Setting Up The Phase Differential Characteristic; Sensitivity Under Heavy Loads - GE P4A Technical Manual

P54A/B/C/E
When assigning the Terminal Address, you must use the following convention:
Terminals must be allocated a Terminal Address from the choice available (A-F).
●
● Starting with Terminal Address A, you must sequentially assign addresses B, C, etc., for the terminals in the
scheme.
You do not have to associate a specific Terminal Address with a specific terminal number, but we strongly
recommend that you observe the convention:
Assign Terminal Address A to terminal 1,
●
Assign Terminal Address B to terminal 2,
●
● For schemes with more than 2 terminals:
Assign Terminal Address C to terminal 3 (for schemes with up to 3 terminals),
○
Assign Terminal Address D to terminal 4 (for schemes with up to 4 terminals),
○
Assign Terminal Address E to terminal 5 (for schemes with up to 5 terminals),
○
Assign Terminal Address F to terminal 6 (for schemes with up to 6 terminals),
○
Besides the communications addresses, you need only to set the clock source for each channel using settings
Clock Source Ch1 and Clock Source Ch2. We strongly recommend that the default value of Internal is always
used.
9.6

SETTING UP THE PHASE DIFFERENTIAL CHARACTERISTIC

The biased phase current differential characteristic is defined by four protection settings. Each can be set
independently. This flexibility allows the characteristic to be set for particular sensitivity and current transformer
requirements. To simplify setting the protection, however, we strongly recommend three of the settings be fixed as:
Phase Is2 = 2.0 pu
●
Phase k1 = 30% (This provides stability for small CT mismatches, while ensuring good sensitivity to resistive
●
faults under heavy load conditions
● Phase k2 = 150% (For 2 terminal applications to provides stability under heavy through fault current
conditions)
● Phase k2 = 100% (For 3 terminal applications to provides stability under heavy through fault current
conditions)
These settings give a characteristic suitable for most applications so that only the Phase Is1 setting needs
changing from the default value.
Phase Is1 is the setting which determines the minimum pick-up of the phase current differential elements. This
value should be set to account for any mismatch between the current transformers at the different terminals, as
well the capacitive charging current if this is not compensated.
If capacitive charging current compensation is not used, the setting of Phase Is1 must be set above 2.5 times the
steady state charging current. Where charging current is low or negligible, the recommended setting of 0.2 pu
(factory default) should be applied.
If there is a mismatch between CTs at line ends, then the lowest primary CT rated current should be used as a
reference current for p.u. calculations (assuming that the load current cannot continuously exceed this value). This
means that the recommended settings Phase Is1 = 0.2 pu is equal to 0.2*(the lowest primary CT rated value). The
same consideration applies for other current settings such as Phase Is2.
9.7

SENSITIVITY UNDER HEAVY LOADS

The sensitivity of the phase current differential protection is governed by its settings and also the magnitude of
load current in the system. For a three-ended system, with devices LOCAL, REMOTE1, and REMOTE2, the following
applies:
|I | = |(Ī + Ī
diff LOCAL
P54xMED-TM-EN-1
+ Ī )|
REMOTE1 REMOTE2
Chapter 6 - Current Differential Protection
119