Electrical Faults in Turbomachinery:

Why They Happen, How They Attack Journal Bearings, and How They Appear in Oil Analysis

Most maintenance and reliability engineers are familiar with VFD-driven electric motors and the classic bearing current failure mode known as fluting in rolling bearings.

But in turbomachinery, especially large compressors, steam turbines, gas turbines, turbo-generators, and motor-driven centrifugal machines, electrical faults are more complex. They may not always produce the beautiful “washboard” fluting marks seen in motor rolling bearings. Instead, they may quietly damage journal bearings, thrust bearings, seals, oil films, control systems, and even the lubricant itself.

From a lubrication and oil analysis perspective, this is a very important subject because electrical discharge does not only damage metal surfaces. It can also create thermal stress, micro-arcing, localized oil cracking, carbonaceous deposits, varnish precursors, abnormal ferrous debris, and misleading oil analysis trends.

In simple Khash language:

Electrical current does not respect your bearing design.
It searches for the easiest path to ground.
If the oil film becomes part of that path, your journal bearing becomes an electrical component.

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1. What Do We Mean by Electrical Faults in Turbomachinery?

Electrical faults in turbomachinery can include:

1. Shaft voltage
2. Shaft current
3. Static electricity discharge
4. VFD-induced circulating current
5. Grounding problems
6. Poor earthing / bonding
7. Generator excitation-related shaft current
8. Magnetic asymmetry
9. Rotor residual magnetism
10. Electrical discharge through journal or thrust bearing oil films
11. Electrostatic discharge inside oil systems and filters
12. Stray current from nearby electrical equipment
13. Insulation failure in motor or generator windings
14. Improper installation or failure of shaft grounding brushes
15. Insulated bearing failure or bypass

In rotating machinery, the key question is not only:

“Is there current?”

The better question is:

“Where is the current going, and is the bearing oil film part of the return path?”

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2. Why Electrical Current Happens in Turbomachinery

Electrical current in turbomachinery usually comes from a voltage potential between the rotating shaft and the grounded machine frame.

Once a voltage difference exists, current will try to discharge through available paths. In many machines, the path may include:

• Shaft
• Coupling
• Gearbox
• Journal bearing
• Thrust bearing
• Oil film
• Seal
• Grounding brush
• Foundation
• Piping
• Instrumentation grounding
• Driven machine bearing

The current may be continuous, intermittent, or discharge-type.

The most dangerous case for bearings is often not a large continuous current. It is repeated micro-discharge across a thin oil film.

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3. Main Sources of Electrical Current in Turbomachinery

3.1 VFD-Induced Shaft Voltage

This is the most familiar source.

Modern VFDs use fast-switching power electronics. These create high-frequency voltage pulses. Because the voltage waveform is not a perfect sine wave, unwanted electrical effects appear, including:

• Common-mode voltage
• Capacitive coupling between stator and rotor
• Shaft voltage
• Bearing discharge current
• Circulating current
• High-frequency current through coupling and driven machine bearings

In rolling bearings, this can cause fluting. In journal bearings, the damage may look different because the shaft is supported by a hydrodynamic oil film.

In turbomachinery, VFD-related current may pass from the motor shaft through the coupling into the compressor, pump, fan, gearbox, or driven equipment.

This is why only protecting the motor bearing is sometimes not enough.

The driven machine bearings can become the electrical discharge point.

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3.2 Generator Shaft Voltage

Large turbine-generator sets can develop shaft voltage due to:

• Magnetic asymmetry
• Residual magnetism
• Uneven air gap
• Excitation system issues
• Ground faults
• Static charge accumulation
• Insulation problems
• Poor grounding brush performance

In turbine-generator trains, shaft grounding brushes are commonly used to drain shaft voltage before it discharges through bearings.

If the shaft grounding brush is dirty, worn, incorrectly installed, contaminated by oil mist, or has poor contact pressure, the bearing may become the grounding path.

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3.3 Static Electricity in Oil Systems

Static electricity can also be generated by oil flow itself.

This happens when oil passes through:

• Fine filters
• Synthetic filter media
• High-efficiency filters
• Small clearances
• High-flow return lines
• Dry oil systems
• Non-conductive hoses
• Plastic or non-metallic components
• Poorly bonded reservoirs or filter housings

As oil moves through the system, charge separation can occur. If the charge cannot safely dissipate, it may discharge suddenly.

