Harnessing Green Energy
FOUNDATION™ fieldbus: Control in the Field helps Nicaragua achieve its
aggressive renewable energy agenda.

Having been awarded the concession for a geothermal field in Nicaragua, US geothermal power specialist Ram Power andtheir design engineer POWER Engineers evaluated the available technologies and opted for a standard control system tobe located centrally in the control building. The decentralized field devices (e.g., pressure and temperature transmitters andcontrol valves) at the San Jacinto Steamfield are linked to the central controller over a FOUNDATION fieldbus (FF) Modbusover Ethernet gateway. In using this approach, Ram Power was able to exploit the advantages of FF control in the field toimplement the required control loops, thereby moving the actual control function from the control room to the field devices.
There’s a renewable energy explosion
underway in Nicaragua and for a country
with the largest dependence on oil in theregion, the lowest percentage of the population with access to electricity and thehighest energy costs in Central America,
it’s not a moment too soon.
The Cordillera de Maribios mountain range is a 70-km-long active volcano chain
lining the Pacific’s Ring of Fire. Home tothe San Jacinto Tizate geothermal project,
it is located in the Nicaraguan Depression, a major topographic and tectonic
geological phenomenon and hotbed ofgeothermal activity. Prospects are good.
In a 2012 report carried out by the Multilateral Investment Fund in collaboration
with Bloomberg New Energy Finance “Climatescope,” Nicaragua ranked second
only to Brazil in its positive geothermal
investment climate and ability to attract
investors.
In 2001, the San Jacinto Tizate geothermal concession and its estimated total
capacity of 277 MW (mean value) wasawarded to US-based Ram Power Corporation, a leader in operating clean, sustai-nable, and renewable geothermal energy
projects in the Americas. Pursuant to theterms of the San Jacinto Exploitation Agreement, Ram Power is developing theproject in two phases. Already completed,
Phase I has been in commercial operation
since January 9, 2012. Phase II is to becompleted in December 2012, bringing inan additional output of 36 net MW.
Both of the concession’s geothermal power plants were built using single-flash
condensing turbine development – themost cost-effective and efficient systemfor extracting geothermal energy. In single-flash technology, high pressure andtemperature two-phase geothermal brine(mostly water and steam) “flash” into a
low-pressure separator. The steam is sent
to the turbine to generate power and theremaining fluid is injected back into thegeothermal reservoir to be reheated.
With the large distances between the central control building and the remote steamfield installations, and need for improved
reliability and availability, Ram Power – together with its design engineer – focusedon devising a decentralized control sys-

tem to operate the power plant. The project team considered several alternatives
for the control system, such as deploying
individual controllers directly at the wells
or direct remote control from the centralcontrol system; however, these were ruledout due to cost and reliability considerations.
The design engineer installed a traditional DCS controller in a centralized roomthat would communicate over Ethernet via
Modbus/TCP. The fiber optics Ethernet
network at San Jacinto Tizate employs
gateways to connect to the power plant’s
individual wells. The gateway serves twopurposes: 1) it links the controller to thelocal FOUNDATION fieldbus segment and 2)
it acts as a FF host for the field devices located directly at the wells. For a schematicof the architecture, please see Figure 1.
After evaluating available options, theproject team selected the Softing FG-110
FF gateway to link the field devices to theFOUNDATION fieldbus technology. The Softing FG-110 FF supports data exchange
between the control system and field devices, and provides connection capabi-Figure 1:
Remote field devices are connected tothe central controller via Modbus/TCPand remote gateways.

