ABB 615 series Technical Manual page 584

Hide thumbs Also See for 615 series:

Table of Contents

Protection functions

The parameter r is the maximum remanence flux density in the CT core in pu from the

saturation flux density. The value of the parameter r depends on the magnetic material

used and also on the construction of the CT. For instance, if the value r = 0.4, the

remanence flux density can be 40 percent of the saturation flux density. The manufacturer

of the CT has to be contacted when an accurate value for the parameter r is needed. The

value r = 0.4 is recommended to be used when an accurate value is not available.

The required minimum time-to-saturate T

(10 ms when f

Two typical cases are considered for the determination of the sufficient actual accuracy

limit factor F

A fault occurring at the substation bus.

The protection must be stable at a fault arising during a normal operating situation.

The reenergizing of the transformer against a bus fault leads to very high fault

currents and thermal stress. Therefore, reenergizing is not preferred in this case. The

remanence can be neglected.

The maximum through-going fault current Ik

short circuit fault close to the supply transformer, the DC time constant T

current is almost the same as that of the transformer, the typical value being 100 ms.

Equation 114

with these values gives the result:

GUID-C510CA46-3857-40D3-B40A-3C237BCE6E79 V2 EN

Reenergizing against a fault occurring further down in the network.

The protection must be stable also during reenergization against a fault on the line. In

this case, the existence of remanence is very probable. It is assumed to be 40 percent

On the other hand, the fault current is now smaller and since the ratio of the resistance

and reactance is greater in this location, having a full DC offset is not possible.

in 87G, 87M is half-fundamental cycle period

1MAC059074-MB A

is typically 6 I

for a motor. At a

of the fault

615 series ANSI

Technical Manual

Chapters

Table of Contents