Electrical Automation Control: Electrical Engineering Terms
Electrical Automation Control: Electrical Engineering Terms
Active Power
In the generation, transmission, and utilization of AC power, the portion of energy converted into electromagnetic form is referred to as active power.
Reactive Power
In the generation, transmission, and utilization of AC power, the portion of energy involved in the exchange of electromagnetic fields within a circuit is referred to as reactive power.
Power System
A power system comprises generators, distribution equipment, step - up and step - down substations, power lines, and electricity consumers.
Neutral Point Displacement
In a three - phase circuit, if the power voltage is balanced and the three - phase load is symmetrical, the neutral point voltage is zero regardless of the presence of a neutral line. However, if the three - phase load is asymmetrical and there is no neutral line or the neutral line impedance is significant, a voltage will appear at the neutral point. This phenomenon is known as neutral point displacement.
Operational Overvoltage
Temporary voltage increases caused by circuit - breaker operations or short - circuit and ground - fault conditions are referred to as operational overvoltages.
Resonant Overvoltage
Voltage increases resulting from resonant conditions in power - system circuits due to circuit - breaker operations or saturation of iron - core components are termed resonant overvoltages.
Electrical Main Connection
In power plants, substations, and power systems, the electrical main connection refers to the high - voltage circuit that defines the interconnection of electrical equipment to meet power - transmission and operational requirements.
Double - Busbar Connection
This configuration features two sets of busbars: a working busbar (I) and a standby busbar (II). Each circuit is connected to both busbars via a circuit breaker and two sets of isolating switches, with the busbars linked by a bus - tie circuit breaker.
One - and - a - Half - Breaker Connection
In this configuration, each pair of elements ( outgoing lines or power sources ) is connected to two busbars via three circuit breakers, forming a "one - and - a - half - breaker" connection, also known as a 3/2 connection.
Factory Power Consumption
* During the startup, operation, shutdown, and maintenance of a power plant, a significant amount of electrical equipment, primarily motor - driven machinery, is required to ensure the normal operation of the plant's main equipment and auxiliary systems such as coal handling, coal crushing, ash removal, dust collection, and water treatment. All electrical devices used for plant operation, control, testing, maintenance, and lighting fall under factory power consumption.
Factory Power Consumption Rate
* The percentage of electricity consumed for factory power purposes relative to the total electricity generated by the plant is termed the factory power consumption rate, which is a key economic indicator of power plant operation.
Continuous Load
* Motors that operate continuously on a daily basis.
Intermittent Load
* Loads that are only used during maintenance, accidents, or during the startup and shutdown of machinery and boilers.
Continuous Load
* Loads that operate for more than 2 hours at a time.
Short - Time Load
* Loads that operate for 10 to 120 minutes at a time.
Cyclic Load
* Loads that repeatedly cycle with a period not exceeding 10 minutes.
Self - Restart of Motors
* In the event of a sudden voltage drop or disappearance at the supply busbar of a factory power system, if the busbar voltage return to normal within a short time (typically 0.5 to 1.5 seconds) while the motor speed has not significantly decreased or come to a stop, the motor will self - accelerate and resume normal operation. This process is called self - restart of the motor.
Loss of Excitation
* The phenomenon where a synchronous generator partially or completely loses its excitation is referred to as loss of excitation.
Excitation Control System
* The entire system comprising the excitation regulator, excitation power unit, and the generator itself is termed the excitation control system.
Self - Compounded Static Excitation System
* An excitation system that uses a transformer connected to the generator's output (referred to as an excitation transformer) as the excitation power source. After silicon rectification, it supplies excitation to the generator. Since the excitation transformer is connected in parallel with the generator's output, this excitation method is termed self - compounded. As the excitation transformer and rectifier are static components, the system is also known as a self - compounded static excitation system.
Instrument Transformer
* Instrument transformers are sensors used in power systems to provide information on primary - circuit electrical parameters to secondary - circuit devices such as measuring instruments, relay protection, and automation equipment. They function by proportionally converting high voltages and large currents to lower voltages and smaller currents.