This can cause:

• Clicking or snapping sounds near filters
• Burn marks on filter elements
• Pinholes in filter media
• Oil darkening
• Carbonaceous deposits
• Increased varnish tendency
• Sensor noise
• Premature oil degradation

This is very important in turbine oils because modern Group II and Group III base oils are usually less polar and may have lower natural conductivity than old Group I oils. That means they may be more sensitive to electrostatic charge accumulation, especially in dry, clean, highly filtered systems.

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3.4 Poor Grounding and Bonding

Many electrical problems in rotating equipment are not due to the machine itself, but due to poor grounding architecture.

Examples:

• Motor grounded at one point, driven compressor grounded differently
• Poor bonding across flexible couplings
• Paint or corrosion under grounding connections
• Non-conductive coupling spacer
• Insulated piping sections
• Poorly bonded skid-mounted equipment
• Separate electrical and instrumentation grounding issues
• Loose or corroded grounding straps
• Inadequate ground reference between VFD, motor, and driven machine

The result is that current may find an unintended path through bearings, seals, or oil films.

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3.5 Residual Magnetism in Rotors and Shafts

Residual magnetism can remain in shafts, rotors, couplings, or gear components after:

• Welding
• Magnetic particle inspection
• Improper demagnetization
• Electrical faults
• Handling with magnetic lifting devices
• Previous electrical discharge events

Residual magnetism can induce circulating currents or attract ferrous particles. In oil systems, this may accelerate localized contamination issues and deposit formation.

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4. Why Journal Bearings Are Vulnerable

A journal bearing works by separating the shaft and bearing surface with a pressurized wedge of oil.

In normal hydrodynamic operation:

• Shaft does not touch the bearing
• Oil film carries the load
• Metal-to-metal contact is minimal
• Bearing temperature remains stable
• Wear debris is low

But electrically, the oil film is a dielectric gap.

This means the oil film can behave like an electrical insulation layer — until the voltage becomes high enough to break through it.

When breakdown occurs, the current jumps across the oil film.

That discharge can create a tiny, localized thermal event.

This can damage:

• Babbit surface
• Tin-based overlay
• Copper/lead intermediate layers
• Steel backing, in severe cases
• Shaft journal surface
• Thrust collar
• Oil molecules near the discharge zone

So the journal bearing becomes both:

1. A mechanical support element
2. An unintended electrical discharge device

That is a dangerous combination.

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5. What Happens During Electrical Discharge Across a Journal Bearing Oil Film?

The sequence is usually like this:

1. Shaft voltage builds up.
2. Oil film initially resists current flow.
3. Voltage exceeds the dielectric strength of the oil film.
4. Micro-discharge occurs across the oil film.
5. Localized temperature rises sharply at the discharge point.
6. Babbit surface experiences tiny melting, pitting, or erosion.
7. Oil molecules crack or oxidize locally.
8. Carbonaceous particles and polar degradation products form.
9. Surface roughness increases.
10. Oil film stability becomes worse.
11. Bearing temperature may start increasing.
12. More discharge and more thermal stress can occur.

This is not normal adhesive wear.
This is not simple particle abrasion.
This is not only oil starvation.

It is an electrical-mechanical-chemical failure mode.

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6. How Electrical Damage Appears on Journal Bearings

Electrical damage in journal bearings may appear as:

6.1 Frosted Surface Appearance

The babbit surface may look dull, matte, or frosted.

Instead of smooth wiping or polishing, the surface may show fine roughness caused by repeated micro-arcing.

This can be mistaken for poor lubrication or fine abrasive wear.

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6.2 Electrical Pitting

Small pits may appear on the bearing surface.

These pits can be randomly distributed or concentrated in the loaded zone depending on the current path and oil film condition.

Electrical pits are often very small, but under magnification they may appear as tiny craters.

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6.3 Spark Erosion Marks

In more severe cases, the babbit may show localized spark erosion.

This is a surface damage pattern caused by repeated discharge energy. It may not look like classical wiping. It can look like roughened, burned, or peppered surface damage.

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6.4 Blackened or Dark Deposits

Electrical discharge can thermally stress oil at very localized points.

This can create black or dark carbonaceous deposits on or near the bearing surface.

