Analysis of an incident on a capacitor bank, reactive compensationand harmonic study

The customer would like to understand causes of the fault observed on a 15kV capacitor bank (shutdown of the bank). Also, he required a study of reactive compensation to avoid additional costs from its supplier.

The study was conducted in four main parts:

• Harmonic measures on the main 15kV switchboards have been executed to estimate harmonics in the electrical network where overheating could be induced in the capacitor banks.
• Incident analysis on the fault capacitor bank has been performed from the electrical network modeling on the ETAP software to estimate harmonic impedance on switchboards. This is to demonstrate, in the conditions on the day of failure, the possible harmonic resonances that increase the values of currents in the capacitor and then the overheating.
• Reactive compensation study has been performed from the electrical bill of the supplier or a representative annual power budget. Then two main axes of study were covered: the hardware (fixed or regulated banks) and location in the plant (top of the network or near the consumers). Finally, criteria were defined to choose a suitable solution to customer’s electrical system: scalability, complexity, integration capability and the cost to calculate the depreciation of the device.
• Harmonic analysis has been conducted to evaluate risks associated with harmonic resonance. The examination of measurements has to justify any filtering device has been installed. However, some resonances require the insertion of anti-harmonic reactor to protect the capacitor banks.

This study is used to analyze and justify the observed incident and to validate the principles of reactive power compensation, from harmonic measurements made on site and harmonic resonances calculated.