Okay, this is a fascinating and frustrating situation! "Ghost tripping" is a nightmare for any plant operator, and the commonality in the events suggests a systemic issue, even if it manifests in individual components. Here's a breakdown of possible causes, considerations, and mitigation strategies based on the information you've provided

Possible Causes & Theories (Prioritized):

1. Cold Temperature Impact on BFS Actuator/Linkage

This is your most likely culprit, and you're right to focus on it.

Material Contraction

Extreme cold can cause differential contraction of materials in the BFS linkage (different metals, plastics, etc.). This could be enough to shift the pushrod position and mimic a blown fuse, activating the safety switch. Remember even minute movements matter here.

Lubricant Issues

If the linkage or pivot points in the BFS actuator system are lubricated, the grease could be thickening or even freezing in the cold. This would increase the force needed for normal operation, and potentially cause binding that translates into false trips.

Ice Formation

While less likely inside a switchgear cabinet, condensation can occur due to temperature fluctuations. This condensation could freeze, impeding movement in the linkage. Check for any signs of moisture in the area.

Combined Effect

The most likely scenario is a combination of material contraction and lubricant issues making the BFS system incredibly sensitive to slight vibrations or movements.2.

Vibration

You mentioned the breakers tripped at the exact same time, and one being on top of the other. This strongly suggests a vibration component.

Resonance

The cold temperatures could be making the materials more brittle, changing their resonant frequency. A slight vibration from nearby equipment (even the running pulverizer or circ pump) could be amplified, enough to trigger the BFS linkage.

Seismic Activity

(Extremely unlikely, but worth mentioning). If you are in an area with minor seismic activity, even small tremors combined with the cold-related sensitivity could be a factor. Check local geological data.

Loose Connections

Vibration could be exacerbating any loose electrical connections (in the control circuit or the BFS actuator circuit itself).3.

Electrical Noise/Grounding Issues

While less likely specifically causing the "blown fuse" signal, electrical noise or grounding problems can contribute to overall instability and possibly interact with the control circuitry.

Failed Surge Suppressors

Check for any surge suppression devices on the control power supply or the input to the relay. These can fail over time and inject noise into the system.

Ground Loops

With multiple trips happening simultaneously, a ground loop might be creating a voltage differential that's affecting the relay inputs.

Harmonics

The operation of the pulverizers and circulating pump can generate harmonics. While the 4160V system should be relatively immune, check harmonic levels if possible.4.

Relay Programming/Configuration Error

Although unlikely if the system has been running reliably for a long time, there's always a chance of a programming error in the Siemens Siprotec relays.

Sensitivity Settings

Double-check the sensitivity settings of the "flx01" input on the relays. Is it possible the threshold for activation is too low?

Logic Errors

Review the logic configured for the "flx01" input. Is there any possibility of unintended interactions with other protective functions?

Firmware Issues

While less likely, check if there are any known bugs or issues with the firmware version of the Siprotec relays.5.

Fuse Holder Issues (Less Likely, but Worth Considering)



Corrosion/Oxidation

Inspect the fuse holders for any signs of corrosion or oxidation, especially on the contacts. This could create a high-resistance connection that generates heat, potentially weakening the fuse element.

Loose Fuse Clips

Ensure the fuse clips are making good contact with the fuses. Loose clips can lead to arcing and premature fuse failure.

Mitigation Strategies (Prioritized)


Environmental Control (Short-Term & Long-Term)



Temporary Heating

If possible, introduce temporary heating to the MV room. Even a few degrees of warming can make a significant difference. Use space heaters carefully and safely, ensuring they are appropriately rated for the environment and do not pose a fire hazard. Monitor temperature closely.

Insulation

Insulate the switchgear cabinets as much as possible to help retain heat. Use appropriate insulating materials that are non-flammable and designed for electrical enclosures.

Permanent HVAC Solution (Long-Term)

This is the best long-term solution. Installing a proper HVAC system to maintain a stable temperature and humidity level in the MV room will prevent these issues in the future.2.