These deposits may be confused with:

• Oxidation varnish
• Coke
• Sludge
• Seal oil contamination
• Thermal degradation from overheating

But the root cause may be electrical discharge.

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6.5 Localized Overlay Fatigue

Once electrical pitting roughens the bearing surface, the oil film becomes less stable. Local stress increases, and mechanical fatigue can follow.

So the failure may start electrically but end mechanically.

This is why, during RCA, we should avoid saying:

“It is only fatigue.”

The deeper question is:

“What initiated the fatigue?”

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6.6 Thrust Bearing Damage

Thrust bearings may also be affected, especially if axial current passes through the thrust collar and pads.

Possible signs include:

• Pitting on thrust pads
• Localized black marks
• Uneven pad temperature
• Abnormal thrust pad wear
• Damage on thrust collar surface
• Increased axial vibration or instability

In turbine-generator applications, thrust bearings are critical locations to inspect when shaft voltage is suspected.

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7. Why Journal Bearing Electrical Damage Is Different from Rolling Bearing Fluting

Rolling bearings often show:

• Fluting
• Washboard pattern
• Electrical pitting on raceways
• Grease darkening
• False brinelling-like marks
• Noise increase

Journal bearings usually do not show classic fluting because there are no rolling elements passing repeatedly over raceway defects.

Instead, journal bearing symptoms may include:

• Babbit pitting
• Frosting
• Spark erosion
• Dark deposits
• Increased bearing temperature
• Unstable vibration
• Oil degradation
• Ferrous/non-ferrous wear debris
• Abnormal particle morphology
• Possible varnish-like deposits

So for journal bearings, the RCA should not search only for fluting. It should search for evidence of electrical discharge across the oil film.

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8. How Electrical Faults Show Themselves in Operation

Electrical faults in turbomachinery may show up as:

8.1 Bearing Temperature Increase

The bearing temperature may rise gradually or intermittently.

The increase may not correlate clearly with:

• Load
• Speed
• Oil supply temperature
• Ambient temperature
• Oil viscosity
• Alignment condition

This makes it difficult to diagnose.

A typical clue is:

Bearing temperature increases even though oil viscosity, oil flow, and cooler performance look acceptable.

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8.2 Unstable Vibration

Electrical discharge damages the bearing surface and changes the oil film behavior.

This may cause:

• Increased subsynchronous vibration
• Increased 1X vibration due to changing bearing support stiffness
• Unstable orbit shape
• Increased shaft centerline movement
• Changes in phase angle
• Occasional vibration spikes

However, vibration alone may not confirm electrical damage.

It gives symptoms.
Oil analysis and bearing inspection give evidence.

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8.3 Instrument Noise

Electrostatic discharge or grounding problems can create noise in sensors and monitoring systems.

Possible symptoms:

• Erratic proximity probe readings
• Spikes in vibration data
• Temperature signal noise
• Unstable online oil sensor readings
• False alarms
• Intermittent instrumentation faults

This is especially important in machines with poor grounding separation between power and instrumentation systems.

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8.4 Repeated Bearing Problems After Mechanical Corrections

One classic sign is repeated bearing distress even after correcting usual mechanical causes.

For example:

• Alignment corrected
• Oil cleanliness improved
• Oil viscosity confirmed
• Oil flow verified
• Cooler cleaned
• Bearing clearance checked
• Rotor balance acceptable

But bearing distress continues.

At that point, electrical current must be investigated.

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9. How Electrical Faults Appear in Oil Analysis

Oil analysis can provide very strong clues, but only if the report is interpreted correctly.

Electrical discharge may appear in oil analysis through:

1. Wear metal changes
2. Particle morphology
3. Oil darkening
4. Increased insolubles
5. Increased oxidation products
6. Abnormal MPC trend
7. Abnormal FTIR trend
8. RULER antioxidant depletion acceleration
9. TAN increase
10. Patch color abnormalities
11. Filter debris
12. Ferrous density changes
13. Abnormal PQ index
14. Carbonaceous particles

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10. Wear Metals: What to Look For

Journal bearings are often babbit-lined. Depending on design, the bearing metallurgy may include:

• Tin
• Lead
• Copper
• Antimony
• Steel backing
• Nickel barrier layers in some designs

Oil analysis may show increases in:

• Sn — tin
• Pb — lead
• Cu — copper
• Fe — iron
• Sb — antimony, if tested
• Ni — nickel, if present in bearing construction

But electrical damage can be tricky.

