Basler BE1-CDS220, Instruction Manual

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BE1-CDS220 Protection and Control 4-15
The tap factors calculated by the auto-tap calculation feature can be determined in several ways. They
are displayed on the optional HMI using Screen 5.#.1.2, \PROT\SG#\87\MVA. Alternatively, the current
check record provided by the differential alarm function includes a listing of the compensation parameters
in the setting group that was active at the time that the record was triggered. See Section 6, Reporting
and Alarm Functions, Differential Current Monitoring Function, Setting Differential Current Monitoring
Alarms, for more details on this report.
Operating Settings for Phase Differential
Operating settings for the 87 function consist of Restrained Pickup, Restraint Slope, 2
nd
and 5
th
Harmonic
Restraint, and Unrestrained Pickup values.
Operating settings are made using BESTCOMS. Figure 4-12 illustrates the BESTCOMS screen used to
select operational settings for the 87 function. To open the screen, select Percentage Differential from the
Screens pull-down menu. Then select the 87 Phase tab. Alternately, settings may be made using S<g>-
87 ASCII command or through the optional HMI Screens 5.#.1.1, \PROT\SG#\87\87.
The operating settings for Phase Differential are provided in Table 4-7.
The settings for restrained minimum pickup and unrestrained trip are set in multiples of tap. If the ideal
taps calculated by Equation 4-1 fell within the acceptable range, the sensitivity settings will be in Per Unit
on the MVA Base used in the equation. For example, a 100 MVA, 115 KV transformer has a full load (1
per unit) current of 500 amperes. A pickup setting of 10 times tap for the unrestrained output pickup
(URO) element is equivalent to 5,000 primary amperes of differential current.
If the taps had to be adjusted upwards or downwards to fit within the acceptable range, the sensitivity
settings for these protective elements should be adjusted as well. Equation 4-2 gives the adjustment
factor. The definitions for the variables in Equation 4-2 are the same as those for Equation 4-1. For
example, the ideal taps
(TAPn
I
) were calculated using Equations 4-2 and 4-3 to be 1.6 and 5.0. They had
to be adjusted upwards so that the actual taps
(TAPn
A
)
are 2.0 and 6.25. Per Equation 4-2,
X
is 0.8. It is
desired that the minimum pickup of the restrained element be 0.35 per unit on the circuit base. The actual
setting should be 0.35
∗
0.8 = 0.28 to achieve the same sensitivity.
The pickup settings in Times Tap can be related to primary amps by Equation 4-3. Minpu is the minimum
pickup setting in Times Tap. The definitions for the remaining variables in Equation 4-3 are the same as
those for Equation 4-1.
CTRn * KVn * 3 * TAPn
COMPn * 1000 * MVA
TAPn
TAPn
X
A
A
I
= =
Equation 4-2. Tab Adjustment Equation
COMPn
CTRn * TAPn * Mpu
Ipri
=
Equation 4-3. Calculate Primary Amps
NOTE
The CT input circuit settings are used by the auto-tap calculation function to
calculate the correct tap adjustment factor for the differential functions. When
entering these settings via the ASCII command interface, the validation routine
and auto-tap calculation is performed on exit after all parameters have been
entered.
When entering these settings using the optional HMI, the validation routine and
auto-tap calculation is performed on exit of each screen. This may cause an OUT
OF RANGE error message from the auto-tap calculation function. The user is
advised to enter valid CT input circuit settings on Screen 6.3.1.1,
SETUP\PWR_S\CON\CTP prior to entering the auto-tap calculation settings. If
the user has previously set the auto-tap calculation settings and needs to change
the CT input circuit settings, it may be necessary to temporarily change the auto-
tap function setting to MANUAL on Screens 5.1.1.3, 5.2.1.3, 5.3.1.3, and 5.4.1.3
\PROT\SG#\87\TAP in order to enter the new CT settings.
See Section 3, Input and Output Functions, Input Current, for more information
on CT input circuit settings.