Switching Massive Power Flows in th...
Switching Massive Power Flows in the Blink of an Eye
2016-06-08 10:26:31
This news is from siemens.com
Siemens' new HB3-100 generator switchgear now holds the record for amperage manageable with vacuum switching technology. This technology is a boon to modern gas-fired power plants that are used as a flexible means of balancing out fluctuating current flows. Compared with a gas-insulated system, the total costs of ownership from purchase to disposal are up to 70 percent lower.
Vacuum circuit-breakers are much cheaper than conventional, gas-insulated variants. In power plants, these generator circuit-breakers interrupt or conduct the flow of current between the generator and the transformer, which feeds the generated electrical energy into the grid. In the event of a short circuit, the circuit-breaker must immediately cut the connection so that there is no damage to the power plant. This is accomplished by separating two metal contacts very quickly, which results in the formation of an electric arc between them. This arc must be quenched as fast as possible so that the circuit-breaker itself does not incur damage.
Safely disconnecting 100,000 amperes
Up until now, this has been accomplished with sulfur hexafluoride (SF6), a special insulating gas that is blown into the circuit-breaker. In a vacuum circuit-breaker, on the other hand, the electric arc is interrupted in a high vacuum. The technology is effectively maintenance-free and results in considerably lower lifetime costs than with the gas-insulated variant. Until now, however, vacuum circuit-breakers have not been suitable for the greatest current strengths. But thanks to the introduction of its new generator switchgear, Siemens has now succeeded in raising the limit for short-circuit currents from the previous value of 80,000 to 100,000 amperes (A). This expands the range of application of inexpensive vacuum technology to power plants with outputs of up to 400 megawatts (MW).Generator circuit-breakers provide protection from the consequences of a short circuit, and they switch so quickly that they can be used to phase-synchronously couple or decouple individual generators to or from the power grid. This functionality is used by modern gas-fired power plants with multiple turbines or blocks, for example. To compensate for fluctuating amounts of solar and wind energy, they can start up their gas turbines very quickly.
Enlarge image
Siemens' model HB3-100 switchgear is the world's first air-insulated generator switchgear with vacuum circuit-breaker technology equipped with short-circuit breaking capacity of up to 100 kiloamperes (kA) at 24 kilovolts (kV).
New contact material, optimized geometry
To increase the permissible amperages for its vacuum switching technology, Siemens engineers essentially had to solve two problems. For one thing, the electric arc that arises when a short-circuit current is broken is extremely hot. The temperatures can exceed 3,000 degrees, and there should be no damage to the electric contacts. This problem was solved with a special layout that shapes the electric arc in such a way that the heat is spread across the contacts as broadly as possible and also quickly escapes from the circuit-breaker.The second development involves the material of the electric contacts. In a vacuum circuit-breaker, the electric arc is not actively quenched with gas. Instead, it dies by itself when the alternating current oscillates to the opposite phase. Despite the vacuum, however, if any free charge carriers — i.e. ions — remain on the contact surfaces then high currents and voltages can give rise to a new electric arc after the zero point has been crossed. The new contact material is therefore a metal with very short recombination times that binds all the free ions on its surface within microseconds.The new HB3-100 generator switchgear switches short-circuit currents of up to 100,000 A and conducts operating currents of up to 12,500 A without requiring any additional cooling. Compared with a gas-insulated system, the total costs of ownership from purchase to disposal are around 25 to 70 percent lower, depending on the type of power plant involved.
Vacuum circuit-breakers are much cheaper than conventional, gas-insulated variants. In power plants, these generator circuit-breakers interrupt or conduct the flow of current between the generator and the transformer, which feeds the generated electrical energy into the grid. In the event of a short circuit, the circuit-breaker must immediately cut the connection so that there is no damage to the power plant. This is accomplished by separating two metal contacts very quickly, which results in the formation of an electric arc between them. This arc must be quenched as fast as possible so that the circuit-breaker itself does not incur damage.
Safely disconnecting 100,000 amperes
Up until now, this has been accomplished with sulfur hexafluoride (SF6), a special insulating gas that is blown into the circuit-breaker. In a vacuum circuit-breaker, on the other hand, the electric arc is interrupted in a high vacuum. The technology is effectively maintenance-free and results in considerably lower lifetime costs than with the gas-insulated variant. Until now, however, vacuum circuit-breakers have not been suitable for the greatest current strengths. But thanks to the introduction of its new generator switchgear, Siemens has now succeeded in raising the limit for short-circuit currents from the previous value of 80,000 to 100,000 amperes (A). This expands the range of application of inexpensive vacuum technology to power plants with outputs of up to 400 megawatts (MW).Generator circuit-breakers provide protection from the consequences of a short circuit, and they switch so quickly that they can be used to phase-synchronously couple or decouple individual generators to or from the power grid. This functionality is used by modern gas-fired power plants with multiple turbines or blocks, for example. To compensate for fluctuating amounts of solar and wind energy, they can start up their gas turbines very quickly.
Enlarge image
Siemens' model HB3-100 switchgear is the world's first air-insulated generator switchgear with vacuum circuit-breaker technology equipped with short-circuit breaking capacity of up to 100 kiloamperes (kA) at 24 kilovolts (kV).
New contact material, optimized geometry
To increase the permissible amperages for its vacuum switching technology, Siemens engineers essentially had to solve two problems. For one thing, the electric arc that arises when a short-circuit current is broken is extremely hot. The temperatures can exceed 3,000 degrees, and there should be no damage to the electric contacts. This problem was solved with a special layout that shapes the electric arc in such a way that the heat is spread across the contacts as broadly as possible and also quickly escapes from the circuit-breaker.The second development involves the material of the electric contacts. In a vacuum circuit-breaker, the electric arc is not actively quenched with gas. Instead, it dies by itself when the alternating current oscillates to the opposite phase. Despite the vacuum, however, if any free charge carriers — i.e. ions — remain on the contact surfaces then high currents and voltages can give rise to a new electric arc after the zero point has been crossed. The new contact material is therefore a metal with very short recombination times that binds all the free ions on its surface within microseconds.The new HB3-100 generator switchgear switches short-circuit currents of up to 100,000 A and conducts operating currents of up to 12,500 A without requiring any additional cooling. Compared with a gas-insulated system, the total costs of ownership from purchase to disposal are around 25 to 70 percent lower, depending on the type of power plant involved.
