Latest News

Overhauling the Snowy Scheme

Upgrading the legacy control and information system of Australia’s Snowy Mountains Hydroelectric Scheme presents challenges on many fronts, writes Rockwell Automation’s Corrie Van Rensburg.

Located in Australia’s Southern Alps, the Snowy Mountains Hydroelectric Scheme was built between 1949 and 1974 to realise two vital goals: to provide water for irrigation and electricity from hydroelectric generation.

The waters of the Snowy and Eucumbene Rivers are diverted to the rich farming areas of the Murray-Darling Basin, and pass en-route through the Scheme’s two pumping stations and seven hydroelectric power stations.

The power stations have a combined capacity of 3756MW and provide the Australian national grid with around 4500GWh of ‘clean’ hydro electricity per annum — providing a key source of rapid-response and peak electricity for eastern Australia. Representing 74 per cent of mainland Australia’s renewable energy, the Scheme is set to grow in importance.

The huge challenge of overhauling the Scheme was taken up in 2005 by its owners and operators — Snowy Hydro — with the Scheme Modernisation Project. This seven-year, $250 million upgrade is the Scheme’s first major overhaul. The project comprises the installation of new high-efficiency turbine ‘runners’; refurbishment of the turbine water passages, pumps, main valves and generator stator windings; plus the replacement of the control, protection and governor systems, HV circuit breakers and generator excitation systems.

The project engineering group of leading industrial automation solutions provider, Rockwell Automation, was selected to upgrade the control systems aspect of the Scheme Modernisation Project. Leveraging Rockwell Automation’s Integrated Architecture strategy — with the Allen-Bradley ControlLogix programmable automation controller (PAC) at its heart — the project engineering group joined with the Snowy Hydro team to tackle the controls overhaul.

Information is empowerment

The controls and information systems in each Snowy power station support a multiplicity of ancillary systems associated with the 31generator/turbine assemblies (known as ‘units’) and two pumping units. These are typically the systems supporting the units’ cooling water, lube oil and hydraulic oil, bearing and winding temperatures, and diagnostics. The aim of the project was therefore to replace the legacy 1960/1970 hardwired relay logic control, basic mechanical gauging and switch-style condition monitoring with state-of-the art PAC and electronic operator interface (EOI) technologies.

According to Darryl Eager, Snowy Hydro’s manager controls technology, the controls upgrade was essential in terms of maintaining reliability. In addition, collecting real-time operational information was an important goal. “The scheme was originally built with a healthy level of conservatism in its design,” he says. “By collecting as much operational information as possible, we can safely gain access to extra capacity, and leverage it to our operational advantage.”

An example was the runner upgrade. Model testing demonstrated that an additional 20 per cent power output could be achieved by upgrading the runners. This additional output capacity requires close condition monitoring of key major electrical plant, such as thermal monitoring of transformer busbar connections, partial discharge monitoring within the generator stator windings, and monitoring of dissolved hydrogen and water in the transformer’s insulating oil. Rockwell Automation’s control system collects these parameters to provide a ‘heart-beat’ indication of the electrical plant’s health, if and when a generator needs to be pushed into the ‘plus 20 per cent’ operational margin.

Sold on ControlLogix

Snowy Hydro has an existing installed base of Rockwell Automation controllers, including the ControlLogix platform, which was introduced in 2003 at Tumut 1 (T1) station to replace the existing turbine electro-mechanical governors. Convinced of the power and stability of the ControlLogix platform, the company once again considered it for the Scheme Modernisation Project.

First, however, Eager and his team toured a number of power stations in the US, New Zealand and Australia to investigate similar hydro-upgrades. “Every one of them had used ControlLogix — there is a fairly large installed base in the power industry using this platform,” he says.

But the clincher, according to Eager, was the platform’s unrivalled connectivity to a wide range of communications protocols — most notably the Distributed Network Protocol (DNP3), which is used to relay essential operation information to Snowy’s SCADA system at the Snowy Mountains Control Centre (SMCC) in Cooma, NSW. “ControlLogix could offer a DNP3 solution that worked with our SCADA system, whereas the other controllers really couldn’t,” he says.

“Being able to ‘speak DNP3’ with the SCADA system was certainly an essential element of this project,” confirms Carl Prowse, Rockwell Automation’s technical project manager. “It was also essential that our Integrated Architecture solution seamlessly interfaced with other systems and protocols used, such as Modbus for the protection and excitation systems.”

