High voltage reactive power compensation is mainly used for capacitive reactive power compensation and inductive reactive power compensation in power systems with power frequencies of 3KV, 6kV, 10kV, 35kV, and 66kV. It is used to adjust and balance the grid voltage, improve power factor, reduce line losses, enhance power quality, and fully utilize the production efficiency of power generation, supply equipment, and electrical equipment.
Centralized compensation refers to the installation of capacitor banks on the busbars of the transformer and distribution room, which are required to be compensated in one go. The characteristic is that the compensation effect is poor. Due to the fixed capacity, it cannot be accurately compensated, and can only compensate for the reactive power of the busbar and high-voltage lines. However, it requires less investment and is easy to maintain.
Structural characteristics
1. The device consists of a high-voltage switchgear (including high-voltage circuit breakers (high-voltage contactors), isolation switches, current transformers, relay protection, measurement and indication parts, etc.), series reactors, zinc oxide lightning arresters and their recorders, discharge coils, isolation switches, grounding switches, high-voltage parallel capacitors and their dedicated fuses, post insulators, connecting busbars, fences, and galvanized steel frames.
2. The outdoor type of device is generally selected as dry-type hollow core reactor, while the indoor type is generally selected as dry-type iron core reactor connected to the neutral point side or power supply side of the device, to limit the closing inrush current, suppress high-order harmonics, and improve the network voltage waveform. Selection of reactor parameters:
Suppress the inrush current during closing, with a reactance rate generally ranging from 0.5% to 1%;
Suppress more than 5 harmonics, with a reactance rate of 4.5-7%;
Suppress more than 3 harmonics, with a reactance rate of 12-14%.
3. Zinc oxide lightning arrester is connected to the capacitor bank circuit to limit the operating overvoltage caused by switching the capacitor bank.
4. The discharge coil is connected to both ends of the capacitor. When the capacitor bank is disconnected from the power supply, it can reduce the peak voltage of the residual voltage at both ends of the capacitor to 0.1 times the rated voltage or below 50V within 5 seconds.
5. Spray type fuses are connected in series with capacitors. When 50-70% of the series connected components inside the capacitor break down, the fuse will activate, quickly cutting off the faulty capacitor from the capacitor bank and effectively preventing the fault from expanding (usually, capacitors above 200Kvar are protected by internal fuses, while external fuses are used below).
6. The layout of capacitor compensation equipment (capacitors, reactors, etc.) configured according to the installation site and usage environment can be divided into outdoor frame type, indoor frame type, outdoor box type, indoor cabinet type, outdoor line compensation, outdoor collective type, and indoor collective type.
A frame structure refers to a capacitor group framework formed by connecting components of a frame (including straight beams, crossbeams, and crossbars) through a series of standard components such as bolts. It is surrounded by grid doors and is suitable for places with stable electrical equipment loads and places with poor electrical environments. The device has the characteristics of low price and convenient transportation.
The cabinet structure means that all the configured components are mounted on a frame similar to a high-voltage switchgear, and the cabinet door is made of steel plate or galvanized steel plate. The device consists of three parts: a reactor cabinet, a discharge cabinet, and a capacitor cabinet. The device has the characteristics of neat appearance and easy installation.
The fence style structure involves the installation of detachable mesh guardrails around equipment such as capacitor banks and reactors, with maintenance access left between the fence and the equipment.
The complete set of integrated capacitors mainly uses integrated capacitors, which are installed on the cabinet frame in three groups of several capacitor units, with one group for each phase. Each component inside the capacitor unit is connected with an internal fuse. When individual components break down, other intact components discharge them, causing the fuse to melt, thereby disconnecting the damaged components and ensuring that the capacitor can continue to operate.
7. For devices with voltage levels of 6KV or 10kV and below, the capacitor casing should be directly grounded during operation. When using star wiring, the neutral point should not be grounded.For devices with voltage levels of 24KV or 35kV and above, capacitors are installed on insulation platforms of the corresponding voltage levels to meet the insulation requirements of the device against enemies.
Technical Parameter
1.Compensation effect: After compensation, the power factor can reach 0.95.
2.High voltage power capacitors using advanced technology and full film dielectric have the characteristics of high reliability, long service life, low loss, low operating temperature rise, and outstanding features such as high discharge starting voltage and good sealing performance.
3. Reasonable structural design, good thermal and dynamic stability. Equipped with high-voltage live display and electromagnetic lock, observation window, with forced locking function;
4.The device can operate for a long time under a steady-state overvoltage of 1.1 times the rated voltage.
5. The device can operate continuously under overcurrent with a root mean square value not exceeding 1.3 times the rated current of the capacitor bank.
6.According to the needs of the system and users, the device can be controlled locally or in the main control room, centralized control, or automatic control.
7.The difference between the measured total capacity of the entire capacitor bank and the total rated value of each capacitor shall not exceed+10%~0, and the deviation of each phase capacitance shall not exceed 5%.
Protection method
The device uses high-voltage spray type fuses or current limiting fuses as short-circuit protection for a single capacitor to ensure safe operation of the equipment.
The device adopts open delta voltage, voltage differential, and neutral unbalanced current protection as backup protection.
The device is also equipped with external protections such as overvoltage, overcurrent, and voltage loss.
The device uses high-voltage circuit breakers without heavy impact to switch capacitor banks, and is equipped with suitable zinc oxide lightning arresters to limit the operating overvoltage generated when switching capacitor banks.