BFS Actuator/Linkage Inspection & Maintenance (Requires Planning & Coordination)



Visual Inspection

Before anything else, perform a thorough visual inspection of the BFS actuator and linkage on all affected breakers. Look for any signs of binding, corrosion, loose components, or damaged parts. Use a flashlight and a magnifying glass for detailed examination.

Lubrication

If appropriate, lubricate the pivot points and linkages of the BFS actuator with a low-temperature grease specifically designed for electrical equipment. Be careful not to over-lubricate, as excess grease can attract dust and dirt.

Actuation Testing

Manually actuate the BFS linkage (with the breaker de-energized and safely disconnected) to check for smooth movement and proper operation. Look for any points where the linkage binds or sticks.

Replacement

If any components of the BFS actuator or linkage are damaged or worn, replace them with new parts.

Important Note

This step requires careful planning and coordination, as it involves working on energized equipment. Ensure you have the proper safety procedures in place and that qualified personnel perform the work.3.

Vibration Analysis



Identify Vibration Sources

If possible, use a vibration analyzer to identify the primary sources of vibration in the area.

Vibration Isolation

If you can identify specific equipment causing excessive vibration, consider using vibration isolation mounts to dampen the vibrations.4.

Electrical System Checks



Grounding Inspection

Thoroughly inspect the grounding system for any loose connections, corrosion, or other issues. Ensure all grounding connections are tight and properly bonded.

Control Power Supply Check

Verify that the control power supply voltage is stable and within the specified range.

Surge Suppressor Testing

Test any surge suppressors on the control power supply or the relay inputs to ensure they are functioning correctly.5.

Relay Configuration Review



Sensitivity Settings

Carefully review the sensitivity settings of the "flx01" input on the relays. Consider increasing the threshold slightly to reduce the likelihood of false trips.

Logic Review

Double-check the logic configured for the "flx01" input to ensure there are no unintended interactions with other protective functions.

Contact Siemens Siprotec Support

If you suspect a relay malfunction, contact Siemens Siprotec support for assistance. They may be able to provide firmware updates or other troubleshooting guidance.6.

Fuse Holder Inspection & Maintenance



Clean Fuse Holders

Clean the fuse holders with a contact cleaner specifically designed for electrical equipment.

Tighten Fuse Clips

Ensure the fuse clips are making good contact with the fuses. If necessary, tighten the clips slightly to improve contact pressure.

Replace Damaged Fuse Holders

If any fuse holders are damaged or corroded, replace them with new parts.

Important Considerations



Safety First

Any work on electrical equipment, especially medium-voltage equipment, must be performed by qualified personnel following strict safety procedures. Lockout/tagout procedures are essential.

Documentation

Keep detailed records of all inspections, maintenance, and repairs performed. This will help you track the effectiveness of your mitigation efforts and identify any recurring problems.

Vendor Support

Don't hesitate to contact Siemens Siprotec or the manufacturer of the 4160V switchgear for assistance. They may have seen similar issues before and can provide valuable troubleshooting guidance.

Phased Approach

Implement the mitigation strategies in a phased approach, starting with the simplest and most likely solutions (environmental control, visual inspection) and then moving on to more complex tasks (BFS actuator maintenance, electrical system checks).

Action Plan (Immediate Steps)


Implement Temporary Heating

Focus on getting some temporary heat into the MV room immediately and monitor the temperature.2.

Visual Inspection of BFS Actuator

Perform a detailed visual inspection of the BFS actuator and linkage on the tripped breakers and at least one breaker that hasn't tripped as a baseline.3.

Record Data: Continue to collect data from the Siprotec relays and document the timing and conditions of any future trips.By systematically investigating the possible causes and implementing the appropriate mitigation strategies, you should be able to resolve this "ghost tripping" issue and prevent future occurrences. Good luck! Let me know if you have any further questions or provide updates as you progress. Flag for review