Transformer Substation Provisional Acceptance in Türkiye: What Does the TEDAŞ Acceptance File Require and What Does the Committee Inspect?

Provisional acceptance (geçici kabul) is the stage at which an acceptance committee inspects a completed transformer substation on site and records in a signed report that it was built in line with its approved design, the applicable regulations, and life and property safety requirements. In Türkiye, substations and distribution facilities that supply consumer installations are accepted under the Regulation on Acceptance of Electrical Installations (Elektrik Tesisleri Kabul Yönetmeliği), while substations that belong to generation assets such as solar power plants (SPPs) and wind farms are accepted under the Regulation on Acceptance of Electricity Generation and Electricity Storage Facilities. For many projects the process runs through TEDAŞ (Türkiye Elektrik Dağıtım A.Ş., the state-owned Turkish Electricity Distribution Company), but the authority that performs the acceptance can vary with the facility type and its licensing status. Until the provisional acceptance report is signed, the substation is not energized for operation.

Design approval, by contrast, sits at the very start of the process: the single-line diagram, transformer and switchgear selection, cable cross-sections, grounding calculation, and protection scheme are reviewed and approved before construction begins. In short, design approval defines what will be built; provisional acceptance verifies that the approved facility was actually built, and built safely.

Provisional acceptance is followed by final acceptance (kesin kabul). Under Article 22 of the Regulation on Acceptance of Electrical Installations, final acceptance takes place at least one year after the provisional acceptance date (at least six months for transformer and conversion substations), and confirms that the defects noted at provisional acceptance have been remedied and that the facility has operated without problems. Final acceptance does not change warranty periods. Design approval is also a cost item in its own right when a substation is budgeted; this article focuses on the acceptance process that follows construction.

The mandatory documents in a TEDAŞ acceptance file are the application documents that are a precondition for forming the committee (including the approved design file), the design and administrative documents, the equipment certificates, and measurement reports signed by an authorized engineer. Because the current checklist and format can vary with the procedures of the unit performing the acceptance, the safest approach is to confirm the requirements with that unit before you apply.

Precondition documents: a written request for provisional acceptance, the approved design file, a ready-for-acceptance report (geçici kabule hazır tutanağı) signed by the distribution company representative and the facility owner, and authorization letters for the contractor's and the distribution company's engineers who will attend the acceptance. If any of these is missing, the committee is not formed, and the date the gap is closed counts as the application date; the acceptance fee is also collected before the committee is formed. Photos or videos documenting the construction stages, with cable trench depth and width clearly visible, should also go into the file; when they are submitted, the committee does not need test pits dug along the cable trenches.

Design and administrative documents: any approved revisions to the electrical design, as-built drawings showing the final site condition, the connection agreement or connection opinion, and the authorization documents of the installing company together with the responsible engineer's professional chamber registration. Equipment documents: certificates of origin and conformity, type test certificates, and factory (routine) test reports for the transformer, MV switchgear cubicles, cables, cable terminations, protection relays, and instrument transformers. The serial numbers on these documents must match the equipment installed on site exactly.

Measurement and test documents: a grounding measurement report signed by an authorized engineer (resistance values plus a step and touch voltage assessment), a relay settings and test report, and the single-line diagram. As good practice, insulation and MV cable test reports and operating and maintenance instructions should be added as well; they serve as reference documents during the committee's checks. Every report should state the test date, the measuring instrument used, and its calibration details.

Under Article 7 of the Regulation on Acceptance of Electrical Installations, the acceptance committee (often called the acceptance board, or kabul heyeti, in practice) consists of a presiding engineer appointed by the accepting authority, the facility owner or their representative, at least one electrical engineer from the distribution company that supplies the power, and the responsible discipline engineers acting for the contractor; additional members can be appointed when needed. The authorization letters of the contractor's and the distribution company's engineers are among the precondition documents of the acceptance file.

The first site check is compliance with the approved design: transformer rating and type, switchgear line-up and functions, and cable cross-sections and routes are compared against the drawings. The committee then inspects the grounding connections of every metal part (switchgear enclosures, the transformer tank or enclosure, doors, cable screens, and panel enclosures), safety clearances, mechanical interlocks, and the condition of the cable trenches. If construction photos are not in the file, the committee has at least one test pit dug for every 250 meters of cable trench to verify trench dimensions on site, and grounding measurements are repeated on a sampling basis.

The committee also looks for operational safety equipment: a single-line diagram posted at the switchgear, warning and danger signs, insulating mats and gloves, an insulated operating stick (hot stick), a grounding and short-circuiting kit, and first-aid instructions are at the top of the list. In building-type substations, ventilation, lighting, and door arrangements are checked; with oil-immersed transformers, the oil containment pit and leak-tightness are checked separately.

