P.3.76
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
Detailed Description of Settings
E87LCC
This setting enables the line charging current compensation logic. Set to Y if
you want the local terminal to use the local voltage to calculate its portion of
the compensating current and use this result in the 87L scheme. Note that all
relays in a given 87L scheme benefit from line charging current compensation,
regardless of whether this setting is Y or N at any particular relay. This setting
instructs the local relay to include itself as one of the compensating relays for
the entire 87L scheme. The relay should have access to a reliable voltage
source if you identify it as a relay performing line charging current
compensation. You can enable compensation in all relays of the scheme even
if some do not have access to voltages to enable the line charging current
quality of compensation bits controlling security of the 87L elements upon a
loss of compensation. Relays lacking access to voltage will provide no
compensation, even when compensation is enabled, but they will benefit from
compensation by other relays, and 87CCB, 87CCD, and 87CCU Relay Word
bits will provide them information regarding the quality of that compensation.
87LINEV
This setting specifies the relay voltage terminal (Y, Z, or OFF) you will use for
line charging current compensation. If possible, select the line-side voltage
with the 87LINEV setting. The relay expects wye-connected VTs. You should
select a voltage identical to the main voltage of the relay per the source
selection logic, ESS (Y voltage input terminal typically). Note that the relay
will suspend compensation if it switches to the alternate voltage the ALINEV
setting specifies in response to the ALTV SEL
OGIC control equation. If the
relay has E87LCC enabled, but there is no voltage available to perform the
compensation, set 87LINEV to OFF.
87CCLPT
This setting specifies the position of the 87LINEV voltage source. Select L if
the application uses line-side voltage. Select B if the application uses bus-side
voltage. It is best to use applications with line-side voltage. In applications
with bus-side voltage, the scheme suspends line charging current
compensation at the local terminal if there is an open-pole condition (see
Figure 3.40). When relays switch their 87MCC multipliers in response to
breaker operation, there may be a slight degradation of line charging current
compensation quality. It is therefore best to use line-side voltages or, if the
application uses the bus-side voltage, to apply larger 87L setting margins for
the line charging current.
87CCB0 and 87CCB1
These settings specify the zero-sequence and positive-sequence susceptances
of the entire line in secondary mS (milliSiemens, S = A/V). For example, a
240 kV line drawing a positive-sequence charging current of 200 A has a
positive-sequence susceptance of about 200/(240/ ) = 1.44 mS primary.
We can calculate the secondary values of the susceptances as
(Primary Values) • (VT ratio) / (CT ratio).
The VT ratio is the ratio of the voltage source we have configured with the
87LINEV setting (PTRY or PTRZ, respectively).
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