Static Transfer Switch (STS)

They are commonly used in

Static Transfer Switch Basic Diagram

The static transfer switch (STS) is a static AC Switch designed and used to transfer, automatically. This works for single-phase or three-phase loads. This consists of back-to-back thyristors connected in parallel. As shown in the figure. The STS functions like a mechanical switch i.e. double pole input one pole out Or three pole input one pole output. Many of such combinations can be achieved automatically. If the main source supplying the loads fails, then STS transfers to the other source automatically.

The STS shall provide an effective solution to the following needs

◗ complete separation of the two sources and of the associated distribution systems;
◗ source redundancy with no-break transfer of the loads, in existing installations;
◗ separation of loads to avoid mutual disturbances.

The STS thus improves the availability of energy, while facilitating operation and maintenance, in installations supplying sensitive loads. The static transfer switch shall comprise two inputs, called Source 1 and Source 2, supplied by two power sources.
The first source is termed as the Preferred source and the second is the alternate source. The STS output shall be connected to a critical load. In the event of a power failure, the STS shall automatically transfer from one source to the other in less than a 5 to 10mes.

Configuration Available
Single Phase
Three Phase

Key Features

  1. The Static Switch consists of Thyristorised Semiconductor Bi-directional Switches based on state-of-the-art technology
  2. Capable of working with Synchronous and asynchronous two power sources.
  3. System control based on Parallel Processor VLSI Technology.
  4. Capable of sourcing the load with crest factor 1:3 as well as inductive and unity pf load.
  5. LED display for Input /Bypass/Output Status.
  6. Designed to work with 48 to 52 Hz AC source 1 phase or 3 phase + Neutral.
  7. Synchronous & Asynchronous Transfer within 10– 20Msec at Zero cross respectively
  8. Auto / Manual Re-transfer selections available.
  9. Change over / switching for each phase at ZC of the Voltage cycle.
  10. Designed to work in Master & Slave UPS, UPS & Utility Power, UPS & Generator, and Utility
    Generator Logic within the specified frequency range.
  11. Capable of 100% overload capacity.
  12. High MTBF of the average of 50000 Hrs.