What Is The Harmonic Killer Of The Power Grid,the High-voltage Tandem Reactor?

Hidden in the power grid is an invisible group of troublemakers-harmonics. They are generated by nonlinear loads such as frequency converters, rectifiers and electric arc, mixed with high-frequency currents such as 5th, 7th and 11th harmonics, distort voltage waveforms, cause equipment to overheat and age and often lead to capacitor banks "death. High-voltage series resistors are silent traps designed specifically to eliminate these harmonics.
Where do harmonics come from and why do they have to be eliminated?
Ideally, the power grid current should be a pure 50Hz sine wave. In reality, however, many electron-electronic devices cut the current into jagged shapes, producing a large number of high-order harmonic elements. Once these harmonic currents flow into capacitor banks, the consequences are severe --the capacitor's impedance to high-frequency harmonics is extremely low, causing the harmonic current to be greatly amplified, causing the capacitor to overheat, insulation breakdown, and even resonate. More dangerously, the capacitor bank can inject harmonics into the grid, creating a "harmonic amplification effect" that degrades the quality of electricity across the region.
That's what high-voltage tandem reactors do.
Their core weapon: the "frequency game" between inductance and capacitance
However, the design of high voltage series reactor is precisely ``anti-resonance ''. By selecting an appropriate reactance rate --usually 1%, 4.5%, 5%, 6%, 12%, etc. --the resonant frequency of the series circuit can be lower than the lowest harmonic frequency (e.g. 250 Hz for 5 harmonics), which makes the circuit a high harmonic impedance and effectively blocks harmonic current. For example, when the response rate is 12%, the resonant point is about 204Hz, effectively suppressing harmonics of magnitude 5 and above. This is the most commonly used configuration to suppress the fifth harmonic.
Not only is it just a "harmonic killer," it's also a versatile device.
The suppression of harmonics is only the main task, not the only function, of the high voltage series reactor.
First, it limits gushing. When the capacitor bank is closed, the inrush current can reach dozens or even hundreds of times the rated current. Through its inductive characteristics, the series reactor reduces the peak inrush current to a controllable range and protects the capacitors and switching equipment.
Secondly, it suppresses operational overvoltages. Because of the damping effect of the reactor, Transient overvoltages produced by the switch operation is greatly reduced, and the safety margin of the equipment is greatly improved.
Third, in the field of ultra-high voltage, 220kV and above series reactors also bear the burden of limiting short-circuit current. The current limiting series reactor the Shanghai Sijing 500kV substation has a rated current of 2400A and a rated impedance of 14 Omega. The 500kV project at Brazil Brazil Tucurui hydroelectric power station further limited short-circuit currents to 40kA; the hollow dry structure weighed only 13 tons but withstood thermal stability test of 20kA/2s.
Dry core, durable;
At present, most of the CKSC and CKSG series reactors widely used in 6~35kV systems are dry core structures, stacked with high-quality cold-rolled silicon steel sheets, vacuum impregnated and hot-roasted. They have a lower operating temperature rise and low noise (≤30dB), can work longer in -25°C to +45°C environments, and have decades of maintenance-free lifespan.
So the next time you hear those frequency converters buzzing around the power grid, remember- high-voltage tandem reactors are quietly capturing every harmonic that tries to pollute the waveform, protecting the purity and safety of the entire power grid. It is unostentatious but indispensable.