Transformers: How Many kVA, What It Costs, and How to Apply or Rent From the Utility
When a large house, shop, farm or factory outgrows a low-voltage meter it must install its own (“dedicated”) transformer and buy power at high voltage. This page condenses the official PEA and MEA rules and fee tables: when a transformer is required, how to size it in kVA from your real load, the fees and deposits the utilities charge, buying versus renting, the high-voltage application steps and the published service timelines — with a straight answer on what has an official price and what needs a quotation.
You need your own (dedicated) transformer once your load exceeds what a low-voltage meter can carry. Under PEA's regulation, a customer with maximum demand of 30 kW or more — or dedicated transformers totalling 100 kVA or more — is a “large user”, and in underground-network areas a load above 250 kVA must take 22/33 kV supply through its own transformer. Rough size = peak simultaneous kW ÷ 0.8–0.9, plus 20–30 % headroom (an 80 kW load → 100–125 kVA). No utility publishes a price for the transformer itself — it depends on kVA, voltage and type, so you need quotations — but PEA/MEA fees and deposits are in official tables (below), and PEA rents transformers with protection gear for temporary and construction supply on contracts of up to one year.
How Much Does a Transformer Cost?
Utility fees and deposits (official tables, excl. VAT)
| Item | PEA — provinces | MEA — Bangkok, Nonthaburi, Samut Prakan |
|---|---|---|
| Inspection fee — HV metering (dedicated transformer) | Below 69 kV: ≤30 A 15,000 THB / >30 A 20,000 THB | 12/24 kV permanent: 300–800 kVA 3,700 · 1,000–1,600 kVA 4,900 · 2,000–2,500 kVA 6,100 · up to 12,200 THB at 10,000–15,000 kVA |
| Electricity-use deposit | HV meter below 69 kV: 400 THB per kVA · 69 kV and above: 4 THB per kVA (max 50,000) · LV CT meter: 100 THB/A (1-phase) / 300 THB/A (3-phase) — waived for new Type 1–2 users | Permanent 12/24 kV: official table shows 0 THB at every size (no deposit from new Type 1–2 applicants) · Temporary 12/24 kV: 105,000 THB (300 kVA) up to 3,750,000 THB (15,000 kVA) |
| Inspection fee — LV CT meter (load above a plain meter, still low voltage) | 1-phase 1,600 THB · 3-phase 4,200 THB | LV permanent meters up to 400 A 3-phase: 700 / 1,500 / 2,500 THB by size |
| Temporary HV supply (construction / events) | Transformer + protection gear can be rented from PEA, contract ≤1 year (renewable) — rental and deposit per PEA's schedule, call 1129 | Connection 10,000–20,000 THB per job + distribution-equipment rental 4,350 THB/month + deposit by kVA (left column) |
Source: PEA's service-application fee table (in force since 1 Jan 2020) and MEA's service-application rates. Figures exclude 7 % VAT and **exclude** line-extension / distribution-construction contributions, which PEA estimates site by site according to the total transformer kVA requested (regulation clause 9.10).
How Many kVA Do I Need? Sizing From Your Load
Standard transformer sizes in the Thai distribution system and the approximate load each carries
| Size (kVA) | Approx. simultaneous load (kW at PF 0.85) | Typical users |
|---|---|---|
| 20 / 30 / 50 / 75 (1 เฟส) | ≈ 17–64 kW | 1-phase 22 kV (PEA): large rural houses / farms beyond the LV line |
| 50 | ≈ 43 kW | Very large homes, small resorts, shops with many air-conditioners |
| 100 | ≈ 85 kW | Large shops, small apartment blocks, shrimp farms with several pumps, small factories |
| 160 | ≈ 136 kW | Small–medium factories, office buildings, small cold rooms |
| 250 | ≈ 213 kW | Ceiling of the LV CT meter in PEA underground areas — above this you take 22/33 kV |
| 300 / 315 / 400 | ≈ 255–340 kW | Medium factories, commercial buildings (300 kVA is an MEA network standard size) |
| 500 / 630 | ≈ 425–536 kW | Medium–large factories, hotels, hospitals |
| 750 / 800 / 1,000 / 1,250 / 1,500 / 2,000 | ≈ 638–1,700 kW | Large factories, malls (often several units; MEA standardises on 750/1,000/1,500 kVA) |
Sizes come from PEA's CT-selection tables by transformer rating (1-phase 20/30/50/75 kVA · 3-phase 50/100/160/250 kVA and the 250–10,000 kVA HV bands) and MEA's equipment-preparation guide (300/500/750/1,000/1,500 kVA), consistent with the IEC/TIS preferred series. The kW column is an estimate at PF 0.85 with no headroom — have an engineer confirm before ordering.
A 100 kVA Transformer: What It Costs and Who It Suits
When Is a Dedicated Transformer Required?
The thresholds in the official regulations and guides — see which applies to you:
The low-voltage meter tops out: PEA moves 3-phase users drawing more than 80 A per phase to an LV CT meter (no transformer yet); MEA's fee table covers LV permanent meters up to 400 A 3-phase — beyond that you move to high voltage.
PEA's definition of a “large user”: maximum demand of 30 kW or more, or dedicated transformers totalling 100 kVA or more — and under the tariff structure, any month in which a small business (Type 2) reaches 30 kW it is reclassified to Type 3/4/5, which adds a demand charge on top of the energy charge.
PEA underground-network areas: demand above 66 kVA up to 250 kVA may stay on low voltage through a CT meter, but above 250 kVA you must take 22 or 33 kV supply through your own transformer.
