Sector applications · Complies to IEEE 80 · IEC 61936-1 · CEA Reg. 43
Substation and Power Grid Protection
Substation protection covers the complete earthing and overvoltage system of a substation: the earthing grid, equipment and fence earthing, neutral earthing, surge protection of control and auxiliary supplies, and portable earthing for safe maintenance.
LPES solution codeSUB
Governing standardIEEE 80 · IEC 61936-1 · CEA Reg. 43
LPES design ruleGrid, risers, neutral earthing and auxiliary SPDs as one system
When it applies
- Transmission and distribution substations
- Industrial main receiving substations
- Solar and wind pooling substations
- Refurbishment of substations with corroded or undocumented earthing
When it does not
- High-voltage surge arresters on the lines and transformers, which are specified with the primary equipment
- Low-voltage-only installations
- Sites without fault-level and soil data
How the system works
- AssessA lightning risk assessment and the sector's own standard set the protection level.
- Earth and bondEvery structure, frame and cabinet is joined to one earthing system.
- Protect the linesCoordinated surge protective devices are fitted on power, DC, RF and data lines.
- Monitor and maintainCounters and status contacts show what happened; inspection keeps the system in service.
Coordinated surge protection
Each device takes its share. The Class I device diverts lightning current at the service entry; Class II and III devices bring the remaining voltage below what the equipment can withstand.
Design parameters
The values a consultant or contractor needs to fix before the system is drawn.
| Parameter | Typical value or rule | Reference |
|---|---|---|
| Earthing grid | Designed for tolerable touch and step voltages | IEEE 80 · IEC 61936-1 |
| Equipment earthing | Two separate connections from each item of equipment to the grid | CEA regulations · IS 3043 |
| Neutral earthing | Solid, resistance or high-resistance, from the system design | IEEE C62.92 · IS 3043 |
| Control and auxiliary supplies | Type 1 or Type 1+2 SPDs at the auxiliary board; data-line SPDs on SCADA and protection signalling | IEC 61643-11 · IEC 61643-21 |
| Portable earthing | Rated for the fault level and duration at the point of work | IEC 61230 |
| Verification | Grid resistance, continuity of risers, and step and touch voltages | IEEE 81 |
Solution pack: component BOQ
Each line opens the LPES product category. Part codes and final quantities are confirmed on your quote from the drawings.
| Component | Role in the system | Quantity rule |
|---|---|---|
| Substation & Switchyard Earthing | Risers, clamps, fence and structure earthing | Two risers per item of equipment; fence earthed at corners and gates |
| Earth Mats & Grids | Grid conductor and operator mats | From the grid design; one operator mat per manual switch |
| Type 1 Lightning-current Arresters | Surge protection of auxiliary and control supplies | One set per auxiliary board |
| Portable & Temporary Earthing | Portable earthing and short-circuiting sets for maintenance | One set per voltage level per maintenance team |
| Neutral Earthing Equipment | Neutral earthing resistors and earthing transformers | One per transformer or generator neutral, from the system design |
From design to handover
- Collect fault levels, soil data and the layout
- Design the grid, neutral earthing and auxiliary surge protection
- Install and weld the grid and connect all equipment with two risers
- Fit SPDs and provide portable earthing sets
- Test grid resistance and step and touch voltages, and hand over the records
Services for this solution
Grid Resistance / Substation Earthing TestStep & Touch Voltage Measurement
Industries that use it
What the standards require
Checked against the current editions held in the LPES standards library.
- IEC 62305-2:2024
- Risk to life and physical damage is compared with a tolerable risk of 10⁻⁵ per year; failure of internal systems is judged separately as a frequency.
- IEC 62305-4:2024
- A coordinated SPD system protects against conducted surges only. Radiated fields need shielding and cable routing.
- IEC 62305-4:2024 Cl. 7
- Where an external LPS exists, a Class I (Type 1) SPD is required at the service entry.
