Sel 411L - Page 367

P.3.259
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Undervoltage Supervision Logic
Calculate the 81UVSP
Setting Value
Because the relay accepts voltage input from the potential transformers (PTs)
in any combination, Valpha can have different values, depending on the
voltage inputs. In general, the following examples use the average (60 percent)
of the 50–70 percent undervoltage range that IEEE C37.117 Guide recommends.
Also, the calculations are based on an RMS phase-to-neutral value of 67 V for
the PT inputs, although the 81UVSP setting is a peak value and not an RMS value.
Case 1: 3-Phase PT Inputs
In this case, VF01 = VA, VF02 = VB, and VF03 = VC (with default settings).
Use Equation 3.93 to calculate the nominal value of Valpha as follows:
Equation 3.94
Equation 3.95
Set 81UVSP to 60 percent of this value:
Equation 3.96
Equation 3.97
Case 2: Single-Phase PT Input, Connected to the A-Phase Input
In this case, VF01 = VA, VF02 = ZERO, and VF03 = ZERO.
Equation 3.98
Equation 3.99
Set 81UVSP to 60 percent of this value:
Equation 3.100
Equation 3.101
Case 3: Single-Phase PT Input, Connected to the B- or C-Phase Input
In this case, VF01 = ZERO, VF02 = VB, and VF03 = ZERO.
Equation 3.102
Equation 3.103
Valpha 1.5 2 67 V=
Valpha 142.13 V=
81UVSP 0.6 142.13 V=
81UVSP 85.28 V=
Valpha 2 67 V=
Valpha 94.75 V=
81UVSP 0.6 94.75 V=
81UVSP 56.85 V=
Valpha 2
67
2
------V=
Valpha 47.37 V=