353 articles
Mass-impregnated cable
A mass-impregnated (MI) cable is a high-voltage power cable insulated with paper tape impregnated with a viscous oil-like compound, used almost exclusively for HVDC submarine transmission since the 1950s.
Merging unit
A merging unit (MU) is a device in a digital substation that converts analog currents and voltages from instrument transformers into digitized IEC 61850 Sampled Values streams.
Metal-clad switchgear
Metal-clad switchgear (MC switchgear) is medium-voltage switchgear in which circuit breakers, buses, and cable terminations are housed in separate compartments enclosed by grounded metal barriers.
Metal-enclosed switchgear
Metal-enclosed switchgear is power switching equipment enclosed on all sides and top in sheet metal, containing switches, circuit breakers, fuses, and buses for medium-voltage distribution, standardized by IEEE C37.20.3.
Microgrid
A microgrid is a group of interconnected electrical loads and local energy resources that operates as a single controllable entity, running connected to the main grid or islanded from it.
Modular multilevel converter
A modular multilevel converter, or MMC, is a high-power electronic converter that spreads AC-to-DC conversion across many series-connected submodules; invented by Rainer Marquardt in 2001, it dominates HVDC transmission.
N-1 criterion
The N-1 criterion is a power system reliability rule requiring that the grid remain secure, within emergency ratings and stability limits, after any single element's loss.
Negative-sequence current
Negative-sequence current is the symmetrical component, from Fortescue's 1918 method, that appears when three-phase currents or voltages are unbalanced, producing counter-rotating fields, rotor heating, and vibration in machines.
NEMA connector
A NEMA connector, or NEMA plug, is a North American plug or receptacle built to standards set by the National Electrical Manufacturers Association, with over 70 defined types.
Net load
Net load, also called net demand or residual load, is total electricity demand minus wind and solar output, and its volatility shapes how much flexibility a grid needs.
Neutral-point-clamped converter
A neutral-point-clamped (NPC) converter is a multilevel power converter topology, introduced in 1981 by Nabae, Takahashi, and Akagi, that produces three voltage levels per phase and is widely used in medium-voltage drives.
Nexans
Nexans is a French multinational manufacturer of cable systems for power transmission and distribution, operating in 39 countries with €6.1 billion in sales in 2025.
NordBalt
NordBalt is a 700 MW high-voltage direct current submarine electricity interconnector linking Klaipėda in Lithuania and Nybro in Sweden, owned by Litgrid and Svenska kraftnät and in service since 2016.
Oil circuit breaker
An oil circuit breaker is a power circuit breaker that quenches the arc by separating contacts in insulating oil, dominating high-voltage switchgear for most of the twentieth century.
Oil-filled cable
An oil-filled cable is a high-voltage power cable in which paper insulation is impregnated with oil kept under continuous pressure, as self-contained or pipe-type designs.
Oil-filled transformer
An oil-filled transformer, also called an oil-immersed transformer, is an electrical transformer with its core and windings submerged in insulating oil that both insulates and cools.
OMICRON Electronics
OMICRON Electronics is an employer-affiliation entry covering Alexander Apostolov, a power-system protection engineer and Principal Engineer at OMICRON electronics in Los Angeles since September 2006.
On-load tap changer
An on-load tap changer (OLTC) is a switching device in a power transformer that regulates output voltage in discrete steps while the transformer remains energized and carrying load.
Optical current transformer
An optical current transformer is a power-system device that measures current via the Faraday effect on polarized light, offering no core saturation and a wide dynamic range.
Optical ground wire
Optical ground wire (OPGW), also called optical fiber composite overhead ground wire, is a metallic cable at the top of transmission towers that shields against lightning while carrying optical fibers, in regular use since the mid-1980s.
Out-of-step protection
Out-of-step protection is the power system protection that detects loss of synchronism on a grid, blocking distance relays during stable swings and tripping breakers during unstable swings.
Overcurrent protection
Overcurrent protection is a power system protection method in which a relay trips a circuit breaker when current exceeds a preset pickup value, after a fixed or inverse-time delay.
Overhead ground wire
An overhead ground wire, also called a shield wire, static wire, earth wire, or skywire, is a grounded conductor atop power lines that intercepts lightning strokes.
Overhead power line
An overhead power line, also known as a high tension line, carries electric power through conductors suspended above the ground on poles or towers, using air as insulation.
Pacific DC Intertie
The Pacific DC Intertie, also known as the Pacific Direct Current Intertie, is a high-voltage direct current power line linking Oregon to Los Angeles, completed in 1970.
Peak shaving
Peak shaving is a load management technique in power engineering that cuts a customer's maximum electricity demand, typically by discharging a battery, to lower demand charges and relieve grid stress.
Per Gunnar Engström
Per Gunnar Engström (1923–2015) was a Swedish electrical engineer at ASEA who led HVDC transmission development and was elected to the US National Academy of Engineering in 1992.
Phase-shifting transformer
A phase-shifting transformer (PST) is a specialized transformer that controls active power flow in three-phase transmission networks by regulating the voltage angle, letting operators direct power along chosen paths instead of physics-decided ones.
Phasor data concentrator
A phasor data concentrator (PDC) is a device or software function in a power system that time-aligns synchrophasor data from multiple PMUs for control centers, defined by IEEE C37.247-2019.
Phasor estimation
Phasor estimation is a signal-processing method that computes the magnitude and phase angle of fundamental-frequency voltage or current waveforms, used in power system monitoring, control, and protection.