- IEC 62305-4:2024
- Earthing conductor to the SPD: 16 mm² copper for Class I, 6 mm² for Class II and 1.5 mm² for Class III.
- CEA Safety Regulations 2023, Reg. 38(3)
- Lightning protection is addressed for multi-storeyed buildings above 15 m and listed public premises such as airports, hospitals and hotels.
- IEEE 80-2013
- A substation grid is judged by touch and step voltage against the tolerable limits, not by its resistance alone.
Regulation and standards cross-check
What Indian regulation and the wider standards add to this solution. Paraphrased; confirm against the current official text, amendments and state notifications before relying on a clause in a tender or inspection.
| Standard | Clause | What it requires |
|---|---|---|
| CEA Safety Regulations 2023 | Reg 50 | Above 650 V the whole switchyard or substation, including non-current-carrying metal, is connected to an earthing system or mat that limits touch and step potential and earth potential rise, including potential transferred through earth wires, cable sheaths, fences and pipelines. |
| CEA Safety Regulations 2023 | Reg 77 | Owners of overhead lines, substations and generating stations exposed to lightning must divert lightning surges to earth. The arrester earthing lead is kept as short and straight as possible, does not pass through steel pipe, and goes to a separate vertical electrode or to a junction of the earth mat. |
| IS 3043:2026 | Clause 10.3, Figure 63, Table 28 | Substation earthing above 1 kV follows a step-by-step flow. A global earthing system is confirmed when the earth potential rise is below the permissible touch voltage. Table 28 limits for interconnection and transferred potential are checked as well. |
| IEC 61936-1:2021 | 10.3.1, Annex D | Design follows a fixed sequence: collect fault data, make an initial design, decide whether a global earthing system exists, find the current into earth, the impedance to earth and the earth potential rise, compare with the permissible touch voltage, then mitigate where needed. |
| IEC 61936-1:2021 | 10.2.3, Table 6 | High-voltage and low-voltage earthing are interconnected where practicable. Where low-voltage circuits leave the high-voltage earthing area, earth potential rise is held to 1,200 V for faults cleared within 5 s and 250 V beyond 5 s, unless a global earthing system exists. |
| IEC 61936-1:2021 | 8.6, Annex E | For outdoor high-voltage installations the analysis method and protection level against direct strokes are agreed with the user. Lightning rods and shield wires shall be earthed. Buildings and similar structures follow IEC 62305. |
| IEEE Std 80-2013 | Clause 16.4, Figure 32 | Grid design runs through twelve steps: field data, conductor size, tolerable voltages, initial layout, grid resistance, grid current, ground potential rise, mesh and step voltage, the two voltage checks, revision, and detail design. A ground potential rise above the touch limit is not a failure by itself. |
| CEA Safety Regulations 2023 | Schedule II Forms II and III | Inspection forms ask for two earth connections, the recorded electrode resistance, tested protective bonding, loop impedance at the origin and for each circuit and every source, annual earth resistance measurement, and arresters near transformers. |
What we ask for before design starts
- Single-line diagram with sources, operating modes and earthing arrangement
- Equipment list with impulse withstand levels
- Cable routes and every point where services enter
- Fault levels and protection clearing times
- Existing earthing and lightning protection records
- Site layout with fences, pipes, rails and neighbouring installations
Engineering depth: from the LPES Knowledge Hub
Topic studies written against the current standards. Open each part for the method, the mistakes to avoid and the checklist.
IS 3043:2026 · LPES Knowledge Hub H-50
Design of a Substation Earthing System
Designing the earthing system of a substation above 1 kV a.c. is not a single calculation but an iterative procedure: collect the fault data and layout, lay out an initial earth grid, check whether the installation already sits inside a global earthing system (if so the design is complete), otherwise work out the current that actually flows into the earth, turn that into an earth potential rise, compare that rise against the permissible touch voltage curve, and if it fails, add additional safety measures, recompute, and check touch, step and transferred-potential limits again until every criterion is satisfied. IS 3043:2026 sets this out as clause 10.3 (steps a to n) and gives the whole logic as a flowchart in Figure 63, which is the master decision diagram the rest of Clause 10's earthing design work hangs on.
