Multi-Function Control ETMFC610
http://www.entecene.co.kr
200
EN
HANCED
TEC
HNOLOGY
8.2.2. Ground Time Overcurrent (51G)
The ETMFC610 has a residual ground time overcurrent element that decides whether it is
overcurrent or not using the residual ground current of CT second. The ground time overcurrent
element offers the trip lag time that accords to the fault current due to the set value applied inverse
time curve such as pickup current, applied T-C curve, applied T-C curve's time dial, applied T-C
curve's time adder, minimum response time(M.R.T), fault reset method and low set definite time.
Due to the inverse characteristic of this applied T-C characteristics, the trip operates slowly if the
fault current is low and the trip operates faster as the fault current gets bigger(only, the current
should be higher than the residual ground pickup current setting value in to operate the trip). The
ground time overcurrent element is enabled in the group setting and both PROTECTION
ENABLED and GROUND ENABLED in user interface panel.
The residual ground time overcurrent element can do smooth protection cooperation with other
protection elements of ETMFC610 and external devices of the power supply system each, due to
various T-C curves, time dial and time adder. The ETMFC610 provides ANSI curve, IEC curve, ES
curve and non-standardized T-C curve.
There are two types of overcurrent fault reinstation(reset) methods: instantaneous and linear mode.
The reinstation method for the linear mode is applied with operating the ANSI, IEC, ES and USER
curve. The reinstation method for the instantaneous mode is used for the cooperation with devices
that do instantaneous reinstation such as the CB inside the power supplying system or other
protection element. In the instantaneous reinstation method, the residual ground time overcurrent
element is immediately reset when the current measured for one cycle drops below the residual
ground pickup current setting value. In the linear reinstation method, the CB is used for the
cooperation with the protection devices that demand lag time for reinstation like the mechanical
relays.
Figure 8-10. Ground Time Overcurrent(51G) Logic Diagram