Schweitzer Engineering Laboratories SEL-751 - Table 4.26 Effect of Settings VSCONN and DELTA_Y on Petersen Coil Directional Elements

4.76
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
These details are important in relay testing, when the signal applied to the VS-
NS terminals represents a 3V
0
zero-sequence voltage signal, and
VSCONN := 3V0. When making test settings or interpreting test results,
remember that the relay scales the measured value by PTRS/PTR before using
it in the Petersen coil directional element and in the various zero-sequence
voltage-polarized directional elements.
EDIRIV—SELOGIC Control Equation Enable
Refer to Figure 4.24 and Figure 4.25.
SEL
OGIC control equation setting EDIRIV must be asserted to logical 1 to
enable the zero-sequence voltage-polarized and channel IN current-polarized
directional elements for directional control of neutral ground and residual
ground overcurrent elements.
For most applications, set EDIRIV directly to logical 1:
EDIRIV = 1 (numeral 1)
For situations where zero-sequence source isolation can occur (e.g., by open-
ing a circuit breaker) and result in possible mutual coupling problems for the
zero-sequence voltage-polarized and channel IN current-polarized directional
elements, SEL
OGIC control equation setting EDIRIV should be deasserted to
logical 0. In this example, connect a circuit breaker auxiliary contact from the
isolating circuit breaker to the SEL-751:
EDIRIV = IN102 (52a connected to optoisolated input IN102)
Almost any desired control can be set in SEL
OGIC control equation setting
EDIRIV.
Ungrounded/High-Impedance Grounded System Considerations for
Setting EDIRIV
On ungrounded/high-impedance grounded systems (when setting
ORDER := U), phase-to-phase or unbalanced three-phase faults can cause the
ungrounded/high-impedance grounded element to operate on false quantities.
To prevent this situation, SEL
OGIC setting EDIRIV may be used as follows:
EDIRIV := V1GOOD * !DIRQE
The V1GOOD Relay Word bit (V1GOOD asserts if the positive sequence
voltage is greater than 75%*VNOM/sqrt(3) and deasserts during a three-phase
fault, and the DIRQE Relay Word bit (see Figure 4.23) asserts during a phase-
to-phase fault. If either one of these occur, the EDIRIV setting evaluates to
logical 0, and the ungrounded/high-impedance grounded directional element
is blocked (see Figure 4.25).
Table 4.26 Effect of Settings VSCONN and DELTA_Y on Petersen Coil Directional Elements
Relay Function
When VSCONN := VS and
DELTA_Y := WYE
When VSCONN := VS and
DELTA_Y := DELTA
When VSCONN := 3V0
(DELTA_Y := WYE or DELTA,
and SINGLEV := Y)
Wattmetric and incremental
conductance elements
(ORDER setting choice “P”).
Use 3V0 calculated from V
A
,
V
B
, V
C
as polarizing voltage.
ORDER cannot be set to con-
tain “P” (no zero-sequence
voltage source is available)
Use V
S
• (PTRS/PTR) as 3V0
polarizing voltage.
a
a
The PTRS/PTR adjustment brings the broken-delta 3V0 quantity to the same base voltage as the relay settings 59RES, DIRWFP, and
DIRWRP, which are based on the VA, VB, VC voltage base.