To: file s_bandtx\breaker_contactor_operation.wpd

From: Jon Hagen

Date: Feb. 26, 2004

Subject: S-Band Transmitter: Main Circuit Breaker and Vacuum Contactor Control

The 4160 3-phase power is fed first through the breaker, then through the contactor, and on to the HV power supply. In this transmitter the breaker is a faster acting device than the contactor, so the breaker provides the immediate disconnect when there is a crowbar event or other emergency stop event.

Contactor control

Normally the breaker is always closed and the transmitter is turned on and off by the vacuum contactor. The "HVON" command energizes the solid state relay K17, which applies ac power to the coil of the contactor. This ac power connection is made via an auxiliary contact in the breaker so that the contactor will also open whenever the breaker trips.

Breaker control

The ac signal that trips the breaker is derived from the emergency off switches, the key switches, various cabinet switches, and via the logic circuitry in the HVPS building, for the following events:

Crowbar command

Crowbar fired

Crowbar triggered

MOV fault

Fiber Optic Receiver A trigger

Fiber Optic Receiver B trigger

HVPS Contactor Status

Test command

Refer to Schematic 190096 "Control Ladder, Emergency Off Sys." This circuit shows that the breaker will be tripped if either of two chains is broken:

The emergency off chain is made up of manual normally closed push button "Emergency Off" switches. This chain is latched on by relay K6. The only way to reset (re-latch) the chain is by the pushbutton switch S3, in the HVPS building. The coil of K5 is in parallel with that of K6; K5 simply provides more contact pairs. One of the contact pairs on K6 provides tripping power to the breaker.

The second chain (call it the command off chain) includes the key-actuated switches in the Dome and in the HVPS building, switches S3 and S4 in the dome, and 1A11K8, a solid state relay driven by the logic in the HVPS control circuitry in response to the various commands and faults listed above. Included in this chain are relays K7 and K27. When this chain opens, both K7 and K27 provide tripping power to the breaker. This chain also includes a contact pair from K5, so the emergency off chain will also open this 'command' chain.

Note that there is a third, but independent, chain on Schematic 190096, made up of auxiliary contact pairs in switches S3 and S4 in the dome and in the key operated switches 4A2S6 in the dome and 1S1 in the HVPS building. This chain connects to the HV Interlock logic in the HVPS building.