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 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 or faults require it to be switched to the other source. The Static Switch is fitted with 2 manual by-passes for each source to enable correct maintenance of the system.
The 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, which, together with the power source priority selection button enable operators to make full use of the apparatus.
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 will be supplied from the preferred source all time provided 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 to it after a delay of 1 or 5 seconds (selectable) or even milliseconds delay.
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. Once the parameters of the power source have returned to normal, if the load is supplied by the source selected as the reserve, it is automatically transferred back to the priority source.
Where switching occurs while sources are unsynchronized, it is possible to choose between transferring in as short a period as possible, as if the sources were synchronized, and introducing a delay (selectable) in the normal transfer time (default condition).
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 and when synchronization is established. If the priority source is out of limits, transfer will be effected only after it has remained stable and within limits for a preset period (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.
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