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What is STS? March 2021

Where you have 2 independent electrical systems, the device that provides energy transfer between these sources without feeling any load is called STS.

It can be fed from different sources as follows.

  • UPS + Network
  • UPS + UPS
  • Solar system + Grid
  • Generator + Network
  • Generator + Generator
  • Generator + UPS
  • Network1 + Network 2 (independent dual energy bus)

Functions of the Static Transfer Switch

  • The static transfer switch (STS) automatically selects the better of the two available electrical sources and supplies critical loads.
  • The ability to switch quickly ensures that the loads are not affected by the transition.
  • Provides remote monitoring of electrical events
  • Provides remote electrical maneuvering
  • Provides remote monitoring of values such as voltage, current and frequency
  • Brings mechanical by-pass transfer advantage
  • Provides neutral switching in 2 or 4 pole models
  • Protects the load in phase sequence rotation
  • Prefers the better of the bad if both input sources are bad

Product features

  • Resistance to high load currents (1000%)
  • Computer connection and remote monitoring with RS232 and TCP / IP communication
  • CE certificate + ISO9001 + ISO14001 audited production
  • Overcurrent, Phase sequence, Phase balance, Overvoltage, Voltage Interruption, Short Circuit and Frequency Out of Tolerance protections
  • Recording of alarms and warnings
  • Voice warning system
  • LCD alphanumeric panel
  • Programmable relay outputs for external automation
  • Mechanical bypass switch
  • Thyristor controlled structure resistant to high currents
  • Switchgear for complete isolation during maintenance
  • Emergency shutdown button
STS3000 Series Block Diagram
STS4000 Series Block Diagram


1- Basic Application

- Loads are transferred very quickly to the good energy source.
- Energy quality is at the highest possible level in the load group.



2. Group STS Application

1st Zone protections
Voltage protection
Frequency protection
from 2nd Zone short circuits
From STS2 failures
1 power supply outage

2nd Zone protections
Voltage protection
Frequency protection
from 1st Zone short circuits
From STS2 failures
1 power supply outage



3. UPS and STS Mixed Application

1St Zone protections
Outage protection
Frequency protection
Voltage protection
from 2nd Zone short circuits

2nd Zone protections
Outage protection
Frequency protection
Voltage protection
From 1st zone short circuits
From UPS failures



4. UPS and STS Mixed Application

1st Zone protections
Outage protection
Frequency protection
Voltage protection
From 2nd Zone short circuits
From 2nd Zone fuse problems
STS2 failures
1 UPS failure

Zone 2 protections
Interruption protection -> 1. Frequency protection from zone fuse problems -> Voltage protection from STS1 faults -> 1 from 1UPS faults.
From zone circuits