The Siemens TLJ is a load tap changer used in Siemens power transformers. It uses a hub-based contact design with a reversing switch. The TLJ presents a parts sourcing challenge not found on most other LTC models: all TLJ contact components are available only as refurbished units, not new manufacture. This means that every contact replacement on the TLJ — hub, neutral stationary, reversing moving, reversing stationary — requires sourcing a refurbished assembly that has been inspected and restored to serviceable condition. Lead times for refurbished TLJ contacts are longer than for new-manufacture components, and maintenance planning must account for this.
The hub contact assembly is the central rotating contact on the TLJ. It carries load current through the tap winding connections and positions the moving contacts at each tap position. Inspect the hub assembly for wear at the contact surfaces, physical integrity of the hub body, and condition of the contact finger mounting. A hub assembly that has worn to the point of reduced contact surface area produces elevated contact resistance at multiple tap positions simultaneously — position-specific resistance readings point to individual stationary contacts, while uniformly elevated resistance across all positions points to the hub assembly itself.
When a hub assembly requires replacement, plan the replacement lead time before scheduling the transformer outage. Refurbished hub assemblies are sourced, inspected, and prepared to order — they are not typically held in stock at the same availability as new-manufacture contact components. Confirm the replacement assembly is on hand before the transformer is taken out of service for maintenance.
The neutral stationary contact carries current in the neutral tap position and does not see arcing duty during normal tap change operations. It accumulates resistance from surface oxidation and age-related contact deterioration. Measure contact resistance at the neutral position at each maintenance interval and compare to baseline. An elevated reading at neutral with normal readings elsewhere identifies the neutral stationary specifically. The refurbished neutral stationary contact assembly is available for replacement when the measured resistance exceeds the serviceable limit or when the contact surface shows deterioration beyond a surface cleaning.
The TLJ reversing switch uses a refurbished moving contact assembly and refurbished stationary contacts for the raise and lower positions. Inspect the moving contact assembly for surface condition and verify that it travels fully to both reversing positions without binding. Inspect the reversing stationary contacts for pitting and erosion at the contact engagement zone. Measure contact resistance in both reversing positions as part of the standard maintenance test sequence. As with all TLJ contacts, replacements are sourced as refurbished units — plan the procurement timeline accordingly before scheduling the maintenance outage.
The refurbished-only parts situation on the TLJ has a direct implication for maintenance scheduling: the inspection results cannot drive immediate parts replacement the way they can on models with new-manufacture contacts in stock. The practical maintenance approach for TLJ-equipped transformers is to inspect contacts at each scheduled interval, document wear measurements and contact resistance, and use trending data to predict when replacement will be required at the subsequent interval. If the trending data indicates a contact will reach its wear limit before the next scheduled outage, initiate the refurbished parts procurement immediately — do not wait until the next maintenance window to begin sourcing.
UnderNERC PRC-005, the standard six-year maximum calendar interval applies to TLJ-equipped transformers. Utilities operating TLJ units should factor the longer parts lead time into their maintenance program planning and initiate procurement as part of the maintenance scheduling process rather than after the outage inspection confirms the need.
All TLJ contacts are sourced as refurbished units. Contact us early — before your outage is scheduled — so lead time doesn’t delay your maintenance window.