How it is applied
- In practice, a designer working through Figure 63 starts by assembling four numbers and one drawing: the prevailing fault current (with the supplier's figure, plus a growth allowance if asked for), the fault clearance time, the preliminary grid layout, and the current actually expected to flow into the earth given the neutral-earthing arrangement at this particular substation.
- The very next decision — "is this part of a global earthing system?" — is deliberately placed before any resistivity survey or grid calculation, because if the answer is yes, the entire chain of touch-voltage, step-voltage and transferred-potential calculations collapses to a single validation measurement (earth potential rise UE below the permissible touch voltage UTp).
- Where the installation stands alone (not part of a global earthing system), the designer must do a proper soil-resistivity survey, lay out the grid, compute IE and ZE for that specific layout and soil, and derive UE. That number is checked first against the permissible touch voltage for the known fault duration (not the step-voltage or transferred-potential limits yet — those are later, separate checks).
- If UE already clears UTp and Table 28's interconnection/separation requirements are met, the basic design is done.
- If not, the designer does not abandon the layout; the Code's explicit next move is to apply Additional Safety Measures and/or credit additional body-path resistances (gloves, footwear, gravel surfacing — but only where the location is restricted to people wearing that PPE), and then re-derive the governing touch-voltage figure, this time as the actual UT or the prospective UvT/UvTp pair.
- Step voltage and, separately, transferred potential and LV stress voltage are checked at this stage as independent hazards, not folded into the touch-voltage number. Only when every one of these checks clears does the flowchart terminate in "Design Complete"; otherwise the designer loops back to "Improvement of design" and repeats.
- The clause's final paragraphs are applied as closing checks rather than new calculations: every exposed-conductive-part must actually be earthed; extraneous-conductive-parts are earthed "if appropriate" (a judgement call, not an automatic requirement); any structural electrode that is bonded in must be treated as part of the system (and verified); and any cathodically protected structure that is deliberately kept out must be clearly labelled so a future maintenance team does not undo the separation.
Common mistakes
- Treating "part of a global earthing system" as a default assumption rather than something that must be established by sample measurement or calculation per 10.2.4; the Code requires this to be actively determined, not presumed.
- Checking UE against UTp and stopping there, without separately checking step voltage and transferred/stress voltage to the LV system — the flowchart treats these as separate, later gates, not as automatically satisfied once the touch-voltage check passes.
- Crediting additional body-path resistances (gloves, footwear, gravel) in locations that are not actually restricted to PPE-wearing personnel; Note 8 is explicit that this credit is only valid where such PPE use is enforced.
- Skipping the "Improvement of design" loop and instead simply recalculating UT with more favourable assumptions without actually changing the design (adding ASM, enlarging the grid, grading the surface, etc.) — the flowchart's loop exists precisely so that a failed check leads to an actual design change, not a recalculation exercise.
- Forgetting that a structural earth electrode left unbonded still requires verification that the rest of the system meets the safety requirements without it; "we didn't bond the rebar" is not itself a safe design unless checked.
- Leaving a cathodically-protected structure's separation from the earthing system unlabelled, so that a later maintenance team re-bonds it and unknowingly defeats the cathodic protection, or conversely assumes it is still separated when it has since been bonded.
Design checklist
- Data collected: IF (with growth margin if used), tf, preliminary layout.
- Global-earthing-system status actively determined (not assumed) — if yes, validated by ZE/UE measurement (UE below UTp) and design closed without further touch/step/transferred-potential work.
- If no global earthing system: soil resistivity surveyed and grid laid out against it.
- IE derived from IF for the actual neutral-earthing condition.
- ZE estimated for the finalised grid and soil.
- UE = ZE × IE calculated.
- UTp obtained from Figure 5 for the correct fault duration.
- UE < UTp and Table 28 requirements both checked.
