Reactive power compensation, referred to as reactive power compensation, plays a role in improving the power factor of the power grid, reducing the losses of power supply transformers and transmission lines, improving power supply efficiency, and improving the power supply environment in the power supply system. Therefore, reactive power compensation device plays a very important role in the power supply system.
Reasonable selection of compensation devices can minimize network losses and improve power grid quality. On the contrary, if improperly selected or used, it may cause many factors such as power supply system, voltage fluctuation, harmonic increase and so on. Today, the editor will take you to understand the advantages and disadvantages of 13 reactive power compensation methods.
(1) Synchronous condenser.
Basic principle: The synchronous motor runs without load, emits inductive reactive power when over-excited, and absorbs inductive reactive power when under-excited;
Main advantages: It can both emit perceptual reactive power and absorb perceptual reactive power;
Main disadvantages: large loss, slow noise response, complex structural maintenance;
Applicable occasions: There are still a few applications in power plants.
(2) Local compensation.
Basic principle: Capacitors are generally connected directly in parallel with the motor transformer and share a switch cabinet;
Main advantages: Terminal compensation can minimize line loss;
Main disadvantages: large number of units and large investment;
Applicable occasions: widely used in water plants and cement plants;
(3) Centralized compensation.
Basic principle: Centrally installed on the system bus, usually with a separate switch cabinet;
Main advantages: The entire substation can be compensated, and the investment is relatively small;
Main disadvantages: Generally fixed compensation, compensation may occur when the load is low;
Applicable occasions: Suitable for systems with small load fluctuations;
(4) Automatic compensation (mechanical switch switching capacitor)
Basic principle: use mechanical switches (contactors, circuit breakers) to cut capacitors according to the instructions of the power factor controller;
Main advantages: It can automatically adjust the reactive power output to balance the reactive power of the system, has mature technology, small footprint and low cost;
Main disadvantages: slow response time, limited by capacitor discharge time;
Applicable occasions: The current mainstream compensation method meets the needs of most industry users;
(5) Thyristor cutting capacitor.
Basic principle: According to the instructions of the power factor controller, the thyristor valve group is used to cut the capacitor at zero crossing;
Main advantages: fast response, no surge, no impact;
Main disadvantages: large floor space and high cost;
Applicable occasions: mostly used in ports and other places where the load changes rapidly;
(6) Thyristor controlled reactor.
Basic principle: It is generally composed of a fixed parallel capacitor and a thyristor-controlled shunt reactor connected in parallel. The reactive power output of the entire device is controlled by changing the thyristor lead angle;
Main advantages: fast response speed, stepless adjustment, which can compensate for both capacitive reactive power and inductive reactive power;
Main disadvantages: large floor space and high cost. For most enterprise users, perceptual reactive power is not needed;
Applicable occasions: mostly used in steel, electrified railways and power transmission and transformation systems;
(7) Magnetic reactor.
Basic principle: Control the reactive power output of the entire device by controlling the size of the excitation current and the saturation of the iron core through the thyristor;
Main advantages: dynamic response, stepless adjustment, two-way compensation, low thyristor voltage resistance, no multi-stage series connection, and small harmonics;
Main disadvantages: response time is slower than TCR and noisy;
Applicable occasions: Advantages of high-voltage systems;
(8) Series compensation.
Basic principle: Series capacitor banks are used to compensate for the inductance of transmission lines to improve transmission capacity and stability. Series capacitors can also adjust the load distribution of parallel lines;
Main advantages: It can effectively compensate for line voltage drop and reduce line losses;
Main disadvantages: fixed compensation, capacitive reactance cannot be changed, which may cause subsynchronous resonance;
Applicable occasions: transmission lines;
(9) Controllable series compensation.
Basic principle: Connect the thyristor-controlled inductor branch in parallel to both ends of the series capacitor compensation, and change the inductor current by changing the firing angle of the thyristor, thereby controlling the change in the equivalent impedance of the LC parallel circuit;
Main advantages: It can effectively compensate for line voltage drop, reduce line losses, and can dynamically adjust to prevent subsynchronous resonance;
Main disadvantages: large floor space and high cost;
Applicable occasions: transmission lines;
(10) Voltage and volume adjustment.
Basic principle: Connect the parallel capacitor device to the secondary side of the voltage regulator, and change the compensation capacity of the entire device by adjusting the withstand voltage of the capacitor;
Main advantages: no need for grouping, no need for cutting switches, more compensation levels;
Main disadvantages: adding a transformer and setting up a transformer room;
(11)Static var generator.
Basic principle: The self-commutated converter composed of IGBT provides advanced and lagging reactive current for compensation through voltage power inversion technology;
Main advantages: fast dynamic response, stepless adjustment, two-way compensation, no large-capacity capacitive reactance, and small footprint;
Main disadvantages: difficult to control and maintain, large losses and high costs;
Applicable occasions: Power electronics reactive power compensation mode;
(12) Active filter.
Basic principle: control the PWM converter to inject current in the opposite direction into the power supply system to achieve harmonic filtering and dynamic compensation;
Main advantages: fast dynamic response, stepless adjustment, two-way compensation, no large-capacity capacitive reactance, and small footprint;
Main disadvantages: difficult control and maintenance, large loss, high cost, small capacity;
Applicable occasions: Low-voltage railways, paper mills, and steel mills have been used;
(13) Integrated power flow controller.
Basic principle: The AC voltage generated by the series thyristor converter is superimposed on the phase voltage of the transmission line, causing the amplitude value and phase angle to continuously change, achieving accurate adjustment of the active and reactive power of the line;
Note: Still in the physical model research stage.