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Functions of Capacitors
In power systems, loads simultaneously possess active power (effective power) and reactive power (invalid power). The transmission of reactive power requires higher voltage, increases power loss in transmission lines, and elevates the total current (the total current squared equals the effective current squared plus the reactive current squared).
Benefits of Parallel Capacitors
In power systems, capacitor banks or parallel capacitors can supply leading reactive power to counteract the lagging reactive power generated by loads (such as motors), thereby improving the power factor of the load. The fundamental benefits of parallel capacitors include reducing the current in the main circuit, improving the voltage at the load side, reducing line losses, and increasing the power supply capacity of the system.
Different Installation Locations and Benefits of Capacitors
The closer the capacitors are to the load devices, the better. Ideally, each load should have its own appropriately sized parallel power capacitor. This approach helps reduce power losses across the entire power system, including high and low voltage lines, transformers, etc., while allowing the equipment to operate with sufficient margin. However, this method tends to involve higher installation costs.
Selection Principles for High-Voltage or Low-Voltage Capacitors for Power Factor Correction in Industrial Power Systems
Both low-voltage and high-voltage capacitors can improve power factor (PF), reduce electricity costs, and ease the load on equipment. Low-voltage capacitors also help reduce line losses between the power supply and the load side.
Harmonic Countermeasures for Power Capacitor Equipment
Among these methods, option 1 is often impractical due to the limitations of the existing power supply system. Option 2 improves tolerance to harmonics but increases cost and is therefore less economical. Option 4 can prevent insulation breakdown and equipment damage, but frequent disconnection of the power capacitors renders them ineffective, defeating their intended purpose.
Resonance and Resonance Frequency
Calculation formula of resonance point and resonance frequency of capacitor in series with reactor
Application, principle and instructions of phase-advancing capacitor
If a capacitor is disconnected while in use and not fully discharged before being switched on again, abnormal high voltage may result. Therefore, avoid re-energizing within 5 minutes after disconnection (within 3 minutes for low-voltage systems). For automatic power factor regulators (APFRs), automatic reconnection should be avoided within 1 minute for low-voltage systems.
Causes of capacitor failure
The capacitor has potential defects. If an abnormal situation occurs in the early stage of power supply, it will accelerate deterioration and cause failure.
Effects of Lightning Strike on Capacitors
In power distribution systems, power capacitors are commonly installed to improve the power factor of inductive loads. Since most loads are inductive in nature, they exhibit high impedance to abnormal voltages and harmonic voltages. In contrast, capacitors exhibit low capacitive reactance to such voltages.
Proper Capacitor Wiring for Y-Δ (Star-Delta) Start Induction Motors [5]
When power factor correction capacitors are used to improve the power factor of an induction motor with Y-Δ (star-delta) starting, incorrect wiring can lead to capacitor damage. Therefore, it is essential to follow the correct wiring method as shown in Figure 1
Precautions for Capacitor Installation
For high-voltage current-limiting fuses , the rated current should be selected at 1.65 to 2.5 times the rated current of the capacitor.
For low-voltage protection , high-interrupting capacity fuse-links or circuit breakers should have a rated current of at least 1.35 times the capacitor’s rated current.
Reference for selection of low voltage capacitor protection equipment
I: Capacitor rated current N: Number of capacitor segments
Maintenance of capacitors
For Safe Operation, Perform the Following Maintenance Inspections
Calculation of improved power factor
Normally, the power factor cosθ is known, and the tangent value (tanθ) of the angle θ can be found in the table below.
Common calculation formulas for general power factor
k=1000,W=Watts,Eff= Motor efficiency,V=Volts,A=Amperes,hp=Horse Power,PF=Power Factor,I=Wire Current(A)...
Capacitors for induction heating furnaces
Formula: Tanδ=P/Q, P=70 x q x Δθ,P: actual work, unit watt; Q: capacitor capacity, unit var...
