More stability for Arizona’s power grid

Especially robust reactors with tank rupture resistant design are helping keep the grid stable in Arizona.. When it comes to stabilizing its power grid, Arizona Public Service Company relys on a shunt reactor as one of its solutions for grid voltage control. 

Grid efficiency for a million homes

Arizona Public Service Company (APS) is the largest energy provider in the U.S. state of Arizona. With a generation capacity of 4,000 megawatts (MW), APS reliably supplies 1.2 million consumers with electricity. The energy provider will now additionally stabilize its grid, with a reactor for optimally compensating reactive power. 

Especially robust reactor

APS opted for a 525 kilovolt (kV) three phase reactor with a reactive power of 170 MVAr. It is installed in a steel tank with oil cooling. The tank has a particularly robust design to minimize damage even in the rare event of an uncontrollable internal arc.


An internal arc is a very rare phenomenon. However, sometimes due to a sudden overload caused by lighting, it is unavoidable. As a result, the internal pressure could increase due to the formation of a gas bubble. As a consequence, the rising pressure could deform the shunt reactor tank. If pressure continues to increase, eventually the tank may break (tank rupture). There is then the risk that the leaking hot insulation fluid in combination with atmospheric oxygen could ignite and start a fire.

With the aid of our reactors, we’re making an important contribution to stabilize the grid while the tank rupture resistant design ensures a high level of safety.
Dr. Beatrix Natter, CEO of Siemens Transmission Products

Maximum safety for people, nature, and technology

The reactor from Siemens is different. It can withstand an internal failure of 20 megajoule (MJ) arc energy. This corresponds to the energy of 2.6 kg of dynamite or 5.3 kg of TNT. If a catastrophic fault causes a tank to rupture, the tank breaks right at the highest possible point, thanks to preventive measures and appropriate material selection. This minimizes the escape of combustible insulation fluid and thus prevents the risk posed to people, nature, and technology. 


“Our innovative company always strives for the best and most advanced technology to increase the reliability of our system. Thanks to Siemens’ reactors with tank rupture resistant design we can now provide a more robust and reliable reactor as well as an even safer working environment for our employees”, comments Jim Zhang, senior apparatus engineer at Arizona Public Service Company.  


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