Ground Current - GE c60 Instruction Manual

GROUPED ELEMENTS
The neutral instantaneous overcurrent element can be used as an instantaneous function with no intentional delay or as a
definite time function. The element essentially responds to the magnitude of a neutral current fundamental frequency
phasor calculated from the phase currents. A positive-sequence restraint is applied for better performance. A small portion
(6.25%) of the positive-sequence current magnitude is subtracted from the zero-sequence current magnitude when
forming the operating quantity of the element as follows:
The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious zero-sequence currents
resulting from:
• System unbalances under heavy load conditions
• Transformation errors of current transformers (CTs) during double-line and three-phase faults
• Switch-off transients during double-line and three-phase faults
The positive-sequence restraint must be considered when testing for pickup accuracy and response time (multiple of
pickup). The operating quantity depends on how test currents are injected into the relay (single-phase injection:

I = 0.9375 I
op injected
5

5.7.5 Ground current

5.7.5.1 Menu
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  GROUND CURRENT
 GROUND CURRENT

5-190
NEUTRAL IOC1

TARGET: Self-reset
NEUTRAL IOC1

EVENTS: Disabled
 
I = 3 I_0 K
–
op
; three-phase pure zero-sequence injection:
Figure 5-92: Neutral IOC1 logic
 GROUND TOC1


 GROUND TOC2


 GROUND TOC3


 GROUND TOC4


 GROUND TOC5


Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
  
I_1 where K = 1 16

I = 3 I
op injected
See below
Note: Seen only if slot F or slot M has an 8H or 8J CT
module installed
C60 BREAKER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
).
Eq. 5-16