Basler Electric BE1-11g - Manual (Page 126)

114 9424200994 Rev N
If one of the calculated taps is outside the acceptable range (2 to 20 for 5 ampere units or 0.4 to 4 for 1
ampere units), the auto-tap calculation feature will select the nearest acceptable tap and calculate the
other tap (two at a time) so that the correct spread ratio is maintained. If the user is manually calculating
the taps, the same adjustment should be made.
BESTCOMSPlus is used to provide auto tap calculation by filling in the appropriate fields on the
Transformer Setup screen and pressing the calculate button or manual tap values can be entered.
Operational Settings
The settings for restrained minimum pickup and unrestrained trip are set in multiples of tap. If the ideal
taps calculated by Equation 13 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 14 gives the adjustment
factor. The definitions for the variables in Equation 14 are the same as those for Equation 13. For
example, the ideal taps (TAPn
I
) were calculated using Equation 14 and Equation 15 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 14, X =
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 15. Minpu is the minimum
pickup setting in Times Tap. The definitions for the remaining variables in Equation 15 are the same as
those for Equation 13.
𝑋 =
𝑇𝐴𝑃𝑛
𝑙
𝑇𝐴𝑃𝑛
𝐴
=
𝑀𝑉𝐴 × 1000 × 𝐶𝑂𝑀𝑃𝑛
𝑇𝐴𝑃𝑛
𝐴
× √3 × 𝐾𝑉𝑛 × 𝐶𝑇𝑅𝑛
Equation 14. Tab Adjustment Equation
𝐼𝑝𝑟𝑖 =
𝑀𝑖𝑛𝑝𝑢 × 𝑇𝐴𝑃𝑛 × 𝐶𝑇𝑅𝑛
𝐶𝑂𝑀𝑃𝑛
Equation 15. Calculate Primary Amps
% of Maximum - The maximum of the compensated input currents is used. For example, the restraint
current for phase A would be
I
RA
= max (I
AXCOMPS
) where x = 2 for two current inputs.
% of Average - The average of the compensated input currents is used. For example, the restraint
current for phase A would be given by Equation 16.
𝐼
𝑅𝐴
=
𝑆𝑢𝑚 𝑜𝑓 𝐼
𝐴𝑥𝐶𝑂𝑀𝑃𝑆
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐼𝑛𝑝𝑢𝑡𝑠
Equation 16. Calculate Restraint Current for Phase A, % of Average
Phase current differential element operational settings are configured on the Phase Current Differential
(87) settings screen (Figure 71) in BESTCOMSPlus. A legend for the chart (Figure 72) is shown by
clicking the Help button on this screen. Setting ranges and defaults are summarized in Table 41.
0BPhase Current Differential (87) Protection BE1-11g