SF₆ Circuit Breaker
* A circuit breaker that employs SF₆ gas, known for its excellent arc - quenching and insulating properties, is termed an SF₆ circuit breaker. It features strong interrupting capacity and compact size but has a complex structure, high metal consumption, and relatively high cost.
Vacuum Circuit Breaker
* A vacuum circuit breaker utilizes the high dielectric strength of a vacuum to extinguish arcs. It is characterized by rapid arc - quenching, resistance to oxidation of contacts, long service life, and compact size.
Working Grounding
* Working grounding refers to grounding measures essential for the normal operation of power systems. For example, the grounding of neutral points in directly grounded neutral - point systems helps stabilize grid potentials and allows for reduced insulation to ground.
Lightning Protection Grounding
* Lightning protection grounding is implemented to meet lightning protection requirements. It ensures that lightning currents are efficiently directed into the earth, thereby reducing lightning - induced overvoltages and is also known as overvoltage protection grounding.
Protective Grounding
* Also known as safety grounding, protective grounding is implemented to safeguard human life. It involves connecting the metal enclosures (including cable sheaths) of electrical equipment to a grounding system to prevent electric shock hazards in the event of equipment insulation failure.
Instrumentation and Control Grounding
* Instrumentation and control grounding refers to grounding measures implemented in thermal control systems, data acquisition systems, computer monitoring systems, transistor - or microprocessor - based relay protection systems, and remote communication systems in power plants. The purpose is to stabilize electrical potentials and prevent interference. It is also termed electronic system grounding.
Grounding Resistance
* Grounding resistance is the resistance encountered as current flows through the grounding electrode into the earth and spreads outward.
Voltage
* Voltage is defined as the work done by an electric field force in moving a unit positive charge from a higher potential to a lower potential.
Current
* Current is the physical phenomenon of the ordered, directional movement of a large number of electric charges under the influence of an electric field.
Resistance
* Resistance is the opposition encountered by current flowing through a conductor. It arises from the collisions between free electrons and atoms or molecules in the conductor during their movement.
Rated Current of a Motor
* The rated current of a motor is the maximum working current at which the motor can operate continuously under normal conditions.
Power Factor of a Motor
* The power factor of a motor is the ratio of its rated active power to its rated apparent power.
Rated Voltage of a Motor
* The rated voltage of a motor is the line voltage at which the motor operates under rated conditions.
Rated Power of a Motor
* The rated power of a motor is the mechanical power output at the motor's shaft when operating under rated conditions.
Rated Speed of a Motor
* The rated speed of a motor is the speed at which the motor operates when supplied with rated voltage, rated frequency, and under rated load.
Power System Oscillation
* Power system oscillation refers to the instability caused by disturbances such as line faults or circuit - breaker trips. It manifests as abnormal frequency indications and significant fluctuations in load and voltage meters.
Protective Grounding
* Protective grounding involves connecting the metal enclosures and frames of electrical equipment to a grounding system. In power systems with ungrounded neutral points, it is a crucial measure for ensuring personal safety.
Protective Bonding
* In power systems with grounded neutral points, protective bonding involves connecting the metal enclosures and frames of electrical equipment to the neutral conductor. This is an important safety measure to protect human life.
Busbar
* A busbar is a conductor that collects and distributes electrical energy. It serves as an electrical node in power systems, determining the number of distribution equipment and indicating how generators, transformers, and lines are connected to complete power transmission and distribution tasks.
Short Circuit
* A short circuit occurs when phases are connected to each other or to ground through a low impedance or directly, causing a sudden increase in circuit current.
Line Voltage
* In a three - phase circuit, line voltage refers to the voltage between any two phase conductors.
Automatic Reclosing
* Automatic reclosing is a device that automatically re - closes a circuit breaker after a fault - induced trip without manual intervention.
