Basler Electric DGC-2020HD - Manual (Page 153)

9469300990 Rev B 143
Control Mode
When set for Control mode of operation, the 51 element is disabled until the measured voltage drops
below the Voltage Restraint threshold. Thus, as long as the voltage on the appropriate phase is above the
Voltage Restraint threshold, the 51 element will be blocked. When set for this mode of operation, the 51
Pickup setting is typically set near or below load current levels.
Restraint Mode
When set for Restraint mode of operation, the pickup of the 51 element is adjusted based upon the
magnitude of the measured voltage. Figure 78 shows how the 51 Pickup setting is adjusted in response
to the measured voltage level. Equation 3 determines the pickup level for the 51 element when the
measured voltage is between 25% and 100% of the Voltage Restraint threshold. Below 25%, the pickup
level stays at 25%. Above 100%, the pickup level stays at 100%. For example, if the Voltage Restraint
threshold is set for 120 V and the measured voltage on the appropriate phase is 100 V (83% of the
Voltage Restraint threshold), the phase overcurrent pickup level will be reduced to 83% of its setting.
When set for this mode of operation, the 51 element Pickup setting is typically set above worst case, load
current levels.
Figure 78. 51 Phase Pickup Level Compensation
𝐴𝑐𝑡𝑢𝑎𝑙 𝑃𝑖𝑐𝑘𝑢𝑝 𝐿𝑒𝑣𝑒𝑙 =
𝑆𝑒𝑛𝑠𝑖𝑛𝑔 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝐿𝑒𝑣𝑒𝑙
𝑅𝑒𝑠𝑡𝑟𝑎𝑖𝑛𝑡 𝑃𝑖𝑐𝑘𝑢𝑝 𝑆𝑒𝑡𝑡𝑖𝑛𝑔 × 51 𝑃ℎ𝑎𝑠𝑒 𝑃𝑖𝑐𝑘𝑢𝑝 𝑆𝑒𝑡𝑡𝑖𝑛𝑔
Equation 3. Restraint Pickup Level
Phase VT Configuration
The 51/27R function monitors Vpp. Table 46 shows which voltage measurements are used by each 51
element for each possible phase VT connection.
Table 46. Phase VT Connection Cross Reference
Phase VT Connection 51A 51B 51C
4W Vab Vbc Vca
3W Vab Vbc Vca
AB Vab n/a n/a
BC n/a Vbc n/a
CA n/a n/a Vca
DGC-2020HD Generator Protection