BESS and solar protection coordination in India, for plants that supply little fault current
Inverters do not drive the fault current your relays were graded for. VB re-grades the AC relays, coordinates the DC side and prepares the settings your RPC must approve.
Is the protection study for your plant still current?
Pick two answers from your plant records. The verdict shows here with the IEGC regulation behind it, without an email.
Free · instant · based on IEGC 2023 Regulations 14 and 15
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Does a solar or BESS plant in India need a protection coordination study for grid connectivity?
Yes. The CERC Indian Electricity Grid Code Regulations, 2023 require every user connected to the grid to keep selective protection, furnish its settings to the Regional Power Committee and have them audited. The CEA connectivity standards set the protection a generating station must provide before it connects.
| Instrument | Clause | What it requires | Interval |
|---|---|---|---|
| IEGC 2023 (CERC) | Reg. 13(1) | All users connected to the integrated grid provide and maintain an effective protection system with reliability, selectivity, speed and sensitivity, to isolate the faulty section. | Continuous |
| IEGC 2023 | Reg. 14 | Users furnish the protection settings implemented for each element to the RPC, obtain RPC approval before any revision or new protection system, and intimate changes within a fortnight. | On every change |
| IEGC 2023 | Reg. 15 | Internal protection audit every year, and third-party protection audit of each substation at 220 kV and above once in five years or earlier as the RPC advises. Audit plans go in by 31 October. | 1 year · 5 years |
| CEA Connectivity Standards | 2007, as amended | The protection, fault ride-through and data a generating station provides to connect. The CEA draft standards of 2026 add technical studies, equipment data and model validation before final connectivity. | At connectivity, and on change |
Protocols differ by region. Each RPC issues its own protection philosophy and settings format, and the SLDC sets intra-state requirements. VB confirms the protocol at your connection point for every project.
Not sure which protocol your connection point falls under?
When does a solar or BESS plant need its protection re-graded?
Five years between audits is the longest a plant should wait. Each event below shifts the fault currents behind your settings, and Regulation 14 needs RPC approval before the new settings go in.
Added storage or changed inverters since your last study?
What relay setting data must a plant submit to the SLDC or RPC?
Each RPC sets its own format, but the same four items come up at every connection point. VB prepares all four from one model.
- Single-line and protection schemeThe as-built single-line with every relay, CT and PT ratio, and the protection functions enabled at the interconnection.
- Settings at the interfacePickup, time multiplier, directional and earth-fault settings for incomer, line and transformer relays, in the RPC format.
- Fault study resultsMaximum and minimum fault levels at the connection point, with inverter and BESS contribution modelled.
- Grading curves and change recordTime-current curves showing grading with the upstream grid relays, and every setting change since the last submission.
How are DC protective devices coordinated in a battery energy storage system?
On the DC side the fault current comes from the battery itself and rises much faster than on the AC side. Coordination works across three levels, from the rack to the 33 kV feeder.
- Module and rack fuses clear an internal rack fault before the DC breaker opens, so one rack is lost, not the whole container.
- Rack fuses and DC breakers are graded against the PCS input protection, using the battery short-circuit data the manufacturer publishes.
- The AC side of the PCS is graded with the 33 kV feeder relay, so a DC fault does not trip the feeder and a feeder fault does not trip the PCS first.
How do you coordinate protection when solar and BESS supply low fault current?
Every inverter, PCS and protective device goes into an ETAP or SKM PowerTools model, using the fault response its manufacturer publishes. Settings come from the software, never from hand working.
Collect plant data
Single-line, relay and breaker settings, CT and PT ratios, inverter and PCS fault response, and battery short-circuit data.Model every source
Grid, pooling transformer, collector feeders, inverters and BESS modelled, with the grid fault level from the transmission utility.Run the fault cases
Faults with the grid connected and with it open, at minimum generation, so each relay is checked at the current it will really see.Grade AC and DC
Time-current curves for every path, with directional or voltage-restrained elements where plain overcurrent cannot discriminate.Set and format
Settings table prepared in the format your RPC or SLDC asks for, with the grading basis stated for approval.Sign and hand over
Report, curves and settings signed by a named VB power system engineer, ready for the protection audit.What does the study deliver?
The single-line model holds every source. The curves prove every setting. Both come from real VB studies.
The single-line model
Incomer over feedersWho stands behind the settings?
A named engineer puts their signature on the settings your RPC approves. Responsibility sits with three people, each recorded in the report.