Breakdown Voltage
* Breakdown voltage is the voltage at which an insulating medium fails and conducts electricity.
Direct Current (DC)
* Direct current refers to electricity where the voltage and current magnitude and direction do not change with time.
DC Equipment
* DC equipment refers to devices that supply DC power for relay protection, control circuits, and emergency lighting.
Short - Circuit Ratio
* The short - circuit ratio of a synchronous generator is the ratio of the excitation current at rated speed and open - circuit voltage to the excitation current at rated short - circuit current.
Induced Electromotive Force (EMF)
* Induced EMF is generated when the magnetic flux through a conducting loop changes, or when a conductor cuts through magnetic field lines.
Generator Efficiency
* Generator efficiency is the ratio of the generator's output power to its input power, expressed as a percentage. It typically refers to the value under rated conditions.
Shaft Current
* Shaft current is the current that flows from one end of a turbine generator's shaft through the bearing and base to the other end, caused by shaft voltage.
Generator Auxiliary Protection
* Auxiliary protection in generators supplements main and backup protection, addressing scenarios such as voltage transformer circuit breaks, circuit - breaker failures, or flashovers during startup, synchronization, or shutdown.
Generator Backup Protection
* Backup protection in generators activates when main protection fails or does not operate, providing additional fault coverage. It includes compound current instantaneous protection, impedance protection, and direction - overcurrent protection initiated by compound voltage.
Field Forcing
* Field forcing is a function where the generator's automatic voltage regulator detects grid voltage below a set threshold (usually 80% - 85% of rated voltage) and rapidly increases excitation voltage to its maximum value. If implemented with relays, it is called relay - initiated field forcing.
Field Extinction
* Field extinction refers to the rapid disconnection of the generator's excitation power supply and the dissipation of stored magnetic field energy in the excitation winding. It is required to minimize damage from internal generator faults or overvoltages during disconnection.
Exciter Peak Voltage Multiple
* The peak voltage multiple of a synchronous generator's exciter is the ratio of the maximum DC voltage it can provide at rated speed and specified conditions to its rated excitation voltage.
Excitation System Voltage Response Ratio
* The voltage response ratio of an excitation system is the output voltage growth rate from the excitation system voltage response curve divided by the rated excitation voltage. It is a key indicator of the excitation system's dynamic performance.
Split Transformer
* A split transformer is a multi - winding power transformer with one high - voltage winding and two or more low - voltage windings of the same voltage and capacity per phase. It primarily transmits energy between high - and low - voltage windings under normal conditions but limits short - circuit currents during faults. The low - voltage windings are also known as split windings.
Isolator
* An isolator is a switch device that, in the open position, has a specified insulation distance and visible break between its contacts. In the closed position, it can carry normal working currents and short - circuit currents. It can switch circuits with small currents or when the voltage between the isolator's terminals does not significantly change before and after operation, serving both operational and isolation functions.
No - Excitation Tap - Changing Device
* A no - excitation tap - changing device is used to switch tap windings for voltage regulation when the transformer is de - energized. It is also known as a no - excitation tap changer. This device is simple in structure, low in cost, and highly reliable but has a limited voltage regulation range, making it suitable for applications where voltage regulation is not frequently required.
On - Load Tap - Changing Device
* An on - load tap - changing device allows for voltage regulation while the transformer remains in operation. Also called an on - load tap changer, it enables voltage adjustment without interrupting power supply, thereby stabilizing grid voltage and improving the reliability and economy of power supply.
Primary Equipment
* Primary equipment refers to devices directly involved in the generation, transmission, and distribution of electrical power, such as generators, transformers, switchgear, and power cables.
Primary Circuit
* The primary circuit is the electrical main connection that starts from the generator, passes through transformers and transmission lines, and ends at the electrical equipment.
Secondary Equipment
* Secondary equipment includes devices used for monitoring, measuring, controlling, protecting, and operating primary equipment, such as instruments, relays, control cables, and signaling devices.
