Load scheduling and load management

Load scheduling is the planned arrangement of the operating times of large loads and processes in a plant so that the total demand stays low and smooth, without reducing production. Load management is the wider set of technical and administrative measures used to control the size and shape of the plant's load curve.

Why load scheduling is important

1. Reduces maximum demand (kVA) charges – industrial tariffs in Nepal (NEA) include a demand charge per kVA per month. If large motors, furnaces and compressors all start together, the peak rises and the demand charge is paid on that peak for the whole month.
2. Uses time-of-day (ToD) tariff – energy is cheaper at night (off-peak) and costliest in the evening peak. Moving flexible loads (pumping, batch furnaces, grinding, charging) to off-peak hours lowers the bill.
3. Improves load factor – a flatter load curve means better use of the transformer, cables and DG set; the same equipment serves more kWh.
4. Avoids overloading of the substation transformer, feeders and backup generator, and reduces voltage dips when big motors start.
5. Reduces losses – I²R losses depend on the square of current, so a flat load gives lower losses than a peaky load for the same energy.
6. Helps the utility – lower system peak reduces load shedding and the need for new generation.

kW  Before scheduling        After scheduling
 |      __                    
 |     |  |                   _________
 |  ___|  |___             __|         |__
 |_|          |_          |               |
 +-------------- time     +--------------- time
   high peak, low LF        lower peak, higher LF

Load management in an industrial plant

Load management techniques fall into these groups:

1. Peak clipping – shedding or limiting non-essential loads (air conditioning, water heaters, some lighting) during peak hours, often with a maximum demand controller that trips selected loads when demand approaches a set limit.
2. Valley filling – adding loads in off-peak hours, e.g. running water pumping, ice/thermal storage or battery charging at night.
3. Load shifting – moving batch processes from peak to off-peak periods; staggering shift start times and motor starting.
4. Strategic conservation – reducing total energy by efficient motors, VFDs, efficient lighting and avoiding idle running.
5. Power factor correction – capacitor banks reduce kVA demand for the same kW, directly lowering the kVA charge.
6. Use of captive generation – running a DG set or captive plant during the costliest hours if its cost per kWh is lower.
7. Monitoring and control – energy meters, SCADA or a load management system to record the load curve, set targets and alarm on excess demand.

Steps: record the existing load curve → identify large and flexible loads → prepare a load schedule matching tariff periods and production needs → install demand controller and PF correction → monitor and revise.

Example: a plant with two 100 kW crushers and a 150 kW pump set that run together in the morning may reach 350 kW peak. Running the pumps at night lowers the peak to 200 kW, saving the demand charge on 150 kW every month.