Trip mechanisms time delay

This is not quite true. Whenever we start a pump, the starting torque required to get the pump spinning requires a surge of motor amps. To avoid tripping off the motor on high amps, there is a time delay built into the trip mechanism. This delay permits the amperage load to greatly exceed the FLA point, for up to 15 to 30 s. This is too brief a period in which to overheat the motor. 

A reactor trip signal acts to open two trip breaker sets connected in series, feeding power to the control rod drive mechanisms (CRDMs). The loss of power to the mechanism coils causes the mechanisms to release the RCCAs, which then fall by gravity into the core. There are various instrumentation delays associated with each trip function including delays in signal actuation, in opening the trip breakers, and in the release of the rods by the mechanisms. The total delay to trip is defined as the time delay from the time that trip conditions are reached to the time the rods are free and begin to fall. 

Explosives may be detonated electrically or nonelectrically. A nonelectric firing system will consist of a blasting cap, a length of time (safety) fuse or a firing device attached to the cap, and a means of activating the system match, fuse lighter, delay mechanism, or trip wire. The electric system requires an electric cap which has two wires attached, perhaps additional wire, and a battery or batteries to provide the current which activates the cap. 

The behavior of a segment s output as a function of the input with respect to time should be accounted for, either in the determination of the trip setpoint or included in the hazard analyses. The selected setpoint should ensure that the SIF responds to achieve or maintain a safe state of the process within one-half of the process safety time with respect to a specific hazardous event. Special attention should be paid to potential delay mechanisms, such as temperature measurements through thermowells and pressure measurement through capillaries, as these mechanisms may obscure dangerous process variations. 

Electrical power interruption to the control rod drive mechanism operating coils must release the control rod drive mechanism drive rod assembly, thereby allowing ihe rod cluster assembly to fall under gravity to its fully inserted position, with a trip delay time of less than or equal to 150 milliseconds. 

---