GE Multilin B30 Bus Differential System 10-110 APPLICATION OF SETTINGS 10.1 OVERVIEW1010 APPLICATION OF SETTINGS 10.1OVERVIEW 10.1.1 INTRODUCTIONThe B30 is a high-speed low-impedance microprocessor-based current differential relay for power system busbars. Therelay is limited to six circuits. The B30 incorporates the dynamic bus replica mechanism that allows for protecting buseswith circuits interconnectable between various sections but with single current measurement points.As explained in the Theory of Operation chapter, the relay uses a dual-slope dual-breakpoint differential characteristic withthe restraint signal created as the maximum among the magnitudes of the circuit connected to the protected bus. The low-impedance operating principle is enhanced by the use of the Saturation Detector and a current directional principle.This chapter provides an example of setting calculations for a sample bus. The selected example includes various bus con-figurations to clarify a number of typical situations. Both the bus configuration and numerical data used are not meant toreflect any specific utility practice or design standards.It is also assumed that the CTs have been selected without considering a B30 application, but the B30 settings are to becalculated for proper relay application. The CT data used in this example are kept to a minimum and in a generic form. TheCT data does not reflect any particular notation or national standards.The analysis provided in this chapter has been performed with the following goals:• The limits of linear operation of the CTs considering zero remanent flux have been determined in order to select thehigh breakpoint settings of the biased differential characteristic.• The limits of linear operation of the CTs considering a remanent flux of 80% have been determined in order to selectthe low breakpoint settings of the biased differential characteristic.• Saturation of the CTs has been analyzed in order to select the higher slope of the biased differential characteristic andthe high set differential overcurrent setting.The analysis tools and safety margins applied are examples only and do not reflect any particular protection philosophy.Typically, for the CT saturation related calculations, it is sufficient to consider the weakest (most prone to saturation) CTconnected to the bus and the total bus fault current combined with the longest time constant among all the circuits con-nected to the bus. This chapter provides more detailed analysis (see the Slopes and High Set Threshold section) in order toillustrate the idea of using setting groups to enhance the B30 performance when the bus configuration changes (see theEnhancing Relay Performance section).10.1.2 SAMPLE BUSBAR AND DATAThe following figure shows a double bus arrangement with North and South buses. This station has five circuits (C-1through C-5) and a tiebreaker (B-7). Circuit C-1 is connected to the North bus; circuits C-2, C-3 and C-4 can be routed toeither bus via switches S-1 through S-6; circuit C-5 can be connected to either bus via breakers B-5 and B-6.Figure 10–1: SAMPLE BUS CONFIGURATION836731A2.CDRNORTH BUSSOUTH BUSCT-8B-5B-6CT-5CT-6S-5S-6B-4CT-4S-3S-4B-3CT-3S-1S-2B-2CT-2CT-1B-1C-1 C-2 C-4C-3 C-5CT-7B-7
