According to an article published in THE TIMES OF INDIA on 23rd May 2021, 11 thousand agricultural workers are dying due to electrocution in India every year. On an average 30 persons are dying every day. The reasons are attributed to standards not being followed in wiring, cut and fallen transmission lines due to ageing, corrosion and formation of conductive path on motor casing and control box under damp conditions.
Whatever be the reason, it is very sad that our farmers, the food providers for our nation, are dying in sincerely carrying out their daily routines.
A normal person feels the sense of current only if the magnitude is more than 1 milli ampere. Currents of magnitude less than this value are not sensed by human body. About 150 micro amperes of current flows through the body of the person using line tester.
Higher voltages allow for more current. Any voltage above 30 V is considered to be capable of delivering shock currents. Effect depends upon current path in the body. Worst condition is the flow of current from hand to hand involving passage through heart. Above 100 milli-amp current passing through human body is considered to be harmful.
Severity of electric shock depends on through which part of human body current flows and also skin condition at that instant (dryness).
Normally, distribution transformers are located close to agricultural lands or in the land itself. 11/33 kV high voltage lines are laid from substation to distribution transformers. Agricultural pumpsets are installed on 440 V side of the transformer at a distance anywhere between 10 to 300 metres. This entire path, which is shown in the figure.2. is electric shock risk zone.
Due to corrosion, ageing and proper standards not being followed during erection, power lines break and fall on the ground. Cut live wire falling on the ground is one of the main causes of electrocution deaths. Most of the times earth offers less resistance but not a perfect short. Magnitude of the current that flows is not sufficient enough to trip the circuit breaker but enough to give fatal shock. The cut wire lying on the soil will not be visible in majority of cases and is merged in damp clayey soil. Humans and animals unknowingly stepping on this wire get electrocuted. Cut electrical wires falling on the ground is more common in agricultural fields due to loose soil, damp weather conditions and weak foundations.
Observe the tilted electric pole shown in Fig.3., about to fall any time. It is due to loose soil and inadequate foundation. Same is the case with majority of installed transmission lines in our agricultural fields.
If standalone (grid independent) system is installed this entire path, which is shock risky zone can be eliminated.
Live conductor coming in contact with casing of the motor or control box due to insulation break down, corrosion and formation of conductive path during humid weather conditions is a frequently occurring phenomenon. Under such condition, physical contact with metal casing of motor pumpset and control box leads to fatal shock if proper earthing is not provided.
In agricultural water pumping systems required care is not being taken for earthing. Even under improper earthing conditions if low operating voltages are chosen, electrical shocks can be completely eliminated.
The size of the pipe used for earth is of 3.8cm diameter and 2.5m in length. More than 2 meters of the rod is buried in the ‘earth pit’. Pit is filled with mixure of powdered coal, salt and sand. Care should be taken to keep the soil of the pit wet.
Fig .4.
The solution
Stand alone dedicated photovoltaic water pumping system with 24V operating voltage is described here. 0.5 HP 24 V DC powered water pumping system approximately costs Rs. 50,000 and 1 HP system costs Rs. 1 lakh.
Cost of the system is directly proportional to power. For higher flow rates, high power motors can be used. At 24 V operating voltage motors are available up to maximum power of 3HP today. These motors are suitable for running aerators in aqua farms. This is one time investment and running cost is zero.
There is a limitation on the suction head of centrifugal pump. It should not be more than the atmospheric pressure in terms of height of water column in pumps. Theoretical limit is 10.3 m (at sea level). If suction head of the pump is more than atmospheric pressure, it won’t function. For drawing water from deep wells (more than 10m deep) submersible pumps are to be installed. Depending on the depth of bore well, number of pump stages are to be decided. DC powered submersible motor pump sets are not available in the local market. Submersible motor pump sets operating on 24V are still in the development stage. We have to make use of the available systems. This system is described below.
The output of PV panels is 24 Volts. This is applied to the input of the inveter. 230V AC output from the inverter is applied to the submersible motor through wireless controlled GSM (Global system for mobile communications) relay switch. On / Off control is through cell phone, which can be operated from anywhere in the country. Status information can be obtained back as sms to cell phone.
As physical contact is eliminated for switching ‘on and off’ of pumpset, it is completely safe from electrical shock point of view even in the worst weather conditions.
Two water pumping systems described above both for shallow water bodies and deep bore wells are fabricated and practically proven.
Implementation of the Paris agreement
The Paris agreement was signed by 175 countries on 22nd April 2016. It is aimed at reducing the global warming to pre-industrial levels. It is by minimizing the usage of fossil fuels and by replacing coal based thermal power generation with renewable energy sources.
For implementing Paris agreement, India has launched Pradhana Manthri’s KUSUM Yojana (Kisan Urja Suraksha Evam Utthaan Mahabhiyan) in the year 2019. Under component B of KUSUM Yojana, 17.5 lakh stand alone, solar powered agricultural pumps each with maximum capacity 7.5 HP will be installed where grid supply is not available. Pumps of capacity higher than 7.5 HP can also be installed, however, the financial support is limited to 7.5 HP capacity. Prevention of farmers electrical shock deaths is additional benefit gained by KUSUM Yojana, a hidden fact, which requires wide publicity. It is necessary to implement component B of KUSUM Yojana with more thrust and dedication. It is the activity towards implementation of Paris agreement, which was signed by 195 countries. It is to reduce global warming by reducing consumption of fossil fuels.
With slight modification, if this scheme is extended to replace grid powered pumps also (now the scheme is not covering grid powered pumps), it helps in reducing farmers electrical shock fatalities to maximum extent.
Conclusion
KUSUM Yojana should be implemented with the highest priority – and to the extent possible is to be extended to cover more number of water pumping systems. This is going to be a great relief to our farmers.
Devanoori Bhanumurthy has a B. E. degree in electrical engineering. He has a long work experience in class 1 Indian companies including TATA Communications Ltd.; Defence Ionospheric Research Station, DRDO unit in Jammu& Kashmir; Defence Electronics Research Laboratory; Geological survey of India; and DLRL, DRDO.