Figure 2:
The CiF’s PID function block uses process values to calculate valve input.

lities with up to four FF H1 segments tooperate as many as 64 field devices. By
offering flexibility in mapping Modbus registers to individual FF functions, the FG110 FF facilitates FF connectivity to a wide
range of standard controllers.
The team’s decision was motivated by thesolution’s easy operation as comparedwith other available options by the parameterization support offered by its integrated website, and the fact that Softing is therecognized leader in FOUNDATION fieldbus
technology (and in fact had written the FF
stack for the motor operator valve being
used in the steamfield). The FG-110 FF
Modbus gateway and linking device use
a Windows-based FF configuration tool
to configure individual field devices anddefine necessary function block linking
and scheduling. Another advantage of
the Softing gateway is that, by processing the Modbus/TCP and FF High Speed
Ethernet (HSE) protocol simultaneously,
the control engineer can use the existing
Ethernet infrastructure to run the complete FF configuration, and conduct monitoring and diagnostic tasks from the central

control room. The final decision to employ
the FG-110 FF was also motivated by theadvantage of utilizing standard FF Device
Description (DD) files. Unlike the specially
adapted DD files used by other gateways,
the standard format makes it possible tointegrate all FF H1 field devices registered at the Fieldbus FoundationTM into theoverall solution.
Once the FG-110 FF gateway is installed, the FF functionality, including CiF,
is hooked up to a standard controller that
supports Modbus/TCP communication.
The CiF feature moves the complete controlling task to the field devices, which define the individual control loops and determine data exchange between the function
blocks. Data exchange between individual
field devices is synchronized using a common clock pulse.
The FF configuration, the FF Link Active
Scheduler (LAS) and the FF Time Masterwork together to define and execute control in the field. Supported by the individual
FF H1 field devices, the configuration tool
first determines the input/output commu-nication interface (i.e., data exchange)and defines the execution schedule forthe individual function blocks. Once theconfiguration is downloaded to the different field devices in the FF H1 segment,
communication between the field devices
is facilitated by the LAS, thereby ensuring
data exchange is compliant to previously
defined control loops. The role of the LAS
is not limited to the FG-110 FF gateway,
but can be exploited by any compatible
field device, thereby building in redundancy for the CiF function. A time master provides consistent timing information within
the FF H1 segment during runtime and,thus, synchronizes the execution of thefunction blocks.
The CiF concept offers some advantages
in comparison with traditional control approaches. For one, by synchronizing thecontrol loop execution and data exchange,
it offers enhanced deterministic controllingand shorter reaction times compared to acentral controller. Second, the supported
redundancy concept increases the availability and reliability of the control task.
And lastly, the CiF application functions

independently and is not reliant on theavailability of the controller in the central
control room or the network connection to
the various wells.
The control application used for the San
Jacinto Tizate geothermal project employs
pressure process values twice deployed
to exploit the advantages of the CiF feature; the input selector (IS) function blockensures redundancy. The resulting information is sent to the PID function block to
calculate input. A schematic overview ofthe CiF can be seen in Figure 2.
Issues identified during implementationand commissioning of the large-scale
geothermal project have been successfully resolved. Up and running, the system
proves how CiF advantages such as truly
distributed control can offer a perfect solution for remote applications such as geothermal wells. As Tom McAuliffe, the POWER Engineers’ responsible control systemengineer sums up, “After researching theavailable options, Ram Power settled on
the Softing FG-110 FF gateway product.
POWER configured and installed the FG110 FF products and commissioned themwith the help of Softing’s technical support. Softing’s technical people were very
responsive and helpful. POWER madeseveral recommendations to Softing as to
how the product could be enhanced andthese modifications have been incorporated in the next firmware version. There
are four Softing modules installed in theSan Jacinto geothermal wellfield that havebeen working reliably for the last year. IfRam Power, or POWER Engineers, wereto implement another FF Control in the
Field project, we would definitely use theSofting gateway product line again.”Author:Georg Suess, Dipl.-Inform., Softing IndustrialAutomation GmbH
http://industrial.softing.com

Figure 3:
Remote cabinets located at the individual wells house the FG-110 FF gateway.

Illustrations:
Softing, Polaris Energy Nicaragua
German article published in:
P&A, ed. 5-2013