A load profile is variation of connected load of a power system with time. In industrial installations, electricity tariff is non uniform throughout the day. The 24 hours of the day are divided in 4 parts, namely Time of Day 1 (TOD 1), TOD 2, TOD 3 and TOD 4. These timings vary from state to state and from country to country. The timings are given here for understanding the philosophy. Typical timings and tariffs for TODs are given in following table.
A generalized power system load profile using Energy Management Techniques is shown in fig – 1.
Plant energy performance (PEP) in an important factor to understand improvement in load profile. PEP is the measure of energy consumption in current year for manufacturing output in an industry compared to energy consumption in previous year for same manufacturing output. If energy consumption reduces, there is improvement in load profile and Energy Management programme is successful. If energy consumption increases, it is indication of decline in load profile and failure of Energy Management programme.
Philosophy of TOD
In India, at present, Time of Day (TOD) tariff is applicable for industries in most of the states, but not in all states. But now, there are plans to implement TOD tariff for commercial establishments also. Now as the awareness of load profile management is spreading rapidly among people as well as policy makers, days are not far when TOD based tariff shall also be applicable for residential consumers, small business owners, shopkeepers etc. This will facilitate to understand and implement load profile management also for residential consumers, small business owners etc. This will in turn result in saving in electricity bills by controlling use of electricity which is suited best for existing tariff structure.
Time of Day (TOD) tariff is a tariff structure in which tariff rates are not uniform and vary with time of day. In simple language, rate of using 1 unit of electricity will be different in different time slots from midnight to back to midnight. Time slots are based on off peak hours and peak hours. So basic philosophy is that for peak hours we pay more and for off peak hours we pay less. Hence, we can manage our load profile accordingly to save electricity.
Electricity grids can be compared to a road or a highway where traffic is not uniform throughout the day. Traffic varies in different time slots of the day. This resembles with a grid where load is not uniform throughout the day. During peak hours highways have over traffic, similarly during peak hours, electricity grids are overloaded. Driving on a highway during off peak hours is safe and smooth, similarly using electricity during off peak hours provides us quality and reliability.
Methodologies for load profile management
As a consumer, our purpose is to optimize the use of energy of all kinds namely thermal, chemical, renewable, electrical etc. In case of electrical energy, our aim is to minimize number of units and kVA demand. This is useful for minimizing financial implication and load on National Grid. There are three Methodologies for load profile management namely Energy Conservation, Modifying Shape of Load Profile and Load Shedding to Control Maximum demand. The Methodologies are described as below
By using energy conservation techniques in electrical systems, we can reduce maximum demand, kVA demand and electricity consumption. By using these techniques, the load profile is shifted downwards equivalent to the energy conservation. This is shown in fig 2. Curve 1 shows the load profile without using energy conservation techniques. Curve 2 shows the load profile using energy conservation techniques.
Energy conservation in Electrical systems
- Energy conservation in lighting system
- Install manual dimming control for areas close to daylight.
- Use electronic ballasts
- Use energy efficient luminaires with high lumen per watt like LED lamps, LPSV lamps, CFLs, Metal halide lamps.
- Switch off lights when not in use
- Use proximity switches to automatically switch off electrical equipments when not in use.
- Use of day light for internal areas of buildings and offices
- Use of photo switches for streets and external lights.
- Use intelligent energy saving device system (IESD). In this system lighting fixtures output is automatically adjusted according to availability of daylight. This is called daylight harvesting.
- Use Intelligent energy saving device system (IESD) for lifts. Here, during off peak hours, lights and ACs of lifts are automatically turned off.
- Experiment was carried out by the author in Relay Testing Lab at Rajasthan Atomic Power Station to understand effect of reducing voltage on lux level of 2 X 40 watt fluorescent tube light fitting. By reducing voltage to a practical value for lighting system, saving in electricity is larger while reduction in lux level in the area is comparatively smaller. This is shown in fig 3
The results of the experiment are tabulated as below.
- Reduce excess lux level in a particular area.
