DG interconnection engineering for solar, BESS, and generator projects.
Tikure builds the technical package utilities require to approve distributed generation interconnection: the protection scheme at the point of common coupling, the protective relay settings behind it, the one-line and three-line diagrams that document it, and the submittal that carries it through utility review.
What DG interconnection engineering is
Distributed generation interconnection is the process of connecting a generation source — solar PV, battery energy storage, a reciprocating or turbine generator, or a hybrid of these — to a utility distribution or transmission system. Before that connection is approved, the utility has to be satisfied on a narrow but non-negotiable set of questions: what happens to their system when your equipment faults, and what happens to your equipment when their system does.
DG interconnection engineering is the work of answering those questions in writing. It is a documentation and protection discipline more than a design discipline. The plant may already be fully engineered; what is missing is the technical record that lets a utility reviewer approve it.
That record centers on the point of common coupling — the electrical boundary between your facility and the utility. The interconnection protection scheme at that boundary must detect abnormal conditions on either side and separate the two systems fast enough to prevent damage, prevent an unintentional island, and keep utility line crews safe during restoration.
Why projects stall here
Interconnection is rarely the technically hardest part of a generation project, but it is disproportionately often the part that delays it. The pattern is consistent: the development team is strong on siting, financing, procurement, and construction, and the protection and utility-documentation work is treated as a deliverable to be produced at the end rather than a design constraint from the beginning.
By the time the application comes back with comments, equipment may already be ordered, the interconnection voltage may already be committed, and the fixes are expensive. Bringing protection engineering in before the application is filed is almost always cheaper than bringing it in after.
Who needs this
- Solar developers — rooftop, commercial, community, and utility-scale PV requiring interconnection approval before permission to operate.
- BESS and storage developers — standalone storage and solar-plus-storage, where bidirectional power flow changes the protection picture.
- Renewable energy and DG project developers — portfolios moving multiple projects through multiple utilities, each with its own requirements.
- EPC firms and electrical contractors — teams that can build the project but need the interconnection protection package and relay settings the utility is holding energization on.
- Engineering firms — firms carrying the project who need protection coordination and settings depth on a specific scope without adding staff.
- Commercial and industrial customers — facilities adding on-site generation behind an existing utility service.
The protection functions a utility reviews at the POC
Interconnection protection is described using IEEE C37.2 device function numbers, and utility technical interconnection requirements are written in that language. These are the functions that appear most often on a distribution-level DG interconnection:
| Device | Function | What it protects against at the interconnection |
|---|---|---|
| 27 | Undervoltage | Detects loss of the utility source and abnormal low-voltage conditions; a core anti-islanding element. |
| 59 | Overvoltage | Detects utility-side overvoltage and generation-driven voltage rise at the POC. |
| 81U / 81O | Under / over frequency | Detects frequency excursions indicating separation from the utility system. |
| 50 / 51 | Instantaneous / time overcurrent | Clears faults on the facility side and limits fault contribution back to the utility feeder. |
| 67 | Directional overcurrent | Distinguishes fault current flowing toward the utility from current flowing into the facility. |
| 32 | Directional power | Detects reverse power or export beyond an agreed limit, common on non-export interconnections. |
| 25 | Synchronism check | Prevents out-of-phase reconnection to the utility system after separation. |
| 87 | Differential | Zone protection for the interconnection transformer or bus on larger interconnections. |
The exact required set comes from the utility's own technical interconnection requirements, which differ by utility, by generation size, and by interconnection voltage. Identifying the utility of record and working to that document — rather than to a generic template — is the first step of every engagement.
When to bring us in
Best case — before the interconnection application is filed. The protection scheme, POC configuration, and interconnection voltage are still open, and the application can go in complete the first time.
Common case — mid-review, with utility comments in hand. The application is in queue and the utility has asked for protection detail, relay settings, or drawings the current package does not contain. We read the comments against what was submitted and produce what the reviewer is actually asking for.
Late case — approaching energization. Equipment is on site and the utility is holding permission to operate on settings, documentation, or witness test readiness. This is the most expensive point to discover a protection gap, but it is recoverable.
The deliverables that make up a DG interconnection package.
Scope is defined project by project. These are the components that typically make up a complete interconnection submittal.
One-line and three-line diagrams
Project one-line showing the utility feeder, POC, disconnect, metering, interconnection transformer, and generation, plus three-line and relay schematics where the utility requires them. Built to IEEE and ANSI symbol conventions with an equipment schedule, legend, and title block. Diagram scope →
Point of common coupling documentation
The POC detail the utility reviews: interconnection device, isolation and visible-break disconnect arrangement, metering location, protective device placement, and the interconnection transformer configuration and grounding.
Protective relay settings
Calculated settings for the interconnection relay and associated protective devices, documented as settings sheets in a format the utility reviewer can check against their requirements. Relay settings scope →
Protection and coordination study
Coordination of the interconnection protection with facility devices and with the utility's upstream protection, documented so the coordination basis is defensible on review. Study scope →
Interconnection application package
Technical portions of the interconnection application prepared and assembled in the utility's expected format, with the drawings, settings, and equipment data cross-referenced so the package reads as one consistent record.
