📊 MAINTENANCE INTENSITY MATRIX (MIM)
The Strategic Brain for Adaptive Maintenance
Dynamic priority calculation based on seasonal conditions and operational stress
⚠️ CRITICAL OPERATING PRINCIPLE
ADAPTIVE MAINTENANCE PHILOSOPHY
- Not All Seasons Are Equal: Wet season (high silt) vs dry season (precision work) require fundamentally different focus areas.
- Dynamic Prioritization: A "low priority" task in dry season may become "critical" in wet season.
- Stress-Based Allocation: Resources should flow to systems under highest environmental and operational stress.
The Seasonal Logic - Two Primary Modes
🌧️ HIGH INTENSITY MODE (Wet Season / Flood Period)
Duration: Typically March-May and September-November (Rwanda rainy seasons)
Characteristics: High river flow, elevated turbidity (> 500 NTU), increased sediment load, cooler water temperatures
Primary Focus Areas:
- Silt Management & Erosion Control
- Daily trash rack inspection for debris buildup
- Increased frequency of silt basin flushing
- Runner blade erosion monitoring (weekly visual if possible)
- Link: Intake SOP
- Cooling Water Filtration
- Shift-level filter checks (every 8 hours) instead of weekly
- Bearing temperature trending for early cooling degradation detection
- Back-flush frequency increased to daily
- Oil Hygiene & Aeration Monitoring
- Water contamination risk increases during floods
- Monthly oil analysis instead of quarterly
- Daily HPU sight glass checks for cloudiness
- Link: Oil Health SOP
- Thrust Balance & Axial Position
- High silt increases runner axial thrust variation
- Weekly thrust bearing temperature monitoring
- Check shaft end-float (axial play) monthly
What to AVOID in Wet Season:
- ❌ Stator wedge tightening (vibration from high flow can loosen fresh work)
- ❌ Precision alignment work (thermal cycling and load variation make measurements unreliable)
- ❌ PID tuning (vortex rope frequency varies with silt content, skewing results)
☀️ PRECISION INTENSITY MODE (Dry Season / Low Flow Period)
Duration: Typically June-August and December-February
Characteristics: Low river flow, clear water (< 50 NTU), stable temperatures, predictable load patterns
Primary Focus Areas:
- Mechanical Alignment & Precision
- Bi-annual shaft run-out measurement
- Labyrinth seal gap verification (0.4-0.6 mm target)
- Guide vane linkage pin inspection for wear
- Link: Precision SOP
- Stator Wedge & Core Integrity
- Annual "tap test" for loose wedges
- Thermal mapping of stator for hot spots (post-rainy season check)
- Insulation resistance testing
- Link: Electrical Health SOP
- Governor PID Tuning & Response
- Stable conditions allow accurate step response testing
- Dead-time measurement and optimization
- Frequency stability evaluation (1-hour test)
- Link: Governor Logic SOP
- Foundation & Structural Integrity
- Annual anchor bolt re-torquing
- The "Hollow Test" for grout voids
- Epoxy injection of micro-cracks (if needed)
- Link: Foundation SOP
What to FAVOR in Dry Season:
- ✅ Extended outages for deep inspection work
- ✅ Bearing replacement (stable ambient temperatures reduce thermal shock risk)
- ✅ Runner cavitation repair welding (clean water = better post-repair testing)
The Criticality Scoring System (Stress Score 1-10)
How to Calculate Stress Score
Formula:
Stress Score = (Environmental Factor × 0.4) + (Load Factor × 0.3) + (Age Factor × 0.2) + (Recent Fault History × 0.1)
Scoring Components:
| Factor | Low (1-3) | Medium (4-6) | High (7-10) |
|---|---|---|---|
| Environmental (Turbidity) |
< 50 NTU (Clear water) | 50-500 NTU (Moderate silt) | > 500 NTU (High silt/flood) |
| Load Factor (% of rated) |
