B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 2-1B30 Bus Differential SystemChapter 2: Product descriptionProduct descriptionThis chapter outlines the product, order codes, and specifications.2.1 Product descriptionThe B30 Bus Differential System is part of the Universal Relay (UR) series of products. It is a microprocessor-based relaythat provides protection and metering for a busbar with up to six feeders. Protection is provided by a low impedancepercent differential element with features that make it immune to current transformer (CT) saturation. Both biased(restrained) and unbiased (unrestrained) differential protection functions are provided.A dynamic busbar replica mechanism is provided by associating the breaker and switch status signals with the differentialzone currents.The biased bus differential function operates using both the differential and current directional comparison protectionprinciples. The differential element uses a dual-slope dual-breakpoint characteristic with the restraining current formed asa maximum of the input currents for better stability during through-fault conditions and faster operation on internal faults.The current directional comparison principle checks the angular relationship between the currents.The biased bus differential protection operates in the two-out-of-two mode for low differential currents. This improvesstability during CT saturation conditions caused by comparatively low currents combined with unfavorable phenomena,such as multiple auto-reclose actions. For high differential currents, the bus differential element operates using thedifferential characteristic alone if CT saturation is not detected. Upon CT saturation detection, the relay switches to thetwo-out-of-two operating mode for better through fault stability.The B30 typical operating time is about 12 ms for fast form-C output contacts and internal usage by user-programmablelogic, and about 15 ms for trip-rated form-A output contacts.A CT failure alarm function that monitors the level of the differential current is provided. A situation when the differentialcurrent stays above a pre-defined level for a pre-defined period of time is declared as a CT trouble event, and an alarm israised. To prevent false tripping due to CT trouble, undervoltage supervision or an external check zone can be used.Voltage and current metering are built into the relay as standard features. Current parameters are available as totalwaveform root mean square (RMS) magnitude, or as fundamental frequency only RMS magnitude and angle (phasor).B30 devices equipped with CT and VT inputs measure power values.Diagnostic features include an event recorder capable of storing 1024 time-tagged events and oscillography capable ofstoring up to 64 records with programmable trigger, content, and sampling rate. The internal clock used for time-taggingcan be synchronized with an IRIG-B signal, using the Simple Network Time Protocol (SNTP) over the Ethernet port, or usingthe Precision Time Protocol (PTP). This precise time stamping allows the sequence of events to be determined throughout