The wear particles may be very fine and localized. Standard ICP may detect only particles below a certain size range. Larger particles may not be fully represented.

So a “normal” ICP result does not always eliminate electrical bearing distress.

That is why oil analysis should include:

• ICP elemental analysis
• Ferrous density or PQ index
• Analytical ferrography
• Membrane patch microscopy
• Filter debris analysis
• Bearing metal baseline comparison

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11. Typical Oil Analysis Pattern for Journal Bearing Electrical Damage

A possible pattern may look like this:

Test	Possible Trend
Tin	Increasing
Lead	Increasing
Copper	Increasing if deeper bearing layer affected
Iron	May increase if shaft or steel backing affected
PQ index	May increase if larger ferrous particles are present
Particle count	May increase, but not always dramatically
MPC	May increase due to polar degradation products and carbonaceous material
FTIR oxidation	May increase locally or trend upward
TAN	May increase if oxidation/acidic products form
RULER	May decline faster due to antioxidant stress
Color	Darkening may occur
Patch test	Dark, carbonaceous, or unusual deposits may appear

The key is trend interpretation.

A single oil sample may not prove the fault.
A sequence of samples can reveal the story.

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12. Why MPC May Increase After Electrical Discharge

MPC measures the tendency of oil to form deposits, especially varnish potential.

Electrical discharge can create localized high-temperature oil degradation. This may generate:

• Polar oxidation products
• Resinous degradation compounds
• Carbonaceous material
• Insoluble degradation particles
• Surface-active byproducts

These products can increase the tendency of oil to deposit on surfaces.

Therefore, electrical faults can indirectly contribute to varnish formation.

Important point:

Not every high MPC is caused by electrical discharge.
But electrical discharge can be one hidden contributor to abnormal MPC increase.

This is especially true when high MPC appears together with:

• Dark patch color
• Black carbon-like deposits
• Abnormal bearing metal trend
• Filter discoloration
• Bearing temperature instability
• Repeated unexplained bearing distress

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13. Electrical Discharge and Black MPC Patches

A normal varnish patch is often amber, brown, or orange depending on oil chemistry and degradation mode.

But electrical discharge, microdieseling, high-temperature coking, or severe thermal stress may produce darker deposits.

A black or very dark patch may suggest:

• Carbonaceous material
• Thermal cracking
• Localized high-temperature degradation
• Soot-like contamination
• Spark erosion byproducts
• Severe oxidation/coking

This is why I always prefer seeing the MPC patch image, not only the MPC number.

The number alone does not tell the full story.

A Delta E or Delta L value gives useful data, but the visual appearance of the patch gives diagnostic direction.

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14. FTIR Clues

FTIR may show increases in:

• Oxidation products
• Nitration, depending on application
• Carbonyl region changes
• Degradation byproducts

But FTIR is a bulk oil test.

Electrical discharge damage is often highly localized. The oil sample may dilute the evidence.

So FTIR may show only mild changes even when local bearing discharge is serious.

That is why FTIR should be interpreted together with:

• MPC
• RULER
• TAN
• Wear metals
• Particle morphology
• Filter debris
• Operating symptoms

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15. RULER / Antioxidant Depletion

Electrical discharge creates localized high-temperature stress.

High thermal and oxidative stress consumes antioxidants.

So RULER may show accelerated depletion of:

• Phenolic antioxidants
• Aminic antioxidants

A suspicious trend would be:

• Faster-than-expected RULER depletion
• MPC increasing
• TAN slowly increasing
• Oil color darkening
• Bearing metals increasing
• No obvious contamination source

This pattern should trigger investigation into local thermal/electrical stress.

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16. TAN Behavior

TAN may increase if electrical discharge contributes to oxidation and acidic degradation products.

However, TAN may not increase immediately.

Why?

Because TAN is a bulk oil parameter. Localized discharge may produce deposits and insolubles before TAN becomes alarming.

Also, modern turbine oils may hold degradation products differently depending on base oil group and additive chemistry.

So never rely on TAN alone to detect electrical damage.

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17. Particle Count May Be Misleading

Electrical discharge damage can produce very fine particles and carbonaceous material.

