amplitude and phase as a continuous function of frequency

"Applying the Fourier transform to the vibration waveform immediately revealed a dominant frequency spike at 120 Hz corresponding to bearing wear in the motor."

"aliasing"

The distortion that occurs when a signal is sampled at a rate below twice its highest frequency component, causing high-frequency content to appear as spurious low-frequency signals

"The aliasing in the digitised audio was eliminated by adding a low-pass anti-aliasing filter before the ADC to remove all frequencies above half the sampling rate."

"convolution"

A mathematical operation that combines two signals to produce a third, used in linear systems to compute the output when the input and the impulse response are known

"The audio processing algorithm used convolution with a measured room impulse response to add realistic acoustic reverberation to the dry studio recording."

"bandwidth"

The range of frequencies over which a signal, channel, or filter operates effectively, typically defined as the interval between the half-power (−3 dB) frequencies

"The communications channel had a bandwidth of 200 kHz, which the engineers verified was sufficient to transmit the baseband data stream without significant inter-symbol interference."

"noise floor"

The level of background noise present in a measurement or communication system, below which useful signals cannot be reliably detected or recovered

"By cooling the preamplifier stage to reduce thermal noise, the research team lowered the instrument's noise floor sufficiently to detect signals 20 dB weaker than previously possible."

"digital filter"

An algorithm implemented in software or dedicated hardware that performs mathematical operations on sampled digital data to pass or reject specific frequency components of a signal

"A 64-tap FIR digital filter was designed with a sharp cut-off at 1 kHz to remove 50 Hz power-line interference and its harmonics from the biomedical measurement data."

"modulation"

The process of varying one or more properties of a high-frequency carrier wave — such as amplitude, frequency, or phase — in accordance with a lower-frequency information signal for transmission

"The satellite uplink used quadrature phase-shift keying modulation, encoding two bits per symbol and achieving an efficient use of the allocated spectrum."

"power spectral density"

A measure of how the power of a random or periodic signal is distributed across frequency, expressed in watts per hertz, used to characterise noise and vibration

"The power spectral density of the current ripple was measured to verify that the switching power supply met the EMC standard's conducted emission limits across the required frequency range."

"maximum power point tracking"

An algorithm used in photovoltaic inverters and charge controllers to continuously adjust the operating point of a solar panel to extract the maximum available power as irradiance and temperature change

"The string inverter's maximum power point tracking algorithm updated every 10 milliseconds, ensuring the array operated within 0.5% of its theoretical maximum output throughout the day."

"capacity factor"

The ratio of a power plant's actual energy output over a given period to the maximum output it could theoretically have produced if operating at full rated capacity for the same period

"The offshore wind farm achieved a capacity factor of 48% in its first year of operation, significantly higher than the 36% typical of onshore sites in the same region."

"grid-scale battery"

A large stationary energy storage system, typically using lithium-ion cells, connected directly to the transmission or distribution network to store surplus generation and discharge during periods of peak demand

"The grid-scale battery installed next to the wind farm could store 100 MWh of energy and respond to a grid frequency drop by injecting full power within 150 milliseconds."

"curtailment"

The deliberate reduction of output from a generating unit below its available level, typically applied to renewable sources when generation exceeds demand or network capacity

"Wind curtailment on the Scottish grid reached 12% of available generation on windy winter nights, highlighting the need for additional interconnection or storage capacity."

"levelised cost of energy"

The average net present cost of electricity generation over a plant's lifetime, divided by total energy output, providing a standardised metric for comparing technologies with different cost and output profiles

"The levelised cost of energy for the new offshore wind project was calculated at £48 per MWh, making it competitive with new gas-fired generation for the first time."

"power purchase agreement"

A long-term contract between an electricity generator and a buyer that specifies the price, volume, and duration of electricity sales, providing revenue certainty for project financing

"The data centre operator signed a 15-year power purchase agreement with the solar farm developer, securing a fixed price for 80% of its electricity needs and enabling the project to reach financial close."

"virtual power plant"

A network of distributed energy resources — such as solar panels, batteries, and flexible loads — aggregated and coordinated by software to behave as a single dispatchable power plant for grid services

"The virtual power plant aggregated 5,000 residential battery systems to deliver 50 MW of frequency response to the grid operator, competing directly with conventional peaking plants."

"inverter-based resource"

Any generating unit or storage device that connects to the AC grid through a power electronic inverter rather than a rotating machine, including solar PV, battery storage, and most wind turbines

"As inverter-based resources displaced synchronous generators, grid operators updated their inertia requirements to mandate synthetic inertia services from new large-scale projects."

"electromagnetic interference"

Unwanted electrical noise generated by one device that disrupts the normal operation of another device operating nearby, transmitted through conducted or radiated paths

"Electromagnetic interference from the variable-speed drive was corrupting data on the nearby programmable logic controller, a problem resolved by installing ferrite chokes on the drive's output cables."

"surge protection device"

A component connected in parallel with sensitive equipment to divert transient overvoltages caused by lightning or switching events to earth before they can damage the protected load

"A Type 1 surge protection device was installed at the main distribution board to handle the direct lightning strike energy that could otherwise propagate through the building wiring."

"differential mode noise"

Electrical noise that appears between the line and neutral conductors of a power supply, usually generated internally by switching circuits and requiring an X-capacitor for suppression

"The conducted emission test revealed excessive differential mode noise between 150 kHz and 500 kHz, which was reduced to compliant levels by increasing the X-capacitor value in the EMC filter."

"residual current device"

A protective device that monitors the difference between current flowing out on the live conductor and returning on the neutral; if a mismatch occurs it trips the circuit, protecting against electric shock and fire caused by earth leakage

"The 30 mA residual current device tripped immediately when the contractor accidentally drilled through a cable, disconnecting the supply before a fatal shock could occur."

"creepage distance"

The shortest path along the surface of an insulating material between two conductors, a critical dimension in high-voltage equipment design to prevent surface flashover under polluted conditions

"The outdoor switchgear design increased the creepage distance on its insulators from 25 mm/kV to 31 mm/kV to meet the heavily polluted environment classification."

"dielectric strength"

The maximum electric field that an insulating material can withstand without breakdown, measured in volts per metre, used to select insulation for cables, transformers, and switchgear

"The transformer oil was tested for dielectric strength after five years of service; the result of 58 kV/2.5 mm confirmed it remained fit for use without replacement."

"protective earth"

A conductor that connects exposed metal parts of electrical equipment to the earthing system so that a fault current flowing to the enclosure will blow a fuse or trip a breaker rather than electrocuting a person who touches it

"The inspector found that the protective earth conductor to the motor frame was not connected, creating a potentially lethal touch voltage hazard that required immediate isolation."

"harmonic distortion"

The presence of voltage or current components at integer multiples of the fundamental power frequency, generated by non-linear loads such as variable-speed drives, LED drivers, and computer power supplies, degrading power quality

"Total harmonic distortion in the voltage supply at the plant rose to 11% after the installation of fifty LED luminaires, causing nuisance tripping of the sensitive CNC machines."