Is it necessary to shut down some capacitors when there is overcompensation in reactive power compensation?

In industrial and commercial power distribution systems, reactive power compensation is a crucial measure for improving power factor, reducing line losses, and avoiding fines from power supply authorities. However, over-compensation, as a common abnormal condition, not only fails to bring benefits but also causes a series of hazards to the power grid and equipment. When the monitoring system detects that the power factor shows a negative value or leads, as well as an abnormal increase in voltage, an urgent question arises before us: Is it necessary to immediately shut down some capacitors?

I. The Hazards of Overcompensation: Why Must They Be Addressed?

1. System voltage increase: Capacitors supply capacitive reactive power to the power grid, which can cause the bus voltage to rise. If the voltage exceeds the rated value of the equipment, it will shorten the lifespan of lighting fixtures, motor insulation, and electronic equipment, and even lead to overvoltage damage to the equipment.

2. Increase line loss: Over-compensation also leads to an increase in current, thereby increasing the copper loss (I²R) of the lines and transformers. This is contrary to the energy-saving goal of reactive power compensation.

3. Triggering resonance risk: In systems with harmonic pollution, over-compensated capacitors may form a parallel resonance with the grid inductance, amplifying harmonic currents and voltages, resulting in excessive harmonics, misoperation of protection devices, overcurrent and overheating of the capacitors themselves, and even explosion.

4. Impact on power grid equipment: The elevated voltage poses a threat to all equipment connected to the power grid, including transformers and cables.

II. Handling Strategy: Is it necessary to shut down some of the capacitors?

1. For the manual switching compensation cabinets

Operation: Immediately arrange for an electrician to manually disconnect the switching devices (contactors or circuit breakers) of some of the capacitors, thereby reducing the number of capacitors connected in parallel to the power grid.

Subsequently: The reactive power demand of the load needs to be re-evaluated, and the number of capacitor banks to be installed under different load conditions should be reasonably planned. Strict operating procedures should also be formulated.

2. For dynamic compensation devices (such as SVG/SVC)

Such devices usually do not experience over-compensation because they can smoothly adjust the reactive power from capacitive to inductive in a continuous manner. If any abnormalities occur, one should immediately check whether there is a fault in the equipment itself or if the parameter settings are incorrect, and then contact the equipment supplier for troubleshooting.

When the reactive power compensation system experiences over-compensation, immediately shutting down some of the capacitors is an essential and urgent operation to prevent damage to the power grid and equipment caused by high voltage and resonance. However, in the long run, it is necessary to identify the root cause of the over-compensation - whether it is a controller failure, improper parameter settings, or an unreasonable system configuration, and then carry out repairs and optimizations accordingly to ensure the safe, efficient, and stable operation of the reactive power compensation system.