BS IEC 61888 pdf download

BS IEC 61888 pdf download Nuclear power plants — Instrumentation important to safety — Determination and maintenance of trip setpoints
1 scope
This standard defines the requirements for assuring that automatic setpoints for nuclearsafety system instrumentation (as defined in clause 3), are established and maintained withinspecified limits in nuclear power plants and nuclear reactor facilities.
2 Normative references
The following referenced documents are indispensable for the application of this document.For dated references, only the edition cited applies.For undated references, the latest editionof the referenced document (including any amendments) applies.
IEC 60050-394:1995, International Electrotechnical Vocabulary (IEV) – Chapter 394: Nuclearinstrumentation: lnstruments
IEC 60671, Periodic testing and monitoring of the protective system of nuclear reactors
IEC 61513:2001,Nuclear power plants – Instrumentation and control for system important tosafety – General requirements for systems
IAEA NS-R-1: 2000,Safety of nuclear power plants: Design
3Definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Additional definitions related to instrumentation terminology may be found in lEC 60050-394.
3.1
allowable value
a limit value that the trip setpoint may have when tested periodically, beyond whichappropriate action shall be taken
3.2
analytical limit (of setpoint)
limit of a measured or calculated variable established by the safety analysis to ensure thata safety limit is not exceeded. The margin between the analytical limit (of the setpoint) andthe safety limit allows to take into account:
– the response time of the instrument channel,
– the range of transients due to the considered accident.
3.3
as found
the condition in which a channel, or portion of a channel, is found after a period of operation and before recalibration (if necessary)
3.4
as left
the condition in which a channel, or portion of a channel, is left after calibration or final setpoint device setpoint verification
3.5
drift
an undesired change in output over a period of time where change is unrelated to the input,environment, or load
3.6
error
the algebraic difference between the indication and the ideal value of the measured signal
3.7
final setpoint device
a component, or assembly of components, that provides input to the process voting logic for actuated equipment
NOTE Examples of final setpoint devices are bistables, relays, pressure switches, and level switches.
4 Abbreviations
SRSS Square-Root-Sum-of-Squares
CU Channel Uncertainty
AL Analytical Limit
TS Trip Setpoint
LSSS Limiting Safety System Setting
5 Determination of setpoints
Trip setpoints in nuclear safety system instruments shall be selected to provide sufficient allowance between the trip setpoint and the analytical limit to account for uncertainties. Detailed requirements for safety system instrument setpoint relationships are given in the following clauses, as illustrated in figure 1 .