Ferranti Packard on-load tap changer upgrades

05/01/2013

On-load tap changers (LTCs) are intricate, electro-mechanical devices often operating under severe service conditions (hundreds of thousands of operations). LTCs may endure mechanical wear on switch components and the drive mechanism requiring readjustment and/or part replacement. Siemens offers a comprehensive portfolio of LTC renewal part solutions and services supported by factory-trained service engineers and original manufacturer engineering departments who understand your equipment design. A preventative LTC maintenance program will help customers avoid unplanned failures, lower maintenance costs and extend transformer service life.

 

Ferranti-Packard manufactured the LRT 25, 34, 69, and 138kV load tap changers (LTCs) from the early 1960s through 2005. The LRT was built to withstand severe operating condition with a minimal amount of maintenance. Siemens has received reports of burning and coking in the reversing switch contacts, most prominently on switches in the 25-35kV class with high amperage applications, that operate in a very narrow tap range and which seldom move through the reversing switch application.

 

Reversing switch contact kit (Part No. 900 458 480)

 

To improve performance and reliability, Ferranti-Packard has redesigned the reversing switch assembly and improved the reversing switch components, including:

  • Stationary contact blades (M,P, & Q) have been upgraded from cast copper to machined copper bar (harder material).

  • Selector stationary contacts have been upgraded from a tin-plated, blunt-leading edge, to a silver-plated, easy-leading edge design. As a result, less mechanical force is required during the transition through neutral. The easy leading edge mates perfectly with the stationary contact to allow smooth transfer while maintaining an excellent contact surface, with a combination of 50% silver and 50% tungsten sintered tip design.

  • Moving contact finger mating edges have been radiused where they contact the stationary blade and ride up into position.

  • Moving finger assembly clamping spring pressure has been doubled.

  • Clamping spring is isolated from the finger contacts with an insulating washer to eliminate heating caused by circulating currents.

  • Clamping spring is centered and held in place around the retaining pin.

  • Contact spring assembly has been upgraded, integrating a larger seating surface to ensure a greater distribution of compression on the moveable contacts.

Notes: 

  • This reversing switch upgrade kit is not applicable to 138kV switches, nor to older switches manufactured using contact posts with porcelain insulators (circa 1960/1970).

  • Although parts are interchangeable with older components supplied on most of the tap changers, it is necessary to change all the components on the reversing switch as they are a mating set.

Diverter switch contact kit (Part No. 102 102 100)

 

The load diverter switch is a quick-break type employing a four-link mechanism, which is stable in two positions. The two side-links of this mechanism carry the four moving contacts. The diverter switch is actuated by two coil springs which are charged by a crank and a slide mechanism. These springs are connected to the center of the upper link. Switches are equipped with a tungsten-copper arcing tip brazed to a copper backing plate approximately 7/32nd thick at the tip. Contacts should be replaced hen worn down to within 1/16th of the backing plate. To improve performance and reliability, Ferrnti-Packard has redesigned the diverter and improved switch components.

 

Although this measurement is a quick visual indicator to the operation of the diverter, many components in the diverter shold also be inspected to ensure proper timing and operation. Gaps, springs and clearance are paramount to the proper operation of the most valued component in the LTC compartment.

 

Other kits available for Ferranti-Packard LTCs:

  • Selector switch contact kit (Part No. 222 224 220)

  • Complete oil seal assembly (Part No. 220 000 001)

  • Transition resistors, diverter switch (Part No. 207 766 001)

  • Complete selector top board assembly (Part No. 208 111 001).

Other parts solutions include:

  • Gasket kits

  • Bushings

  • Coolers, radiators, and fans

  • Motors

  • Gauges

  • Replacement nameplates.

These upgrades, depending on your transformer, can be field installed. Siemens can support you with factory trained field service engineers who are familiar with OEM recommended procedures to minimize downtime and maximize transformer reliability and performance.

 

LTC maintenance training:

 

When combined with a scheduled maintenance outage, LTC field service and on-site training provides the following hands-on experience for maintenance crews:

  • Maintenance and repair sequencing

  • Factory adjustment procedures and tolerances

  • Part identification

  • Troubleshooting, failure analysis.