Basler BE1-CDS220, Instruction Manual

Page: 85 / 476

BE1-CDS220 Protection and Control 4-19
Table 4-8 summarizes the BESTlogic settings for Neutral Differential.
Table 4-8. BESTlogic Settings for Neutral Differential
Function Range/Purpose Default
Mode
0 = Disabled
1 = IG vs. CT Input 1 Neutral
∗
2 = IG vs. CT Input 2 Neutral
∗
0
BLK Logic expression that disables function when TRUE. 0
∗
If the unit does not have an independent ground input, a NO GROUND CT PRESENT error message
will be returned if you try to set the mode to 1 or 2.
Auto-Tap Compensation Settings for Neutral Differential
The tap adjustment factors are automatically calculated such that Equation 4-5 is TRUE. CTRn is the CT
ratio for the three-phase CT input circuit designated by the 87ND setting in the active logic. The CTR
settings are entered using BESTCOMS (see Figure 4-12). See Section 3, Input and Output Functions,
Input Current, for more details on these settings.
The CT input with the highest CTR is selected as the driving tap and set to the minimum setting (2.0 for 5-
ampere units or 0.4 for 1-ampere units). Equation 4-8 is solved for the other tap. The currents can be tap
adjusted up to a spread ratio of 10:1. If the ratio between TAPN and TAPG is greater than 10, it will be
necessary to adjust CT ratios to bring the tap factors closer together. The relay will give an error message
if the spread ratio is greater than 10.
CTRG * TAPG CTR * TAP
=
n n
n
= Input 1 or 2.
Equation 4-5. Solve for the other Tap (TAPn or TAPG)
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.#.2.1, \PROT\SG#\87ND\87ND. 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 Neutral Differential
Operating settings are made using BESTCOMS. Figure 4-17 illustrates the BESTCOMS screen used to
select operational settings for the 87ND function. To open the screen, select Percentage Differential from
the Screens pull-down menu. Then select the 87ND tab. Alternately, settings may be made using S<g>-
87ND ASCII command or through the optional HMI Screen 5.#.2.1, \PROT\SG#\87ND\87ND.
The operating settings for Neutral Differential are provided in Table 4-9.
The minimum pickup is set in multiples of tap. Equation 4-6 can be used to convert the Minpu setting to
primary current. The 87ND auto-tap calculation routine uses the minimum allowable taps to allow the
minimum pickup to be set to allow maximum sensitivity to ground faults.
n n CTR * TAP * Minpu Ipri
=
Equation 4-6. Convert the Minpu setting to Primary Current
NOTE
Since the calculated neutral used by the 87ND function is designated by
BESTlogic, you may get an auto-tap error when changing the 87ND logic setting
in the user programmable logic settings.