4.53
Date Code 20080213 Instruction Manual SEL-351A Relay
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control Settings (Not in SEL-351A-1)
If the desired zero-sequence voltage pickup for the Wattmetric element in
primary 3V
0
is 400 V primary, obtain the proper setting for 59RES by
dividing the primary voltage by the PT ratio for voltage inputs VA, VB, and VC:
Equation 4.19
If the desired forward Wattmetric element threshold is 24 kW primary, and the
desired reverse threshold is 10 kW primary, the correct settings are:
Equation 4.20
Equation 4.21
When VSCONN = 3V0, with a broken-delta 3V
0
voltage source connected to
the VS channel (terminals VS-NS), group setting PTRS must be properly set to
give the signal on the VS channel the correct scaling in primary units, as
displayed under VS in the METER command response, available via serial
port or front panel. The example value PTRS = 96, as shown in Potential
Transformer Ratios and PT Nominal Secondary Voltage Settings on
page 9.39, is used for subsequent examples.
The relay internally converts the VS channel signal to the VA, VB, VC voltage
base before using it as the 3V
0
quantity, as shown in Table 4.5. Thus, when the
zero-sequence voltage pickup for the Wattmetric element is known in terms of
the system primary voltage level, the required calculation for setting 59RES is
the same as the calculation for the VSCONN = VS example shown previously,
which converts the primary zero-sequence voltage value into a secondary
value on the VA, VB, VC input terminal base.
Using the example quantities from the VSCONN = VS subsection:
Equation 4.22
Note that the primary voltage is divided by the PTR setting, not the PTRS
setting.
Similarly, the derivation of the 32WFP and 32WRP settings, if they are known
in primary Watts, follows the same formula as before:
Equation 4.23
59RES
V primary
PTR
------------------------
400 V primary
60
----------------------------------- 6.67 V secondary== =
32WFP
W primary
PTR CTRN•
-----------------------------------=
24000 W primary
60 10•
------------------------------------------ 4 0 . 0 0 0 W s e c o n d a r y=
32WRP
W primary
PTR CTRN•
-----------------------------------=
10000 W primary
60 10•
------------------------------------------- 16.667 W secondary=
59RES
V primary
PTR
------------------------
400 V primary
60
----------------------------------- 6.67 V secondary== =
32WFP
W primary
PTR CTRN•
-----------------------------------=
24000 W primary
60 10•
------------------------------------------ 4 0 . 0 0 0 W s e c o n d a r y=
Courtesy of NationalSwitchgear.com
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