EN
Tightness Inspection
Tightness control of MV cells and switchgear: busbar-joint torque audit, insulator sealing and leakage verification by engineers, with reports.
Tightness inspection audits, in medium voltage cells, panel-busbar systems and switchgear, that mechanical fasteners are at their correct tightness and sealing preserved: busbar joints, cable heads, bolt-nut-washer combinations, lid gasket and insulator perimeter enclosure integrity are verified with torque wrench, visual-marking and field leakage readings. A loosened busbar joint grows contact resistance and travels toward hot-spot and arc fault under load; weak sealing begins surface leakage currents and insulator deterioration through dust-moisture ingress.
Inspection Items
- Joint tightness: Bolt control with manufacturer torque values; slip-trace scan on painted-torque-sealed joints; reassessment of re-torqueing need on lines that saw thermal cycling. Cable lug pressure surface, washer and stainless clamp integrity examined.
- Sealing: Cell lid gasket, cable gland, insulator perimeter seal; dust-water ingress lowers the IP rating. On gas insulated (GIS) types, leak survey with detection instrument is the special case of this item.
- Surface and leakage: Tracking-blanching-mud on insulator surfaces, colour change on busbars; conductor-support clearance and vibration traces. Suspicious surfaces verified with leakage current/UV (corona) monitoring.
- Mechanical: Lid hinge-safety locks, disconnector-damper control links, slide-interlock dialogue (earthed position lock); spring-clip wear and displacement.
- Thermal verification: Under load, thermographic scan measures whether tightness-sealing findings turned into reality (hot spot); ΔT thresholds set by phase-to-phase comparison.
Application and Importance
Tightness control generally runs de-energised; hence the OSAS (dead work) permit, earthing-RCD audit and voltage presence test procedure are the first step. Intervening on a live joint (re-torqueing) is risky; thermal findings are moved to the planned shutdown. Marking and record after torquing is the most practical audit for catching assembly errors (missing-double bolt). In switchyards wind-vibration and short-circuit magnetic forces loosen connections over time; periodic control therefore works with a settlement schedule tightened in early years. A first tightness round within 6-12 months of new cells is the most economic practice to catch assembly-origin loosening before a fault.
Legislation and Outcome
The control is within the periodic switchgear examination programme under Law No. 6331, the High Current Installations Regulation and maintenance specifications. Technical reference: the IEC 62271 series (MV control-gear), IEC 62230 (cable accessories) and IEC 61439 on the panel side. The result connects to a signed report with the measurement table (torque, leakage, ΔT), photos and proposals. Tightness controls are in our Transformer Tests and Analyses group; for complete panel audits see Terminal Inspection and Cell Inspections, or contact us for a programme.
FAQ on Torque Tightness Control
A loose bolt-nut-tap connection at a joint is the most common defect producing resistance in a high-current transformer: a small slack grows I²R heating and oxidation on the contact surface, which raises resistance toward a leakage-arc-fire chain. That is why torque-tightness is verified on all critical bolted joints (primary-secondary-bushing-tap-neutral-earthing-tank-support).
The manufacturer torque table (by nut-size-class-plating) and any maintenance specification are the basis. A pre-torque comparison is made with a calibrated torque wrench; loose nuts are retightened to the proper torque. Before control, surface-corrosion-dirt-burr is removed, the gasket-spring washer state and contact surface-plating are reviewed. Where needed it is verified with joint resistance (micro-ohm) and thermal scanning (thermal control).
Under-torque (nut turning-free play by hand), shifted marking paint, contact-surface oxidation-discolour-darkening, worn nut-washer, crushed spring washer or rusted-corroded joint, seepage trace at the bushing nut; these come from thermal cycling, vibration or first-assembly error. Removal: cleaning-plating check-correct retorque-marking; replacing damaged nut-bolt. Over-torque is also dangerous: it produces thread damage-surface crush.
Tightness control is generally inside the yearly periodic package, but is repeated after an overload event, transport-vibration, first commissioning and a network arc-short-circuit. Torque-value-applicator-date-temperature and thermal photo are logged per joint; marking paint (tamper-proof) eases later leak observation. Results above limit-hot spot-removal-follow are kept as a trend and stored in the OHS-repair file.