4 Protection Functions and Specifications
D02706R02.30
L-PRO 4000 User Manual
4-31
27 Main/
Auxiliary
Undervoltage
The relay provides undervoltage protection from both the bus and line PTs.
These functions are definite time delay functions.
The definite time main undervoltage function looks at the phase-to-neutral
voltage of all 3 phases to determine an undervoltage condition. The fundamen-
tal RMS voltage is used for this calculation. If any of the phase-to-neutral volt-
ages is below the set value, the function starts the definite time delay timer. The
user can set this function to be an AND or OR logic.
The auxiliary undervoltage function operates exactly the same way as the main
undervoltage function except that it uses the voltages from the auxiliary PT in-
puts.
Figure 4.16: 27 Undervoltage
60 Loss of
Potential (LOP)
Figure 4.17: Loss of Potential Logic
The relay distance elements (21P and 21N) are supervised by both instanta-
neous non-directional overcurrent and the loss of potential (LOP) logic to pre-
vent false trip due to the loss of potential, where the phase distance elements
are supervised by the delta current (i.e. Ia-Ib, Ib-Ic and Ic-Ia), and the ground
distance elements are supervised by both the phase current and the zero se-
quence (3
I0
) current.
27 Va Main
27 Vb Main
27 Vc Main
T
O
Gate Switch (Setting)
5ms
12ms
0
17ms
50 Ipos
168
171
173
174
169
167
170
172
50 3I0
50 ILA (4% I nominal)
50 ILB (4% I nominal)
50 ILC (4% I nominal)
dVpos/dt < -3V/cycle
dVpos/dt > 3V/cycle
ABS | dIpos/dt | > 0.1A/cycle
27 VLa (0.75 pu fixed)
27 VLc (0.75 pu fixed)
27 VLb (0.75 pu fixed)
0
20ms
59 VLa (0.1 pu fixed)
59 VLc (0.1 pu fixed)
59 VLb (0.1 pu fixed)
175
176
Summary of Contents for L-PRO 4000
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