ANSI Type A Aluminum Vertical Break Switches Type: TMK40A Orientation: Upright mounting Ratings: 345 kV through 765* kV Ratings A: 1200, 1600, 2000, 3000* and 4000* Amperes Request Bulletin B105 Download PDF Catalog *Refer to factory for details for 500 and 765 kV as well as 3000 and 4000 Ampere ratings.

The ANSI Type A three-insulator vertical break switch has been available to the electric power industry since the early 1920's. With one of the two hinge insulators rotating and controlling the opening and closing of the blade through various linkage designs, these switches became one of the preferred types for three- pole gang operation from the ground level.

As voltage, continuous current and short-circuit current ratings increased, further improvements in switch design evolved. In 1939, the MK-39 switch was developed and patented. It had an ingenious ball bearing angle pin feature that transferred the rotation of the insulator to a raising-lowering-twisting motion of the blade. The twisting motion was utilized to develop high pressure current interchange contacts at reduced operating efforts. Flexible braids were eliminated.

The result was a durable, low maintenance heavy-duty switch with minimum moving and current interchange parts.

In 1948, the improved MK-40 design was manufactured and furnished. This switch had slanted jaw and hinge contacts and an improved angle pin construction. The MK-40A Aluminum switch followed in the early 1960s. In the mid 1960s a new and patented feature was incorporated in the basic angle pin design, and a locking feature was added to the jaw end of the closed switch blade.

Finally, in the late 1960s the patented MK-40A/MARK-40 design was introduced that incorporated the blade counter-balancing spring within a tubular housing, which in turn conducted the current from the blade to the hinge terminal.

In 1998, Turner Electric acquired the DELTA-STAR line, name and product rights.

Standards
The "TMK40A" vertical break, air break switches described here are designed and tested to meet the requirements of the latest revisions of ANSI & NEMA Standards. It is recognized that, over the past several decades, these switches have undergone design variations intended to meet a different set of criteria, particularly temperature rise requirements. Some system requirements include adherence to earlier standards for the purposes of uniformity of equipment. Whenever possible, every effort will be made to provide switches adhering to those earlier standards.

DELTA-STAR air break switches have found a home on electrical systems around the world. In recent years, international practice is to use IEC Standards for electrical systems. Our air break switches meet or exceed applicable IEC Standards.

Design Features
The DELTA-STAR vertical break, air break switches types "TMK40A" live parts are fabricated from Aluminum alloys with tinned copper moving contact interchanges. These switches are designed for upright mounting. In special application, the "TMK40A" switches from 8.25 to 230kV can also be furnished for vertical or underhung mounting. Ordering Information at the end of this page lists the availability of the three types for different voltage, current and momentary ratings.

Our construction results in a perfectly counterbalanced blade that can be stopped in any intermediate position from fully closed to fully open without danger of the blade failing to the closed position. Having the counter moment always equal to the blade moment provides a low, uniform operating effort.

Fully Controlled Blade Mechanism
The fully controlled blade mechanism of the switches is simple in construction and extremely rugged. It consists of three moving parts that keep the blade under positive control during the entire operating cycle. Double rows of stainless steel balls running on machined races are used throughout to assure ease of operation.

Factory sealing of the entire driving mechanism assures permanent adjustments and eliminates maintenance for the life of the switch.

High Pressure Contacts
The switches utilize the same type of contacts at both the hinge and jaw ends. They are of the high-pressure-point design and are fully accessible for easy inspection and maintenance. Contact shoes are of hard-drawn copper with heavy silver inlays, fully tinned after fabrication. Inlays are brazed in position by special equipment that applies heat and pressure simultaneously to assure a permanent high-conductivity bond. Point contact is established at the intersection of the round surface of the blade and silver inlay.

Contact pressure is provided by stainless steel, multiple leaf springs located outside the current path. Stainless steel bolts and lock washers are used to bolt the contact shoes and springs to the castings.

Positive Closed Position Lock
A closed position lock is provided to eliminate blade movement even during severe short circuit conditions. As the blade enters the contact jaws and rotates, the blade edges engage the offset in the contact shoes, locking the blade in position. A positive engagement of the blade and contact shoe offset is accomplished by a disc attached to the contact spreader pin. On opening, the blade is rotated away from the contact shoe offset, leaving the blade free to rise. On switches rated below 46kV this feature is omitted since the shorter blades are sufficiently rigid and will not move under short circuit conditions.

Accessories
A complete line of accessories for the switches is available.

1. Motor operating mechanisms for use with the switches are available in various speeds and torque values. See "Automation and Motor Controls/SF100/200/300".
2. Grounding switches for grounding contact and/or hinge end of the switches.
3. Interrupting devices for interrupting load, line-charging current, transformer magnetizing current and some capacitor switching. See "Vacuum Interrupters".
4. Vertical operating shaft auxiliary switches have two (2) to twelve (12) adjustable contacts.
5. Outriggers and wire guides, both switch-supported and line swivel types.
6. Mechanical-type interlocks.
7. Lugs for rigid and stranded bus, including bronze Aluminum, or tinned bronze. Expansion connectors are also available.

A typical switch includes:

1. Arcing horn for upright switches up to and including 230 kV.
2. Single-throw operating mechanisms having one offset bearing or two universal joints.
3. Manual operating mechanisms with standard vertical operating pipe, couplings, guides, levers, clevises and position indicators.
4. One of the following manual operators:
   1. Torsional swing handle (36' or 54" collapsible).
   2. Gear box.
5. Motor mechanisms, where required in lieu of manual operators.
6. Flexible grounding braid for grounding the vertical pipe above the handle.
7. Standard station post insulators as listed in Ordering Information.
8. Base mounting holes per ANSI C37.32-2.4.4 can be furnished when required.
9. Standard terminal pad drillings per NEMA CC 1-4.05 are furnished. For special drillings or arrangements please refer to the factory.