IEEE 741:2017 pdf free download – IEEE Standard for Criteria forthe Protection of Class 1E Power Systems and Equipment in Nuclear Power Generating Stations
Where an instrumentation and control power bus is supplied by an inverter with current-limiting characteris-tics and an automatic transfer has been provided to an alternate source with higher available current, this alter-nate source may be used in order to achieve the previously described coordinated protection.
Ground detection monitoring shall be provided for ungrounded systems.
The instrumentation and control power system shall be provided with undervoltage, overvoltage, and under-frequency protection.Where its power is supplied from a static inverter,overfrequency protection shallalso beprovided. For recommended practice on alarms and indication, refer to IEEE Std 944-1986.
5.4 Primary containment electrical penetration assemblies
An electrical penetration assembly shall be considered as part of the cable system between the load and the pri-mary interrupting device.For guidance in the application of electrical circuit protection, refer toIEEE Std 242,which includes information also applicable to electrical penetrations. Short-circuit, overload, and continuouscurrent ratings and capabilities of the electrical penetration are defined in IEEE Std 317.
The electrical penetration assemblies installed as part of the containment structure may require special con-sideration in the selection of their protection.This special consideration arises where the potential exists for afault inside containment to result in a penetration seal failure, such that a breach of containment could occur.Where a penetration assembly can indefinitely withstand the maximum current available due to a fault insidecontainment, no special consideration is required.
Electrical penetrations requiring special consideration (i.e., where protection is required to ensure contain-ment integrity) shall be provided with dual primary protection operating separate interrupting devices, orprimary and backup protection operating separate interrupting devices.
The time-current curves of the dual primary protection or the primary and backup protection shall coordinatewith the time-current capability curve of the electrical penetration to be protected.
Protection for non-Class 1E circuits using containment penetration assemblies do not need to be treated asClass 1E.The protection for these non-Class 1E circuits is acceptably provided by the previously specifiedrequirements.1@ For protection circuits requiring special consideration, the surveillance requirements of 6.3shall apply.
5.5 Valve actuator motors (direct gear driven)
The selection of a protective device for the direct geared VAM shall cnsure that the time-current characteristicof the protective device is coordinated with the time-current characteristic of the motor, as derived from motortime-temperature data. In addition, the coordination shall ensure the allowable duty cycle of the valve (sceAnnex B) is completed without compromising the motor thermal withstand capability, while allowing marginfor variations in current drawn by the motor, or in the thermal characteristics of the protective device, or both.Refer to Annex B for guidelines for selection of the protective devices. See also IEEE Std 1290.The criteriafor setting mechanical devices within the valve actuator, such as torque and limit switches, are not within thescope of this standard.
This annex also provides a description of a protection scheme that meets these requirements, including con-siderations for determination of the relay voltage setpoints and their associated time delays.However, it is rec-ognized, because of the diversity of nuclear plant auxiliary system designs, there are other protection schemesthat provide the desired level of protection.Also, this annex does not address the capability of various relaytypes, but rather discusses the philosophy behind the desired actuation times and voltage levels. Figure A.1depicts the significant parameters associated with degraded voltage and loss of voltage protection.For eachvoltage and time delay relay, Figure A.l shows some of the applicable criteria used to determine the setpointsalong with the relay tolerance bandwidth.