Luz del Sur S.A.A. is one of the largest distribution system operators (DSOs) in Peru, supplying almost 1.2 million customers with electricity in the area southeast of the capital, Lima. This gives it a national market share of almost one-third. The company is currently expanding its 220-kV network. The expansion of the 220-kV high-voltage substation at SET Los Sauces, which was commissioned in February 2020, is part of this large project.
SET Los Sauces substation
The SET Los Sauces 220/10-kV substation is equipped with 2 to 50 MVA transformers, gas-insulated switchgear (GIS) at both voltage levels and eight outgoing 10-kV feeders. The 220-kV double busbars were expanded to accommodate two additional 220-kV underground cables, 3 km (1.86 miles) in length, installed from the existing 220-kV SET Industriales substation, constructed and commissioned by Siemens with GIS technology in 2014.
One of the specific aims associated with the SET Los Sauces substation was to develop and implement an advanced protection and automation concept. This comprised the associated protection and control technology with line differential, distance, transformer differential, overcurrent time and busbar protection, a station automation system with human machine interface (HMI), a link to the control center, as well as a centralized fault recorder.
The engineering decision-makers at Luz del Sur emphasized the need for the system to be viable in the future and for it to have the ability to keep pace with the ongoing digitalization of electricity distribution. At the same time, the system had to be designed in a way that was systematic and efficient, without compromising on safety. Overall, the system had to satisfy these main design features:
- All components were to be as compact as possible.
- The installation should have minimal space requirements.
- Minimal planning and delivery times to ensure that the substation could be commissioned as soon as possible.
The reduction in the time taken to commission the protection and control systems coupled with the optimization in the civil design adds to the fact that investing in these systems with the latest technology is key for any company opting for this solution.
The selected process bus-based solution
Luz del Sur S.A.A. selected the overall concept developed by Siemens in accordance with the engineering, procurement, and commissioning (EPC) contract, which met all the specified requirements using state-of-the-art technology. The implemented solution uses International Electro-Technical Commission (IEC) 61850 for the whole system, including a process bus for the 220-kV section. The purpose was to ensure digitalization as close to the process as possible for the interface between the primary system and secondary technology.
Figure 1. The process bus technology in substations digitalizes the information at the process level and communicates via fiber optic cables to the protection and station control system.
Instead of conventional 1:1 cabling between the transducer and the protection device, equipment known as a merging unit records the measured values from the transducer, converts them into digital format, and sends them to the respective protection units via a fiber-optic ethernet cable. The merging unit is a modular, interoperable, and powerful solution between primary and secondary technology that offers multifaceted process data recording, self-sustaining automation, and secure communication. 13 SIPROTEC 6MU85 merging units are used in this latest installation in SET Los Sauces substation, which is one of the first to use this technology on a large scale.
Control functionality is implemented in the protection units, which allows additional savings to be made as independent station control units are not required. The 220-kV circuit breakers, disconnectors, and ground connections are controlled by the protection equipment via the process bus that uses IEC 61850 Generic Object Orientated Substation Event (GOOSE) via the merging units. The circuit breaker’s time-critical protective tripping function is also implemented via the merging unit. In the process, the SIPROTEC 5 merging unit can access modular functionalities from the SIPROTEC 5 kit. Luz del Sur uses this and supplements the two merging units in each bay by adding an on-site control display and the control function. It is also possible to enable backup protection systems in the merging unit.
The process bus ensures that a second communication network is available alongside the station bus. The full potential of digital technologies can be exploited up to the process level. This ensures that data can be assigned more flexibly and analyzed more extensively. For instance, it is also possible to incorporate the process level into control systems. The process and station bus are physically separate to meet the necessary cybersecurity and operational requirements. The protection technology, sampled measured value system and networks have also been designed to be redundant, which is commonplace in the high-voltage range.
Figure 2. Energy automation diagram shows above the secondary technology on substation control level while below the process level with the merging units in the line, coupler and transformer feeder is shown.
Further significant benefits
In addition to the general options that a digitalized process level offers, there are also other significant benefits on offer with a process bus, which tipped the scales in its favor in regard to the SET Los Sauces project. For example:
- Protection and control cabinets save on space and there is no requirement for expensive copper cabling.
- Protection equipment is smaller and a conventional process connection is not required.
- Fully digitalized secondary technology ensures that extensive engineering and testing is the main focus, resulting in faster commissioning for the whole system.
