Open CT circuits create extremely high voltages in the circuits, which
may damage the insulation and cause further problems. This must be
taken into consideration especially when the protection functions are
blocked.
When the reference current is not connected to the protection relay, the
function should be turned off. Otherwise, the
FAIL
output is activated
when unbalance occurs in the phase currents even if there was nothing
wrong with the measurement circuit.
Reference current measured with core-balanced current transformer
CCM compares the sum of phase currents to the current measured with the core-balanced
CT.
CCM
I_A
I_B
ALARM
FAIL
I_C
I_REF
BLOCK
protection relay
Core 1
(p
ro
tecti
o
n)
IL1
IL2
IL3
I_A
I_B
I_C
I_REF
Co
re
ba
lance
d CT
GUID-DA7A48EF-0F07-4665-9A09-87188E5A9982 V2 EN
Figure 437:
Connection diagram for reference current measurement with core-
balanced current transformer
1MAC059074-MB A
Section 6
Supervision functions
615 series ANSI
849
Technical Manual
Summary of Contents for Relion 615 series
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