Astre Systems - SoftStart Update/Retrofit

Considerations In a Townsend
SoftStart Update/Retrofit
These apply to each amplifier beam power supply retrofitted

The SoftStart units replace the vacuum contactors in a typical Townsend transmitter. http://www.astresystems.com/softstart.html. The SoftStart is wired into the primary side of the 480 VAC beam power supply. A NEMA type 1 electrical enclosure with the dimensions 36" X 30" X 12" is used to hold the SoftStart circuitry. The wiring configuration is open delta. That is, each side of the primary winding of each phase coil is fed from the SoftStart unit. This requires that SIX leads go to the beam supply where usually only THREE were used previously. Because of the open delta configuration, only one half of the current of each phase is drawn on each lead, and the wire is sized accordingly. A typical 60 kW klystron draws about 200 amps per wire (3 wires) on the three phase 480 line. In open delta the draw will be about 100 amps per wire (6 wires), less with pulsing. Your local electrical contractor will need to remove the old vacuum contactor enclosure, replace it with the new SoftStart enclosure, and install the additional wiring and conduit if not present. Additionally, 13 conductors, usually number 16 or 18 AWG are needed for control purposes. A small electrical conduit from the SoftStart to the transmitter cabinet will be needed for this purpose. The size of the primary current circuit breaker is not changed since the total three phase primary current will be the same, although since in-rush current is greatly reduced or eliminated, your peak demand factor will reflect an electrical energy saving on the monthly power bill. The type of beam power supply used must have access to both ends of the primary windings. This modification can usually be done in 6-8 hours depending on exact circumstances of each installation, amount of help, and skill of the local licensed electrician used.