ABB 615 series Technical Manual page 518

Hide thumbs Also See for 615 series:

Table of Contents

Protection functions

value basically allows the no-load current of the power transformer and small

inaccuracies of the current transformers, but it can also be used to influence the

overall level of the operating characteristic. At the rated current, the no-load losses of

the power transformer are about 0.2 percent. If the supply voltage of the power

transformer suddenly increases due to operational disturbances, the magnetizing

current of the transformer increases as well. In general the magnetic flux density of

the transformer is rather high at rated voltage and a rise in voltage by a few percent

causes the magnetizing current to increase by tens of percent. This should be

considered in Low trip value

In section 2, where End section 1 < Ib/In < End section 2, is called the influence area

of Slope section 2. In this section, variations in the starting ratio affect the slope of the

characteristic, that is, how big a change in the differential current is required for

tripping in comparison with the change in the load current. The starting ratio should

consider CT errors and variations in the transformer tap changer position (if not

compensated). Too high a starting ratio should be avoided, because the sensitivity of

the protection for detecting inter-turn faults depends basically on the starting ratio.

In section 3, where Ib/In > End section 2, the slope of the characteristic can be set by

Slope section 3 that defines the increase in the differential current to the

corresponding increase in the biasing current.

GUID-739E1789-778D-44BF-BD4A-6BD684BF041D-ANSI V1 EN

Setting range for biased low stage

If the biasing current is small compared to the differential current of the phase angle

between the winding 1 and winding 2 phase currents is close to zero (in a normal situation,

Curve 2 ( Default settigs )

1MAC059074-MB A

615 series ANSI

Technical Manual

Chapters

Table of Contents