Siemens voltage regulators: condition of drive springs in type TLG tap changers

05/01/2004 - Volume I - Issue II

Safety tips


Note: Verification of the condition of tap changer drive springs is a necessary part of periodic inspection and maintenance procedures.


The proper spring-driven tap change is a very quick, "snapping" movement from one contact to the next. Without the benefit of the drive spring, the tap change is a slow sliding movement from one contact to the next, resulting in excessive arcing and burning of the contacts.


Checking the condition of the drive springs is best performed while the regulator is de-energized accordingly, Siemens recommends that the regulator be de-energized before making this check. However, if necessary, the condition of the drive spring can be determined with the regulator in service as follows:


Testing drive springs in Siemens Type TLG tap changer while regulator is energized.


  1. Before manually operating the tap changer, observe the position indicator pointer. The initial manual move of the tap changer must NOT move the pointer into the neutral position. (Without benefit of the drive spring, moving the tap changer into the neutral position can activate the reversing switch and jam the operating mechanism.)
  2. If the pointer movement is slow while changing taps or if it seems to "slide" from one position to the next instead of snapping, then block the regulator from further operations until it can be de-energized from its high-voltage source, and remove from service. DO NOT BY-PASS!
  3. The test of drive springs should be performed in both directions- RAISE and LOWER- in order to verify both drive springs.
  4. If the tap change is not a quick snapping from one position ot the next, discontinue any further operations. Continued tap changing will result in more arcing and burning of contacts. HOWEVER, if the energized regulator to be tested is found to be ALREADY in the neutral position, immediately block operation of the tap changer by turning off the control and removing fuses. Then proceed to by-pass and isolate the regulator by taking it out of the source/load circuit, observing all By-Pass safety rules at all times. After regulator is properly isolated, operate in both the RAISE and LOWER directions to determine if the springs are working properly.