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2 CALCULATION OF SETTINGS
2.3 PROTECTION FUNCTION SETTINGS
There are eight user-configurable output relays included in the DGP system. Four of these are high-speed
relays intended for tripping and four are standard-speed relays intended for alarm. Each of the protection func-
tions described below includes two four-digit settings, TRIP and ALARM, which configure the function to oper-
ate any number of these relays. An output relay is selected or de-selected by setting a code to 1 or 0,
respectively. The four-digit code of the TRIP setting applies to the 94G, 94G1, 94G2, and 94G3 relays, in that
order. The four digit code of the ALARM setting applies to the 74A, 74B, 74C, and 74D relays, in that order.
Any number of the protection functions can be disabled by setting both the TRIP and ALARM codes for the
function or functions to 0000.
The configurable trip and alarm outputs can be used to customize the DGP in accordance with a number of
user-defined trip and alarm strategies.
Algorithm: Function 87G operates when the following inequality is met:
I
where:
= Generator return-side phase current
1
I
= Generator system-side phase current
2
K = an adaptive variable
where K1 = 87G K1 setting in percent (Setting 203: K1)
1. The algorithm is processed only if
2. The algorithm is processed separately for each phase.
3. The initial characteristic slope can be calculated using the formula:
Characteristics: The following four graphs show the curves for selected values of Setting 203: K1 and 204:
PICKUP. The curve for any combination of the 203: K1 and 204: PICKUP settings can be derived using the
algorithm above.
This function should be set as sensitive as practical, keeping adequate margin for CT errors under all through-
load and through-fault current conditions. K1 and PICKUP settings of 2% and 0.3 A, respectively, are recom-
mended for most applications where the system and neutral side CTs are of identical design. Higher settings
must be considered if the CTs are not of identical design or if a higher CT error margin is desired.
For the sample generator system, set K1 = 2% and PICKUP = 0.3 A.
GE Power Management
2
>
(
I
–
I
K I
1
2
1
⁄
if I
=
K1 100
×
⁄
15
K1
100
if I
=
>
I
I
87G PICKUP
–
1
2
⋅
% slope
100
=
DGP Digital Generator Protection System
2.3 PROTECTION FUNCTION SETTINGS
2.3.1 TRIP AND ALARM OUTPUT RELAYS
2.3.2 STATOR DIFFERENTIAL 87G
⋅
)
I
2
⋅
≤
I
81
1
2
⋅
>
I
81
1
2
K1
--------- -
100
2
2-
13
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