Reactive power compensation, referred to as reactive compensation, plays a role in improving the power factor of the power grid in the power supply system, reducing the loss of power supply transformers and transmission lines, improving power supply efficiency, and improving the power supply environment. Therefore, reactive power compensation devices are in an indispensable and very important position in the power supply system.
Reasonable selection of compensation devices can minimize network losses and improve the quality of the power grid. On the contrary, improper selection or use may cause many factors such as power supply system, voltage fluctuations, and increased harmonics. Today, the editor will introduce 13 types of reactive power compensation methods and their advantages and disadvantages.
(1) Synchronous phase regulator
Basic principle: Synchronous motors run without load, and emit inductive reactive power when overexcited; absorb inductive reactive power when underexcited;
Main advantages: It can both emit inductive reactive power and absorb inductive reactive power;
Main disadvantages: large loss, high noise, slow response speed, and complex structure maintenance;
Applicable occasions: There are still a small number of applications in power plants.
(3) On-site compensation
Basic principle: Generally, the capacitor is directly connected in parallel with the motor transformer, and the two share a switch cabinet;
Main advantages: end compensation can minimize line loss;
Main disadvantages: large number of units and large investment;
Applicable occasions: more applications in water plants and cement plants;
(3) Centralized compensation
Basic principle: Centrally installed on the system bus, generally a separate switch cabinet is set up;
Main advantages: The entire substation can be compensated, and the investment is relatively small;
Main disadvantages: generally fixed compensation, over-compensation may occur when the load is low;
Applicable occasions: suitable for systems with small load fluctuations system;
(4) Automatic compensation (mechanical switch switching capacitor)
Basic principle: Use mechanical switches (contactors, circuit breakers) to switch capacitors according to the instructions of the power factor controller;
Main advantages: Can automatically adjust reactive power output to keep the system reactive power balanced, mature technology, small footprint, low cost;
Main disadvantages: Slow response time, limited by capacitor discharge time;
Applicable occasions: Currently the mainstream compensation method, meeting the needs of most industry users;
(5) Thyristor switching capacitor
Basic principle: Use thyristor valve group to switch capacitors through zero according to the instructions of the power factor controller;
Main advantages: Fast response speed, no inrush current, no impact;
Main disadvantages: large footprint, high cost;
Applicable occasions: mostly used in places where the load changes rapidly, such as ports;
(6) Thyristor-controlled reactor
Basic principle: generally composed of a fixed parallel capacitor and a parallel reactor controlled by a thyristor in parallel, and the inductive current is changed by changing the conduction angle of the thyristor, thereby controlling the reactive output of the entire device;
Main advantages: fast response speed, stepless adjustment, can compensate for both capacitive reactive power and inductive reactive power;
Main disadvantages: large footprint, high cost, and for most corporate users, inductive reactive power is not required;
Applicable Occasions: mostly used in steel, electrified railways and power transmission and transformation systems;
(7) Magnetically controlled reactor
Basic principle: The inductor current is changed by controlling the magnitude of the excitation current and the saturation of the core through the thyristor, thereby controlling the reactive output of the entire device;
Main advantages: dynamic response, stepless regulation, bidirectional compensation, low thyristor withstand voltage, no need for multi-stage series connection, and small harmonic generation;
Main disadvantages: slightly slower response time than TCR, high noise;
Applicable occasions: has an advantage in high-voltage systems;
(8) Series compensation
Basic principle: Series capacitor groups are used to compensate for the inductance of transmission lines to improve the transmission capacity and stability of the lines. Series capacitors can also adjust the load distribution of parallel lines;
Main advantages: can effectively compensate for line voltage drop and reduce line loss;
Main disadvantages: fixed compensation, capacitive reactance cannot be changed, and may cause subsynchronous resonance;
Applicable occasions: used for transmission lines;
(9) Controllable series compensation
Basic principle: a thyristor-controlled inductor branch is connected in parallel at both ends of the series capacitor compensation, and the inductor current is changed by changing the trigger angle of the thyristor, thereby controlling the change of the equivalent impedance of the LC parallel circuit;
Main advantages: can effectively compensate for line voltage drop and reduce Line loss, and can dynamically adjust the capacitive reactance to prevent subsynchronous resonance;
Main disadvantages: large footprint, high cost;
Applicable occasions: used for transmission lines;
(10) Voltage and capacity regulation
Basic principle: connect the parallel capacitor device to the secondary side of the voltage regulator, and change the compensation capacity of the whole device by adjusting the capacitor's withstand voltage;
Main advantages: no need for grouping, no need for switching switches, and more compensation levels;
Main disadvantages: adding transformers, and setting up transformer rooms;
(11) Static VAR generator
Basic principle: using IGB The self-commutated converter composed of T provides leading and lagging reactive current for compensation through voltage power supply inversion technology;
Main advantages: fast dynamic response, stepless regulation, bidirectional compensation, no need for large-capacity capacitors, and small footprint;
Main disadvantages: difficult to control and maintain, high loss, and high cost;
Applicable occasions: reactive power compensation mode of power electronics;
(12) Active filter
Basic principle: Control the PWM converter to inject current equal to and opposite to the detected harmonic and reactive components into the power supply system to achieve Filter out harmonics and dynamically compensate for reactive power;
Main advantages: fast dynamic response, stepless regulation, bidirectional compensation, no need for large-capacity capacitors and reactance, small footprint;
Main disadvantages: difficult to control and maintain, high loss, high cost, small capacity;
Applicable occasions: already used in low-voltage railways, paper mills, and steel mills;
(13) Integrated power flow controller
Basic principle: an AC voltage generated by a thyristor converter is connected in series and superimposed on the phase voltage of the transmission line, so that its amplitude and phase angle can be continuously changed, thereby achieving accurate regulation of the active and reactive power of the line;