Ground Current Input - GE 489 Instruction Manual

2.2 ELECTRICAL
The 489 has a dual primary isolating transformer for
ground CT connections. There are no internal ground con-
nections on the ground current inputs. The ground CT cir-
cuits are shorted by automatic mechanisms on the case if
the unit is withdrawn. The 1 A tap is used for 1 A or 5 A
2
secondary CTs in either core balance or residual ground
configurations. If the 1 A tap is used, the 489 measures up
to 20 A secondary with a maximum ground CT ratio of
10000:1. The chosen ground CT must be capable of driv-
ing the ground CT burden (see SPECIFICATIONS).
The HGF ground CT input is designed for sensitive ground
current detection on high resistance grounded systems
where the GE Power Management HGF core balance CT
(50:0.025) is used. In applications such as mines, where
earth leakage current must be measured for personnel
safety, primary ground current as low as 0.25 A may be
detected with the GE Power Management HGF CT. Only
one ground CT input tap should be used on a given unit.
Only one ground input should be wired. The other
input should be unconnected.
NOTE
DO NOT INJECT OVER THE RATED CURRENT TO HGF TERMINAL (0.25 to 25 A PRIMARY)
CAUTION
The exact placement of a zero sequence CT to detect ground fault current is shown below. If the core balance CT is placed
over shielded cable, capacitive coupling of phase current into the cable shield may be detected as ground current unless
the shield wire is also passed through the CT window. Twisted pair cabling on the zero sequence CT is recommended.
2-10
Figure 2–13: CORE BALANCE GROUND CT INSTALLATION
489 Generator Management Relay

2.2.5 GROUND CURRENT INPUT

Figure 2–12: RESIDUAL GROUND CT CONNECTION
2 INSTALLATION
GE Power Management