As a core reactive power compensation device in power systems, 10kV capacitor banks need to operate in synergy with series reactors to suppress inrush currents during switching and filter harmonics. However, in practical operation, core-burning failures in reactors supporting capacitor banks are common. Such failures not only cause the shutdown of capacitor banks but also may trigger cascading issues like such as grid voltage fluctuations and equipment damage. Based on real accident cases, this article deeply analyzes the core causes of reactor core burning, proposes targeted preventive measures centered on the coordinated operation of capacitor banks and reactors, and provides references for power enterprises to ensure equipment safety.
I. Capacitor Banks and Series Reactors: Core Value of Coordinated Operation
10kV capacitor banks, as mainstream reactive power compensation devices, mainly function to inject capacitive reactive power into the power grid, improve power factor, and stabilize bus voltage. However, capacitors generate massive inrush currents during switching (without reactor suppression, the inrush current peak can reach dozens of times the rated current), which may damage equipment such as fuses and capacitor bodies.
The connection of series reactors effectively solves this problem: the inductive characteristics of reactors limit the inrush current of capacitors during switching (usually controlling the peak to within 5 times the rated current) and filter high-order harmonics in the power grid to prevent capacitors from overheating due to harmonic overload. The matched operation of the two is the foundation for ensuring the safe and efficient operation of the reactive power compensation system—reactor parameters must be accurately adapted to the capacity of capacitor banks; otherwise, problems such as core overheating and insulation aging may occur.
II. Accident Review: The Whole Story of Core Burning in Reactors Supporting 10kV Capacitor Banks
A series reactor supporting a 10kV capacitor bank in a substation suddenly emitted smoke and a burning smell during operation. After the power shutdown, inspections revealed that the insulation cylinder and epoxy resin of the Phase B reactor core had melted and decomposed due to high temperatures, the anti-noise paint had peeled off, and a large amount of wood chips and dust had accumulated on the surface of the core column. An overcurrent protection activation occurred two days before the accident, and further tests confirmed the root cause of the failure:
1. Key Test Data Reveal Core Problems
Temperature rise tests on the faulty reactor showed an abnormal surge in the temperature of the Phase B core:
- The temperature of Phase B was 21.7~23.6℃ before the test and rose to 118.1~120.3℃ after 2 hours, with a temperature rise of 96.4~96.7℃;
- The temperature rise of Phase A and Phase C was only 14.9~20.4℃, but anatomical inspections found that their insulation materials had also cracked and aged.
Further testing confirmed that the Phase B core caused insulation material combustion due to high temperatures, and the heat affected Phase A and Phase C through thermal conduction. However, the capacity matching between the capacitor bank and the reactor was normal, and there were no abnormalities in system harmonics, ruling out these two common causes.
2. Root Cause Identification: Air Gap Short Circuit Caused by Loose Silicon Steel Sheets
Reactor cores adopt a laminated structure of silicon steel sheets. The insulating coating of silicon steel sheets can increase the resistance of eddy current loops and reduce eddy current losses (eddy currents are the main cause of core heating). The core cause of this accident was:
- During the production, transportation, or installation of the reactor, some silicon steel sheets in the Phase B core were improperly bound, loose, or misaligned, leading to the failure of air gaps between iron disks and causing air gap short circuits;
- Air gap short circuits sharply increased eddy current losses, and the core temperature continued to rise, exceeding the tolerance threshold of insulation materials (usually 105℃), eventually causing insulation decomposition and combustion;
- The continuous power supply from the capacitor bank caused the reactor core to accumulate heat continuously, eventually leading to the burning of the Phase B core and damaging the insulation of Phase A and Phase C through thermal conduction.
III. Three Core Causes of Reactor Core Burning in Capacitor Bank Support Systems
Combined with case analysis and industry experience, the causes of reactor core burning in capacitor bank support systems all revolve around the "destruction of basic conditions for coordinated operation of capacitors and reactors" and can be categorized into three types:
1. Production and Installation Defects: Damaged Core Structural Integrity
Improper lamination and binding of silicon steel sheets are the primary causes. If silicon steel sheets are loose, misaligned, or the clamping parts are not firmly fixed, the air gap structure of the core magnetic circuit will be damaged, increasing eddy current losses. In addition, insufficient cutting accuracy of silicon steel sheets, damaged insulation coatings during production, or core deformation caused by severe vibrations during transportation will lay hidden dangers for subsequent overheating. These defects will gradually emerge during the long-term operation of capacitor banks and eventually lead to core burning.