- Use dual wattage HPSV lamps in street lights. Here wattage of the lamps is reduced to half for predefined time at night.
- Energy conservation in motors
Supply to the motor must be balanced. Motors must operate near to its rated value. Where variable speeds are required use variable frequency drive (VFDs). Use Energy efficient motors. Input voltage variation must be ± 6% as per IS 325.
- Power factor improvement
Power factor can be improved by using power capacitors and harmonic filters at power supply bus. This results in reduction in kVA demand. With respect to electricity bills, this results in reduction in fixed charges and incentives from power supply company if power factor > 0.95. Clean motor body at regular intervals to reduce losses.
- Energy conservation in transformers
Use energy efficient transformers. These transformers use a metallic glass alloy material for. Energy losses are around 70% of traditional transformers. They give 98.5 % efficiency at 35 % of rated load. Regular cleaning of radiators is required to improve efficiency.
In addition to energy conservation in electrical systems, energy conservation is also done in process systems as summarized below.
- Energy conservation in boilers
- Implement regular steam leak survey
- Installation of condensate lines
- Investigate economics of additional insulation on already insulated lines
- Install automatic boiler blow-down control.
- Energy conservation in chilled water plants
- Chiller retrofits
- Cooling tower retrofits
- Resizing of chillers
- Staging of multiple chillers
- Energy conservation in compressors and fans
- Create air movement with fans
- Free cooling/injector cycle
- Heat recovery through de-superheating
- Reduce ammonia head pressure
- Energy conservation in heat pumps and cooling systems
- Install booster pumps on hot water systems
- Install add-on heat pumps
- Install roof-spray cooling systems
- Install secondary pumping systems
- Energy conservation in HVAC systems
- Install modular HVAC units
- Install air cleaners
- Install exterior shading
Modifying shape of load profile
This can be done by shifting non priority loads to TOD 4. This will result in reduction in load demand during TOD 1, TOD 2 and TOD 3. This will result in saving in electricity bill and overloading of Grid during peak demand hours. Load profile before shifting of non-priority loads to off peak hours is shown in curve 1 of fig 4. Load profile after shifting of non-priority loads to off peak hours is shown in curve 2 of fig 4.
Some of the non-priority loads are given as below.
- Hot water heating
- Water pumping to overhead tanks
- Filling swimming pool water
- Functioning of laundry
Load shedding to control maximum demand
In some industrial installations maximum demand of connected loads is predefined. The power system has both critical and noncritical loads. The critical loads are personnel and equipment safety related loads. Non critical loads are non-safety related loads. In case load demand increases more than maximum demand, the load shedding mechanism comes into action by load demand controller to switch off noncritical loads according to predefined sequential priority i.e. load with lowest priority is switched off first and load with highest priority is switched off at last till the load demand falls below predefined maximum load.
Methodology to control maximum demand –
For the purpose of load demand control, use of PLC based load demand controller in coordination with SCADA system may be used. Functioning of the controller is summarized as below.
Energy meter (kWh meter) is designed to transmit one pulse for 1 unit of consumption of electricity to the SCADA system. This is done to define 1 unit of consumption in power system for load management. The SCADA system is programmed to have real time status of circuit breakers (CBs) of all loads.
Digital outputs are provided by SCADA system to closing or tripping circuits of CBs according to programmed logics for load management. The programmed logic compares the load demand with predefined maximum demand. If the load demand is more than predefined maximum demand, the load management mechanism activates for load shedding.
The list of important critical and noncritical loads is given as below
These loads are non-safety related loads. If these loads are made OFF there is no hazard to personnel or equipments of an organization. Some common examples are given as below
- HVAC compressors/pumps
- Luxury equipment such as swimming pools, hot tubs, etc.
- Office or commercial space.
