A box-type substation packs a transformer, medium-voltage switchgear and low-voltage distribution into one enclosure. Regular checks keep it reliable; when a fault does occur, a methodical approach finds the cause quickly.
Before you start
- Qualified electrical staff who know the unit’s layout and wiring
- The manual, single-line diagram and wiring diagrams
- Test instruments (multimeter, insulation resistance tester, winding resistance meter) and personal protective equipment
- Isolation, earthing and lock-out of every supply before any work inside
Inspection and testing
- Look for enclosure damage, corrosion, oil leaks, cracked bushings, tracking marks and blocked radiators or vents
- Measure winding DC resistance; a clear imbalance between phases points to a winding or connection fault
- Measure insulation resistance HV–LV, HV–earth and LV–earth and compare with the commissioning values; a sharp drop suggests moisture or ageing
- Check the turns ratio against the nameplate
- Measure no-load current and loss; a rise can indicate a core fault such as unintended multiple earthing
Common repairs
- Windings: local repair of minor damage, or a rewind to the original turns, conductor size and direction for serious faults
- Core: find and remove an unintended earth path; repair damaged lamination insulation
- Insulation: dry out moisture with controlled heating; replace aged insulation
- Tap changer: clean or replace burnt contacts; repair a sticking mechanism
After repair
Repeat the electrical tests, then energise off-load and watch for abnormal noise or heating before connecting load in steps.
See our YB and ZGS11 box-type substations, or our service page for support.