Ground Ct Inputs - GE 889 Instruction Manual

CHAPTER 2: INSTALLATION
CAUTION:

Ground CT Inputs

889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
IMPORTANT: The phase and ground current inputs correctly measure up to 46 times the
current input's nominal rating. Time overcurrent curves become horizontal lines for
currents above 20 × PKP.
The ground input (Terminals J7 and J8) is used in conjunction with a Zero Sequence CT as
source, or in the neutral of wye-connected source CTs. The ground current input can be
used to polarize both the neutral and sensitive ground directional elements. When using
the residual connection, set the GROUND CT PRIMARY setpoint to a value equal to the
PHASE CT PRIMARY setpoint. The sensitive ground current input is intended for use either
with a CT in a source neutral of a high-impedance grounded system, or on ungrounded
systems. On ungrounded systems it is connected residually with the phase current inputs.
In this case, the SENSTV GND CT PRIMARY setpoint should be programmed to a value
equal to the PHASE CT PRIMARY setpoint. The sensitive ground current input can be
connected to a Zero Sequence CT for increased sensitivity and accuracy when physically
possible in the system.
Figure 2-21: Ground Inputs
ELECTRICAL INSTALLATION
2–21