GE 489 - Manual (Page 26)

2-10 489 Generator Management Relay GE Multilin
2.2 ELECTRICAL 2 INSTALLATION
2
b) GROUND CURRENT
DO NOT INJECT OVER THE RATED CURRENT TO HGF TERMINAL (0.25 to 25 A PRIMARY)
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.
Figure 2–13: CORE BALANCE GROUND CT INSTALLATION
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the unit is withdrawn.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
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 Multilin 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 Multilin 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.
Figure 2–12: RESIDUAL GROUND CT CONNECTION
NOTE
CAUTION