Grounding measurements, insulation tests, MV cable tests, and protection relay tests must be completed and reported before acceptance day, and the committee may have some of them repeated on site. The grounding measurement covers the resistance of the system (operational) and protective grounding, and step and touch voltages are assessed under the Regulation on Grounding in Electrical Installations (Elektrik Tesislerinde Topraklamalar Yönetmeliği). The report should state clearly which fault current and clearing time were assumed; we explain this in detail in our grounding measurement guide.

On the insulation side, the insulation resistance of the transformer windings (MV to LV, MV to ground, LV to ground), the busbars, and the cables is measured with an instrument at the appropriate test voltage. After installation, MV cables undergo a withstand voltage test by the method the relevant standard specifies (commonly VLF) and an outer sheath test; the cable terminations must be installed before these tests are run.

On the protection side, relay settings are entered according to the approved coordination study or the values issued by the distribution company, and pickup values and trip times are verified by secondary current injection. You also need to demonstrate that the relay actually trips the circuit breaker, that current transformer ratios and polarities are correct, and that the transformer protection contacts (a hermetic transformer protection relay or Buchholz relay on oil-immersed units, a temperature relay on dry-type units) are wired into the trip circuit. Checking the transformer's turns ratio and tap position is part of the same preparation.

The most common reason an acceptance application is returned is that the installation on site differs from the approved design. Changing the transformer rating or switchgear type during procurement, shifting a cable route, or adding a feeder without getting a revised design approved shows up directly as a non-conformity at acceptance. If the nature of the design has changed, acceptance cannot be completed until an approved modification design is submitted.

The second large group is documentation gaps: a missing ready-for-acceptance report or authorization letters, unsigned or outdated test reports, grounding reports without a step and touch voltage assessment, and certificates of origin or test reports whose serial numbers do not match the equipment on site. Even when these gaps are not technical defects, they get the file returned and push the project back to waiting for a new acceptance date.

On site, the most frequent shortcomings are missing grounding bonds at points such as doors and cable screens, missing safety equipment and warning signs, no posted single-line diagram, incomplete cable trench covers, and relay settings that do not match the coordination study. Minor deficiencies that do not prevent operation are recorded in the report with a deadline for correction; however, if the value of incomplete and defective work exceeds 5% of the approved cost estimate (keşif bedeli), acceptance is not granted. Running an internal pre-acceptance that covers everything the committee will inspect prevents most of these returns.

In outline, the process moves through application, file review, site acceptance, the signed report, distribution company procedures, and energization. Once the precondition documents are complete and the acceptance fee is paid, the committee and the acceptance date are set. During acceptance preparations, test voltage is applied to the facility at the owner's written request and the acceptance tests are carried out under voltage; if the facility is found compliant, the provisional acceptance report is signed.

Minor deficiencies recorded in the report are corrected within the period given; if any condition affects life safety, acceptance is not granted and a new application is required after correction. In practice, the provisional acceptance report is the precondition for the substation's energization permit. After acceptance, the connection and system use procedures with the distribution company are completed, and the metering circuit is checked and sealed.

In many cases, documentation that a responsible operating engineer (işletme sorumlusu) has been appointed for the MV installation is also requested before energy is supplied for operation. On energization day, working with the distribution company's crew, the substation is first energized at no load; once phase sequence, voltages, and protection status have been checked, load is picked up in stages.

A transformer substation has to be transferred to the distribution company when it will supply not only the owner's own consumption but also other users as part of the distribution network. A customer substation that supplies only the owner's own factory or business generally stays in the owner's possession, together with responsibility for its operation, maintenance, and periodic inspection.

Connection facilities are treated differently: under the Electricity Market Connection and System Use Regulation (Elektrik Piyasası Bağlantı ve Sistem Kullanım Yönetmeliği), connection facilities built by a user are deemed transferred to the distribution company on the energization date without any further procedure, and responsibility for operation and maintenance passes to the distribution company from that date. MV connection lines longer than 500 meters outside settled areas, however, keep their connection line status for five years. In practice, the transfer is documented by handing the acceptance report and the as-built file over to the distribution company.

Miratek Elektrik runs transformer substation projects across Türkiye as a single point of contact, from design and design approval through site installation and testing and commissioning to preparation of the acceptance file. Working in the 1–35 kV medium-voltage range, with 48 MV switchgear cubicle installations completed, our engineers prepare each file with the committee's site checks in mind. Under our Project Approval and Permits consultancy, the file is prepared against a checklist, an internal pre-acceptance is carried out, and the tests in front of the committee are conducted by our engineers, with the goal of making the client's energization date predictable. The gaps and timeline for your own project's acceptance become clear after a site survey and a review of the file.