Basler Electric BE1-11t - Manual (Page 107)

9424200995 Rev H 95
Settings
Tap Compensation Settings
The measured currents must be tap adjusted to eliminate magnitude mismatch prior to being used by the
Current Differential Protection (87) element. The tap adjust factors can be manually calculated per
Equation 13. Or, the user can enter the MVA and kV base parameters (Table 34) and the BE1-11t will
calculate the tap-adjust factors using CT Ratio (CTR) and Compensation Factor (COMP) parameters from
the current measurement input function settings. For a transformer application, the mismatch will be at a
minimum if the actual transformer voltage ratings are used, taking the no-load tap changer into
consideration. If the transformer has a load tap changer, the voltage rating at the middle of the adjustment
range should be used. This is generally at neutral.
𝑇𝐴𝑃𝑛 =
𝑀𝑉𝐴 × 1000 × 𝐶𝑂𝑀𝑃𝑛
√3 × 𝑘𝑉𝑛 × 𝐶𝑇𝑅𝑛
Equation 13. Calculate Tap Adjust Factors
Table 34. MVA and kVn Base Parameters
Parameter Description Explanation
Tapn Restraint winding The BE1-11t has 2 restraint windings (2 taps).
MVA MVA base Full load MVA or top rating of the protected equipment.
kVn kV base for CT input n L-L Voltage in kV for each CT input circuit.
CTRn CT ratio for CT input n Actual ratio not effective ratio.
COMPn
Phase compensation
adjustment factor for
CT input n
√3 if CTs are connected in Delta (CTcon = DAB or DAC).
1 in all other cases.
See the
Configuration chapter.
The input currents can be tap adjusted up to a spread ratio of 10:1. If the ratio between TAP1 and TAP2
is greater than ten, it will be necessary to adjust the CT ratios to bring the tap factors closer together.
When the auto-tap calculation feature is used, the BE1-11t will give an error message if the spread ratio is
greater than ten.
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.
BE1-11t 0BPhase Current Differential (87) Protection