Most plant owners look at the electricity bill once a month, see the total, and move on. But an industrial HT or LT bill in India is not just "units × rate". It is made of several parts — energy charges, demand charges, power factor adjustments, time-of-day (ToD) rebates or surcharges, electricity duty and fuel adjustment. Two of those parts, power factor and maximum demand, are almost entirely within your control. The problem is that you only find out how you did after the billing month has closed.
This article explains how each part works, what typically goes wrong, and how continuous monitoring with alerts turns them from a monthly surprise into something your maintenance team manages every day.
1. Understand what you are actually billed for
Tariff structures differ between DISCOMs and states (DGVCL, MGVCL, PGVCL, UGVCL and Torrent Power in Gujarat, MSEDCL in Maharashtra and so on), and they change with each tariff order. Always check your own tariff schedule. Broadly, an industrial bill contains:
| Component | What it depends on | Can you control it? |
|---|---|---|
| Energy charge | kWh (or kVAh) consumed | Yes — by reducing waste and idle load |
| Demand / fixed charge | Contract demand and recorded maximum demand (kVA) | Yes — by managing peaks |
| Power factor adjustment | Average PF over the month | Yes — with capacitor banks / APFC |
| ToD charge or rebate | When during the day you consume | Partly — by shifting flexible loads |
| Duty, taxes, fuel adjustment | Set by state / regulator | No |
2. Power factor: penalty, incentive and kVAh billing
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). Motors, transformers, welding sets and induction furnaces draw reactive power (kVAr), which pulls PF down. The utility has to supply that reactive current even though it does no useful work, so most tariffs reward a high PF and penalise a low one.
A common structure is a penalty when the monthly average PF falls below a threshold (often 0.90) and an incentive or rebate when it stays above a higher level (often 0.95). Many states have moved industrial consumers to kVAh billing, where you pay for apparent energy directly — so every point of PF below unity raises the bill even without a separate penalty line.
Why PF goes wrong even when you have an APFC panel
- Capacitor stages fail or lose capacity over time and nobody notices until the bill arrives.
- The APFC relay is set incorrectly, or its CT is in the wrong phase.
- Load pattern changes — a new machine, a shift change — and the existing kVAr rating is no longer enough.
- Over-correction at light load (night, Sundays) pushes PF leading, which some tariffs also treat as poor PF.
With PF logged every few seconds from the main incomer, you can see exactly when PF drops, for how long, and on which feeder. An alert at 0.92 gives the maintenance team time to check capacitor contactors before the monthly average is ruined.
3. Maximum demand: the most expensive 15 minutes of your month
Demand charges are calculated on the highest average kVA recorded in any demand interval (typically 15 or 30 minutes) during the billing month, usually subject to a minimum percentage of your contract demand. If the recorded maximum demand exceeds the contract demand, many tariffs apply a much higher rate on the excess.
That means one bad interval — say, all compressors and a furnace starting together after a power cut — can set your demand charge for the whole month.
What demand monitoring lets you do
- See the running demand of the current interval live, not just the meter's monthly MD reading.
- Get an alert at, for example, 90% of contract demand so someone can delay a non-critical load.
- Find out which machines or feeders contribute to peaks by monitoring sub-meters.
- Decide with real data whether to increase or reduce contract demand at the next revision.
Many plants pay for a contract demand far above what they use, "just to be safe". Others are regularly crossing it. A few months of interval data usually makes the right number obvious.
4. Time-of-day tariffs
Under ToD tariffs, energy consumed in peak hours costs more and energy in off-peak (often night) hours costs less. The exact windows and rates are fixed in your state's tariff order. Loads such as water pumping, batch heating, charging, chillers with thermal storage or non-urgent grinding can often be shifted. Hour-wise consumption reports show how much of your kWh falls in each slot and what moving one load would save.
5. Idle and base load: the hidden kWh
Look at your plant's consumption at 2 a.m. on a Sunday. Compressors leaking into an idle air network, lighting, HVAC, transformer losses and machines left on standby often add up to 10–20% of a working-day load. A "night base-load" chart makes this visible in a week. Fixing compressed-air leaks and switching off idle equipment are usually the cheapest savings you will ever find.
6. What to monitor, and where
- Main incomer — kW, kVA, kVAr, PF, phase-wise voltage and current, frequency, kWh/kVAh and demand. This matches what the utility meter sees.
- Major feeders or machines — compressors, furnaces, chillers, large motors. This tells you who is using the energy.
- APFC panel — PF before and after correction, to check that capacitor stages are working.
- DG set, if you have one — kWh and run hours, to compare grid and diesel cost.
Almost every modern multifunction energy meter (from brands commonly used in Indian panels) has an RS-485 port speaking Modbus RTU. You do not need to replace meters — you need a way to read them continuously.
7. Turning data into action
Data alone does not cut bills. A simple routine works well:
- Daily: check yesterday's kWh, cost, peak demand and average PF on one screen.
- Instantly: alerts for PF below limit, demand above 90% of contract, phase failure or voltage unbalance.
- Weekly: compare night base-load and shift-wise consumption.
- Monthly: a report that matches the utility bill, with a forecast during the month so there are no surprises.
Where SensorLoop fits
This is exactly the workflow we built the SensorLoop platform around. A ModbusSudo gateway reads your existing energy meters over Modbus, and the energy dashboard shows live load, PF, demand versus contract demand, daily cost with your tariff, night base-load and a month-end bill forecast — with WhatsApp alerts when something crosses a limit. If you want to see it on your own panel, talk to us.