2. Inadequate Maintenance: Blocked Heat Dissipation Channels and Debris Accumulation
The wood chips and dust accumulated on the reactor surface in the case not only affected surface heat dissipation but also blocked the heat dissipation air ducts, preventing the heat generated by the core from being discharged promptly. Capacitor banks and reactors are usually installed outdoors in substations or in distribution rooms; if not cleaned for a long time, dust, oil stains, and debris will accumulate on the core surface and coil gaps, reducing heat dissipation efficiency and causing continuous heat accumulation to exceed temperature limits.
3. Abnormal Parameter Matching and Operating Conditions (Secondary but Critical)
Although this factor was ruled out in the case, vigilance is still required in practical operation:
- Mismatched capacities between reactors and capacitor banks (e.g., improper selection of reactor reactance rate) can cause resonance in the series circuit, increasing core losses;
- When power grid harmonics exceed standards, capacitor banks are prone to forming harmonic amplification circuits with reactors, increasing the current distortion rate of reactors and eddy current losses of the core;
- Frequent switching of capacitor banks (e.g., multiple starts and stops within a short period during peak load periods) causes repeated magnetization of the reactor core, intensifying heating.
IV. Safe Operation of Capacitor Banks: Comprehensive Measures to Prevent Reactor Core Burning
In response to the above causes, a systematic prevention plan should be formulated around the entire life cycle of "production-installation-operation-maintenance" of capacitor banks and reactors:
1. Strictly Control Production and Installation Quality to Lay a Solid Safety Foundation
- Production Stage: Strengthen the quality control of cutting, lamination, and binding processes for reactor core silicon steel sheets to ensure neat arrangement of silicon steel sheets, intact insulation coatings, and firm clamping of parts; conduct temperature rise tests and DC resistance tests before delivery to ensure balanced three-phase parameters (DC resistance difference ≤ 2%).
- Transportation and Installation: Choose flat routes for transportation, implement anti-vibration measures to avoid core deformation; lift and place with care during on-site installation, construct strictly in accordance with design drawings, prohibit impact and collision, and conduct a comprehensive inspection of fasteners after installation to ensure no looseness.
- Matching Verification: Verify the parameters of reactors and capacitor banks before installation to ensure that the reactance rate and rated current are compatible with the capacitor capacity (e.g., 6% reactance rate reactors are commonly used in 10kV capacitor banks to suppress 5th harmonics).
2. Strengthen Daily Maintenance to Ensure Heat Dissipation and Cleanliness
- Regular Cleaning: Conduct monthly inspections to clean dust, wood chips, oil stains, and other debris from the reactor surface, core column, and heat dissipation air ducts to ensure unobstructed heat dissipation; increase the frequency of cleaning during peak load periods.
- Temperature Monitoring: Install temperature sensors at key parts of the reactor core to monitor temperature changes in real time and set a high-temperature alarm threshold (recommended ≤ 85℃); use infrared thermometers to regularly detect three-phase temperatures and shut down the equipment for inspection immediately if the temperature difference exceeds 10℃.
- Condition Assessment: Combine the operation records of capacitor banks to inspect the insulation status and coil integrity of reactors every six months, and check for hidden dangers such as insulation cracking and coil strand breakage.
3. Optimize Operating Conditions to Reduce Abnormal Losses
- Harmonic Management: Measure the harmonic components of the substation regularly; if 3rd, 5th, and other harmonics exceed standards, add dedicated filtering devices to prevent capacitor-reactor circuits from amplifying harmonics.
- Standardize Switching Operations: The dispatching department should reasonably arrange the operation mode of capacitor banks, avoid frequent switching during sudden weather changes or severe load fluctuations, and reduce additional losses caused by repeated magnetization of the reactor core.
- Emergency Handling: If overcurrent protection is activated, the reactor temperature rises abnormally, or abnormal odors occur, immediately cut off the capacitor bank, troubleshoot the fault, and then resume operation to prevent fault expansion.
V. Conclusion: Coordinated Operation of Capacitor Banks and Reactors, Safety as the Core Premise
The safe operation of 10kV capacitor banks is inseparable from the reliable cooperation of reactors. The prevention of core burning failures requires efforts in three aspects: "parameter matching, quality control, and maintenance monitoring" to ensure the coordinated balance of capacitors and reactors. Only by implementing safety measures throughout the entire life cycle can the shutdown of capacitor banks and power grid losses caused by failures be avoided, and the effectiveness of the reactive power compensation system can be truly exerted.
If your power system operates 10kV capacitor banks, please feel free to provide the capacitor capacity, reactor parameters, and operation years. Hengrong Electric CO., LTD. will customize an exclusive condition assessment and maintenance plan for you to help capacitor banks and reactors operate stably for a long time!