Angola Dadi Energy Storage 35 kV Power Quality Improvement Solution

Equipment thermal protection

• Transformer protection: after harmonics are filtered out, skin and eddy-current losses in the transformer drop significantly and temperature rise returns to normal. In accordance with the IEC 60076-7 thermal aging model, insulation aging is effectively slowed down.
• Capacitor protection: preventing harmonic current from flowing directly through the capacitors avoids dielectric breakdown or swelling caused by overcurrent and overvoltage.

Intelligent switching and control

• A low-restrike (restrike-free) vacuum circuit breaker with controlled (point-on-wave) closing keeps the closing inrush current within 1.5 times the rated capacitor bank current (see Section 3.3).
• The monitoring system collects grid data in real time and automatically switches filter branches according to the reactive power deficit, achieving "on-demand compensation".

Bidirectional operation adaptability

Because the harmonic signature of the energy storage PCS differs between charging and discharging, the filter branches are designed based on the harmonic spectrum measured across the full PCS operating range (charge/discharge), with switching margin reserved so that harmonics are effectively suppressed in both directions of operation.

Resonance verification

After the filter compensation bank is commissioned, the capacitive branches and the 35 kV system may form parallel resonance points. At the design stage, resonance must be verified using the on-site measured background harmonics and system impedance as inputs, and the equipment may be energized only after confirming that the resonance points avoid the characteristic harmonic frequencies such as the 5th and 7th.

3.3 Capacitor Bank Switching Safety — Point-on-Wave Closing and Low Restrike

Given the frequent switching of capacitor banks caused by frequent regulation of the energy storage plant, a two-fold protection mechanism is adopted:

• Low-restrike vacuum switchgear: CuCr alloy contacts and an axial magnetic field (AMF) vacuum interrupter ensure that no restrike occurs when breaking capacitive current, effectively suppressing switching overvoltages.
• Intelligent point-on-wave closing controller (optional/recommended): tracks the grid voltage phase in real time and closes the contacts precisely at the voltage zero crossing (within ±1 ms). This keeps the closing inrush current within 1.5 times the rated capacitor bank current (compared with 10–20 times for random closing), greatly extending capacitor and switch life and preventing voltage shocks to the PCS.

4. Features and Advantages

• Highly targeted: H5+H7 parameters are customized to the PCS load characteristics, avoiding "over-treatment" or "under-treatment".
• Strong environmental adaptability (for Angolan conditions): considering the local climate, all reactors use Class H insulation, capacitor enclosures use UV-resistant, corrosion-resistant materials, and control system PCBs receive an extra-thick conformal coating — suited to hot, humid environments.
• Integrated design: harmonic mitigation, reactive compensation and equipment protection are addressed together — one investment, multiple benefits.
• Reliable operation: a complete package with low-restrike switchgear and comprehensive protection, suited to the frequent regulation duty of energy storage plants.

5. Expected Results and Benefits

5.1 Technical Benefits

• Improved waveforms: after commissioning, the 5th and 7th harmonic current filtering rate is expected to exceed 85%, with voltage distortion meeting GB/T 14549-1993 and the project technical specification.
• Interference eliminated: mal-operation rates of protection and monitoring systems drop significantly and the station operating environment is purified.
• Grid stability: system impedance characteristics are optimized, substantially enhancing immunity to interference.

5.2 Economic and Social Benefits

After commissioning, the key power quality indicators are expected to improve as follows (consistent with the Section 2.3 targets; subject to acceptance measurement):

Note: the "after" figures above are expected values derived from equipment performance and system evaluation. Final values are subject to commissioning acceptance measurements.

6. Project Implementation and O&M Support

6.1 Implementation Process

1. On-site survey: measure background harmonics on the 35 kV busbar and load characteristics (including PCS charge/discharge conditions).
2. Simulation: build a system model to verify filtering performance and resonance points.
3. Manufacturing: factory prefabrication with strict routine tests (withstand voltage, partial discharge, protection commissioning).
4. Installation & commissioning: on-site installation, secondary wiring, integrated system testing.
5. Acceptance & commissioning: load test, verification of targets, handover.

6.2 After-Sales Service

• Technical training: principles, operation and troubleshooting training for the owner.
• Periodic inspection: regular checks of capacitor capacitance, reactor temperature and connection point tightness.
• Emergency response: 7×24 technical support for rapid fault response.

Conclusion

Through the scientific configuration of a 7500 kvar H5+H7 filter compensation bank, this solution not only resolves the current power quality pain points of the Dadi Energy Storage project in Angola, but also builds a solid electrical safety defense line for the plant.

By addressing equipment protection and system stability alongside harmonic mitigation, it delivers both economic and safety benefits — a reliable power quality improvement solution for energy storage plants.