40-70% (Optimal efficiency) | 70-90% or 30-40% (Acceptable) | > 90% or < 30% (Stress zones) |
| Age Factor (Time since overhaul) |
< 2 years | 2-5 years | > 5 years |
| Fault History (Last 6 months) |
0 faults | 1-2 faults | > 2 faults |
Criticality Matrix: 25 Modules Ranked
| Module / System | Wet Season Score | Dry Season Score | Primary Stress Driver |
|---|---|---|---|
| Intake & Silt Management | 9-10 | 2-3 | Turbidity, debris load |
| Cooling Water System | 8-9 | 3-4 | Filter clogging from silt |
| Oil Hygiene (HPU) | 7-8 | 4-5 | Water contamination risk |
| Runner Cavitation / Erosion | 8-9 | 3-4 | Suspended solids abrasion |
| Thrust Bearing | 7-8 | 4-5 | Axial load variation |
| Guide Vane Linkage | 6-7 | 5-6 | High cycling frequency |
| Governor Response | 5-6 | 3-4 | Load variation, vortex |
| Draft Tube Vortex | 7-8 | 4-5 | Part-load operation |
| Precision Alignment | 2-3 | 8-9 | Optimal for dry season work |
| Stator Wedges | 2-3 | 7-8 | Post-wet season loosening check |
| Foundation Integrity | 3-4 | 7-8 | Annual re-torque cycle |
| PID Tuning | 2-3 | 8-9 | Requires stable conditions |
| Bearings (Guide/Thrust) | 6-7 | 5-6 | Continuous monitoring |
| Generator Brushes | 5-6 | 5-6 | Wear rate independent |
| Sensors & SCADA | 6-7 | 5-6 | Moisture sensitivity |
Holistic Correlation - System Interdependencies
High Silt → Cascading Effects
Primary Impact: Elevated turbidity (> 500 NTU) during wet season
Downstream Consequences:
- Runner Erosion Acceleration
- Suspended solids act as abrasive particles
- Cavitation pitting deepens faster with silt presence
- Result: Increased vibration → Triggers need for #2
- Thrust Balance Degradation
- Uneven runner erosion changes hydraulic forces
- Axial thrust increases on one side
- Result: Thrust bearing temperature rises → Triggers need for #3
- Oil Hygiene Compromise
- Increased bearing load → Higher oil operating temperature
- Hot oil degrades faster, loses viscosity
- Moisture ingress more likely during heavy rains
- Result: Oil aeration risk → Governor becomes "spongy" → Triggers need for #4
- Governor Response Issues
- Aerated oil reduces hydraulic bulk modulus
- Guide vane response becomes erratic
- Result: Frequency hunting → Load instability
💡 Strategic Insight: In wet season, a single uncorrected issue (high silt) can cascade through 4 interconnected systems. This is why "Intake Management" scores 9-10 during floods - it's the leverage point for system-wide stability.
Thermal Cycling → Alignment Drift
Mechanism: Wet season brings cooler water temperatures (15-18°C) vs dry season (22-25°C)
Impact Chain:
- Cooler water → Lower bearing temperatures → Thermal contraction of shaft
- Shaft contracts → Labyrinth seal gaps increase (+0.05-0.10 mm)
- Increased gaps → Higher seal leakage → Efficiency loss (0.5-1%)
- Conclusion: Alignment work in wet season is futile - measurements will shift when dry season returns. Wait for thermal stability.
Maintenance Calendar Integration
Recommended Annual Cycle (Rwanda Context)
March-May (Long Rains):
- FOCUS: Silt management, cooling water, oil quality
- DAILY: Trash rack, HPU sight glass, bearing temps
- WEEKLY: Oil analysis if turbidity > 800 NTU
June-August (Dry Season 1):
- FOCUS: Precision alignment, PID tuning, foundation work
- SCHEDULE: Plan 1-week outage for deep inspection
- TARGET: Complete stator wedge tightening, bearing replacement if needed
September-November (Short Rains):
- FOCUS: Return to silt management mode
- VERIFY: All June-August precision work remains stable
December-February (Dry Season 2):
- FOCUS: Annual overhaul planning for next wet season
- CRITICAL: Runner cavitation welding repair (if needed) - must be completed before March rains