Secondary Circuit
* A secondary circuit is the electrical circuit formed by connecting secondary equipment in a specific sequence.
Low - Voltage Switch
* A low - voltage switch is a switching device used to make or break circuits with voltages below 1000 V AC or DC.
Contactor
* A contactor is a low - voltage switch used to remotely connect or disconnect circuits with load currents. It is widely used in circuits requiring frequent motor starting and control.
Automatic Air Switch
* An automatic air switch, also known as an automatic switch, is a highly versatile low - voltage switch. It can interrupt both load currents and short - circuit currents and is commonly used in low - voltage, high - power circuits as a main control device.
Extinction Magnetic Switch
* An extinction magnetic switch is a specialized single - pole DC air automatic switch used in the excitation circuit of generators.
Isolating Switch
* An isolating switch is a switch with a visible break and no arc - quenching mechanism. It is used to switch circuits with voltage but no load. It can also be used to connect or disconnect unloaded lines, voltage transformers, and no - load transformers of limited capacity. Its primary function is to isolate power voltage during equipment maintenance.
High - Voltage Circuit Breaker
* A high - voltage circuit breaker, also known as a high - voltage switch, can interrupt or close the no - load and load currents of a high - voltage circuit. In the event of a system fault, it can also interrupt short - circuit currents through the action of relay protection devices. It features a complete arc - quenching structure and sufficient current - breaking capacity.
Arc - Suppression Coil
* An arc - suppression coil is a variable inductor with an iron core, connected to the neutral point of a transformer or generator. During single - phase ground faults, it reduces ground fault currents and aids in arc extinction.
Reactor
* A reactor is an inductive coil with very low resistance. The turns of the coil are insulated from each other, and the entire coil is insulated from ground. Reactors are connected in series in circuits to limit short - circuit currents.
Eddy Current Phenomenon
* When a coil is wound around a solid iron core, the iron core can be considered as composed of numerous closed iron rings perpendicular to the magnetic flux direction. Each iron ring forms a closed conducting loop. When alternating current flows through the coil, the magnetic flux through the iron rings continuously changes, inducing electromotive forces and currents in each iron ring. These induced currents form vortex - like patterns around the iron core axis, known as eddy currents.
Eddy Current Loss
* Eddy current loss refers to the energy dissipation in the form of heat due to eddy currents in the iron core, similar to the heating effect of current flowing through a resistor.
Low - Current Grounding System
* A system where the neutral point is either ungrounded or grounded via an arc - suppression coil.
High - Current Grounding System
* A system where the neutral point is directly grounded.
Armature Reaction
* When there is no armature current, the air - gap main magnetic field is solely produced by the excitation current. When armature current is present, the air - gap main magnetic field is the superposition of the magnetic fields produced by the excitation current and the armature current. The influence of the armature current on the main magnetic field is termed armature reaction.
Induction Motor
* Also known as an asynchronous motor, it operates based on the principles of induced electromotive force in conductors cutting magnetic field lines and the force exerted on current - carrying conductors in a magnetic field. Since the rotor speed is always less than the synchronous speed to maintain relative motion between the magnetic field and rotor conductors, it is called an induction motor.
Synchronous Speed
* When three - phase symmetrical currents are supplied to the three - phase symmetrical windings of an induction motor, a rotating magnetic field is generated in the air gap. The speed of this rotating magnetic field varies with the number of motor poles. The higher the number of poles, the slower the speed. This speed is referred to as synchronous speed.
Slip
* Slip is defined as the ratio of the difference between synchronous speed (n1) and motor speed (n) to synchronous speed, expressed as a percentage: S = (n1 - n)/n1 × 100%.
Star - Delta Starting
* A starting method where the motor's stator windings are connected in star configuration during startup and switched to delta configuration after startup.
Absorption Ratio
* The ratio of insulation resistance values measured at 60 seconds to 15 seconds after applying a DC voltage to an insulating specimen.
