SOP: Regulating Ring & Eccentric Pins

Advanced SOP: Regulating Ring & Eccentric Pins

The "Forgotten" Friction - Stiction Analysis & Vane Synchronization

⚠️ THE HUNTING PROBLEM

Context: The regulating ring is the mechanical translator between the hydraulic servomotor and all 20 guide vanes. It moves on rollers or slides, converting linear hydraulic force into rotational motion.

  • The Risk: If the ring's sliding surfaces are not perfectly lubricated, the governor will "hunt" (oscillate power output).
  • Root Cause: Stiction (static friction) creates resistance that the HPU overcomes with pressure spikes, causing jerky movement instead of smooth modulation.
  • Impact: Every oscillation causes wear on all 20 vanes simultaneously, accelerating bushing failure and creating unstable power delivery to the grid.
SOP 1: Friction Analysis - Measuring Stiction

Stiction is invisible but measurable through HPU pressure behavior during slow movement.

1.1 The "Dry-Start" Risk

Critical Context for Unit 1: After the extended shutdown (seal replacement), the regulating ring's sliding surfaces have been bone-dry for weeks. The lubricant film has evaporated or drained away.

  • Consequence: The first HPU stroke after restart will encounter maximum stiction, potentially causing a violent "jump" that damages the linkage pins.
  • Mandatory Pre-Start Action: Manual grease application to all sliding surfaces BEFORE energizing the HPU.

1.2 Stiction Measurement Procedure

  1. Instrumentation: Monitor HPU pressure gauge in real-time (analog or SCADA).
  2. Test Sequence: Command governor to move from 0% to 10% open at slowest possible speed (manual mode).
  3. Observe Pressure Profile:
    • PASS (Smooth): Pressure rises gradually to ~140-150 bar and holds steady during movement.
    • FAIL (Stiction): Pressure spikes to 160-180 bar, then drops suddenly as ring "breaks free", creating a sawtooth pattern.
  4. Diagnostic: If sawtooth pattern observed, the ring is experiencing stick-slip friction. Lubrication is inadequate.
ACCEPTABLE PRESSURE BEHAVIOR:
Nominal: 140-150 bar (steady)
Warning: 155-165 bar (marginal lubrication)
Critical: >165 bar or sawtooth pattern (insufficient lubrication - STOP and re-grease)
SOP 2: Eccentric Pin Adjustment

The eccentric pins on each guide vane arm allow fine-tuning of the vane's angular position. The goal: All 20 vanes must touch their mechanical stops simultaneously.

2.1 The Synchronization Requirement

Physics: If vane #1 closes at 0° but vane #12 closes at 0.5°, the water flow distribution becomes asymmetric, creating turbulence and reducing efficiency by ~2-3%.

Mechanical Logic: Each vane arm has an eccentric bushing that can be rotated to adjust the effective length of the linkage.

2.2 Adjustment Procedure

  1. Safety Lockout: Unit stopped, MIV closed, hydraulic pressure released, mechanical safety pin installed.
  2. Command Position: Set governor to "Fully Closed" (0%) position using manual override.
  3. Visual Inspection: With flashlight, inspect each guide vane gap at the closed position.
    • Target: All vanes should have identical clearance to the "stop" surface (typically cast into the turbine casing).
    • Feeler Gauge: Measure the gap. Target: ≤ 0.2mm variation between any two vanes.
  4. Eccentric Adjustment: For vanes not touching the stop:
    1. Loosen the lock nut on the eccentric pin.
    2. Rotate the eccentric bushing using a specialized wrench (typically 2-3° rotation = 0.5mm vane travel).
    3. Re-tighten lock nut to manufacturer torque specification (record in logbook).
  5. Verification: Repeat the "Fully Closed" command and re-measure all gaps. Iterate until all vanes synchronized within 0.2mm.
[DIAGRAM PLACEHOLDER: Servomotor → Regulating Ring → 20x Linkage Arms with Eccentric Pins → Guide Vane Stems]

Recommended Visual: Cross-section showing eccentric bushing rotation effect on vane angle.
SOP 3: Pre-Start Lubrication Protocol

MANDATORY for Unit 1 Recovery: This protocol MUST be executed before the first HPU stroke after extended shutdown.

3.1 Manual Lubrication Procedure

  1. Access: Remove inspection cover for regulating ring chamber.
  2. Clean: Wipe all sliding surfaces with clean lint-free cloth to remove any debris or oxidation.
  3. Grease Application: Apply high-temperature water-resistant grease (same as used in central greasing system) to:
    • All roller contact surfaces
    • Sliding guide tracks
    • Eccentric pin bushings (all 20 vanes)
  4. Manual Movement: Manually rotate the regulating ring through its full range (0-100%) to distribute grease evenly. Movement should be smooth with no "dry" spots.
  5. Re-install Cover: Ensure no tools or rags left in mechanism chamber.
Diagnostic Troubleshooting

Symptom: Power Output "Hunting" (±5% oscillation)

  • Root Cause 1: Stiction in regulating ring → Check HPU pressure for sawtooth pattern.
  • Root Cause 2: Poor vane synchronization → Verify eccentric pin adjustment using feeler gauge.
  • Root Cause 3: Worn linkage bushings → Perform manual "wiggle test" on each vane arm (ref: Linkage SOP).

Symptom: High HPU Pressure (>165 bar during normal operation)

  • Immediate Action: Stop unit, release pressure, manually lubricate ring.
  • Investigation: Check central greasing system - verify pump is building pressure and all dosage valves are flowing.
Summary Checklist
  • Before First Start After Shutdown: Manual greasing of regulating ring surfaces (SOP 3).
  • Monthly: Monitor HPU pressure during slow movement for stiction indicators.
  • Annually: Eccentric pin adjustment verification (all 20 vanes synchronized within 0.2mm).
  • On Overhaul: Full disassembly and inspection of regulating ring roller bearings and sliding surfaces.
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