Australia Leads With Process Bus

Powerlink Queensland has undertaken an aggressive program of research, development and implementation of IEC 61850-based system solutions. The intent is to move towards an IEC 61850 process bus using a two-step approach.

Powerlink is a government-owned corporation that owns, develops, operates and maintains the state of Queensland's high-voltage electricity transmission system for approximately half of Australia's eastern seaboard. The utility's internal engineering group develops in-house standard designs for substation automation systems (SAS) based on commercially available products from global suppliers. Project-specific designs based on the standard designs are implemented by the in-house engineering group as well as external contractors.

The Two-Step Approach

Powerlink's first step in moving towards an IEC 61850 process bus is the development and implementation of a new multi-vendor SAS standard design based on IEC 61850 station bus by 2012. The second step includes the implementation of technology facilitated by an IEC 61850-9-2 multi-vendor process bus, such as nonconventional instrument transformers (NCITs) and smart switchgear with electronic interfaces. The optimum time for the second step depends on the ongoing development of international standards and the availability of products compliant with those standards.

Powerlink is undertaking several projects trialing the implementation of IEC 61850-9-2 process bus to investigate this technology and the current maturity of the market. Projects include the refurbishment of the Loganlea SAS and the trial of a fiber-optic current transformer (FOCT) on a 275-kV line reactor bay at Powerlink's 330/275-kV Braemar Substation.

These two projects, coupled with Powerlink's participation in university research projects and the international working group developing the IEC 61850 standard, will allow Powerlink to establish a valuable understanding of the technology developments and further refine the technology road map for implementation of IEC 61850 process bus.

The first substation will be the 275/110-kV Loganlea Substation project, which employs NCITs communicating with the protection system through a switched Ethernet network using an IEC 61850-9-2 sampled value (SV) process bus. This is the world's first commercial installation of a substation protection system outside of China based entirely on IEC 61850-9-2 SV process bus communication.

In 1999, Powerlink introduced ABB's iPASS (intelligent plug and switch system) hybrid outdoor gas-insulated switchgear (GIS) with a series of turnkey projects. Four of the turnkey projects were part of the 275/330-kV Queensland-New South Wales Interconnector (QNI) and two further substation upgrades that used iPASS.

The QNI substations are the backbone of the essential interregional interconnection. With a design life of 15 years for SAS, Powerlink is planning to refurbish six substations.

The existing iPASS switchgear is based on a single-phase unit, with each unit containing a circuit breaker, isolator and earth switch, and a NCIT at each bushing. Separate electronic modules, built into the primary switchgear, are used for the control and supervision of the switchgear (circuit breakers and disconnector/earth switches) and for the acquisition of current and voltage samples derived from the NCITs. The electronic modules are an integral part of the SAS. The interface of the iPASS switchgear with the bay-level equipment uses a proprietary fiber-optic point-to-point process connection.

Refit Kit

With the approaching end of design life for the SAS, Powerlink and ABB jointly developed a generic retrofit product that can be progressively applied to all six iPASS substations.

With the kit, the circuit breaker and disconnector/earth switch control are replaced with a conventional hard-wired solution. A new electronic module for the existing NCITs is included as part of the iPASS refit kit, providing a SV process bus interface based on the UCAlug implementation guideline for IEC 61850-9-2, also termed the 9-2 light edition (9-2LE).

The refit kit has been tested and proven in a field trial conducted on a 275-kV line reactor bay at Powerlink's Braemar Substation. The 275/110-kV Loganlea Substation was the first site for the refurbishment solution.

One of the main components of ABB's NCIT solution for iPASS includes a CP (current/potential) transformer combination, electronic current and voltage sensor (single-phase unit), which is designed for use in GIS products. The CP is a modular design and has two fully redundant measuring systems. The existing primary sensor, which is built into the GIS enclosure, is retained. This unit contains two Rogowski coils for current measurement and a gas capacitive divider for voltage measurement.

A redundant set of secondary converters (CP-SC) samples the current and voltage transducer outputs and then sends these to the IEC 61850-9-2 merging unit for protection (CP-MUP). Transmission of the signal is through one of two fiber-optic data outputs. Both outputs can be used for protection applications or, alternatively, one output can be used for revenue metering. The point-to-point data link between CP-SC and CP-MUP is a proprietary ABB solution. The CP-SC is mounted on the primary equipment, and the CP-MUP is installed in the substation control room.

The CP-MUP synchronizes the current and voltage samples received from the various secondary converters. The port mapping of the built-in Ethernet switch is configurable, allowing the user to direct the SV data streams produced by the internal MU logical devices to specific Ethernet ports on the switch.

