IEEE 741-2007 pdf download IEEE Standard Criteria for the Protection of Class 1E Power Systems and Equipment in Nuclear Power Generating Stations
5. Principal design criteria and requirements
5.1 AC power distribution systems
5.1.1 Switchgear and bus protection
For recommended practices in application of overcurrent relays, directional relays. differential relaysfor bus protection,and ground fault relaying, refer to IEEE Std 141-1993, IEEE Std 242-2001, andEEE Std 666-1991. The protection systems for the ac distribution system should be coordinated inaccordance with IEEE Std 242-2001. For supplementary information on ground protection practices, referto IEEE Std 142-1991.
If the power distribution system design cannot accommodate paralleling of bus supplies, or if parallelingcan be allowed only under certain conditions, interlocks or procedural restrictions shall be provided torestrict such paralleling. Consideration shall be given to the higher fault current that could exist duringparallel operation when selecting protective devices.
If the power distribution design allows for automatic bus transfers, consideration shall be given to theimpact of the bus transfer on the coordination of protection devices (see Annex C).
5.1.2 Bus voltage monitoring schemes
Bus voltage monitoring schemes that are used for disconnecting the preferred power source, load sheddingand starting the standby power sources are part of the protection and shall meet the criteria that follow.Voltage monitoring schemes, which are used only for alarms, do not have to meet these criteria.
a) Bus voltage shall be detected directly from the Class 1E bus to which the standby power source is connected.
b) Upon sensing preferred power supply degradation, the condition shall be alarmed in the main control room. On sensing preferred power supply degradation to an unacceptable low voltage condition, the affected preferred power supply shall be automatically disconnected from the Class 1E buses.
c) Each division shall have an independent scheme of detection of degraded voltage and loss of voltage conditions. Within each division, common equipment may be used for the detection of both conditions (see Annex A).
d) Each scheme shall monitor all three phases. The protection system design shall be such that a blown fuse in the voltage transformer circuit or other single phasing condition does not cause incorrect operation, nor prevent correct operation, of the scheme. Means shall be provided to detect and identify these failures.
e) The design shall minimize unwanted operation of the standby power sources and disconnection of the preferred power supply. The use of coincident logic and time delay to override transient conditions is a way to accomplish this.
f) Capability for test and calibration during power operation shall be provided.
IEEE 741-2007 pdf download
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