Upper limits: PEA — more than 10,000 kVA of transformers at 22/33 kV is considered for 115 kV supply · MEA — more than 15,000 kVA must take 69 or 115 kV (≤24 kV equipment guide), and MEA feeds high voltage at 12 kV or 24 kV depending on the area, so ask the district office before ordering equipment.
Effect on your bill: tariffs are split by supply voltage (below 22 kV / 22–33 kV / 69 kV and above) — high-voltage supply gets lower energy and demand rates than low voltage (tables on the factory electricity cost page), but if the meter sits on the low-voltage side of a transformer you own, the utility adds 2 % to billed units and kW to cover transformer losses.
Buying Your Own vs Renting From the Utility
Buy (permanent supply) — the main route for large users
A transformer installed to supply you alone is the customer's property (PEA regulation clause 22.3): you finance it, maintain it and pay for any future relocation. A transformer you source yourself must pass PEA's inspection or test before energization, for a service fee (clauses 27–28; the test is not a quality certification). MEA accepts TIS- or IEC-standard transformers with a specification and routine test report signed by a licensed electrical engineer; transformers built to other standards need type-test reports (impulse, temperature-rise, and partial-discharge for dry types) reviewed before purchase.
Rent from the utility — temporary and construction supply
PEA regulation clause 9.13 lets temporary-supply applicants — building or bridge construction, festivals, events — rent a transformer with protection gear from PEA on a lease of up to one year (renewable yearly). Temple- or government-run events pay no rental; private organisers pay rental plus a transformer deposit at PEA's scheduled rates (ask your PEA office / 1129). On the MEA side, the temporary 12/24 kV table lists a 10,000–20,000 THB connection charge, 4,350 THB/month distribution-equipment rental and a deposit by kVA — details on the temporary construction electricity page.
For permanent supply there is no general monthly transformer-rental scheme from the utilities — private rental firms exist, but their units must pass the same utility inspection or test as a purchased transformer.
How to Apply for High-Voltage Supply With a Transformer: Documents, Costs, Timeline
The sequence in PEA's service-quality standard (MEA follows the same logic through MEA e-Service and its ≤24 kV equipment guide):
File the request with documents
Individuals: ID card (passport for foreigners), house or building registration and proof of ownership or right of possession · Juristic persons: company certificate ≤6 months old, the authorised director's ID, building registration, proof of right to the premises and a sealed power of attorney if someone files on your behalf — at the local utility office or online (PEA Smart Plus / eservice.pea.co.th · MEA e-Service), together with the load layout and an engineer-signed single-line diagram.
Pay the survey / design-review fee
The utility collects the survey and design-review fee and issues a receipt — the service-standard clock has not started yet.
Survey, design and line-extension estimate
Staff survey the site, design the supply point and system layout, and estimate the line-extension works (new poles, lines or feeders if needed) plus, for 22/33 kV applicants, the distribution-construction contribution based on total transformer kVA.
Approval and cost notice
The utility approves the design and notifies the amounts due: line-extension cost, the application / metering-inspection fee and the electricity-use deposit (cash, bond or bank guarantee).
Pay and post the deposit — the clock starts
PEA's service standard counts from the day you pay and meet all conditions: transformers totalling up to 250 kVA are energized within 35 working days · above 250 up to 2,000 kVA within 55 working days (where the distribution system already exists, no external line work is needed, and excluding time spent fixing an internal system that failed inspection).
Construction, transformer installation and inspection
Your contractor installs the transformer, HV switchgear, incoming cable and grounding to the approved design and EIT/utility standards — the utility inspects the internal wiring and equipment and inspects/tests a self-sourced transformer (PEA charges an extra inspection fee after two failed appointments).
Meter installation and energization
Once inspection passes and payment is complete, the utility installs the HV metering (CT/VT) or an LV CT meter, signs the supply contract and energizes — from then on you are billed at the rate class and voltage level you take supply at.
Costs people forget
Contribution and extension: every 22/33 kV applicant pays a distribution-construction contribution by total transformer kVA and co-invests in extending the line from the existing network to the site boundary; the internal system is entirely yours to fund (PEA clause 9.10.1).
A deposit that moves with size: increasing or reducing transformer size, relocating it, changing rate class or running bills above the deposit all trigger a top-up or refund (clauses 12–13).
Transformer and equipment testing: a self-bought transformer must pass the utility's test (fee applies), and you supply, install and maintain the disconnecting and overcurrent-protection gear yourself (clauses 25, 27–28).
The bill after the transformer: a meter on the LV side of your own transformer → units and kW billed +2 % · Type 3 and above carry a demand charge and a minimum bill (not below 70 % of the highest demand charge in the past 12 months) — see the demand charge explainer.
Keeping Your Transformer Healthy
Everything behind the meter, including a dedicated transformer, **is the customer's responsibility to maintain** (PEA clause 22.2), and PEA itself offers paid transformer-maintenance and thermal-imaging hot-spot inspection as auxiliary services. The routine basics:
Check oil level and condition, silica gel, leaks, rust and abnormal noise at least once a year (oil-immersed units).
Tighten connections, clean bushings and insulators, check surge arresters / dropout fuses and the grounding — during a planned outage, by licensed technicians.
Thermal-scan joints and terminals under full load to catch hot spots before they burn.
Review actual load against rating every year — sustained use above 80–90 % of kVA means planning an upsize (the utility must inspect before any transformer change, clause 25.2); if you add rooftop solar, see the interconnection rules and transformer ratios on the grid interconnection page.
About the Author
Compiled by CapSolar's engineering team under Frank Lee (Founder). CapSolar is a commercial & industrial solar EPC/PPA provider in Thailand that works with dedicated transformers and factory high-voltage systems daily, and condenses utility regulations from official documents so business owners can decide with confidence.
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