Aspects of Water-Cooled Transformers

Transformers are one of the key and costliest components of the electrical power system, which play vital roles for power transmission and distribution systems. A transformer remains present from power generation point up to the place of domestic and industrial consumer. The transmission and distribution of power without transformer is very uneconomical, in other words, we can say that is extremely difficult. This device converts the voltage from one level to another as per the requirement of the application without changing frequency.

This device is the amalgamation of the various engineering like electrical, mechanical, civil, material science, chemical engineering, information science etc.  This is a static device and functioning on the principle of electromagnetic induction – means electrical and magnetic theory is the working principle of the transformer. It comprises various components and out of them most important are winding, core, bushings tap changer, radiator, tank etc. If we talk about material, copper, Cold Rolled Grain-Oriented sheet steel (CRGO), oil, insulation, mild steel are the most essential.  For the long life and hassle-free function of transformers, it must be reviewed and analyzsed for voltage stress withstand capability, short circuit withstand capability, temperature rise phenomenon.

While transformer is connected with load and running on the full load capacity continuously, its cooling is an important engineering to be taken care of – starting from design to manufacturing. There are various cooling methods prevailing for cooling of transformer. Transformer tank along with active part assembly (core and winding), if filled with electrolyte grade oil, which is called transformer oil. This oil extracts heat from the active assembly inside tank and then it gets heated up. This oil later gets cooled by various methods as discussed hereafter.

• Natural Air Cooling (AN):  This is used for dry type transformer and cooling happens by natural convection of air
• Forced Air Cooling (AF): Air is blown to transformer assembly either by fan or blower to enhance the cooling capacity
• Oil Natural Air Natural (ONAN): Oil routes through radiator and that radiator gets cooled by natural air convection. This is simply on principle of thermodynamics. It is called 1st stage cooling
• Oil Natural Air Forced (ONAF): The 2nd stage of cooling is happening by addition of fans or blowers that enhance heat dissipation by increasing airflow to the radiator.
• Oil Forced Air Forced (OFAF): The 3rd stage of cooling is happening by addition of oil flow pumps with existing radiator and fan cooling system. It circulates oil fully inside the tank.
• Oil Force Water Force (OFWF):  Oil is getting cooled by water with active involvement of heat exchanger.

Water cooled transformer engineering and construction

A water-cooled transformer operates exactly in the same way as the conventional transformer – but it is specifically designed to handle the extreme condition of cooling or to accommodate in the conservative place. Water cooled transformers are mostly used for furnace applications, and that environment operates under severe electrical and thermal stress, they utilize a water-based cooling system to regulate their temperature. The cooling system consists of heat exchanger in which the transformer oil gets routed through copper tubes, which remain in indirect contact with water flow. This process efficiently removes the heat generated during operation, preventing thermal breakdown and ensuring stable performance.

This type of water-cooled transformers are widely being used for steel manufacturing, foundries, glass industry, chemical processing, mining and metallurgy. Where the instantaneous loading on transformer comes momentarily. On the other side where the space constraint for accommodation of transferee, water cooling system is being considered. It is also used for power transformers where space is a constraint.

The construction of the water-cooled transformer is also the same as the conventional transformer except the cooling system is completely different compared to the conventional transformer. Instead of radiator and cooling fan in ONAN cooled transformers, this water-cooled transformer uses heat exchanger, water flow pump, oil flow pump, water flow indicator, oil flow indicator, differential gauge (Oil & water flow pressure difference equalization), temperature gauge. The selection of heat exchanger and flow pump is important for the engineering competency.

For generalized understanding the following data to be considered for this type of water-cooled transformers.

Typical water requirements

•  Small transformers up to 2000 kVA:  10 – 50 L/min
•  Medium transformers up to 10000 kVA: 50 – 200 L/min
•  Large transformers (10 MVA and above): 200 – 1000 L/min

Heat exchanger capacity

• 500 kW heat losses to be dissipated: Requires approximately 80 – 100 L/min  with a 10°C temperature rise.
• 1000kW heat losses to be dissipated: Requires approximately 160 – 200 L/min (with a 10°C temperature rise.
• 2000kW heat losses to be dissipated: Requires approximately 320 – 400 L/min with a 10°C temperature rise.

Selection of optimum sized heat exchanger and optimum continuous flow of water is most essential for the best performance of this cooling methodology.

The following figure is showing the ready transformer with Oil Forced Water Forced (OFWF) cooling methodology which accommodated all fittings and accessories.

Merits of the selection of water-cooled transformers

• Higher cooling effectiveness: Compared to air-cooled systems, water cooling provides superior heat dissipation, allowing the transformer to operate at higher efficiency.
• Compact design: Water-cooled transformers are typically more compact than their air-cooled counterparts, making them ideal for space-constrained industrial setups.
• Extended lifespan: Effective and more efficient cooling proved extended life to the insulation system inside the transformer and finally become key element for Effective prolonging life of the transformer.
• High performance under heavy loads: Water has high heat dissipation capability compared to air, so the transformers can sustain high current loads without overheating, ensuring consistent power transmission.
• Lower noise levels: Water cooling significantly reduces the noise generated by the transformer, creating a better working environment.
• Increased safety: Proper cooling mechanisms reduce the risk of overheating, minimizing potential hazards in an industrial environment.

When selecting a water-cooled power transformer, several factors must be considered to ensure optimal performance and longevity.

• Cooling system design: The optimum equipment selection is a very important factor and that’s why, the efficiency of the cooling system depends on the quality of water circulation and heat exchanger efficiency.
• Maintenance requirements: Regular monitoring and maintenance of the water-cooling system, including checking for leaks and ensuring water quality, are essential for preventing the mixing of water and oil due to heat exchanger internal leakage. Scaling and corrosion also one of an import factor for maintenance view point.
• Environmental considerations: Efficient cooling systems should minimize water wastage and align with sustainability regulations.

Maintenance and best practices

To ensure longevity and reliable operation, water-cooled power transformers require periodic maintenance, including.

• Checking for water leaks and oil leaks: Any leaks in the cooling system can reduce efficiency and lead to overheating.
• Water and oil quality monitoring: Maintaining proper pH levels and preventing contaminants ensures efficient cooling. Periodical oil testing in context of water particle(ppm) is very important for insulation life.
• Inspecting electrical connections: Loose or corroded connections of water and oil pumps can lead to power loss and performance issues.
• Replacing cooling components: Over time, water pumps, heat exchangers, and piping may require replacement to maintain efficiency.

Conclusion

The popularity of water-cooled power transformers is increasing day by day due to industrialisation and becoming indispensable in modern electrical systems, particularly in high-load industrial and power distribution applications only because of their radical cooling abilities, compact design, and ability to handle high electrical loads.

It has become preferred choice for demanding cooling efficiency, especially in steel industries. By employing proper maintenance approaches can maximize efficiency, enhance safety, and prolong equipment lifespan.

Dr. Chiragkumar N Parekh is from Hyundai Powerr Traansformers, USA. He is also a Technical Advisor at JSN Electricals, USA.

Prof. Gaurangkumar K Sharma is from the Electrical Engineering Dept, BVM Engineering College, India. He is also a Technical Advisor at JSN Electricals, USA and NGET.