Six Unifications, New Six Unifications, and Nine Unifications:
Main Protection:
Protection that meets system stability and equipment safety requirements by selectively and rapidly removing faults from protected devices and lines.
High-Frequency Blocking Distance Protection:
High-frequency protection using distance protection start elements and directional elements to control transceivers, sending blocking signals to both sides of the protection.
Secondary Equipment:
Low-voltage electrical equipment used to monitor, control, regulate, protect, and provide operational or production command signals for primary equipment.
Repetitive Grounding:
Reconnecting a neutral line to the ground at one or more points.
Distance Protection:
A protection device using impedance elements to detect short-circuit faults based on the ratio of voltage to current (U/I=Z), which correlates with the distance to the fault.
Zero-Sequence Protection:
Relay protection systems utilizing zero-sequence current, voltage, and power generated during grounding faults in high-current grounding systems.
Backup Protection:
Protection that removes faulty components with a longer delay when the main protection or circuit breaker fails to operate.
High-Frequency Protection:
Protection that converts phase or power direction information into high-frequency signals transmitted via transmission lines for comparison at both ends.
Power System Automatic Safety Devices:
Devices to prevent loss of system stability and avoid large-scale blackouts.
Power System Accident:
Events caused by equipment failures or human errors that affect the quantity or quality of power supply beyond acceptable limits.
Resonant Overvoltage:
Severe overvoltage in certain system components due to series resonance formed by inductive and capacitive elements during operations or faults.
Circuit Breaker Failure Protection:
Protection that trips adjacent breakers at the same substation or remote breakers when a circuit breaker fails to trip upon fault detection.
Resonance:
A phenomenon where a circuit comprising resistance, inductance, and capacitance exhibits zero reactance, making it purely resistive with voltage and current in phase.
Comprehensive Auto-Reclosing:
A system combining single-phase reclosing for ground faults and three-phase reclosing for interphase faults.
Auto-Reclosing:
An automatic device that re-closes a tripped circuit breaker after a fault.
In-Service Electrical Equipment:
Equipment fully or partially energized, or equipment that becomes energized upon operation.
Remote Backup Protection:
Protection provided by adjacent components on the power supply side when the main protection or breaker fails.
Energy Management System (EMS):
A comprehensive term for modern grid dispatch automation systems, consisting of basic and application functions.
Near Backup Protection:
Enhanced element protection using dual configurations and breaker failure protection to ensure fault clearance.
Compound Voltage Overcurrent Protection:
Protection combining a negative-sequence voltage relay and a low-voltage relay to detect faults.
Automatic Underfrequency Load Shedding:
A system that disconnects non-critical loads to restore frequency stability during active power shortages.
Line Pilot Protection:
Protection that simultaneously trips breakers at both ends of a line during faults, serving as the main line protection.
Dynamic Stability of Power Systems:
The ability of a power system to maintain long-term stability after small or large disturbances.
"Permission" in Dispatch Terminology:
Approval from a dispatcher for changing equipment status or grid operation modes.
Comprehensive Command:
A single operation task issued by a dispatcher, with detailed steps executed by on-site personnel.
Primary Frequency Adjustment:
Automatic adjustment by generator governors without changing speed settings.
Secondary Frequency Adjustment:
Manual or automatic adjustments to generator settings to restore frequency.
Tertiary Frequency Adjustment:
Optimal allocation of active power loads among generators for economic operation.
Static Frequency Characteristics of Generator Governor Systems:
The relationship between frequency changes and generator output adjustments.
Reverse Voltage Regulation:
Adjusting central point voltage to compensate for load variations.
Constant Voltage Regulation:
Maintaining central point voltage slightly above rated levels regardless of load changes.
Forward Voltage Regulation:
Allowing central point voltage to vary within specified limits during minimum and maximum loads.
Dispatch Plan Modification Rights:
Limited rights to modify daily dispatch plans under special circumstances.
Transformer No-Load Loss:
Power consumed by a transformer at rated voltage, approximately equal to core loss.
Clock Representation of Transformer Connection Groups:
Representing transformer winding connections using clock-like vectors.
Transformer Over-Excitation:
Increased magnetic flux density due to higher voltage or lower frequency, leading to core saturation.
Transformer Inrush Current:
Transient current during full-voltage energization of a transformer.
Power System:
The integrated system of generation, transmission, transformation, distribution, and consumption equipment.
Power Grid:
The network connecting generation and consumption through transmission, transformation, and distribution equipment.
Transmission Capacity:
The maximum allowable power transfer in a transmission system.
Main Grid:
The backbone of the highest voltage transmission network.
Grid Structure:
The configuration of the main grid, including wiring methods and load characteristics.
Line Charging Power:
Reactive power generated by line-to-ground capacitance.
Subsurface Current:
Current supplied to a faulted line after disconnection.
Wave Impedance:
The ratio of traveling wave voltage to current.
Natural Power:
The active power level at which reactive power generation and consumption balance in a transmission line.
High-Grounding Current System:
Systems with significant grounding fault currents due to direct neutral grounding.
Voltage Collapse:
Progressive voltage decline leading to system instability.
Frequency Collapse:
Progressive frequency decline leading to system instability.
Post-Reclosing Acceleration:
Immediate fault clearance upon reclosing onto a permanent fault.
Transformer Compound Voltage Overcurrent Protection:
Backup protection combining negative-sequence and low-voltage relays.
Step Voltage:
Voltage difference across a grounded surface causing potential hazards.
Backflashover Voltage:
High potential differences causing flashovers from lightning protection systems to nearby equipment.
System Collapse:
Large-scale blackouts caused by stability loss, cascading failures, or natural disasters.
Cascading Failures:
Sequential equipment trips triggered by initial faults.
Three Defense Lines:
Strategies for maintaining grid stability under various disturbance scenarios.
Differential Instantaneous Protection:
Rapid fault clearance based on differential current exceeding maximum inrush levels.