Particle count may increase, but the pattern may not always be dramatic.

Also, if the system has high-efficiency filtration, the particle count may look acceptable while the root cause continues.

This is one of the traps:

Clean oil does not always mean electrically safe oil.

You may have ISO 4406 cleanliness under control while electrical discharge is still attacking the bearing surface and degrading the oil locally.

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18. Filter Debris as Evidence

Filters can tell the truth.

When electrical discharge is suspected, inspect used filters for:

• Blackened media
• Burn marks
• Metallic shimmer
• Fine grey/black paste
• Carbonaceous deposits
• Unusual smell
• Localized holes or damage
• Fine non-ferrous bearing material
• Ferrous particles

Filter debris analysis can be extremely useful because the filter collects what the small oil sample may miss.

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19. Practical RCA Approach

When electrical fault is suspected in turbomachinery, do not start only from oil analysis. Use a combined approach.

Step 1: Review Operating Symptoms

Check:

• Bearing temperature trend
• Vibration trend
• Shaft orbit
• Shaft centerline
• Phase changes
• Oil supply temperature
• Oil flow
• Oil pressure
• Load changes
• Start/stop history
• Trip history
• VFD operating conditions
• Generator excitation events
• Grounding brush maintenance history

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Step 2: Measure Shaft Voltage and Shaft Current

This is essential.

Measure:

• Shaft-to-ground voltage
• Shaft current
• Common-mode voltage, if VFD-driven
• High-frequency discharge activity
• Grounding brush current
• Current through grounding straps
• Current across coupling, if applicable

Use proper instruments and competent electrical specialists. Normal multimeters may miss high-frequency events.

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Step 3: Inspect Grounding and Bonding

Check:

• Grounding brush condition
• Brush contact pressure
• Brush contamination
• Brush wear
• Shaft contact surface condition
• Insulated bearing integrity
• Grounding straps
• Coupling bonding
• VFD grounding
• Motor grounding
• Driven machine grounding
• Skid grounding
• Foundation grounding
• Cable shielding termination
• Instrument grounding separation

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Step 4: Inspect Bearings

During shutdown, inspect journal and thrust bearings for:

• Frosting
• Pitting
• Spark erosion
• Black marks
• Local melting
• Surface roughness
• Overlay damage
• Wiping
• Fatigue initiation points
• Damage distribution around the bearing
• Loaded zone versus unloaded zone location

Use magnification. Some electrical pits are very small.

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Step 5: Upgrade Oil Analysis Scope

For suspected electrical damage, oil analysis should include:

• ICP wear metals
• Particle count
• Ferrous density / PQ index
• Analytical ferrography
• MPC with patch image
• RULER
• TAN by ASTM D664
• FTIR oxidation
• Moisture by Karl Fischer
• Membrane patch microscopy
• Filter debris analysis
• Elemental comparison with bearing metallurgy

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20. How to Differentiate Electrical Bearing Damage from Other Failures

Electrical Damage vs Oil Starvation

Oil starvation often produces wiping, overheating, and directional rubbing damage.

Electrical damage often produces fine pitting, frosting, or spark erosion without classic starvation evidence.

But both can coexist. Electrical pitting can disturb the oil film and later cause wiping.

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Electrical Damage vs Contaminant Abrasion

Abrasive contamination usually creates scratches or scoring aligned with shaft rotation.

Electrical damage creates pits or crater-like surface damage.

Oil analysis for abrasion may show high particle count and hard contaminants such as silica. Electrical damage may show more bearing metals, carbonaceous material, and localized deposits.

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Electrical Damage vs Varnish-Only Problem

Varnish causes sticky deposits, servo issues, temperature control issues, and restricted oil flow.

Electrical discharge may create dark carbonaceous deposits and bearing pitting.

However, electrical discharge can also accelerate varnish formation.

So do not separate them too much. They may be connected.

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Electrical Damage vs Misalignment

Misalignment often creates predictable load-zone distress and temperature/vibration patterns.

Electrical damage may appear more scattered or discharge-path dependent.

But again, misalignment and electrical discharge can work together. Misalignment reduces oil film stability, making dielectric breakdown easier.

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21. Why Oil Film Thickness Matters

Electrical discharge is more likely when the oil film is thin or unstable.

