Static Switch Systems – Understanding How a Power Continuity Static Switch Operates
Description of the Static Switch Power Continuity System
A Static Switch is a two-way, three phase 4 ways automatic switch.
Powered by two independent synchronous or asynchronous AC power supply sources. The switching device are SCR. Under no operation conditions is simultaneous current switching between the two sources possible (Break Before Make).
The Static Switch makes a rapid switch from one source to the other.
This happens in the event of a fault to the power supply used to power the load, or carry out test/maintenance.
One of the two sources can be designated as the preferred power supply, to which the Static Switch will transfer the load. It remains there until different designations/faults require it to be switched to the other source. The Static Switch has 2 manual by-passes. Each source enables correct maintenance of the system.
STS 4P 100(400-600), a Static Switch is fitted with a block diagram with LED indicators and a 4 line 20char display.
Capable of providing all information concerning equipment operation status. Together with the power source, priority selection button enables operators to make full use of the apparatus.
Power Source Priority Selection
The manual selector A/B on the front panel of the STS selects one of the two input sources as the priority one.
The LED associated with the selected source SA or SB switches on.
The other source then becomes the reserve power source. The load supplied from the preferred source at all times. This is providing it is within acceptance parameters.
When a power failure occurs, the load is transferred to the reserve power source. When the preferred source returns within acceptance parameters, the load is automatically re-transferred. With a delay of 1 or 5 seconds (selectable)/even milliseconds delay.
Static Switch – Switching Due to Power Failure
Switching occurs if the characteristic parameters of the active power source (preferred or reserve) supplying the load go outside defined limits. The parameters tested are the root mean square (rms) and instantaneous values of voltage, which must remain within a defined acceptance window. Automatic transfer back to the priority source, once the parameters of the power source have returned to normal.
This happens if the load is supplied by the source selected as the reserve.
Where switching occurs while sources are unsynchronized, it is possible to choose between transferring in as short a period as possible. And to introduce a delay (selectable) in the normal transfer time (default condition).
Static Switching Due to Re-Transfer of Load to Priority Source
In conditions where the priority source is not the one supplying the load (switching due to fault condition or change of priority via button),
Static Switches will automatically transfer the load to the priority source as soon as possible.
Specifically, automatic switching to the priority source will occur only when the parameters of this source are within acceptable limits. When synchronization is established and remains stable within limits for a preset period. This is usually 1 second by default.
In the case of loss of synchronization, transfer will only take place when the phase difference between the two sources is less than a preset value (10° by default), and remain so for a preset period.
Static Switching – Must have reliable and robust sources
The extended switching time will require that the down stream equipment is operating with internal backup. The industry standard is minimum 20 milliseconds.
