Does a plant connect to the transmission or the distribution grid, and what do TEİAŞ and the DSO (EDAŞ) each do?
The connection voltage decides it: plants connecting above 36 kV deal with TEİAŞ (TEIAS), the Turkish transmission system operator, while plants connecting at 36 kV or below deal with the regional distribution company (EDAŞ, the DSO). The threshold comes from Electricity Market Law No. 6446, which defines transmission as carrying electricity over lines above 36 kV. The connection voltage and point are fixed in the connection opinion, based on plant capacity and the grid capacity available in the region.
TEİAŞ operates the transmission system. It signs connection and system use agreements with transmission-connected users and runs the feeders in its 154 kV and 380 kV substations. The DSO issues the connection opinion for plants connecting to its MV network, signs the agreements and seals the metering. Even for a large plant connecting at distribution level, TEİAŞ stays in the background through regional capacity and substation loading.
In what order are the connection opinion, connection agreement and system use agreement obtained?
For licensed plants the order is connection opinion, connection agreement, then system use agreement: the opinion comes during the pre-licence stage, the connection agreement normally follows the generation licence, and the system use agreement is completed before physical connection and provisional acceptance. Under the Electricity Market Connection and System Use Regulation, TEİAŞ submits its opinion on the substation and connection capacity to EPDK, the energy regulator, within 45 days of notification. For distribution-connected plants, the DSO issues the opinion at EPDK's written request.
The applicant must apply for the connection agreement, to TEİAŞ or the DSO, within the pre-licence period and before applying for the generation licence. On transmission, these agreements cannot be signed before the generation licence is issued, although EPDK may allow a pre-licence holder to sign the connection agreement once TEİAŞ gives a positive opinion. On distribution, the licence holder submits its licence to the DSO within 60 days of receiving it, and the connection agreement is signed within the following 30 days.
The system use agreement is the precondition for actually using the grid. On transmission, the user must apply to TEİAŞ at least one month before the planned physical connection date; on distribution, the agreement is signed before partial or full provisional acceptance. The contract capacity in these agreements caps what the plant may export. Unlicensed projects follow a separate call-letter route, covered in our guide to unlicensed solar power plant applications in Turkey.
Who builds and operates the power line and switchyard up to the connection point?
The investor builds and operates the plant switchyard; connection assets beyond the end pole after that switchyard become part of the grid they connect to and are operated by TEİAŞ or the DSO. For connections above 36 kV, the regulation places everything from that end pole onward within the transmission ownership boundary. On distribution, the lines after the end pole, excluding the slack span to the switchyard, and any underground cable connected to the plant switchyard are distribution assets.
Who builds them is a separate question. Sometimes a new transmission line or substation is needed before TEİAŞ has the funding or investment schedule for it. In that case the regulation lets connecting parties build or finance it; ownership and operation stay with TEİAŞ, and the spend falls under the regulation's reimbursement mechanism. On distribution, the applicant can build the required network on the DSO's behalf under a construction agreement and is then responsible for the design.
In practice the investor's contractor usually builds the line. From design approval to materials and acceptance testing, however, it must meet the requirements of the operator that will take it over. Routing, easements and permits are often the longest items on the schedule, so planning for both sides from day one avoids rework.
Which protection, metering and SCADA requirements must be met for grid connection?
Grid connection requirements are set in the connection opinion and agreements, the Electricity Grid Code and the operator's technical specifications. The main headings are protection at the connection point, settlement metering and data exchange with the system operator. Line and transformer protection, overcurrent and earth-fault protection, and voltage and frequency protection are graded selectively with the protection of the feeder the plant connects to, and relay settings go to the operator for approval. The Grid Code also requires capabilities such as reactive power support and fault ride-through from wind and solar plants.
