The Westinghouse UTT and UTTA are load tap changers used in Westinghouse power transformers predating the UTTB. They share the same transfer switch operating concept as the UTTB but use a different contact geometry — specifically a sliding finger contact assembly rather than the arcing contact design of the UTTB. Parts between the UTT/UTTA and the UTTB do not interchange. Before ordering any contact component, confirm whether the transformer is fitted with a UTT, UTTA, or UTTB by checking the LTC nameplate on the transformer tank.
The defining characteristic of the UTT and UTTA is the sliding finger contact assembly at the transfer switch. During each tap change operation, the contact arm slides across the stationary contact surface rather than making and breaking at a discrete arcing contact point. This distributes wear across a broader contact surface compared to a point-arcing design, but it also means that the entire contact face — moving finger and stationary — must be evaluated for wear, not just an arcing tip.
The sliding finger contact assembly includes the moving arm and its contact fingers. Inspect finger pressure against the stationary surface — fingers that have lost their spring tension will slide across the stationary without making reliable electrical contact, which produces resistive heating at the contact interface and accelerated surface deterioration at both the finger tips and the stationary face. This type of wear does not produce visible arcing craters but shows up as elevated contact resistance and roughened contact surfaces.
With the LTC oil drained and the transfer switch accessible, inspect the moving arcing contact for erosion and the stationary contact assembly for wear. The stationary contact assembly on the UTT/UTTA is a multi-piece unit — inspect each component of the assembly for wear and confirm all mechanical fasteners are secure. A loose stationary assembly allows the contact surfaces to move under the load current, producing fretting wear that accelerates contact deterioration even without tap change operations.
Measure contact resistance across the transfer switch at each tap position. Elevated readings at one tap position but not others indicate a problem specific to that position — check the corresponding stationary contact and verify the sliding finger assembly reaches full engagement at that tap. Elevated readings across all positions point to the sliding finger assembly itself or the collector ring.
The selector switch stationary contacts engage the tap winding connections and see full load current between operations. Inspect selector switch stationary contacts for oxidation, surface roughness, and evidence of overheating. A contact that has been running hot from poor engagement will show discoloration and surface pitting that extends beyond what arcing alone would produce. Check selector switch stationary contact alignment against the moving contact arm travel path and verify that each contact is seated correctly in its mounting.
The reversing switch operates infrequently but carries the full load current when engaged. Inspect the reversing switch moving contact assembly for worn contact surfaces and confirm that the reversing switch drive mechanism moves the assembly fully to both positions. Measure reversing switch contact resistance in both the raise and lower positions as part of the maintenance test record.
Maintenance intervals follow operation count as the primary trigger. Most Westinghouse LTC service documentation specifies inspection at 50,000 to 75,000 operations. UnderNERC PRC-005, the maximum calendar interval for time-based maintenance is six years regardless of operation count. Transformers in active tap regulation service typically reach the operation-count trigger first. Check the operations counter at each scheduled outage.
When ordering replacement contacts, confirm the model designation — UTT, UTTA — from the LTC nameplate before ordering. UTTB contacts will not fit. If the transformer was retrofitted at some point in its service life, the LTC nameplate is the authoritative source; the transformer nameplate may not reflect a retrofit.
Southern Switch stocks UTT and UTTA contact components. Confirm the LTC model from your nameplate before ordering — UTT/UTTA and UTTB parts do not interchange. Contact us with your unit details and we’ll verify the correct parts.