1. Voltages and substation schemes of Transmission network
- Nominal voltages to be used in transmission networks are 330 kV and 110 kV. Another nominal voltage levels are permitted on interconnections between power systems of different countries. Networks with above mentioned nominal voltage levels will provide forecasted power flows for the next 10 years.
- When building new or refurbishing existing substations and switching stations, basic schemes of these substations and switching stations are selected according to the list of approved standard schemes for 110 and 330 kV substations.
2. Refurbishment and development of electric networks
- Development of electric network is organized in accordance with the Transmission System development plan. Refurbishment of 110 kV and 330 kV substations and switching stations, refurbishment of 330 kV and 110 kV power transmission lines, replacement and maintenance of autotransformers and transformers are planned according to “Criteria of evaluation for necessity of maintenance of transmission network elements”.
- When refurbishing or constructing new transformer substations, cable or overhead transmission lines, estimated service time of the components should be at least 40 years.
- When selecting primary schemes of 110 kV substations, their location and territories, load forecasts of at least 10 year period should be considered.
- When modernizing or installing substation supervision, control, data acquisition systems as well as relay protection and preventive automation systems fast action digital relay systems are to be used and optical communication links are preferred to be used.
- When refurbishing existing or constructing new substations, wherever technically and financially viable, new technologies are to be used. In the territories of planned or existing public or residential buildings indoor type switching stations and transformer substations are to be constructed. GIS (Gas Insulated Switchgear) switchgear is to be used in indoor type substations and switching points.
- When refurbishing or constructing new 110 kV power transmission lines, conductor wires of at least 600 A continuously permitted current are to be used (in radial lines it is allowed to use conductors of smaller current rating according to forecasted loads). When refurbishing or constructing new 330 kV power transmission lines, conductor wires of at least 1600 A continuously permitted current are to be used.
- When refurbishing or constructing new 110 kV power transmission cable lines within Riga city, cables with copper or aluminum conductor of at least 1000 A continuously permitted current are to be used. In other regions or towns cables with smaller conductor current rating are permitted according to the forecasted loads.
- When constructing cable sections into the existing 110 kV overhead transmission lines it is advised not to build more than 2 “overhead line-cable” transitions. Cross section and current rating of the cable section should not diminish the initial rating of the overhead line prior to the refurbishing.
- When constructing new or refurbishing existing substations supervision, control and data acquisition technologies are to be implemented in them.
3. Operation and Maintenance
- Maintenance and inspection of the installed transformers, primary and secondary equipment, SCADA systems in the substations and distribution points are to be performed according to the principles of periodicity and approved technology cards of complex maintenance and in the amount defined by LEK 002 “Technical Operation of Electric Equipment”.
- Operation of the installed transformers, primary and secondary equipment, SCADA systems in the substations and distribution points is to be performed according to LEK 002 “Technical Operation of Electric Equipment” and according to operation manuals by equipment producers.
- Maintenance and inspection of the power transmission lines are to be performed according to the principles of periodicity and approved technology cards of complex maintenance, according to the results of line surveillance and diagnostics and in the amount defined by LEK 002 “Technical Operation of Electric Equipment”.
- Operation of substations and power transmission lines should be secure, environmentally friendly and economical, based on the skills of personnel.
- Operation of the 330kV and 110kV power transmission equipment is to be organized utilizing SCADA/EMS systems and operative mobile crews.
- Operation and maintenance of security alarm systems and video surveillance systems has to be provided according to requirements by the producers of above mentioned systems.
- Operation and maintenance of the fire alarm systems is to be provided according to relevant rules and recommendations..