Overview
The operation of “Bus differential” elements is completely dependent on the dynamic bus replica, which must be defined first. Both restrained (biased) and unrestrained (unbiased, instantaneous) bus differential protection functions are provided for each bus differential zone.
For more detailed information on “Bus differential” element, refer to GE, Universal Relay (UR) family of products, Version 8.0x manuals.
To view other supported elements, click here.
Setting Parameters
Modbus memory map for Setting parameters
| Products | Hex address | Register name | Range | Units | Step | Format | Default |
| B30, B90 | 121 | Bus Zone 1 Function | 0 to 1 | — | 1 | F102 | 0 (Disabled) |
| " | 122 | Bus Zone 1 Pickup | 0.05 to 6 | pu | 0.001 | F001 | 100 |
| " | 123 | Bus Zone 1 Low Slope | 15 to 100 | % | 1 | F001 | 25 |
| " | 124 | Bus Zone 1 Low Breakpoint | 1 to 30 | pu | 0.01 | F001 | 200 |
| " | 125 | Bus Zone 1 High Slope | 50 to 100 | % | 1 | F001 | 60 |
| " | 126 | Bus Zone 1 High Breakpoint | 1 to 30 | pu | 0.01 | F001 | 800 |
| " | 127 | Bus Zone 1 High Set | 0.1 to 99.99 | pu | 0.01 | F001 | 1500 |
| " | 128 | Bus Zone 1 Seal In | 0 to 65.535 | s | 0.001 | F001 | 400 |
| " | 129 | Bus Zone 1 Block | 0 to 4294967295 | — | 1 | F300 | 0 |
| " | 012B | Bus Zone 1 Events | 0 to 1 | — | 1 | F102 | 0 (Disabled) |
| " | 012C | Bus Zone 1 Target | 0 to 2 | — | 1 | F109 | 0 (Self-reset) |
| B90 | 012D | Bus Zone 1 Supervision | 0 to 4294967295 | — | 1 | F300 | 1 |
| B90 | 012F | Bus Zone 1 Trip | 0 to 4294967295 | — | 1 | F300 | 0 |
| B30, B90 | 131 | Bus Zone 1 Check Zone | 0 to 1 | — | 1 | F126 | 0 (No) |
| " | 132 | Bus Zone 1 Aux Zone Trip | 0 to 4294967295 | — | 1 | F300 | 0 |
| " | 134 | Bus Zone 1 Supervision Voting | 0 to 2 | — | 1 | F264 | 0 (OFF) |
| " | 135 | Bus Zone 1 Supervision 1 | 0 to 4294967295 | — | 1 | F300 | 0 |
| " | 137 | Bus Zone 1 Supervision 2 | 0 to 4294967295 | — | 1 | F300 | 0 |
| " | 139 | Bus Zone 1 ID | 0 to 2 | — | 1 | F202 | (none) |
| " | 143 | …Repeated for Bus Zone 2 | |||||
| " | 165 | …Repeated for Bus Zone 3 | |||||
| " | 187 | …Repeated for Bus Zone 4 | |||||
| " | 01A9 | …Repeated for Bus Zone 5 | |||||
| " | 01CB | …Repeated for Bus Zone 6 |
| F102 | 0 = Disabled, 1 = Enabled | ||||||
| F109 | 0 = Self-reset, 1 = Latched, 2 = Disabled | ||||||
| F126 | 0 = No, 1 = Yes | ||||||
| F202 | 10 registers, 16 Bits: 1st Char MSB, 2nd Char LSB | ||||||
| F264 | 0 = OFF, 1 = OR, 2 = AND | ||||||
| F300 | 0 : Off (This is boolean FALSE value), 1 : On (This is boolean TRUE value) | ||||||
Logics & highlights
Biased differential operating characteristic
Bus zone 1 differential logic
Definition of Setting Parameters
BUS ZONE 1 DIF PICKUP — This setting defines the minimum differential current required for operation of the biased bus differential protection element. This setting is chosen based on the maximum magnitude of the differential current that might be seen under no-load conditions. This setting prevents relay maloperation in the situation when the bus carries little power and the restraining signal is too low to provide enough bias in the first slope region of the differential characteristic.
This setting can also be set above the maximum load level to ensure security during CT trouble conditions. However, voltage supervision or a check-zone are better alternatives.
