How to Solve High Temperature Problems in EV Charging Station Pad-Mounted Transformers

As electric vehicle (EV) charging infrastructure continues to expand worldwide, charging stations are increasingly operating under high-power and continuous-load conditions. One of the most common challenges faced by charging station operators is excessive temperature rise inside pad-mounted transformers (prefabricated substations), which can significantly affect equipment reliability, service life, and operational safety.

This article explains the main causes of overheating in EV charging station transformers and provides practical solutions for emergency cooling, long-term thermal management, load optimization, and routine maintenance.

Why Do EV Charging Station Transformers Overheat?

Several factors contribute to excessive temperatures in pad-mounted transformers used for EV charging applications:

• Continuous high-power charging loads

• Simultaneous operation of multiple charging piles at full capacity

• Poor ventilation inside enclosed transformer enclosures

• Direct sunlight exposure during summer months

• Aging equipment and overloaded electrical systems

To effectively address overheating issues, solutions can be divided into four categories:

1. Emergency Cooling Measures

2. Permanent Ventilation Improvements

3. Load and Equipment Optimization

4. Preventive Maintenance

1. Emergency Cooling Measures

Install Sunshades and Thermal Insulation

Direct solar radiation can increase internal transformer temperatures by an additional 15–25°C.

Recommended measures include:

• Installing aluminum reflective sunshades above the transformer enclosure

• Adding thermal insulation panels on exposed surfaces

• Applying reflective heat-resistant coatings to the enclosure exterior

Strengthen Forced Ventilation

Proper airflow is essential for heat dissipation.

Actions include:

• Inspecting and cleaning existing axial fans

• Replacing damaged ventilation fans immediately

• Ensuring airflow follows a bottom-inlet and top-exhaust configuration

• Installing temporary industrial exhaust fans at the upper section of the enclosure

• Adding dust-proof air intake louvers at the lower section

Keep all ventilation openings unobstructed and maintain at least 1.5 meters of clearance around the transformer for adequate airflow.

Implement Load Management

During peak temperature periods:

• Schedule charging sessions to avoid simultaneous full-load operation

• Apply load balancing among charging stations

• Limit charging power during extreme heat conditions

Reducing transformer loading directly lowers copper and core losses, thereby reducing heat generation.

2. Permanent Cooling System Upgrades

Standard Convection Ventilation Design

A properly designed airflow path provides the most cost-effective long-term solution.

Lower Air Intake

Install:

• Dust-proof and rain-proof louvers

• Air filters

• Low-position ventilation openings

These allow cooler ambient air to enter the transformer compartment.

Upper Air Exhaust

Install temperature-controlled exhaust fans at the top of the enclosure.

Recommended settings:

• Fan Start Temperature: 40–45°C

• Fan Stop Temperature: 35°C

This ensures hot air is efficiently discharged without recirculation.

Compartmentalized Ventilation

Separate the following sections:

• Transformer compartment

• Medium-voltage compartment

• Low-voltage compartment

• EV charging cable termination compartment

Independent ventilation prevents transformer heat from affecting switchgear and control equipment.

Advanced Cooling Solutions

For locations with extreme ambient temperatures or continuous heavy loads, additional cooling methods may be required.

Evaporative Cooling Systems

Industrial air coolers can introduce cooled fresh air into the enclosure, making them suitable for outdoor installations in regions where summer temperatures exceed 38°C.

Industrial Air Conditioning

For sealed transformer enclosures or dusty environments:

• Install industrial-grade air conditioners with IP54 or higher protection ratings

• Maintain enclosure temperatures around 40°C

• Prevent dust and hot air intrusion

Transformer Cooling Enhancement

Oil-Immersed Transformers

• Clean radiator fins regularly

• Remove accumulated oil and dust contamination

• Install auxiliary cooling fans when necessary

Dry-Type Transformers

• Inspect built-in cooling fans

• Remove dust accumulation from windings

• Add supplemental side-mounted ventilation fans if required

3. Reduce Heat Generation at the Source

Evaluate Transformer Loading

If the transformer continuously operates above 85% of its rated capacity, overheating risks increase significantly.

Recommended actions:

• Conduct load studies

• Upgrade transformer capacity

• Distribute loads across multiple transformers

Inspect Cables and Electrical Connections

Loose or oxidized connections can create localized hotspots.

Regular inspections should include:

• High-voltage terminals

• Low-voltage terminals

• Busbars

• Charging station output connections

Infrared thermal imaging is highly recommended for identifying abnormal temperature rises.

Verify Temperature Protection Systems

Ensure proper operation of:

• Temperature sensors

• Thermostats

• Over-temperature alarms

• Fan control systems

• Protective trip functions

Faulty monitoring devices can allow overheating to go undetected.

4. Routine Preventive Maintenance

Quarterly Cleaning

Regularly clean:

• Air filters

• Ventilation fans

• Transformer radiators

• Internal enclosure surfaces

Dust accumulation significantly reduces cooling efficiency.

Infrared Temperature Monitoring

During summer months, monthly thermal inspections should be conducted on:

• Transformer windings

• Busbars

• Cable terminations

• Electrical connections

Early detection helps prevent equipment failures.

Site Environment Inspection

Maintain a clean operating environment by ensuring:

• No vegetation blocks ventilation openings

• No combustible materials are stored nearby

• Airflow pathways remain unobstructed

Special Considerations for Different Transformer Types

Oil-Immersed Pad-Mounted Transformers

Key focus areas:

• Keep radiator surfaces clean

• Maintain unobstructed airflow around cooling fins

• Ensure adequate oil cooling performance

Dry-Type Transformers

Commonly used in EV charging applications, dry-type transformers require:

• Regular winding cleaning

• Effective forced-air cooling systems

• Proper enclosure ventilation

Dust accumulation can reduce insulation performance and severely impair heat dissipation.

Excessive temperatures in EV charging station pad-mounted transformers are typically caused by a combination of high electrical loads, insufficient ventilation, environmental conditions, and inadequate maintenance.

By implementing emergency cooling measures, optimizing enclosure airflow, improving load management, and maintaining equipment regularly, operators can significantly reduce transformer temperatures, extend equipment lifespan, and improve overall charging station reliability.

As a professional manufacturer of medium-voltage switchgear, low-voltage distribution systems, pad-mounted substations, and EV charging power distribution solutions, Beike Electric provides customized solutions designed to ensure safe, reliable, and efficient operation under demanding environmental conditions.