Do you need HT supply?
If your required demand goes above the LT limit in the KERC Electricity Supply Code, your ESCOM (BESCOM, MESCOM, CESC, HESCOM or GESCOM) supplies you at HT, usually 11 kV, and you own and maintain the transformer and HT equipment. HT supply also gives steadier voltage for motors and machines, and HT tariffs are structured differently from LT, with demand charges based on your contract demand in kVA.
Very large loads are supplied at 66 kV or above from KPTCL substations. That involves a dedicated line or bay and a longer feasibility process.
Sizing the transformer
Transformers are rated in kVA. A simple way to estimate the size:
- Add up the connected load in kW.
- Apply a diversity factor, because not everything runs at once. This gives the maximum demand.
- Divide by the power factor to get kVA.
- Add a margin for growth and pick the next standard rating.
Connected load 180 kW × diversity 0.8 = 144 kW maximum demand. 144 kW ÷ 0.9 power factor = 160 kVA. With about 25% growth margin you need around 200 kVA, so a 250 kVA transformer is the practical choice.
Common standard ratings are 100, 160, 200, 250, 315, 400, 500, 630 and 1000 kVA. Oil-filled transformers suit outdoor yards. Dry-type transformers suit indoor electrical rooms and high-rise buildings where fire risk must be kept low.
Limits, charges and forms are set by KERC, your ESCOM and the Electrical Inspectorate and are revised from time to time. Use this guide to prepare, and confirm the current requirement for your case before you apply. We check it for every project.
What goes into an HT installation
| Equipment | Purpose |
|---|---|
| HT incoming line or cable | Tapping from the ESCOM 11 kV / 33 kV feeder to your premises |
| AB switch, DO fuse, lightning arresters | Isolation and surge protection on overhead incomers |
| VCB or RMU | HT switching and protection with relays |
| HT metering cubicle (CT/PT) | The ESCOM's energy metering at HT |
| Transformer | Steps 11 kV down to 433 V |
| LT main panel (ACB / MCCB) | Distributes 415 V to your loads |
| APFC panel | Keeps power factor high to avoid tariff penalties |
| DG set and changeover | Backup power with interlocking |
| Earthing system | Separate neutral, body and lightning arrester earths |
The approval and work sequence
- Load study and contract demand. We calculate demand and agree the contract demand you will apply for.
- Application and feasibility. The ESCOM checks which feeder and substation can supply you and whether line extension is needed.
- Estimate and charges. The ESCOM issues an estimate. You pay the applicable charges and deposits.
- CEIG drawing approval. SLD, layout, earthing layout and equipment details are submitted and approved.
- Procurement and installation. Transformer, HT and LT panels, cabling and earthing are installed as per the approved drawings.
- Testing and commissioning. All pre-commissioning tests are carried out and documented.
- CEIG safety inspection. The inspector visits and issues approval for energisation.
- Metering, agreement and supply release. The ESCOM tests and seals the HT meter, the supply agreement is signed and the line is charged.
Steps 4 and 5 are where time is saved. Ordering the transformer and panels while the drawing approval is in progress, with specifications fixed in advance, avoids weeks of waiting.
- 1Load study and contract demand
- 2ESCOM feasibility and estimate
- 3CEIG drawing approval, while equipment is ordered
- 4Installation and pre-commissioning tests
- 5CEIG safety inspection
- ✓HT metering, agreement and line charging
Tests before energisation
- Transformer: insulation resistance, winding resistance, turns ratio, oil breakdown voltage (BDV)
- HT cables: insulation resistance and high-voltage test after termination
- Protection: relay testing by secondary injection, breaker trip checks
- CT/PT: ratio and polarity checks
- Earthing: resistance of each earth pit and the combined grid
- LT panels: insulation resistance, busbar tightness, interlocks
Questions
Should I choose 11 kV or 33 kV supply?
It depends on your demand and which network the ESCOM has near your site. Most commercial and mid-size industrial consumers are supplied at 11 kV. Larger loads may be supplied at 33 kV. The ESCOM decides during feasibility.
Who maintains the transformer after the connection?
For an HT consumer, the transformer and HT equipment on your side of the meter are your responsibility. An annual maintenance contract covers periodic oil testing, cleaning, relay checks and earth testing.
Can I buy the transformer from any manufacturer?
The transformer must meet the relevant standards and come with test certificates. For equipment that will be handed over to the ESCOM, such as in layouts, the ESCOM may specify approved makes.
What is contract demand?
The maximum demand in kVA you agree with the ESCOM. Demand charges on your bill are calculated on it, so it should be set realistically, not too high or too low.
Need this done for you?
We handle the electrical work and the ESCOM, KPTCL and CEIG liaisoning anywhere in Karnataka, with BESCOM, MESCOM, CESC, HESCOM and GESCOM. Email basavalalith.electricals@gmail.com or use the enquiry form.
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