BUS ZONE 1 DIF LOW SLOPE — This setting defines the percentage bias for the restraining currents, from zero to the lower breakpoint (LOW BPNT). This setting determines the sensitivity of the relay for low current internal faults. The value chosen needs to be high enough to accommodate the spurious differential current resulting from inaccuracy of the CTs operating in their linear mode, that is, in load conditions and during distant external faults. When adjusting this setting, it must be kept in mind that the restraining signal used by the biased bus differential protection element is created as the maximum of all the input currents.
BUS ZONE 1 DIF LOW BPNT — This setting defines the lower breakpoint of the dual-slope operating characteristic. The percentage bias applied for the restraining current from zero to the value specified as LOW BPNT is given by the LOW SLOPE setting. This setting needs to be set above the maximum load current. The LOW BPNT can be moved to the AC current under which all the CTs are guaranteed to transform without saturation. This includes the effect of residual magnetism.
When adjusting this setting, keep in mind that the restraining signal is created as the maximum of all the input currents.
BUS ZONE 1 DIF HIGH SLOPE — This setting defines the percentage bias for the restraining currents above the higher breakpoint (HIGH BPNT). This setting affects stability of the relay for heavy external faults. Traditionally, the value chosen for this setting needs to be high enough to accommodate the spurious differential current resulting from saturation of the CTs during heavy external faults. This requirement can be considerably relaxed in favor of sensitivity and speed of operation as the relay detects CT saturation and upon detection applies the directional principle to prevent maloperation. When adjusting this setting, keep in mind that the restraining signal is created as the maximum of all the input currents.
BUS ZONE 1 DIF HIGH BPNT — This setting defines the higher breakpoint of the dual-slope operating characteristic. The percentage bias applied for the restraining current above the value specified as HIGH BPNT is given by the HIGH SLOPE setting. The HIGH BPNT setting needs to be set below the minimum AC current that is likely to saturate the weakest CT feeding the relay. When adjusting this setting, it must be kept in that mind the restraining signal is created as the maximum of all the input currents.
The dual-slope operating characteristic of the biased bus differential protection element is shaped to ensure true percentage bias for high restraining currents (see the following figure). This means that the straight line defining the upper slope intersects the origin of the differential-restraining plane and a discontinuity appears between the low and high slope regions (between the LOW BPNT and HIGH BPNT settings). This discontinuity is handled by approximating the operate/nooperate boundary of the characteristic using a certain connection function. This ensures smooth transition of the slope from LOW SLOPE (lower value) to HIGH SLOPE (higher value).
The following parameters of the biased operating characteristic are used by the saturation detector: LOW SLOPE, HIGH SLOPE, and HIGH BPNT. The saturation detector uses these settings to detect specific relations between the differential and restraining currents. The values of these settings are selected based on the aforementioned criteria related to the art of bus differential protection.
BUS ZONE 1 DIF HIGH SET — This setting defines the minimum differential current required for operation of the unbiased bus differential protection function. This setting is based on the maximum magnitude of the differential current that might be seen during heavy external faults causing deep CT saturation. When selecting this setting, keep in mind that the unbiased bus differential protection function uses the full-cycle Fourier measuring algorithm and applies it to pre-filtered samples of the input currents. As a result, the transient measuring errors including the effect of the DC component are below 2%.
During heavy CT saturation when the currents are significantly distorted, the magnitude of the differential current as measured by the relay and used by the unbiased bus differential function is significantly lower than both the peak values of the waveform and the true RMS value. The measured magnitude practically reflects the power system frequency component alone. This allows for lower values of the HIGH SET setting.
The unbiased (high set) differential function can be virtually disabled by setting its operating threshold, HIGH SET, very high.
BUS ZONE 1 DIF SEAL-IN — This setting defines the drop-out time of the seal-in timer applied to the BUS 1 OP FlexLogic operand.
BUS ZONE 1 DIFF SUPV — This setting specifies a FlexLogic operand that supervises operation of the element. Typical applications include undervoltage condition and overall (check) zone. In a sense the setting is similar to the blocking input, but does not stop the element from running. This is important for saturation detector, as the latter requires some historical data. The Bus Differential element shall not be supervised from the blocking input. The blocking input (BUS ZONE 1 DIF BLK setting) is meant to block the element permanently, not dynamically from a fault depended condition such as undervoltage.
BUS ZONE 1 DIF TRIP — This setting specifies a FlexLogic operand that forces operation of the zone. Typical applications include forced trip of the healthy phase from the faulted phase, or a trip command from the BF function to isolate the entire zone of busbar protection.