Targeting 33

The hard work began in 2005, when the first of the 33 unit control upgrades commenced. A ‘standard’ unit control architecture was developed, featuring two ControlLogix processors (one for the unit’s governor and the second for the remainder of the turbine/generator), plus a third for the transformer associated with each pair of generators. It also included a PanelView Plus 1500 EOI for local control and monitoring, and an Allen-Bradley Powermonitor 3000 power quality and sub-metering monitor to oversee critical generator power parameters.

DeviceNet communications link the controller to generator floor devices, including Allen-Bradley E3 Plus intelligent motor protection, and Allen-Bradley XM series temperature modules. The latter provide connectivity and monitoring of the unit’s resistance temperature devices and support the unit protection and control systems.

Dual-redundant ControlNet peer-to-peer communications links the controller to remote I/O chassis, PanelView Plus EOI and Powermonitor 3000, while EtherNet/IP facilitates controller monitoring and maintenance, together with unit-to-transformer and unit-to-unit communications. The MVI56 DNP interface module from Rockwell Automation Encompass Partner, Prosoft, enables DNP3 connectivity with the Scheme’s SCADA system and protection relays.

The Rockwell Automation project engineering group site team analysed and fine-tuned each and every element of the proposed design. Every single circuit had to be looked at, considered, refined and proven.

Redundancy vs ‘run-on’ mode

While reliability was the primary objective, Eager and his team are great proponents of the ‘unitisation’ principle — where each unit is operationally independent of the other. It was ultimately resolved that redundancy is inherent in the multiplicity of units in each station, where each unit acts as a ‘spare’ for the others. “There is a huge amount of redundancy in hydro-generation. This drove us down the path of avoiding the complexities of control system redundancy,” says Eager.

The importance of keeping a unit running in the event of a fault was also highlighted. “In the electrical industry we always strive to keep producing, while it is safe to do so,” explains Warren Heard, Snowy Hydro’s operations coordinator at Cooma. “This is unique to this industry; we don’t store or stockpile our ‘product’ — we have to instantaneously generate exactly what is demanded.”

The importance of ‘keeping the unit running’ inspired a project design strategy — ‘Run-on mode’ — conceptualised by Rockwell Automation. “Rockwell Automation determined precisely what components needed to be kept operational to keep the generating unit running,” Heard says. “And this ‘run on’ was achieved through an elegant design.”

The application of ‘run-on mode’ is demonstrated in the use of the Allen-Bradley E3 Plus intelligent motor protection with DeviceLogix. The starter circuits have each been designed so that the onboard I/O and logic configured within the E3 Plus intelligent protection relay can do all that is required, from a ‘run-on mode’ perspective, in the event of a DeviceNet communications or main controller failure.

“The DeviceLogix in the E3 Plus ensures that we can tolerate all sorts of failures, and still allow the unit as a whole to continue operating for a period long enough to start another unit,” says Prowse. “People are often surprised when we open the motor starters on site and they see how little is actually in there. This was our goal — to simplify the design as far as possible.”

Integrated Architecture advantages

While ControlLogix was a key attraction, Eager notes that the Integrated Architecture approach has brought many benefits. “Everything is driven by the same Rockwell Automation software tools — it all has the same look-and-feel. This really helps our guys in learning and maintaining the systems,” he says. “It also provides Snowy with access to the latest technologies.”

A case-in-point is Snowy’s recent deployment of Rockwell Automation FactoryTalk AssetCentre — a powerful software tool for monitoring and maintaining automation assets. “Every day here in Cooma, I interrogate more than 40 PACs across the scheme, then get an email if anything has changed,” says Eager. “Having compatible control platforms across the Scheme makes this possible.”

Throughout 2009, the project has been progressing well. “There’s been an understanding by Rockwell Automation from the very beginning that this is going to be the same upgrade 33 times,” says Eager. “Effectively, what Rockwell Automation has done is automate the automation!”

A mid-2008 independent study of the control system reliability for the first two completed units demonstrated very positive outcomes. The upgraded units are approaching ‘five nines’ control reliability, with measurable improvements in reliability, availability and forced outage rates.

“Reliability has always been our main goal, and we have clearly achieved it,” says Eager. According to Eager, Snowy Hydro now has around ten times the amount of real-time operational data coming back to the SMCC in Cooma, which paves the way for future improvements. Importantly, a model that will see the controls upgrade element of the Scheme Modernisation Project successfully completed through to 2012 is now well established.

[Corrie Van Rensburg is the industry solutions manager for Rockwell Automation.]

Send this to a friend