Utility comment response
Response to utility review comments, revised drawings and settings under revision control, and management of the package from application through approval.
Solar, BESS, and generator interconnection
Solar interconnection
Inverter-based PV contributes fault current very differently from rotating machines — typically limited to a small multiple of rated current and shaped by inverter control rather than by machine impedance. That changes how overcurrent elements can be set and how much a utility can rely on fault magnitude for detection, which is why voltage and frequency elements carry more of the protection burden on a PV interconnection.
BESS interconnection
Battery energy storage adds bidirectional power flow and distinct charge, discharge, and idle modes. Directional elements have to distinguish normal charging from a genuine reverse-flow condition, export limits may be enforced by protection rather than only by controls, and the protection scheme must remain valid across every operating mode the plant will actually run in.
Generator interconnection
Synchronous generators contribute substantially more fault current, and for longer, than inverter-based resources. That makes overcurrent coordination more conventional but raises questions about interrupting duty, synchronism check on reconnection, and generator-side protection that inverter projects rarely face.
Non-export and limited-export interconnections
Where a project is not permitted to export, or may export only up to a limit, the utility's concern shifts to whether that limit is enforced reliably. Directional power protection, export limit settings, and the documentation showing how the limit is held become the center of the review.
Reference convention only. Project-specific drawings are produced under engagement.
DG interconnection questions we answer most often.
What does a DG interconnection engineer actually do?
A DG interconnection engineer translates a generation project into the technical record a utility needs in order to approve it. In practice that means defining the protection scheme at the point of common coupling, calculating the protective relay settings that scheme depends on, producing the one-line and three-line diagrams that document it, assembling the interconnection application package, and answering the utility's review comments until the project is approved to energize.
It is not the same as the electrical design of the plant itself. The plant designer sizes conductors, inverters, and equipment; the interconnection engineer establishes how that plant behaves at the utility boundary and proves it on paper.
What is the point of common coupling, and why does the utility care about it so much?
The point of common coupling (PCC, often written POC or POI on utility drawings) is the boundary where your facility connects to the utility system. Everything the utility is exposed to — fault contribution from your generation, the risk of an unintentional island energizing a de-energized utility circuit, voltage and frequency behavior during a disturbance — is determined at that point.
That is why the interconnection review concentrates there. The utility is not assessing whether your plant works. It is assessing whether your plant can hurt their system or their line crews, and the POC protection scheme is the answer to that question.
Which protective functions does a DG interconnection typically require?
It varies by utility, by generation size, and by interconnection voltage, but a typical distribution-level DG interconnection relay carries undervoltage (27), overvoltage (59), under/over frequency (81U/81O), instantaneous and time overcurrent (50/51), and often directional overcurrent (67) and directional power (32) to detect reverse flow or motoring. Larger or more sensitive interconnections may add differential protection (87), synchronism check (25), or a direct transfer trip scheme.
The specific list comes from the utility's technical interconnection requirements document, not from a generic standard, which is why identifying the utility of record is the first thing we do.
Do you handle the interconnection application itself, or only the drawings?
Both. We prepare the technical portions of the interconnection application, assemble the submittal package in the format the utility expects, and manage the application through the review cycle — including responding to utility review comments and issuing revised drawings and settings as the review requires.
How long does DG interconnection approval take?
The engineering work on our side is usually measured in weeks; the utility's review cycle is what sets the calendar, and it varies widely by utility, by queue position, and by whether the project qualifies for a fast-track or simplified process. What is inside your control is how many review rounds you go through. A package that is complete, internally consistent, and formatted the way the reviewer expects tends to clear in fewer cycles than one assembled piecemeal.
Can you take over a project that is already in the utility queue and getting comments?
Yes, and it is a common way projects reach us. We review the application as submitted, the utility's comments, and the existing drawings and settings, then identify what the reviewer is actually asking for. Often the comments point to a documentation gap rather than a design problem — a missing three-line, an unstated relay function, or a POC detail that was never drawn.
Do you work on solar, battery storage, and conventional generators?
Yes. The protection questions differ — inverter-based resources contribute fault current very differently from a synchronous machine, and storage introduces bidirectional flow and charge/discharge modes that affect directional elements — but the interconnection process and deliverable set are the same. We support solar PV, battery energy storage (BESS), solar-plus-storage, and generator interconnection projects.
Is a PE stamp required on interconnection documents?
It depends on the utility and the jurisdiction. Many utilities require PE-sealed one-lines, three-lines, or study reports as a condition of interconnection; others accept unsealed technical documentation for smaller projects. We identify that requirement during the scope call. Deliverables submitted as engineering record are sealed by our licensed Professional Engineer.
The rest of the interconnection scope.
Have a DG project heading for utility review?
Tell us the utility of record, the system size, and the interconnection voltage, and we can usually scope the protection work on the first call.