11 kV Interconnection for a Solar Plant: HT Works, Metering and the DISCOM Feasibility Study

Connecting a solar plant at 11 kV means the plant steps up through its own transformer to the DISCOM's high-tension network, and the DISCOM studies its feeder before agreeing. You add an HT breaker panel, protection relays, CT/PT metering, an interconnection study, Electrical Inspector approval and power quality metering. Those HT works sit outside most per-kW solar quotes.

When does a solar plant connect at 11 kV?

The voltage is fixed by your supply and the state supply code, not by the solar contractor. Two situations are common.

The first is a factory that already takes an 11 kV supply and owns its transformer. The plant feeds the low-voltage bus behind that transformer, and the 11 kV side is the existing HT installation. The question is whether the transformer and the HT metering can take reverse flow, which is covered in our note on transformers and DG sets.

The second is a plant that injects directly into the DISCOM's 11 kV network through a dedicated step-up transformer: a large ground-mount or multi-roof system, a gross-metered plant, or a captive or open-access plant that is not tied to a single bus. This is the case this article describes.

Size drives the route. The Electricity (Rights of Consumers) Rules, as amended in 2021, let a state commission allow net metering up to 500 kW or the sanctioned load, whichever is lower, with net billing for other loads. A plant of several hundred kilowatts or more at an HT connection therefore often lands outside net metering. Check your sanctioned load first with the sanctioned-load calculator, and read the 500 kW and 1 MW cost pages for how these sizes are usually built.

What HT works does the plant add?

The table lists the usual items. Equipment names vary by DISCOM, but the functions are the same everywhere.

Two points from the CEA texts matter for the specification. Under the connectivity regulations, a distributed generator operating in parallel must trip on voltage above 110% or below 80% with a clearing time of up to two seconds (the licensee may set a narrower range), must trip on frequency above 50.5 Hz or below 47.5 Hz within 0.2 seconds, must stop energising a faulted or dead circuit, and may reconnect only after voltage and frequency have been stable for at least sixty seconds. The metering regulations set the accuracy class for consumer meters above 650 volts and up to 33 kV at 0.5S or better; interface meters are 0.2S. The CTs and PTs must be good enough to deliver that class, so ask for their class on the quote.

What does the DISCOM's interconnection study decide?

Under the CEA connectivity regulations the licensee carries out an interconnection study to determine the point of interconnection, the facilities and modifications needed on its network, the maximum net capacity at that location, the likely effect on quality of service to other consumers, and the safety measures. It also carries out an adequacy and stability study of the network before permitting connection. Every connection is then covered by a connection agreement.

Behind those clauses sit two physical limits. The Forum of Regulators' 2019 report names them: the thermal capacity of the feeder and its equipment, and the voltage rise at the point of connection. If the plant's output exceeds what the load on that feeder absorbs, the surplus flows back towards the substation, and either limit can be hit first. A feeder that looks lightly loaded at noon on a Sunday is the usual problem.

The result of the study is a sanction with conditions. Typical outcomes are a named connection point, a required protection scheme, a meter specification, and sometimes work on the DISCOM's side such as a bay extension or a conductor change. The Rights of Consumers Rules provide that upgrades needed between the feasibility study and installation, including line or transformer strengthening, are carried out by the licensee or the consumer depending on the case. Ask who pays, in writing, before ordering equipment.

What is the sequence from approval to energisation?

1. Prepare the single-line diagram, load and generation data, and the protection philosophy, and apply to the DISCOM for feasibility.
2. Receive the feasibility sanction with its conditions, and sign the connection agreement when the DISCOM issues it.
3. Submit the drawings to the state Electrical Inspector. A CEA presentation on the 2023 safety regulations lists, for first-time charging, the work completion certificate, updated single-line diagram, earthing and site layouts, equipment list, manufacturer and pre-commissioning test reports, and the contractor and supervisor licences.
4. Build, test and calibrate. The connectivity regulations require inspections and tests to be completed, in consultation with the licensee, before physical connection, and drawings, specifications and test records to be made available to it.
5. Get the inspector's approval, have the DISCOM seal the meter, and energise.

After energisation the installation is inspected periodically, at intervals not exceeding five years according to that presentation. Our guide to CEIG approval for factories covers the inspector's side, and why protection settings stall exports covers the DISCOM's.

Which HT costs do per-kW quotes leave out?

Our published band for commercial and industrial rooftop solar is ₹24,000–32,000 per kW, excluding GST, and its stated exclusions include HT-side works and a transformer or bay addition where the site needs one. That is the right way to read any per-kW price: it covers the solar plant, not necessarily the HT connection. The items to ask each bidder to price separately are the step-up transformer, the HT panel and VCB, the relays and their settings study, the CT/PT cubicle, the power quality meter, the HT cable or line to the DISCOM's point, the Electrical Inspector's fee, and any DISCOM supervision or augmentation charges. We do not quote a figure for these here, because they depend on the voltage, the distance and the DISCOM's conditions.

Compare bids on the same boundary. A plant priced to the inverter AC terminals and a plant priced to the DISCOM's meter are different scopes, and the second is usually the one you actually need.

How Secured Engineers helps

We design the plant and its HT interconnection in-house, and file the DISCOM application and the Electrical Inspector submission ourselves. MEPF and solar are delivered under one contract, so the transformer room, the HT cabling and the earthing are scoped once. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients. Our industrial solar EPC service is where this scope sits for factories.

If you have a DISCOM sanction letter or a quote with an unclear boundary, send it to us. We will mark what is solar, what is HT, and what is the DISCOM's. See our electrical infrastructure service, message us on WhatsApp or call +91 70099 85817, or ask for a free proposal.