Checking engineer
Checks the model and the grading basis independently of the modeller.Power system engineer of record
A named VB power system engineer signs the study and stands behind every setting.Settings on file
The signed settings table is what the RPC repository and the protection audit ask to see.Illustrative case: one collector fault, the whole plant offline
Modelled on a typical finding. A utility-scale solar park in western India, with a battery block added two years after commissioning, saw its 33 kV pooling incomer trip for a fault on one collector feeder. The study traced it to settings graded for grid fault levels alone.
| Checked | Finding |
|---|---|
| Inverter and BESS infeed | Never modelled; settings carried over from commissioning |
| Incomer and feeder curves | Overlapping, so either could trip first |
| Corrective action | Directional relay on the BESS feeder, feeder pickups reset, revised settings submitted for RPC approval |
Share this with whoever plans your plant outages.The VB Engineering capability brochure, covering power system studies for solar and storage plants.
Questions plant electrical heads ask about solar and BESS protection
What is BESS protection coordination?
BESS protection coordination is the grading of relays, breakers and DC fuses in a battery storage plant so the closest device isolates a fault before anything upstream operates. It covers the DC racks, the PCS and the AC feeder up to the grid interface, using fault currents that include the limited inverter contribution.
Why does normal overcurrent grading fail on inverter-based plants?
Overcurrent relays are graded on fault current. Inverters limit their output close to rated current, so with the grid side open a feeder fault may never reach the relay pickup. Directional, voltage-restrained or undervoltage elements are used where plain overcurrent cannot discriminate.
Is a protection coordination study required for grid connectivity of a solar plant in India?
Yes. The IEGC 2023 requires every user connected to the grid to keep selective protection (Regulation 13), furnish its settings to the RPC and get approval before revising them (Regulation 14), and have protection audited (Regulation 15). A coordination study is how those settings are produced and justified.
What is a solar relay coordination study?
A solar relay coordination study grades the relays and breakers of a solar plant from the inverter to the grid interface. It is built on a short circuit study that includes inverter contribution, and is delivered as a settings table and time-current curves.
How often must protection settings be reviewed under the IEGC 2023?
Regulation 15 calls for an internal protection audit every year and a third-party audit of each substation at 220 kV and above once in five years, or earlier if the RPC advises. Any settings revision needs RPC approval first under Regulation 14.
What is the difference between a protection coordination study and a grid impact study?
A grid impact study checks load flow, voltage and stability at the connection point. A protection coordination study sets the relays so faults inside and outside the plant are cleared by the right device. Most new connections need both.
Does a BESS also need a DC arc flash study?
Yes. Battery fault current creates an arc flash hazard at racks, DC combiner panels and PCS inputs. VB runs the DC arc flash study on the same model, so the clearing times used for incident energy match the coordinated settings.
What data does VB need to start?
The single-line, existing relay settings, inverter and PCS datasheets with fault response, battery rack short-circuit data and the grid fault level at the connection point. Anything missing is collected on site.
What is a power system study for a solar plant?
It is the set of studies a solar plant needs to connect and run safely: load flow, short circuit, protection coordination, harmonics and, for larger plants, stability. Protection coordination depends on the short circuit results, so the two are done on one model.
Can VB prepare the settings in the format our RPC asks for?
Yes. VB prepares the settings table, curves and fault data in the format of the RPC or SLDC your plant reports to, and updates the record after every change so the next approval is quick.
Your plant has a question we have not covered? Ask it here.
Studies that sit next to protection coordination
These pages answer the next questions: the full relay study, the DC arc flash hazard and the studies that come before connection.
Relay coordination study
Scope, deliverables and how a relay coordination study is priced.
Done togetherBESS arc flash study
DC incident energy at racks and PCS inputs, on the same model.
Before connectionRenewable integration study
Load flow, voltage and stability at the connection point.
Industrial plantsRelay coordination in India
Relay setting review for refineries, chemical and pharma plants.
When were your plant relays last graded?
Share the year the relays were last graded and any storage, inverter or feeder change since. A protection engineer tells you whether re-grading is due and what your RPC will want to see.
- Settings checked against the five-year audit and every plant change since
- We name the protocol and settings format your RPC or SLDC uses
- The reply is yours to keep, whether or not we quote
Check your plant
- Read and answered by a protection engineer
- Your position checked against IEGC 2023 Regulations 13 to 15
- The RPC protocol at your connection point, named
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