Working Grounding
* Grounding performed to ensure the safe and reliable operation of electrical equipment under normal and fault conditions, preventing the occurrence of high voltages due to equipment faults.
Protective Grounding
* Grounding the metal enclosures or frames of electrical equipment to prevent electric shock hazards caused by insulation failure.
Protective Bonding
* In a power system with a grounded neutral point, connecting the metal enclosures or frames of electrical equipment to the neutral conductor. This is an important measure for ensuring personal safety.
Electric Arc
* An electric arc is formed by a large number of point sparks.
Phase Sequence
* The order in which the phases of a sinusoidal quantity pass through the same value. Any set of asymmetrical three - phase sinusoidal voltages or currents can be decomposed into three sets of symmetrical components: positive - sequence, negative - sequence, and zero - sequence.
Relay Pickup Current
* The minimum current value that can cause the relay to operate.
Current Relay
* A relay that operates based on the magnitude of the current through its coil.
Voltage Relay
* A relay that operates based on the applied voltage level.
Fast Relay
* A relay with an operating time of less than 10 milliseconds.
Instantaneous Protection
* Protection that operates instantly without time delay when the current reaches the set value.
Differential Protection
* Protection that operates based on changes in electrical current during equipment faults.
Zero - Sequence Protection
* Protection that responds to the zero - sequence currents and voltages characteristic of ground faults in power systems.
Distance Protection
* A protective device that reflects the distance from the fault point to the installation location of the protection.
Automatic Reclosing
* A device that automatically re - closes a circuit breaker after a fault - induced trip without manual intervention. Reclosing can be single - phase or combined.
Combined Reclosing
* A reclosing function where single - phase faults trigger single - phase tripping and reclosing, with three - phase tripping if unsuccessful; phase - to - phase faults trigger three - phase tripping with reclosing, and unsuccessful reclosing leads to three - phase tripping.
Reclosing Acceleration
* After reclosing onto a permanent fault, the protection device operates again without time delay to trip the circuit breaker and does not attempt reclosing again.
Protection
* A protection system that satisfies stability and equipment safety requirements, selectively and rapidly removing faults along the protected equipment and the entire line.
Backup Protection
* Protection that removes faults when the main protection fails to operate or the circuit breaker refuses to trip.
Power Factor
* The ratio of active power (P) to apparent power (S).
Switching Operation
* Switching operations refer to a series of operations performed when electrical equipment transitions from one state to another or the system operating mode is changed. These operations include:
* Transformer energizing and de - energizing.
* Line energizing and de - energizing.
* Generator starting, paralleling, and isolating.
* Network closing and opening.
* Busbar configuration changes (bus transfer operations).
* Neutral grounding method changes and arc - suppression coil adjustments.
* Modifications to relay protection and automatic device settings.
* Installation and removal of grounding wires.
No - Load Loss
* No - load loss is the power consumed by a transformer when a rated frequency sinusoidal voltage is applied to one of its windings (at the rated tap position) while the other windings are open - circuited. It primarily accounts for core losses (eddy current and hysteresis losses).
No - Load Current
* No - load current is the magnetizing current that establishes the main flux during transformer no - load operation. The rated no - load current is the average of the three - phase currents drawn by the transformer when a rated frequency sinusoidal voltage is applied to one winding (at the rated tap position) with the other windings open - circuited, expressed as a percentage of the rated current.
Short - Circuit Loss
* Short - circuit loss is the power consumed by a transformer when a rated frequency current flows through one of its windings while the other winding is short - circuited. It represents the copper loss (I²R loss) in the transformer windings at the rated tap position and a temperature of 70°C.
Short - Circuit Voltage
* Short - circuit voltage is the rated frequency voltage applied to one winding to produce a rated current in the other short - circuited winding (at the rated tap position), expressed as a percentage of the rated voltage. It reflects the transformer's impedance (resistance and leakage reactance) parameters and is also known as impedance voltage (at 70°C).