- If the above fails: ASM and/or restricted-location additional resistances applied, then UT (or UvT/UvTp) recalculated.
- Step voltage checked separately (5.2.4).
- Transferred potential and LV stress voltage checked separately (Table 28, Figure 5).
- Every exposed-conductive-part confirmed earthed; extraneous-conductive-parts earthed where appropriate.
- Structural electrode bonding decision made and, either way, verified.
- Cathodically-protected structures' separation (if any) clearly labelled.
IEC 62305-4:2024 · LPES Knowledge Hub H-49
Selecting SPDs by lightning current test class I II III and telecom classes D1 C2, when class I is mandatory
Once you know where an SPD has to sit in a structure's electrical system, the next decision is which discharge capability that SPD needs to have — in plain terms, how much lightning current it must survive without failing. Getting this choice wrong in either direction is expensive: an under-classed SPD tested only to class II sitting where partial lightning current actually flows will fail catastrophically on the first real strike; an over-classed class I SPD installed everywhere "to be safe" adds unnecessary cost and, in some circuit positions, unnecessary follow-current and coordination complexity. The clause gives the rule for making that call correctly, and points to IEC 62305-2:2024 Annex B for the numeric current values that then size the SPD.
How it is applied
- In practice, an engineer working through Annex C classification for a given SPD position runs through this sequence: (1) confirm, from C.2.1 / Figure C.1, which source(s) of damage (S1-S4) that SPD position is exposed to; (2) check whether the structure carries an external LPS, or whether direct-lightning protection is otherwise specified for it — if yes, class I / D1 is required at the entrance SPD without further debate; (3) if there is no external LPS, check whether a direct or partial strike to the incoming overhead line between the last pole and the service entrance is a credible event for that specific site — if yes, class I / D1 may still be needed at or near the origin of the installation; (4) for any SPD not caught by rules (2) or (3), and for any secondary equipment-proximate SPD flagged by Figure C.1 items 2 or 4, apply class II / C2 by default, and only escalate to class I / D1 if the specific oscillation/induction or source-of-damage condition at that position calls for it; (5) where the classification is borderline on S1/S3 exposure alone, check the NOTE 1 frequency condition (ND + NL + NDJ ≤ 0,01/year) against the site's own IEC 62305-2 risk assessment before finalising the lighter class; (6) once class I or class II is settled for each SPD position, take the classification into IEC 62305-2:2024 Annex B, together with the structure's required LPL and the specific source of damage, to read off the actual numeric Iimp or In value the SPD must be rated to.
- This clause's decision therefore feeds directly into procurement and specification documents: it is what an engineer points to when a datasheet is checked for "Class I, tested to IEC 61643-11" versus "Class II, tested to IEC 61643-11" (or the D1/C2 telecom equivalents), and it is the clause that should be cited on a design basis or SLD annotation whenever an SPD's test class is specified.
Common mistakes
- Specifying class II everywhere on a structure that has an external LPS, on the assumption that "the SPD just needs to handle surges" without checking whether the specific position sits in a genuine lightning-current path — C.2.2's should/shall wording makes class I mandatory, not optional, once the structure is LPS-protected.
- Treating class I and class D1 (or class II and class C2) as separate, unrelated classification schemes rather than recognising they are the same underlying discharge-capability tier expressed for two different product/circuit types (power versus telecommunication/signal).
- Reading NOTE 1's 0,01-per-year frequency condition as a blanket exemption from class I anywhere on a low-risk site, when it only addresses the S1/S3-based justification for class I — it does not override the separate, unconditional LPS-presence rule.
- Confusing Iimp (class I test parameter, associated with charge transfer Q and specific energy W/R) with In (class II test parameter, an 8/20 waveshape current) when reading SPD datasheets — the two are tested to entirely different stress regimes and are not interchangeable ratings.
- Assuming the numeric current value an SPD needs to be rated to can be derived from C.2.2 alone — this clause only sets the class (I/D1 vs II/C2); the actual amperage comes from IEC 62305-2:2024 Annex B.
