Flexible actuation supports a go-ahead approach to power
Since the early 1990s, triggered by economic reforms, there has been strong growth in Peru in the GDP (gross domestic product). As a result, the basis for the introduction of a programme to improve the supply of electric energy has been provided.
With over 20percent of the population without electricity in the region, Peru’s investments into power generation and power transmission are to be doubled in the next five years: the anticipated total investment between 2007 and 2012 is US$2.35billion.
Peru relies on two energy sources. The first is water, due to the abundant availability of the resource from the Andes, and the second is gas that is produced in Peru or in neighbouring Columbia. The decision to use gas power is based on flexibility: it has a quick start-up and is therefore suitable to cover peak demands.
The country’s move to invest in gas power plants has been supported by a capping of gas prices. Significantly reduced gas prices are paid by the first gas and steam power plant at Ventanilla, which remains the only plant of its kind in Peru.
The initiative taken by Peru to adopt a combined plant philosophy is widely seen as symbolic of the political will of the region to introduce progressive technology. With gas and steam power plants, efficiency levels of 50percent can be reached and a significant contribution is made to the reduction of CO2 emissions.
The Ventanilla power plant is located north of the capital Lima. It is operated by the power supplier Edegel which is owned by the Spanish public utility company Endesa.
Initially, it was solely a gas power plant with 315MW. However, in 2006, significant developments were made with the renewal of the gas stage and addition of the steam processes. Today, the power plant generates an electric capacity of 490MW from two gas and one steam turbine. The retrofitting programme represented a capital expenditure of US$135millio.
Electric actuators
As previously mentioned, a major advantage of gas power plants is the high flexibility during start-up and shut-down procedures. For this reason, rapid controls are required to the fuel feed to the gas turbines and the steam feed. This is performed via high pressure gate valves that are controlled remotely via electric actuators.
While a gate valve is of simple design, the electric actuator required to operate it is a complex, electro-mechanical device. Despite this complexity, it is necessary for all actuators to operate reliably, since a failure can lead to serious impairment of the plant.
The basic features of an actuator are:
- Electric modification of the valve position based on an external operation command.
- Automatic tripping of the actuator as soon as a valve end position is reached, which requires a device for measuring the valve travel.
- Automatic switch-off of the actuator when the valve or the actuator is threatened by an overload which could be caused, for example, by foreign matter within the valve. For this reason, a torque measuring device needs to be located at the valve.
A robust, flexible actuation solution with minimum maintenance requirements was needed for the Ventanilla plant. A plug-in electrical connection to the actuators installed was a key feature of the actuators supplied as this facilitates rapid mounting/removal of an actuator to the valve.
The ability to commission a device without direct contact with a colleague in the control room was also important: this was achieved by integral controls which locally operate the device.
A third key selection criterion was regional support with a representative from the manufacturer’s organisation locally available to provide advice.
Michael Herbstritt is an Electronic Engineer and Technical Author working with AUMA Riester GmbH & Co KG, Muellheim, Germany. www.auma.com