- Ethernet cable is inserted and the installation is complete without the need to waste time testing individual copper connections.
In addition, transferring data using fiber-optics is generally less prone to faults and requires lower maintenance. This also applies to electromagnetic compatibility (EMC), which plays a crucial role in a substation. The costs involved in installation, maintenance, and operation are, therefore, lower as a result.
The benefits linked to using a process bus are not limited as there are also benefits in terms of personal and system protection. It is much easier to safeguard from the outset compared with live copper line installations. The risk of open transducer circuits is also significantly reduced.
Special requirements
Siemens was also able to solve some special requirements at SET Los Sauces by using process bus technology in an intelligent way: the time for all equipment in the network and the measured values is synchronized by a Grand Master Clock. In accordance with IEC 1588v2 Precision Time Protocol (PTP), the maximum time discrepancy is less than a microsecond. The measured values are transmitted at 4.8 kHz for protection applications and at 15.36 kHz for the full recorder in accordance with IEC 61869-9 and IEC 61850-9-2 standards.
Virtual Local Area Networks (VLANs) have another special feature in accordance with the IEEE 802.1Q standard. VLANs, such as these, make it possible to virtually divide a network’s physical infrastructure. Each bay with a protection unit and the associated merging unit forms its own logical segment in a physical process bus network. An own virtual network is implemented, which is separate from other data traffic, even for the busbar protection system with the associated merging units that are bay units at the same time. VLANs also allow you to reliably meet the stringent safety and performance standards required.
The incoming overhead line feeders are protected by a SIPROTEC 7SL87 line differential protection system. This line differential protection system compares the process bus-based sample measured value system in SET Los Sauces with the conventional sampled measured value system in the existing SET Industriales substation at the other end of the transmission line. The Siemens solution supports this hybrid system to ensure that the existing protection units can continue to be used, thereby eliminating the need to carry out any expensive remedial work on the outstation.
Figure 3. The line differential protection on both line ends communicate with each other via protection interface and fiber-optic cable, whereas the relay in Los Sauces operates with sampled measured values and the remote device receives conventional analog transducer values.
Partnership with Siemens
Luz del Sur’s perspective reasons were not just limited to the impressive overall concept developed by Siemens, there were other reasons for its decision. The manufacturer was able to provide all the required functionalities on a consistent basis with equipment from the SIPROTEC 5 product range.
The result is a standardized solution with components that are in perfect harmony with one another. SIPROTEC 5 also has a powerful engineering tool up its sleeve, namely, the DIGSI 5 planning software, which enabled Siemens to complete the planning in a very short period of time. Luz del Sur also greatly appreciated the on-site support from the local Siemens experts in Peru, during and even after the new substation was commissioned.
The experiences obtained by Luz del Sur in this technology supports the position that future protection and control projects in Luz del Sur will be implemented based on the IEC61850-9-2 standard because it allows the utility to be efficient in compliance with all the company’s objectives. At the same time, the company facilities are in position to adopt all the future technological developments that the energy market needs for its sustainability.
Retrofitting the process bus-based solution
Process bus is a solution that offers numerous benefits for retrofitting projects as grid operators are able to replace the existing and commission the protection, automation, and control systems without risk and in minimum time. The benefits can be summarized as follows:
- Improved interchange of information via communication with the protection and automation schemes as the complete data is available on the process network that all devices can access and process during commissioning.
- Reduction in cabling activities in installation, connections, and testing.
- Reduction in commissioning time, offering financial benefits in terms of logistics. For example, health and safety executive (HSE) site supervision, container rental, and so forth.
- Following commissioning, grid operators are able to secure improved data transparency from the process level thanks to digitization close to the current and voltage transformers.
Figure 4. The merging unit is a modular, interoperable, and powerful solution between primary and secondary technology, which offers multifaceted process data recording, self-sustaining automation, and secure communication. In total, 13 Siprotec 6MU85 merging units are used in this latest installation in Los Sauces substation in Peru.
The solution that has now been put in place in SET Los Sauces substation will now be the standard for all future high-voltage substations in Luz del Sur and a further order has already been approved.
This all-in-one solution from Siemens ensures that the Peruvian DSO Luz del Sur’s new high-voltage substation in SET Los Sauces sets the benchmark for future-proof design. The system is one of the first installations of its kind to be designed in its entirety using process bus technology. Crucially, this means that the industry’s stringent safety and operational requirements can be met in a more cost-efficient, compact, and simple way.
