Basler BE1-CDS220, Instruction Manual

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BE1-CDS220 General Information 1-13
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D2837-16
12-14-98
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Delta CT Connection
Wye/Delta (DAB)
Transformer with Ground
Bank on Delta Side
Wye CT Connection
GROUNDING
BANK
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87T
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Figure 1-7. Traditional Zero-Sequence Trap for Application with Ground Banks
The setup parameters for each of the current input circuits are described in Section 3, Input and Output
Functions, Power System Measurement Functions. The parameters specifying CT connection,
transformer connection, and ground source for each current circuit determines the angle and zero
sequence compensation used on each current input.
Problem 6: Transformer Energization Inrush and Overexcitation
General
When the zone of protection includes a transformer, excitation and energization inrush currents appear as
differential current because they flow into the zone of protection and not back out again. Normally,
transformer excitation losses are small. However, when the transformer is overexcited, or upon initial
energization or sympathetic inrush conditions, this can cause sensitive differential protection to operate.
BE1-CDS220 Solution
Overexcitation and inrush are non-linear and the currents have high harmonic content. Inrush is
characterized by high, even harmonics such as the second harmonic. Overexcitation is characterized by
NOTE
The BE1-CDS220 relay does not automatically remove the zero sequence
components from all currents presented to the differential protection functions as
that can unnecessarily reduce the relay’s sensitivity to internal ground faults by
33%. Also, since the zero sequence components are removed from all phases, it
can result in confusion during single-phase testing by introducing differential
current in phases not under test.