Siemens Live Tank Circuit Breaker seismically isolated with ITT Wire Rope Dampers. System is installed at a Siemens HVDC Project in New Zealand.

A year and half ago ITT Corporation’s ITT Control Technologies released that their company is partnering with the Power Transmission Division of Siemens AG to engineer new seismic damping and isolation systems. They utilize ITT’s Enidine brand technologies to help protect high voltage transmission substations from earthquakes and other Earth vibration. This co-operation was planned to secure the availability of electricity in seismic areas around world.

Dr. Christos Kotanidis, senior expert of the Seismic Engineering Team of Siemens AG Power Transmission Division gives a brief explanation of the technology.

– HVDC (High Voltage Direct Current) transmission systems connect two separate high voltage AC Systems via a DC link.The basic principle of operation of an HVDC system is based on the conversion of AC to DC and vice-versa by means of converter valves comprising power thyristors, which are the heart of a converter station.

– Today, electric power is normally transmitted as alternating current as this is the easiest and most economical solution when power is consumed near the location it is generated. With the idea of increasing the use of renewable energy like wind or solar power, system development strategies go clearly in the direction of hybrid transmissions, consisting of integrated AC/DC interconnections and point-to-point bulk power transmission “highways” (DC backbones).

– The most economical solution for long-distance bulk power transmission, due to lower losses, is transmission with HVDC. Typically, DC line losses are 30–40 percent less than with AC lines, at the same voltage levels for long-distance cable transmission as well as to connect two independent AC systems with incompatible electrical parameters DC is the optimal solution, technically and economically.

Main HVDC (High Voltage Direct Current) components are:

• Power Transformers
• Filter Reactors
• Converters  (Thyristor Valves)
• Voltage Transformers
• Circuit Breakers
• Disconnect Switches
• Current Transformers
• Capacitor Banks
• Surge Arresters

Isolation from ground

Detail of base plate with wire rope isolators.

– ITT Control Technologies has worked decades on finding a solution for the damping and isolation challenges related to vibration and noise absorption around the globe, tells Managing Director Peter Bauer from ITT Control Technologies EMEA GmbH. They offer a whole range of isolation and absorption technologies e.g. Industrial Shock Absorbers.

Peter Bauer is the Managing Director of ITT Control Technologies EMEA GmbH.

The seismic damping and isolation systems include an interconnected and finely-tuned set of viscous dampers and wire rope isolators to isolate the high-voltage components’ base from shock and vibration coming from the earth. The new seismic damping and isolation systems created by ITT and Siemens can be customized for each project, anywhere in the world where seismic activity is of concern. The partners’ work focuses on eliminating, or greatly reducing the motion that travels from the earth through the base supporting the high-voltage components and, ultimately, to the components themselves.

– We’re able to customize, recommend and fine-tune these systems because we have experience with preventing the structural failure of power plant turbines as well as bridges, high-rise buildings and stadiums. Due to modern modelling we are also able to simulate the behaviour of engineered products, confirms Peter Bauer.

Industrial Shock Absorbers include:

• Heavy Duty Shock Absorbers
• Heavy Industry Buffers
• Wire Rope Isolators
• Compact Wire Rope Isolators
• Air Springs
• Custom Elastomers
• WEAR® Pipe Restraints
• Seismic Dampers
• Filter Resistors

Simulation and testing

The converter transformer can weigh from 350 to 500 tons. Because of differing heights each component creates varying centres of gravity for each base and its seismic damping and isolation system to support.

– Thanks to our close cooperation with ITT, we have managed to develop advanced finite element models of the high voltage equipment including base isolation in order to accurately simulate their complex combined seismic response, says Dr. Christos Kotanidis.

Dr. Christos Kotanidis is a senior expert of the Seismic Engineering Team of Siemens AG Power Transmission Division.

– Modern equipment specifications for seismic (based on standards IEEE693 and IEC 62271) require that HVDC equipment should be tested under expected seismic motion. Tested equipment including its supporting structure is mounted on a so-called “shake-table”, a slab that can be accelerated along three orthogonal axes, thus simulating the motion of the ground during an earthquake.

– HVDC equipment is very expensive. Before reaching the shake-table, where the equipment is tested to withstand a severe earthquake event, detailed simulation of its expected performance during the shake-table test is conducted using finite element software and advanced analytical techniques.

– Possible weaknesses of the equipment and its supporting structure are identified and rectified before the equipment is shake-table tested, in order to ensure that the test will be successful. So it will ensure that the equipment will remain unharmed and functional during and after the severe earthquake event and the test will not have to be repeated using a new expensive test specimen.

Standard IEEE693 specifies how to qualify electrical equipment for substations. Inside the IEEE693 are different working groups with experts from the utilities, equipment suppliers, solution providers, shake-table laboratories and for seismic simulation. Both ITT Control Technologies and Siemens are involved in the working group for Base Isolation Systems. Siemens is also involved among others in the working group for DC equipment. The new version of IEEE693 is expected for 2015.

The qualification tests for smaller components include several phases, explains Dr. Christos Kotanidis.

– Equipment including its supporting structure, assuming their size allows for testing, is mounted on the shake-table and a series of tests is conducted. There are resonant frequency search tests for determining the dynamic characteristics of the undamaged structure (Eigen-frequencies along orthogonal directions and damping) to be used for calibration of the analytical model and as reference values for the rest of the seismic tests.

– Time history triaxial test in which the equipment is subjected to acceleration histories along the three orthogonal directions, thus simulating the expected earthquake event, an earthquake that takes place only once in 2500 years or has a 2 percent probability to happen in the following 50 years.

– Parallel to Time History tests, functionality tests are conducted, during which the equipment’s ability to function properly during the earthquake is checked.

– Sine beat test in which a sinusoidal beat motion consisting of a sinusoid of the equipment’s resonant frequencies modulated by a lower frequency sinusoid is applied on the tested equipment and its supporting structure.

– Resonant frequency search test at the end of the tests in order to determine if the dynamic properties of the tested equipment have remained unchanged or within acceptable limits, implying that no damage has happened to the equipment and its supporting structure.

For global markets

The importance of electricity is the driver to invest in a more reliable power grid. California has been the first U.S. state requesting seismic damping and isolation for high voltage substations.

– Siemens is now offering High Voltage Direct Current (HVDC) and Flexible AC Transmission Systems (FACTS) solutions to utility companies all around the world. For projects located in earthquake-prone areas, Siemens offers solutions and products that meet international and local seismic requirements and add redundancy on existing power grids. Markets combining rapid financial growth with relatively high seismic risks are South America, Pacific Coast of North America, India, China, New Zealand and the eastern Mediterranean.

New Zealand is a good example. Most of the power generated in the country is provided by hydroelectric power plants situated on the South Island, whereas the highest power demand is on the North Island, mainly in the region of Auckland. Therefore, large amounts of electric power have to be transmitted over long distances via a reliable link in an efficient way.
The distance from production area to the main demand region is 1000 km and the transfer capacity is over 1000 MW. DC voltage levels are up to 350 kV.

According to Dr. Christos Kotanidis, there is an increasing market demand.

– The demand for power in the modern metropolises is constantly increasing. In parallel, advanced societies are heading towards cleaner, renewable power sources like wind power. In addition to that, there is an increasing demand for minimizing the financial and social impact of an electrical outage due to damages in power transmission infrastructure as a result of a severe earthquake.

– HVDC and FACTS systems enable the cost-effective transmission of electrical power from remote sources to the energy-hungry megacities and increase the stability of the existing power grids. n

For more information, visit:
http://itt-infrastructure.com/Assistance/