Main and backup meters sit at the connection point with instrument transformers of the required accuracy class. For licensed plants on the distribution grid, the DSO seals the user's metering equipment before provisional acceptance and records the first meter reading at provisional acceptance. Over SCADA, active and reactive power, breaker positions and alarms go to the relevant load dispatch centre or the DSO's control centre. Remote commands such as curtailment and voltage control are tested end to end during commissioning. Our article on what a SCADA system is explains the building blocks of the architecture.
What is different about grid connection for storage-integrated (BESS) plants?
The key difference is that a storage unit integrated into a generation plant does not get its own connection. Under the Connection and System Use Regulation it connects through the plant's connection point and is treated as a unit of that plant. Plant and battery must therefore be controlled together so that combined export stays within the contract capacity.
On site this has three consequences. A power plant controller (PPC) at the connection point manages solar or wind output and battery charge and discharge under one setpoint. Because power can flow both ways, protection settings and metering are assessed for export and import, and whether the battery may charge from the grid is settled in the licence and connection terms. Finally, relay settings for the new BESS feeder are checked for selectivity with the existing feeders and the incoming panel. We compare AC-coupled and DC-coupled designs in our article on solar-plus-storage electrical infrastructure.
Standalone storage facilities, with no generation or consumption plant attached, follow separate rules. When they connect to the distribution grid, for example, the user builds all the connection assets and remains responsible for their operation, maintenance, repair and renewal.
Which tests and steps must be completed before first energization and provisional acceptance?
Before first energization, the design must be approved, the de-energized site tests completed and the metering arrangement ready. Under the Regulation on Acceptance of Electricity Generation and Electricity Storage Facilities, TEİAŞ or the DSO then applies voltage temporarily, at the plant owner's written request, for pre- and post-synchronization tests. Provisional acceptance follows synchronization and site testing; it is carried out by the acceptance committee, and the plant moves into commercial operation after it.
De-energized site testing typically covers VLF and tan delta tests on MV cables, transformer ratio, winding resistance and insulation measurements, switchgear and circuit breaker function tests, ratio and polarity checks on instrument transformers, secondary injection of protection relays, and earthing measurements. End-to-end protection and SCADA tests with the remote end and metering circuit checks come next, and first energization and synchronization follow a programme agreed with the operator. The acceptance application is made only after all pre- and post-synchronization site tests are complete. Our guide to substation provisional acceptance explains what goes into the acceptance file on the substation side.
Miratek Elektrik builds MV and transformer works across Turkey in the 1–35 kV range: to date we have installed 120 MVA of total transformer capacity, laid 85 km of MV/LV cable and installed 48 MV switchgear cells. We deliver our Transformer Substations and Overhead and Underground Power Networks services together with High Voltage design and Project Approval and Permits consulting. For plants connecting at distribution level (36 kV and below), we act as one technical counterpart up to the connection point; for transmission-connected plants, we cover the plant's MV collection system and the MV transformer and switchgear works. Contact us to discuss your scope.
Frequently Asked Questions
Who decides whether a plant connects to transmission or distribution in Turkey?+
The connection voltage and point are set in the connection opinion. Connections above 36 kV go to the transmission system under the opinion of TEİAŞ (TEIAS); at 36 kV and below, the regional DSO issues the opinion. For licensed plants, EPDK requests the opinion during the pre-licence stage.
Does the investor build the connection line?+
Usually the investor's contractor builds it, but beyond the end pole after the plant switchyard it becomes part of the grid, operated by TEİAŞ or the DSO, so it must follow that operator's requirements.
Does adding a BESS to an existing plant need a new connection point?+
Under the regulation, a storage unit integrated into a generation plant connects through the plant's existing connection point and counts as a unit of the plant. Total export must stay within the contract capacity, and protection and metering need to be reassessed.
What does Miratek do on grid connection projects?+
Miratek builds MV cable and overhead lines, transformer substations, MV switchgear, earthing, testing and commissioning across Turkey in the 1–35 kV range: up to the connection point for distribution-connected plants, and on the plant's MV side for transmission-connected plants. It also provides High Voltage design and permitting consultancy.