Senseible

How do the 50 kilovolt-ampere (kVA) and 75 kVA voltage stabiliser reports for rice mills work out their saving, and does the loss figure mean power wasted?

A voltage stabiliser saves 7,518 kilowatt hours a year on a 50 kVA rice mill set and 9,503 on a 75 kVA set in the Bureau of Energy Efficiency (BEE) Ganjam reports, both exactly 10% of the mill's power. On our reading, the reports' loss is power drawn, not power wasted, so measure first.

What the stabiliser is for, in plain words

Many Ganjam mills sit at the end of a transformer that serves too many users. The reports measured only 270 to 350 volts (297 to 350 in the summary) where 415 is needed, and say about 30% of units face this. Motors on low voltage draw more current and run hot, like a pump struggling on low water pressure. A voltage stabiliser is a box that lifts the supply back to 415 volts, a bit like a pressure regulator on a water line. The kVA rating is its size, like the engine size of a car.

The two reports side by side

How the saving is worked out

In plain words: both reports call the whole power the mill draws a loss, then say the stabiliser saves a share of it. The sums are below if you want to follow them.

Each report takes a measured mill. It writes down the voltage V1 and current I1, then a 'resistance' R = V1 / I1, and a 'power loss' P1 = I1 x I1 x R. Then it assumes the stabiliser lifts the voltage to V2 = 415, that the same power is drawn so the current falls to I2 = I1 x V1 / V2, and works out P2 = I2 x I2 x R. The saving is P1 minus P2.

Because R is V1 divided by I1, P1 is simply V1 x I1. For the 50 kVA mill that is 310 x 21.1 = 6,541, the 6.54 printed. This is the power the load draws, not the heat lost in the motor wiring. The loss is the whole load. The saving then works out as P1 x (1 minus (V1 / V2) x (V1 / V2)): 6.54 x (1 minus 0.558) = 2.89 kW.

That is our own reading of the printed tables. It means the reported saving is a function of the measured volts only, and says nothing about how much of the current is actually wasted in windings and cables. A true loss from low voltage is a smaller share of that 2.89 kW. The reports do not show a measured before and after.

One more pattern worth knowing

The 50 kVA saving is 7,518 / 75,000 = 10.0% of the mill's yearly power. The 75 kVA saving is 9,503 / 95,000 = 10.0%. Two mills at different voltages, 310 and 360, land on the same share. The reports do not say why. Treat 10% as the ceiling of a claim, not a measured result.

Before you pay for one

  1. Log the three phase voltages at the mill's board over a week, at the hours the mill runs.
  2. Ask the electricity supplier whether the transformer will be upgraded. That fixes the cause.
  3. If you do buy, read the mill's meter for two weeks of similar paddy before and after, and compare kWh per tonne of paddy.

The 50 kVA mill, line by line

These are the reports' printed figures with our own arithmetic on top. The volts times amps reading is ours. Costs are the reports' 2010 prices.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. The standard read is those bills, so any change after fitting shows as units on your bill. Voltage logging can be added as a custom service, on request. Meanwhile keep your own voltage log beside the bills.

Sources: BEE and SAMEEEKSHA detailed project report: voltage stabiliser 50 kVA, Ganjam rice mill cluster, BEE and SAMEEEKSHA detailed project report: voltage stabiliser 75 kVA, Ganjam rice mill cluster, CEA CO2 Baseline Database for the Indian Power Sector, version 22.0 (FY 2025-26 grid factor)

Last reviewed 2026-11-07. Costs and paybacks are at the reports' 2010 prices. The volts times amps reading and the 10% pattern are our own arithmetic on the printed tables; confirm with a measured before and after.