- Air handlers
- Non-emergency lighting
- Medical imaging systems
The critical loads are personnel and equipment safety related loads. Their unavailability is hazardous or fatal for personnel and equipments. Some common examples are given as below
- Emergency Diesel Generator sets
- Emergency lighting
- Fire water pumps
- Life-support systems
- Cooling water systems for fuel bundles in Nuclear Stations
- Control power supply systems of a power system
- Power UPS
- Air supply system for air operated valves
- Cooling water system for transformers, DG sets jacket and turbine generators stator.
- Hydrogen cooling system for TG rotor
- Life Saving equipments in hospitals
Benefits of load profile management
Reduction in financial implication.
As mentioned above, Energy conservation, shifting of non-priority loads to off peak hours and controlling maximum demand shall result in reduction in financial implication in electricity consumption.
Impact of COVID – 19 on load profile
COVID-19 has become a global health hazard, impacting more than 200 countries and the World Health Organization (WHO) declaring it as a global pandemic.
- Case study of a typical paper industry
First we will analyze the real case of a paper industry to understand the impact of Covid – 19 on load profile. The graph between per day unit consumption and lockdown period is illustrated in fig 5. The graph between maximum demand and lockdown period is illustrated in fig 6.
The impact of Covid 19 is also given in following table. The data has been collected from daily log of the organization.
- Global impact of COVID 19 on load profile
Most of the governments have taken severe measures to combat against COVID 19 by locking down most of the industrial and commercial activities and giving relaxation to only essential services. In view of this, there is considerable reduction in power consumption due to closure of Industrial and commercial establishments during lockdown. Hence, there has been considerable impact of COVID 19 on load profile of all the affected countries. To describe in statistical terms, in most of the countries peak loads are drastically decreased by as much as 20% while the peak-to-valley load difference on the load profile is increased by 5%. This impact on load profile shall force the power generating companies to rethink and manage their strategies and priorities.
Figure 6(a) and 6(b) indicates the thermal load profiles in a typical power distribution company during the months of January and March of 2020 respectively, for comparing the load profiles before and after the spread of COVID-19. In January, when COVID-19 started to spread, few measures were taken to close down electricity consuming operations. During this period, as per fog 6 (a), maximum demand was 16.8 GW, peak to valley difference for thermal power was 5.3 GW and solar PV generation was 4.3 GW. But in March, spread of COVID-19 was extensive and it had reached to most of the countries and most of the electricity consuming operations were closed down globally. During this period, as per fig 6(b), maximum demand reduced to 14.6 GW, peak to valley difference for thermal power increased to 5.7 GW and solar PV generation increased to 4.9 GW. Accordingly, in March peak load was decreased by about 13%. According to Figure 6b, while the peak load demand in March has decreased by 13%, the peak to valley load difference has increased by around 5%.
Solar PV generation increased in summer season. This scenario resulted in larger peak to valley load differences and hazards of over generation by thermal units. In this situation, thermal power companies wanted to reduce solar PV generation for the purpose of running the thermal units at reasonable capacity factor during day time. Though, in evening, the thermal units had no competition from solar units and they achieved desired capacity factor.
- Impact of Covid 19 on load profile of a typical Metropolis city
Load profile of a typical metropolis city before lockdown due to Covid 19 is illustrated in Fig 7a. The profile is drawn for daily load demand for a period from March 16 to 20, 2020. It can be understood from the profile that minimum load at 4 am is around 13000 MW. The maximum demand is around 17000 MW at 10 pm. Load profile of a typical metropolis city after lockdown due to Covid 19 is illustrated in Fig 7b. The profile is drawn for daily load demand for a period from March 30 to April 3, 2020. It can be understood from the profile that minimum load at 4 am is around 12000 MW. The maximum demand is around 16000 MW at 10 pm.
- Impact of Covid 19 on states electricity tariff structure
Maharashtra government, which is severely affected by Covid 19 pandemic, has declared a sharp reduction in industrial power tariff to boost struggling industry.
From subsidized electricity to relief package, state governments have declared a number of relief measures for the industries in view of the COVID-19 pandemic that has severely impacted the economy. The industry has been offered concessions, tax exemptions etc. to boost economic activity during the pandemic.