Conditions that reduce oil film thickness include:

• Low viscosity
• High oil temperature
• Low speed during turning gear or coastdown
• High load
• Misalignment
• Bearing clearance issues
• Poor oil supply
• Foaming
• air entrainment
• Water contamination
• Varnish deposits
• Surface roughness
• Start/stop operation

This means electrical damage may be worst during:

• Startup
• Shutdown
• Low-speed operation
• Turning gear operation
• Load changes
• High-temperature operation
• Transient events

The machine may look fine at full hydrodynamic speed but suffer during transitional conditions.

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22. Water Makes the Situation Worse

Water contamination affects electrical and lubrication behavior.

Water can:

• Reduce oil film strength
• Promote corrosion
• Change oil conductivity
• Support additive depletion
• Increase oxidation
• Promote emulsions
• Destabilize hydrodynamic film
• Increase risk of electrical leakage paths

In turbine oils, even low water levels can become serious if the machine is electrically sensitive.

For journal bearings, water is not only a corrosion problem. It can also influence oil film behavior and electrical discharge risk.

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23. Varnish Makes the Situation Worse

Varnish deposits can affect electrical problems in several ways:

1. Varnish changes surface condition.
2. Deposits disturb oil film formation.
3. Deposits increase local temperature.
4. Deposits may restrict oil flow.
5. Deposits can affect bearing heat transfer.
6. Deposits may create uneven surface conductivity.
7. Deposits may retain polar degradation products.

So electrical discharge can create varnish precursors, and varnish can make bearing conditions more favorable for discharge.

This is a dangerous loop:

Electrical discharge → oil degradation → deposits → hotter bearing → thinner oil film → more discharge → more damage.

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24. Why Modern Turbine Oils May Be More Sensitive

Modern turbine oils are excellent products, but the system environment has changed.

Many modern systems use:

• Group II / Group III base oils
• High-efficiency filtration
• Very clean oil targets
• Synthetic filter media
• Fine filtration
• Dry oil systems
• VFD-driven auxiliaries
• Higher electrical noise environments
• More sensitive control systems

Group II and Group III oils are generally less polar than old Group I oils. They also have different solvency and conductivity behavior.

This may increase sensitivity to:

• Varnish formation
• Electrostatic charging
• Poor deposit solubility
• Low conductivity events

This does not mean modern turbine oils are bad.
It means the maintenance strategy must be more sophisticated.

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25. Prevention and Mitigation

25.1 Shaft Grounding Brushes

Use properly designed shaft grounding systems.

Important points:

• Correct brush material
• Proper contact pressure
• Clean shaft contact surface
• Regular inspection
• Low-resistance path to ground
• Protection from oil contamination
• Monitoring of brush wear
• Verification that current is actually passing through the brush, not the bearing

A grounding brush that exists on the drawing but is not working in reality gives false confidence.

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25.2 Insulated Bearings

Some machines use insulated bearings to interrupt current paths.

But insulation must be verified.

Problems include:

• Damaged insulation
• Contaminated insulation surfaces
• Incorrect installation
• Bypass through instrumentation
• Bypass through piping or coupling
• Maintenance modifications that unintentionally defeat insulation

Insulation is not “install and forget.”

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25.3 Proper VFD Cable and Grounding Design

For VFD-driven motors:

• Use correct shielded cable
• Proper shield termination
• Low-impedance grounding
• Correct VFD grounding practice
• Common-mode chokes or filters where needed
• dv/dt filters or sine filters where needed
• Bearing protection on both motor and driven equipment, where required

A VFD solution must be system-level, not only motor-level.

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25.4 Coupling Conductivity Control

Depending on machine design, the coupling may either need to conduct or isolate.

This must be engineered intentionally.

A coupling that accidentally allows current through the driven machine can damage the driven machine bearing.

A coupling that accidentally blocks current may force voltage buildup somewhere else.

So the question is not simply:

“Conductive or insulated coupling?”

The question is:

“What is the designed current path, and is it verified?”

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25.5 Oil Cleanliness and Dryness

Maintain:

• Correct ISO 4406 cleanliness
• Low water contamination
• Good demulsibility
• Low air release tendency
• Controlled foaming
• Healthy antioxidants
• Low varnish potential

Good oil condition improves oil film stability and reduces secondary damage.

But again:

Clean oil cannot replace proper electrical grounding.

