2–10
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
ELECTRICAL INSTALLATION
CHAPTER 2: INSTALLATION
Current inputs
The 345 relay has eight (8) channels for AC current inputs, each with an isolating
transformer. There are no internal ground connections on the current inputs. Current
transformers with 1 to 6000 A primaries may be used.
CAUTION
CAUTION:
Verify that the relay’s nominal input current of 1 A or 5 A matches the secondary rating
of the connected CTs. Unmatched CTs may result in equipment damage or inadequate
protection.
CAUTION
CAUTION:
IMPORTANT: The phase and ground current inputs will correctly measure up to 20
times the current input’s nominal rating. Time overcurrent curves become horizontal
lines for currents above the 20 × CT rating. This becomes apparent if the pickup level is
set above the nominal CT rating.
CAUTION
CAUTION:
Before working on CTs, they MUST be short circuited.
Ground and sensitive ground CT inputs
Two ground inputs - one per winding - are referred to throughout this manual as the
Ground Current
or
Sensitive Ground Current
inputs. Before making ground connections,
consider that the relay automatically calculates the neutral (residual) current from the sum
of the three phase current phasors. The following figures show three possible ground
connections (or three possible sensitive ground connections).
The ground inputs (Terminals D8 and E8 for W1, and D12 and E12 for W2) are used in
conjunction with a Zero Sequence CT as source, or in the neutral of wye-connected source
CTs. When using the residual connection set the GROUND CT PRIMARY setpoint to a value
equal to the PHASE CT PRIMARY setpoint.
In cases where the relay is equipped with sensitive ground CT (terminals D8 and E8 for W1,
and D12 and E12 for W2) the sensitive ground current input is intended for use 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.
NOTE
NOTE:
The Sensitive Ground input must only be used on systems where the maximum ground
current does not exceed 100 times the rated current for 1 second.
The ground CT wiring in the figure below, shows 3 possible ways for wiring the Winding 1
ground CT (terminals D8, E8). The Winding 2 ground CT wiring (terminals D12, E12) is similar.
