GE Multilin DTP-B, Инструкция по эксплуатации

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2. APPLICATION
GEK-106243E DTP Digital Transformer Protection 2-3
2.2 CALCULATIONS
2.2.1 METHOD
The calculations required to determine the proper relay taps and CT ratios are described below. A sample
calculation, for the transformer shown in Figure 6, is presented.
2.2.2 PHASE SHIFT COMPENSATION
The secondary currents applied to the relay must be in phase if the EXTERNAL COMPENSATION mode is used.
The differential and through currents are obtained directly from the relay input currents, and any required phase
shift compensation or zero-sequence current elimination must be obtained by proper connection (i.e., either wye
or delta) of the current transformers.
In the INTERNAL COMPENSATION mode, phase shift compensation and zero-sequence current elimination are
taken care of in the DTP relay
2.2.3 CALCULATION OF CT TRANSFORMATION RATIOS AND RELAY TAPS
For this calculation, the following steps must be taken:
•
For each winding, determine the maximum line current (Ip max.) based on the maximum forced-cooled kVA
rating of the power transformer:
(Maximum transformer kVA)
Ip max=
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
√
3 x (kV - LL)
•
For each winding, determine the rated line current (100%Ip) based on the full self-cooled kVA rating (or the
“equivalent self-cooled rating”) of the power transformer.
(100% transformer kVA)
100% Ip=
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
√
3 x (kV - LL)
These calculations do not necessarily mean that each winding is going to carry these currents continuously. This
is only a convenient way of calculating the currents in the other windings in proportion to their voltage ratings. This
is the requirement for selecting the relay tap settings so that the relay will not operate for an external fault.
•
Select CT ratios so that the secondary current corresponding to Ip max does not exceed the CT secondary
thermal rating. Also, select CT ratios so that the relay currents can be properly matched by means of the relay
taps.
When the DTP is set in INTERNAL COMPENSATION mode, the wye-delta changes imposed by the transformer
time group as detailed in the PHASE SHIFT COMPENSATION section can be carried out by settings in the relay
through the front keypad or the communications program. It is not necessary to perform these changes on the CT
secondaries, which can always be wye connected. In this case, the taps will be chosen on the basis of currents
resulting from the CT’s wye configuration, no matter how the transformer winding is connected (wye or delta). By