Supplying electrical power to an entire facility is not a matter that should be taken lightly. Many times we do not consider the power switches that are used with the backup energy source. This is where the importance of a power transfer switch comes in. A transfer switch helps ensure that electricity is safely transferred from a secondary power source to the facility by isolating a whole electrical service panel. The use of a transfer switch eliminates the need for manual switching of standby power sources. It is also a safer alternative given the high voltages involved.
A delay may be experienced with this type of power switch. The amount of time that it takes to turn on standby power may depend on the kind of transfer switching used. This may range anywhere from a few seconds to minutes. In situations where power is interrupted, every second counts. Getting electricity back up again becomes crucial.
A number of standby generators make use of Automatic Transfer Switches (ATS) with open transition. A break is made before power is provided from the standby. During this time a period of 3 to 5 cycles or 50 to 80 milliseconds may elapse for systems of about 60 Hz. Although this may be considered fast enough for homes and small businesses, it may not be fast enough for large facilities.
Faster systems have been produced in the line of power transfer switches. These consist of ATS that use closed transition in the form of static transfer switches (STS). Similarly these provide a break before the restoration of power as electricity is transferred. However it may be much quicker than that of open transitions. A delay of only two cycles takes place and loss would only be about 1/6 of a second. When even this amount of time cannot be risked systems may be synchronized given they are compatible. Generally with a closed transition no interruption takes place. Although there may be a time lapse between the transfer, it is not largely felt.
Seamless transfers are also often made possible with soft-loading: a process wherein the transfer switch adjusts the quantity of load received by the generator. In this case the power load is carried by the primary source until the secondary source is running. In the case of a standby generator or power source this may not be useful. Both sources must be live during the time or transfer and a failure in the primary source or a start up of the standby will create a time lapse. If this is to be used in a facility an uninterruptable power supply is best used with it.
The choice of a fast or slow transfer and the choice of power switches may depend largely on the needs of a facility. In places where a short time lapse is acceptable open transition ATS may be good enough for use. Those in need of seamless transfers may be better off with a closed transition ATS.