The CP-MUP port-mapping feature also allows the user to receive a SV data stream from another MU device on one Ethernet port and direct that data to any of the intelligent electronic devices (IEDs) connected to the other CP-MUP Ethernet ports. This functionality overcomes limitations associated with an IED with only one physical Ethernet port for a SV process bus where it requires SV data streams from multiple physical MU devices.

Substation Automation System Architecture

The application of SV according to 9-2LE results in two mission-critical networks: a process bus Ethernet-based local area network (LAN) and a 1-pulse per second (1PPS) time synchronization network.

The protection and control IEDs support 9-2LE on one physical Ethernet port, leaving a second Ethernet port for the station-level communication according to IEC 61850-8-1 (generic object-oriented substation event [GOOSE] and manufacturing message specification). The IEDs also feature one 1PPS input to synchronize sampling of conventional current transformer inputs and SV data streams for the purposes of differential protection.

The majority of Powerlink's iPASS installations have the switchgear laid out as a breaker-and-a-half diameter. The configuration of the switchgear (including the number of NCITs — six per diameter) will not change as a result of the refurbishment and installation of a new SAS. The original design philosophy for fully overlapping protection zones using all NCITs in each diameter will continue with the new SAS. The number and location of NCITs were already determined by the location of the switchgear; the issue to be addressed was the number of MUs per diameter and their connection to both the NCITs and the protection and control IEDs.

To address the requirements of Australia's national electricity rules, the protection system is duplicated. All MUs are configured as time masters, supplying the connected IEDs with the 1PPS signal. There is no constraint or dependence between the MU clocks as these operate as time islands. The MU connections for this layout use the second output signal (PPL2) from both CP-SCs on the Q30 coupler breaker.

The protection IED for feeder 1 in the Loganlea Substation requires the summation of two separate current NCITs to determine the total current flowing on the feeder. The substation configuration allows the summation to take place in the protection IED by receiving the two currents from a single CP-MUP, removing the requirement to synchronize with any other CP-MUP. The same also is true for the protection IED for feeder 2.

The bay control functions for the Q10, Q20 and Q30 bay control IEDs are each derived from a single CP-MUP and, therefore, are independent of the time-synchronization system used by the other CP-MUPs. CP fail and bus zone protection are performed in ABB's REB500 system, with each bay unit connected to a different CP-MUP.

The station bus architecture for Powerlink's iPASS SAS refurbishment is a single-ring LAN topology. GOOSE has been used for the auto-reclosing function that resides in the bay controller. Both the main 1 and main 2 protection can initiate auto-reclosing through the station bus LAN with GOOSE messages.

The main 1 and main 2 duplicate protection systems installed are to remain physically and electrically separated at all times to satisfy the redundancy requirements of the national electricity rules. The process and station-level networks are physically separate 100-Mb/sec LANs. The process-level network is only being used for the transmission and distribution of SV data, and each bay has its own process bus LAN. Communications gateways and human-machine interface have a dual attachment to the two station Ethernet switches for improved availability. The GPS clock provides time synchronization for the time-stamp accuracy of events through the station-level network.

Handling the Transition

Powerlink has developed considerable knowledge on the existing iPASS substations since their introduction in 1999. The knowledge continues to grow now that the technology is being used with the implementation of the new SAS solution.

The new IEC 61850-based solution offers a more integrated system. The sending and receiving of protection, control commands and indications, and monitoring information over the same equipment or network will need to drive changes to existing work practices and procedures. The identification of a protection or control IED's boundaries will not be possible in the same manner that it has been to date.

The personnel working with the SAS will need a combined knowledge and understanding of protection and control equipment, systems and philosophies, as well as data networking skills. There is a change in skills, knowledge and requirements for designers and field staff alike. Powerlink was intimately involved in the design process for the Loganlea solution. From this experience, it is apparent a centralized approach to the IEC 61850 system design and configuration (including network addressing and data flows), where all SAS design information is drawn together at a systems level, will be required for the successful delivery of IEC 61850-based systems.

From a utility perspective, this requires the review and redevelopment of roles, reallocation of responsibilities within the design groups and associated skills development. Change management to existing roles within the automation and protection areas is where the most effort and benefit will be gained to ensure the process is a success.

It also is likely some of the maintenance activities that currently require attendance on-site for existing systems may be undertaken remotely in the future. In addition to the higher skill and aptitude requirements of the field staff responsible for the operation and maintenance of substations, there will be a need to maintain and develop a support group consisting of highly skilled subject matter experts because of the complexity and level of integration of the IEC 61850-based systems.

