Application - ABB RELION 620 Series Technical Manual

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Protection functions

GUID-7E298CD4-05F7-4764-9408-E3DC37C6CBE6 V1 EN

Connection of current transformers of Type 2 and example of currents

during external fault

In case of three-winding transformer, the above consideration applies between winding 1

and winding 2. A similar consideration is done between winding 1 and winding 3 using the

CT connection 1-3 setting.

If the rated primary current of the current transformers is not equal to the rated current of

the power transformer on the concerned side of the transformer, the setting parameters CT

ratio Cor Wnd 1, CT ratio Cor Wnd 2 and CT ratio Cor 3 must be used for correcting the

transformation ratios. CT ratio Cor Wnd 1 and CT ratio Cor Wnd 2 are used to correct the

ratios on winding 1 and 2 while the use of CT ratio Cor 3 depends on the setting Current

group 3 type. If Current group 3 type is "Tertiary", the CT ratio Cor 3 setting is used to

correct the ratios on the winding 3. If Current group 3 type is "Wnd 2 restraint", the ratio

correction is made to the ratios of the second restraint on winding 2. If Current group 3

type is "Wnd 1 restraint", the ratio correction is made to the ratios of the second restraint

on winding 1.

Application

The transformer differential protection is a unit protection. It acts as the main protection

of transformers in case of winding failure. The protective zone of a differential protection

includes the transformer itself and the bus work or cables between the current transformer

and the power transformer. When bushing current transformers are used for the

1MAC504801-IB E

620 series ANSI

Technical Manual

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