Okay, this is a classic problem. Hot environments are murder on motors, and it sounds like you've got a doozy! Let's break down the options and considerations.

Understanding the Problem



High Ambient Temperature

This is your primary enemy. Class B insulation is typically rated for a maximum winding temperature of 130°C (266°F) assuming a 40°C ambient. If the ambient is consistently higher, the motor will overheat and its lifespan will be drastically reduced. Every 10°C above the rating halves the life expectancy of a motor.

Explosion Proof

This limits your motor choices significantly. Explosion proof motors are designed to contain an internal explosion, and they often run hotter because of their enclosed design.

Single Phase Constraint

As you've discovered, single-phase motors are less common, especially in larger frame sizes and higher insulation classes. They also tend to be less efficient than three-phase motors.

Duty Cycle

How often and for how long is the fan running? Continuous duty puts more strain on the motor.

Motor Load

Is the fan properly sized for the exhaust requirements? An undersized fan will cause the motor to work harder and generate more heat.

Evaluating Your Proposed Solutions and Additional Ideas


Upping the Motor to 3 HP (Single Phase)



Pros

Potentially less heat generation if the fan is running at a lower percentage of its rated load. A larger motor, even with the same insulation class, might have slightly more thermal mass and tolerate the high ambient a bit better.

Cons

Single-phase motors are inefficient. A 3 HP single-phase motor will draw significantly more current. You need to verify that the existing circuit can handle the increased load. It won't fundamentally solve the insulation class problem. If the fan doesn't need the extra HP, the motor will be less efficient.2.

Installing a VFD and Using a 3-Phase Motor with a Higher Insulation Class



Pros

This is generally the best long-term solution, but the most expensive.

Efficiency

Three-phase motors are significantly more efficient than single-phase.

Insulation Class

You'll have a much wider selection of three-phase motors with Class F (155°C) or Class H (180°C) insulation.

VFD Benefits

The VFD can also provide speed control for the fan, potentially reducing energy consumption and noise when full exhaust capacity isn't needed.

Motor Protection

VFDs typically offer built-in motor protection features like overcurrent, overload, and over-temperature protection.

Soft Starting

VFDs provide soft starting, reducing mechanical stress on the fan and motor.

Cons



Cost

VFDs and explosion-proof three-phase motors are expensive. You'll also need to factor in the cost of wiring and conduit changes.

Complexity

VFDs add a layer of complexity to the system. Maintenance and troubleshooting might require specialized skills.

VFD Location

The VFD itself might need to be located in a cooler, cleaner environment if it is not explosion-proof rated. Some VFDs can be explosion-proof rated, adding to the cost.

Harmonics

VFDs can generate harmonic distortion on the power system, which might require mitigation measures.3.

Other Options (and most of what I think you should do)



Improved Ventilation

This should be your first priority. Can you introduce cooler, fresh air into the compressor building, specifically around the motor? Consider:

Dedicated Air Duct

Run a duct from a cooler location (outside the building, if possible) to supply fresh air directly to the motor.

Additional Fans

Install other fans to improve air circulation within the building and remove hot air. A large, slow-speed fan moving a lot of air can make a huge difference.

Heat Shielding

Shield the motor from radiant heat coming off the engine. Even a simple piece of sheet metal can significantly reduce heat exposure.

Motor with a Higher Ambient Temperature Rating

Some explosion-proof motors are specifically designed for higher ambient temperatures (e.g., 50°C, 60°C, or even higher). Look for motors with temperature codes (T-codes) that are appropriate for your environment. Check Baldor's catalog carefully, or contact a Baldor application engineer. You may have to special order.

Motor with Thermal Overload Protection

Ensure that the motor has properly sized thermal overload protection (either built-in or external). Make sure it's set correctly according to the motor's nameplate current rating. This will help prevent the motor from burning up if it gets overloaded or overheats.

Forced Air Cooling

Consider a blower that is specifically designed to cool the motor. These blowers attach to the motor and force air across the motor's fins.

Temperature Monitoring

Install a temperature sensor on the motor windings and monitor the temperature. This can provide early warning of overheating and allow you to take corrective action before the motor fails.

Check the Fan Itself

Ensure that the fan blades are clean and unobstructed. A dirty fan will require the motor to work harder. Also, verify the fan is correctly sized. Is it possible someone replaced the fan with one too small for the job?

Proper Lubrication

Make sure the motor bearings are properly lubricated. Friction from dry bearings can contribute to motor overheating.

Remote Mounting (If Possible)

Can the motor be moved to a cooler location outside of the explosion-proof environment and belt-drive the fan? This might not be feasible depending on the application, but it's worth considering.

Recommendations


Start with Ventilation

Focus on improving ventilation immediately. This is often the most cost-effective solution, and it can significantly reduce the motor's operating temperature.2.

Investigate Motor Specs

Contact Baldor and inquire about explosion-proof motors specifically rated for higher ambient temperatures. Ask about motors with Class F or Class H insulation.3.

Check Fan Load

Confirm the exhaust fan is correctly sized for the required airflow. An undersized fan will overload the motor.4.

Consider VFD Solution

If improved ventilation and a higher-rated motor don't solve the problem, the VFD/3-phase motor option is likely your best bet for long-term reliability, but factor in the cost.5.

Implement Monitoring

If budget allows, install a temperature sensor on the motor to monitor winding temperature.

Important Considerations



Safety

Working in an explosion-proof environment requires strict adherence to safety procedures and regulations. Ensure that all electrical work is performed by qualified personnel.*

Documentation: Keep thorough records of all changes made to the system, including motor specifications, wiring diagrams, and VFD settings.Good luck! Let me know if you have any other questions. Flag for review