Stub Bus Scheme; Transformer Differential Protection Ct Requirements; Ct Requirements - Transformer Application; Figure 61: Stub Bus Scheme Logic - GE P642 Technical Manual

Chapter 6 - Transformer Differential Protection
5.9.1.3 STUB BUS TRIPPING
You can protect the Stub Bus zone by a non-directional DT phase overcurrent element with a delay time set to zero
second. To issue a Stub Bus trip, the overcurrent element and the relevant Stub Bus active DDB signals must both
be high. You can configure the Stub Bus tripping scheme in PSL.
5.9.2

STUB BUS SCHEME

Idiff Trip
HV UndCurrent
89 a
Input L 1
89 b
Input L 2
POC 1 I>3 Trip
V03129

Figure 61: Stub Bus Scheme Logic

5.10

TRANSFORMER DIFFERENTIAL PROTECTION CT REQUIREMENTS

The CT requirements detailed below are applicable to standard CTs.
5.10.1

CT REQUIREMENTS - TRANSFORMER APPLICATION

We strongly recommend Class X or Class 5P current transformers for transformer differential protection
applications.
The current transformer knee-point voltage requirements are based on the following settings:
Parameter
This sets the minimum differential current threshold required for the transformer differential
Is1
protection to trip.
This defines the bias current threshold at which the second slope of the bias current
Is2
characteristic becomes active.
K1 This setting defines the gradient of the first slope in the bias current characteristic.
K2 This setting defines the gradient of the second slope in the bias current characteristic.
This setting defines the first High set threshold on the bias current characteristic. This setting
Is-HS1
is only used in advanced mode.
This setting defines the second High set threshold on the bias current characteristic. This
Is-HS2
setting is only used in advanced mode.
Transient Bias This setting enables or disables the transient bias factor
Zero seq filt HV This setting enables or disables zero sequence filtering on the HV winding
Zero seq filt LV This setting enables or disables zero sequence filtering on the LV winding
Zero seq filt TV This setting enables or disables zero sequence filtering on the TV winding
138
Blocking
Activation
&
&
Tripping
This example applies to the HV element only . The LV and TV elements follow the same principles .
In this example, the following applies :
·
The differential trip output is connected to output relay 4
·
The HV Stub bus trip output is connected to output relay 1
·
The HV stage 3 phase overcurrent element is used
·
The 89 a contact is connected to opto -input 1
· The 89 b contact is connected to opto -input 2
Description
100
& Dwell
S
Q
R
100
&
Dwell
Idiff Trip
Output R4
0
HV StubBus Act
HV StubBus Trip
Output R1
0
Value
0.2 pu
1 pu
30%
80%
10 pu
32 pu
Enabled
Enabled
Enabled
Enabled
P64x-TM-EN-1.3
P64x