Some of Powerlink's key design and field test staff were involved in the delivery of the Loganlea project to ensure the utility had a detailed understanding of the technology and the solution satisfied all of Powerlink's requirements. The Loganlea system successfully passed its factory acceptance test in Switzerland and was commissioned in 2011. The experience Powerlink gained from this project will greatly assist it in the future development of a standard design for an IEC 61850 process bus solution.

Looking Forward

SAS products have a typical operating life of 15 to 20 years, but the primary plant is expected to operate for 40 to 60 years. This presents an opportunity to implement SV process buses in existing substations with conventional instrument transformers, a manner similar to Powerlink's refurbishment of Loganlea. An Ethernet-based process bus provides well-documented safety and engineering benefits, but, to realize these benefits, the merging units generally need to be mounted at the primary plant. With the ABB iPASS refit kit, the CP-MUP merging units can be installed in the control room because of the legacy fiber-optic process connection. Installation of merging units in the field with a switched process bus further reduces field cabling, as Ethernet switches can aggregate the SV data from several merging units.

Merging units for conventional instrument transformers take industry-standard current (1-A/5-A) and voltage (100-V/110-V) inputs. NCIT merging units are a little different in that digital connections from NCIT secondary converters (CP-SC in this project) to merging units are proprietary. It is the role of the merging unit to convert measurement data into the format specified by IEC 61850-9-2.

Point-to-point (un-switched Ethernet) IEC 61850-9-2 systems, available from several vendors, may be a way of gradually moving to a station-wide process bus, as this topology is similar to existing analog systems. Different network architectures also offer design diversity, so a point-point system could be used in parallel with a whole-of-substation switched Ethernet process bus.

Future Challenges

Many manufacturers have implemented 9-2LE, but only two merging units, including the CP-MUP from ABB, have received certificates from UCAIug for Part 9-2 of IEC 61850 at this time. Powerlink's investigations have shown that many SV implementations comply with 9-2LE; however, there have also been products that do not implement the standard correctly. This prevents interoperability, suggesting that products need to mature further. Vendors need to be testing their SV publishers and subscribers with products from their competitors.

Vendor diversity is widely practiced in Australia, with the only exception being for certain turnkey substation contracts. The diversity of the make and model of IEDs and merging units is intended to mitigate the risk of common mode failures, but the complexity of IEC 61850 systems works against this for two reasons:

Many IEC 61850 vendors use commercially available stacks to implement their products, so there is a chance X and Y protection IEDs are based on the same software.
In-house implementations will take considerable effort to perfect. Errors in 9-2LE encoding of data from both large and small vendors confirm this is the case.

Powerlink is looking to implement a SV process bus but is constrained by the lack of commercially available products, particularly for merging units. Western protection manufacturers have yet to bring a merging unit for the connection of conventional instrument transformers and switched Ethernet to market, while Asian manufacturers have sufficient home market demand so there is little promotion of their products in Australia.

Single-vendor IEC 61850-9-2 process bus products are available that use a proprietary, yet documented, dataset. These systems may have application in parallel with conventional process connections, but multi-vendor support is needed for a whole-of-substation implementation.

A major impediment to the widespread introduction of 9-2LE process buses is the very limited availability of SV subscribing revenue meters, phasor measurement units (PMUs) and transducers. Powerlink is building many new substations to satisfy customer growth or new power station connections. Both of these require revenue metering and cannot be achieved with a digital process bus at this time. Wide-area measurement systems using PMUs located throughout the country may miss out on critical data unless PMUs that can use SV data are developed. A major benefit of a switched Ethernet process bus is that a single device can perform the PMU function for all feeders, and a single Ethernet connection is all that is required.

Pascal Schaub ([email protected]) holds a bachelor's degree in computer science from the Technical University in Brugg-Windisch, Switzerland, and is the principal consultant of power system automation for Powerlink Queensland. Prior to joining Powerlink, he worked for ABB in Switzerland. Schaub is a member of the Standards Australia Working Group EL-050 ‘Power System Control and Communications’ and the International Working Group IEC/TC57 WG10 ‘Power System IED Communication and Associated Data Models.’

Anthony Kenwrick ([email protected]) holds a bachelor's degree in computer and electrical engineering from the Queensland University of Technology and is a secondary systems support engineer at Powerlink Queensland. He has worked in several different positions on secondary system design, construction, commissioning and testing. Kenwrick is a registered professional engineer of Queensland.

David M.E. Ingram ([email protected]) holds a bachelor's and master's degree in electrical and electronic engineering from the University of Canterbury and is a Ph.D. candidate at the Queensland University of Technology. He has worked for several utilities including Powerlink before commencing his current study. Ingram is a senior member of the IEEE, a chartered professional engineer and a registered professional engineer of Queensland.