Design checklist
- Has the source of damage (S1-S4) at this specific SPD position been established from Figure C.1 / the related topic?
- Does the structure carry an external LPS, or is direct-lightning protection otherwise specified? If yes, has class I/D1 been specified at the relevant entrance SPD(s) without exception?
- If there is no external LPS, has the credibility of a direct/partial strike to the incoming overhead line (last pole to entrance) been assessed, and class I/D1 applied at or near the origin if that risk is real?
- For every secondary, equipment-proximate SPD (Figure C.1 items 2 and 4), has the oscillation/induction exposure at that specific position been checked to confirm class II/C2 is sufficient, rather than defaulting without review?
- Where class I is being waived on S1/S3 grounds alone, has the NOTE 1 frequency condition (ND + NL + NDJ ≤ 0,01/year) actually been checked against the site's IEC 62305-2 risk assessment, rather than assumed?
- Has the correct telecom-line equivalent (D1 for class I, C2 for class II) been specified for any telecommunication or signal-line SPD, matching the power-line classification logic?
- Has the classification decision (class I/D1 or II/C2) been carried forward correctly into the IEC 62305-2:2024 Annex B lookup for the actual Iimp/In numeric rating?
Try the numbers
Protection level explorer
- Rolling-sphere radius
- 45 m
- Mesh size
- 15 × 15 m
- Down-conductor spacing
- 15 m
- Peak current covered
- 100 kA
- Coefficient ki
- 0.04
- Interception efficiency
- 90%
Values from IEC 62305-1 and IEC 62305-3. The level for your structure comes from the risk assessment.
Tolerable touch and step voltage
- Tolerable touch voltage
- –
- Tolerable step voltage
- –
- Surface derating Cs
- –
IEEE Std 80-2013, equations 27 and 29 to 33. Set the thickness to 0 for no crushed-rock layer. These are limits; the grid design must keep mesh and step voltage below them.
What we find on audits
- Equipment earths and lightning earths kept separate
- Surge protective devices chosen without coordination or the right voltage rating
- Long connecting leads that add kilovolts to the protection level
- Data and signal lines left unprotected while power lines are protected
- No inspection after a strike, so failed devices stay in service
What you receive: the LPES Protection Passport
- As-built drawings of the installed system
- Risk assessment and design calculations
- Test results: earth resistance, continuity, SPD checks
- Component list with part codes and type-test references
- Inspection schedule for the protection level
Lightning to Load: one accountable partner
- Assess
- Design
- Specify
- Supply
- Implement
- Verify
- Assure
Standards basis
IEC 62305-2, -3 and -4:2024 (Ed. 3) · IEC 61643 series · IEEE 80-2013 · IEC 61936-1:2021 · IS 3043:2026 · CEA Safety Regulations 2023 · IS 732:2019 · IEC 60364-6:2016 · IEC 61936-1:2021
Reviewed by LPES engineering, November 2026. Clause and table numbers follow IEC 62305:2024 (Edition 3) and IS 3043:2026.
Questions engineers ask
Why two earth connections per item of equipment?
So that the loss of one connection does not leave the equipment unearthed; it is required practice in Indian substations. Substation & Switchyard Earthing
When is a neutral earthing resistor used?
To limit earth-fault current on medium-voltage systems and reduce damage and voltage rise. Neutral Earthing Equipment
Do substation control rooms need SPDs?
Yes. Auxiliary supplies, SCADA and protection circuits are exposed to switching and lightning surges. Type 1 Lightning-current Arresters
How is portable earthing selected?
By the short-circuit current and its duration at the point of work, to IEC 61230. Portable & Temporary Earthing
How is the finished grid tested?
By fall-of-potential grid resistance measurement, with step and touch voltage measurement where required. Grid Resistance / Substation Earthing Test
Get this solution quoted for your site
Send the drawings or the basic dimensions. LPES returns the design parameters, the BOQ with part codes and the price in one offer.
