Rfid Tag,Uhf Rfid Tag,Passive Rfid Tag,Rfid Chip CIXI MEMBRANE SWITCH FACTORY , https://www.cnjunma.com
Harm and prevention of shunt capacitor over-compensation
Overcompensation in power systems can lead to several serious issues, primarily due to the excessive reactive power supplied by capacitors. One of the main hazards is the increase in network voltage, which typically occurs in transformers. To explain this, we can refer to the equivalent circuit of a transformer.
In the equivalent circuit (as shown in Figure 1), R1 and r2 represent the resistances on the primary and secondary sides, while x1 and x2 are the corresponding reactances. U1 is the primary voltage, U2 is the secondary voltage referred to the primary side, and C' represents the capacitive load. By combining the resistances (r = r1 + r2) and reactances (x = x1 + x2), the circuit can be simplified into Figure 2.
Because the load is capacitive, the current I1 leads the voltage U'2 by an angle Φ. In transformers, the reactance is significantly larger than the resistance (x >> r), so we can draw a vector diagram as shown in Figure 3. From this diagram, it is clear that U'2 is greater than U1. If U1 equals the rated voltage (Ue), then U'2 will exceed Ve, leading to an overvoltage condition.
This voltage rise poses risks not only to the transmission lines and equipment but also to the capacitor itself. According to Chinese standards for capacitor products, the maximum operating voltage is specified in Table 1. As shown, if the voltage exceeds 1.1 times the rated voltage, the capacitor must be disconnected immediately. Otherwise, it may overheat, reduce its lifespan, or even fail catastrophically.
Another consequence of overcompensation is increased active power loss. This happens in three ways:
1. **Reactive Power Reversal Loss**: When reactive power flows in the reverse direction, it causes voltage and power losses similar to forward transmission. The more reactive power is reversed, the greater the losses.
2. **Active Loss from Excess Capacitance (ΔC)**: The main source of active loss in capacitors is dielectric loss, which accounts for over 98% of the total. The formula for dielectric loss is:
ΔP = 2πfCV²tgδ
Where:
- f = power frequency (Hz)
- C = capacitance (μF)
- V = terminal voltage (kV)
- δ = dielectric loss angle
For excess capacitance, the loss becomes:
ΔP = 2πf(ΔC)V²tgδ
3. **Voltage Rise Loss**: The additional loss caused by voltage increase is proportional to the square of the voltage rise. If the voltage increases by ΔU, the added loss is:
ΔP = 2πfC(ΔU)²tgδ
In addition to these losses, overcompensation also reduces the power factor and increases the electricity burden. Power supply departments now use bidirectional reactive energy meters (DXT-M type) that record reactive power consumption regardless of the direction. The power factor (cosφ) is calculated as:
cosφ = AP / √(AP² + AQ²)
Where:
- AP = active energy (kW·h)
- AQ = reactive energy (kvar)
As AQ increases, cosφ decreases. According to the "Power Factor Adjustment Method," if the power factor falls below the standard, electricity costs will rise, resulting in higher bills.
To prevent overcompensation, several measures can be taken:
1. **Capacitor Automatic Switching Device**: This device uses electronic technology to monitor load changes and automatically switch capacitor banks on or off. It is the most effective method to avoid overcompensation.
2. **Limit Compensation Capacity and Strengthen Monitoring**: While automatic switching is ideal, it requires significant investment and is not always feasible. Therefore, during design, the compensation capacity should be limited to avoid excessive power factor improvement. Once the power factor reaches 0.9, further improvements become economically inefficient. Additionally, strict monitoring and regulation of capacitor operation are essential to ensure safe and efficient performance.
By implementing these strategies, overcompensation can be effectively controlled, ensuring stable and economical operation of the power system.