Namibia Power Corporation (Pty) Ltd (NamPower) uses RuggedCom Switches and Routers for State-of-the-Art IEC 61850 Substation Protection, Automation and Control Systems
Objective
Provide a reliable and highly flexible networking infrastructure to implement the IEC 61850 standard for NamPower’s strategic Substation Protection, Automation and Control (PAC) Systems.
Solution
Redundant topology based on a backbone ring with redundant mesh utilizing RuggedSwitch® RSG2100 and RuggedRouter® RX1100 makes it possible to cater for the critical nature of the underlying network infrastructure requirements of IEC 61850 for a flexible system design to ensure a secure, fast and solid networking solution.
Company Overview
NamPower is the national power utility in Namibia with a transmission network that spans the entire country (approximately half the size of the state of Alaska). Namibia is a country rich in natural resources and NamPower has recently invested in strengthening its transmission network by building a 980 km 300 MW -350 kV HVDC interconnecting link to directly connect potential suppliers in the north with the Namibian grid. The HVDC line links the 400kV AC system at Gerus Substation in central Namibia with the 330kV AC system at Zambezi Substation in the Caprivi Strip. The link would then make it possible for Namibia to import electricity from countries like Zambia, Zimbabwe and Angola. Electricity exports would also be possible.
NamPower’s vision for substation PAC solutions hinges on the well-defined and internationally accepted substation automation standard, namely IEC 61850. The IEC 61850 compliant PAC system specifications for these projects were developed jointly by NamPower and their consulting partner, Trans-Africa Projects. The underlying networking infrastructure designs were developed by Trans-Africa Projects using industry best-practice design philosophies. The substation compliant PAC systems were integrated by Consolidated Power Projects using primarily Schweitzer Engineering Laboratories’ Intelligent Electronic Devices (IEDs) and RuggedCom networking equipment which is supplied and supported in Southern Africa by H3iSquared.
Customer Requirements
The requirements of the substation automation network equipment had to comply with industry standards. These requirements are specified in the IEC 61850-3 standard which describes the environmental conditions that the equipment is expected to operate under. The ratings the equipment is expected to meet or exceed in terms of temperature, humidity, EMI radiation and immunity are specified. Furthermore, factors that would increase the network’s reliability in terms of MTBF and MTTR were considered essential. As such, equipment with dual power supplies, self-monitoring capabilities and extended warranties were given preference.
With regards to availability, it is ssential that a substation automation network is always available, secure and dependable for the purpose of protection tripping, interlocking, automation of operating procedures and other necessary functions. The network was expected to meet design principles that applies a minimum of n-1 redundancy capabilities. From a performance perspective the network is expected to meet and if possible exceed the performance of a hard-wired system. High speed Generic Object-Oriented Substation Event (GOOSE) messaging as defined in the IEC 61850 standard needs to be available under all operating conditions. The architecture of the network was to provide for flexibility, availability and scalability thereby allowing for future growth and modification without impact to system operations. The substation network is expected to provide for various shared services including substation automation, Voice over IP telephony, video surveillance, substation control and data acquisition (SCADA), and access control and security. Network design in terms of suitable traffic engineering principles was required in order to ensure all performance criteria were met for all the planned services.
Application and Implementation
The design of the network architecture for the NamPower substations PAC systems comprises a switched Ethernet topology that uses a main Gigabit backbone ring with a fiber optic 100Mbit mesh connecting protection bays in a redundant manner as shown on Figure 3. The design was selected because of its performance characteristics and inherently enhanced redundancy options. The design is also scalable and allows for extension without impacting system operation or otherwise compromising its redundancy. A redundant IED device connection to the network was not a requirement for the project, because this aspect is not conclusively addressed in the first edition of the IEC 61850 standard. In addition, various redundancy methods being standardized within IEC 61850 vary significantly in the IED and network architecture requirements. For this project, only the bus zone IEDs were connected redundantly to two separate backbone switches.
A major design requirement of the network was to allow for flexibility when applying future technologies to the substation network without impacting the real-time performance requirements of the network. In order to facilitate this requirement, extensive use was made of VLANs (Virtual Local-Area Networks) and priority tagging for time-critical GOOSE messaging. This design approach allows for the incorporation of enabling technologies, such as VoIP (Internet Protocol telephony), to use the same network infrastructure without impacting the performance of the protection and control functionality.
The concern that network congestion can cause delays in the delivery of GOOSE messages was addressed by fully leveraging Ethernet’s prioritization scheme (as defined in IEEE 802.1p) and a traffic isolation mechanism by means of VLANs (as defined by IEEE 802.1Q). Filtering of GOOSE messages at the bay level switches using VLAN tags embedded within the Ethernet frame of the GOOSE message was applied. Unique destination multicast addresses and carefully designed VLAN filtering are considered essential on large networks.
A highly reliable, meshed network design using industry standard redundancy features is very effective in addressing overall system availability. Many utilities apply a redundancy philosophy that can also be extended to the substationswitched Ethernet network. This project made use of redundant backbone switches with redundant connections from the bay switches to the backbone switches. The bus zone IEDs used redundant connections in two separate backbone switches. Should the highly unlikely catastrophic condition arise where the substation network is rendered unavailable, the protection will still operate, because all instrument transformer inputs and trip coil outputs are wired directly to the protection IEDs.
RuggedRouter® RX1100 substation routers with enabled Virtual Router Redundancy Protocol (VRRP) were used to ensure redundant connection to the Wide Area Network and thus each substation to be connected to NamPower’s information backbone and the National Control Center. Future design considerations for the substation LAN include changing to the Multiple Spanning Tree Protocol (MSTP) standard thereby allowing better load balancing across VLANs. The network design also lends itself to migration to the IEC 62439 Parallel Redundancy Protocol (PRP) which is being considered as a high availability redundancy solution.
RuggedCom’s reliable and cutting-edge communications technology for the substation environment helped NamPower install an efficient, robust and cost-effective solution for modern IEC 61850 compliant PAC systems for high voltage installations.
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