Patent ID: 11870254
Assignee: TIANJIN UNIVERSITY
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H | IPC H

Claim 1:
2. The multi-terminal differential protection setting method for a distributed generator T-connected distribution network according to claim 1, wherein step S3 of calculating the overall maximum error of superimposed multi-terminal current errors according to the multi-terminal current comprises:
expressing the power frequency current phasor involved in a group of n(n≥3)-terminal current differential protection by a set P:

P={İ1,İ2, . . . ,İn}  (2)

the action criterion of the multi-terminal current differential protection is:

Iop≥Iset  (3)

wherein Iop is differential current; and Iset is a protection setting value;
expressing the relationship between the measured value and the actual value of each power frequency current phasor as follows:

İ{dot over (ι)}.ms=İ{dot over (ι)}.tr+Δİ{dot over (ι)}  (4)

{dot over (ι)}=1, 2, . . . , n
wherein İ{dot over (ι)}.ms represents the measured value of the power frequency current phasor, İ{dot over (ι)}.tr represents the actual value of the power frequency current phasor, and Δİ{dot over (ι)} represents the error between the actual value and the measured value;
at this moment, the differential current is:, I
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     (
     5
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according to the Kirchhoff's Current Law, meeting the formula below during normal operation and during failure outside a protected area:

İ1.tr+İ2.tr+ . . . +İn.tr=0  (6)

according to formula (5) and formula (6), the differential current during normal operation and during failure outside a protected area is:

Iop=|Δİ1+Δİ2+ . . . +Δİn|  (7)

denoting the overall maximum error of superimposed multi-terminal current errors as ΔIΣ:

ΔIΣ=|Δİ1+Δİ2+ . . . +Δİn|  (8).