Maximum Demand and Time-of-Day Tariffs: Plan the Expansion on Interval Data

When a plant expands, two things on the electricity bill move: the maximum demand the meter records, and the share of energy used in expensive or cheap hours. Both are priced by tariff orders that differ by state and are revised regularly, and both are decided by the shape of the load — which machines run together, and when. Monthly totals cannot show that shape. The meter's interval data can.

This guide sets out the data to collect, how measured demand relates to contract demand, how to compare shift and tariff scenarios for the expanded plant, and what to verify in your tariff order before deciding. For the supply-side headroom, use the factory electrical spare-capacity calculator.

Read the interval load profile

A billing meter integrates demand over a fixed period — your bill or tariff order states it — and records the month's highest value as maximum demand. Its load survey, or a power analyser on the incomer, shows every interval, which is what planning needs.

Interval load profile checklist

Measured demand versus contract demand

Contract demand is the maximum demand, in kVA, that the DISCOM has sanctioned. PSPCL's connection FAQ defines it that way, and separates it from sanctioned load (in kW) and from connected load (the total of equipment ratings). Maximum demand is what your meter actually recorded. The tariff order connects the two:

• Demand or fixed charges are commonly billed on the higher of recorded maximum demand and a set percentage of contract demand, so a contract demand far above real peaks costs money every month. Whether a floor applies, and at what percentage, is in your tariff order.
• Demand recorded above contract demand is usually charged at a higher rate, and repeated exceedances can lead to the sanctioned figure being revised.
• For consumers with smart meters, the Electricity (Rights of Consumers) Amendment Rules, 2023 (Ministry of Power, G.S.R. 437(E), 14 June 2023) provide that a month in which recorded maximum demand exceeds the sanctioned load is billed on the actual recorded maximum demand; that where the sanctioned load is exceeded at least three times in a financial year, the lowest of those monthly maximum demands becomes the revised sanctioned load; and that reductions follow the state supply code.

Contract demand also shapes the connection itself. PSPCL's FAQ notes that demand up to 100 kVA is usually supplied at LT, above 100 kVA and up to 5,000 kVA at HT, and above 5,000 kVA at EHT. Crossing a band changes the supply voltage, the substation and the connection charges, not just the bill (see transformer capacity for factory growth).

Shift and tariff scenarios for the expanded plant

Model the expanded plant as a few concrete scenarios rather than one average. For each, build the interval profile, then price it with your tariff order:

1. Baseline — the new load added to the existing shift pattern.
2. Shifted — the new line, or the movable loads (batch starts, water pumping, compressed-air top-up, thermal storage, EV charging), moved to other time blocks.
3. Peak-managed — staggered starts, interlocks on motors that tend to start together, a demand controller, and power-factor correction at the loads and the incomer.
4. With on-site generation or storage — rooftop solar reducing daytime import, or a battery charging in cheap blocks and discharging into the peak.

For each scenario record the maximum demand (kVA) and the power factor at the peak, the energy in each time-of-day block (in kWh, or in kVAh if your tariff bills kVAh), and any operating cost of the change, such as night-shift labour, storage or noise limits. The bill is then the demand charge on the billing demand, plus the energy in each block at that block's rate, plus the other charges in the order.

The national rule sets the direction of time-of-day pricing. Under the same 2023 amendment rules, time-of-day tariffs for commercial and industrial consumers with maximum demand above 10 kW were to take effect no later than 1 April 2024. For these consumers the peak-period tariff is not less than 1.20 times the normal tariff, the tariff in "solar hours" (eight hours a day, specified by the State Commission) is at least 20% below the normal tariff, and the time-of-day tariff applies to the energy charge. The hours of each block and the actual rates are your State Commission's.

Decision table: which lever moves which charge

For the power-factor leg, the power factor correction calculator sizes the kVAr and how power factor inflates industrial bills explains the charges. For the storage leg, see battery energy storage systems; for solar, the solar payback calculator.

Verify each current tariff order before deciding

Tariff orders are revised regularly and differ by state, category and supply voltage. Before acting on any scenario, check the current order and supply code for your category:

• the basis of demand charges and any billing-demand floor;
• the charge for exceeding contract demand;
• the time-of-day blocks by season, and the peak and solar-hour rates;
• whether energy is billed in kWh or kVAh, and any power-factor incentive or penalty;
• the procedure for reducing or increasing contract demand, and any minimum period after a change;
• the demand integration period your meter uses.

Rule 8B of the 2023 amendment rules requires DISCOMs to display each category's tariff on their website and to notify consumers of a tariff change at least a month ahead, so the current schedule should be available from your DISCOM. The consumer-rights rules themselves are amended from time to time; check the version in force.

If the answer is a contract-demand change or a new connection, that is a DISCOM application. Secured Engineers' design and approvals service prepares DISCOM filings alongside the electrical design, and our electrical infrastructure team builds the supply-side works; to have your scenarios reviewed, request a scope review.

Sources and how to verify

• Ministry of Power, Electricity (Rights of Consumers) Amendment Rules, 2023, G.S.R. 437(E), 14 June 2023: rule 5(5A)–(5B) (smart-meter maximum demand), rule 8A (time-of-day tariff) and rule 8B (display of tariff). Gazette copy hosted by the APSERC; announced in a PIB release of 23 June 2023.
• Punjab State Power Corporation Ltd, FAQs — new connection and extension of load: definitions of connected load, contract demand and sanctioned load, and supply-voltage bands.
• Uttar Pradesh Power Corporation Ltd, application form for an industrial electricity connection: the information a DISCOM asks for with new or additional load (not evidence of current fees or timelines).

Confirm locally: the current tariff order for your category and voltage, your supply code's procedures for changing contract demand, and the integration period your meter uses.