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25.6 Electrostatic-Safe Filtration

For oil systems sensitive to electrostatic discharge:

• Avoid excessive flow velocity through filters
• Select filter media with low charging tendency
• Use anti-static filter designs when needed
• Ensure filter housings are grounded
• Avoid poor bonding of bypass loops
• Monitor filter differential pressure
• Inspect filters for burn marks
• Avoid over-filtration without understanding electrostatic behavior

Very fine filtration is not always automatically better if it creates electrostatic stress.

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26. Recommended Monitoring Plan

For critical turbomachinery, I would recommend combining electrical, mechanical, and lubricant monitoring.

Electrical Monitoring

• Shaft voltage
• Shaft current
• Grounding brush current
• Insulation resistance
• Grounding resistance
• VFD common-mode issues
• Coupling current path check

Mechanical Monitoring

• Bearing temperature
• Vibration amplitude and phase
• Shaft orbit
• Shaft centerline
• Axial position
• Bearing metal temperature
• Start/stop transient data

Oil Analysis

• Viscosity
• TAN by ASTM D664
• RULER
• MPC with patch image
• FTIR oxidation
• Karl Fischer water
• Particle count
• Ferrous density / PQ index
• ICP wear metals
• Analytical ferrography
• Filter debris analysis

The best RCA is not done by one department.

Electrical, mechanical, vibration, lubrication, and operations teams must look at the same event together.

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27. Practical Field Red Flags

I would become suspicious of electrical discharge if I see the following combination:

• Journal bearing temperature slowly increasing
• Bearing metal wear trend increasing
• MPC increasing faster than expected
• RULER depletion faster than expected
• Dark MPC patch or black deposits
• No major water or particle contamination
• Vibration pattern not fully explained by balance/alignment
• VFD-driven motor or generator application
• Shaft grounding brush not recently verified
• Repeated bearing distress after mechanical corrections
• Filter elements showing black spots or unusual deposits

One clue alone is not proof.
A pattern is the proof.

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28. Example Case Pattern

Imagine a motor-driven centrifugal compressor with journal bearings.

Oil analysis shows:

• ISO 4406: acceptable
• Water: acceptable
• Viscosity: normal
• TAN: slightly increasing
• RULER amine: faster drop than expected
• MPC: increasing from 12 to 28 to 45
• Patch: dark brown to black
• Tin and lead: increasing slowly
• Bearing temperature: 8°C higher than historical baseline
• Vibration: intermittent instability
• VFD motor installed one year ago
• Shaft grounding brush inspection not documented

In this case, many teams may focus only on varnish removal.

But the better RCA question is:

Why is the oil generating degradation products faster than expected?

Possible answer:

Electrical discharge across the bearing oil film is creating localized thermal degradation and bearing surface distress.

In such a case, installing varnish removal alone may clean the symptom, but the electrical cause remains.

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29. Khash Reliability Message

Electrical faults in turbomachinery are dangerous because they hide between disciplines.

The electrical engineer may say:

“Grounding looks acceptable.”

The vibration engineer may say:

“The vibration is not clearly mechanical.”

The lubrication engineer may say:

“Oil analysis shows varnish and abnormal metals.”

The bearing engineer may say:

“The babbit surface looks pitted and strange.”

But the real failure mechanism may be the combination:

Shaft voltage + unstable oil film + electrical discharge + localized thermal oil degradation + bearing surface erosion.

This is why turbomachinery reliability cannot be managed in silos.

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30. Final Conclusion

Electrical faults in turbomachinery are not only electrical problems.

They are:

• Bearing problems
• Lubrication problems
• Oil degradation problems
• Varnish problems
• Vibration problems
• Reliability problems

For rolling bearings, electrical current often announces itself as fluting.

For journal bearings, it is more subtle:

• Pitting
• Frosting
• Spark erosion
• Dark deposits
• Bearing temperature increase
• Abnormal wear metals
• Carbonaceous material
• Faster antioxidant depletion
• Increased MPC
• Possible varnish acceleration

The bearing may not scream immediately.
The oil may whisper first.

A good lubrication specialist should listen to that whisper before the machine trips.

Khash, CLS, MLE, MLA III, MLT II, VIM, VPR

P.S Below is the best sparking video I have seen happening in Turbine Oil Tanks, It can happen in filters and bearings as well