Output Relays; Solid State Trip Output; Analog Outputs - GE Multilin 745 Instruction Manual

745
Transformer Management Relay

Output Relays

Solid State Trip Output

Analog Outputs

3–12
current source for the purpose of cancelling out the resistance of the wires
connecting the RTD to the 745. Terminal B12 is the return path for the two current
sources.
In the three-wire connection scheme, the connection from terminal B11 to B12 is
made at the RTD. The three-wire connection scheme compensates for the resistance
of the wiring between the 745 and the RTD.
In the two-wire connection scheme, the connection from terminal B11 to B12 is
made at the terminal block on the rear of the 745. This connection must not be
omitted. The two-wire connection scheme does not compensate for the resistance of
the wiring between the 745 and the RTD.
Eight output relays are provided with the 745. Output Relays 2 through 5 have Form
A contacts while Output Relays 6 to 8 and the Self-Test relay have Form C contacts.
Since Output Relays 2 to 5 are intended for operating a breaker trip coil, the Form A
contacts have higher current ratings than the Form C contacts. Note that the
operating mode of the Self-Test relay is fixed, while the other relays can be
programmed by the user via the FlexLogic™ feature.
A high-speed solid state (SCR) output is also provided. This output is intended for
applications where it is necessary to key a communications channel.
The 745 provides 7 analog output channels whose full scale range can be set to one
of the following ranges: 0 to 1 mA; 0 to 5 mA; 0 to 10 mA; 0 to 20 mA; and 4 to 20
mA. Each analog output channel can be programmed to represent one of the
parameters measured by the relay. For details, see Analog Outputs 1 to 7 on page
5–37.
As shown in the typical wiring diagram, the analog output signals originate from
Terminals A6 to A12 and share A5 as a common return. Output signals are internally
isolated and allow connection to devices which sit at a different ground potential.
Each analog output terminal is clamped to within 36 V of ground. To minimize the
effects of noise, external connections should be made with shielded cable and only
one end of the shield should be grounded.
If a voltage output is required, a burden resistor must be connected at the input of
the external measuring device. Ignoring the input impedance, the burden resistance
is:
If a 5 V full scale output is required with a 0 to 1 mA output channel, R
0.001 A = 5 KΩ. Similarly, for a 0 to 5 mA channel this resistor would be 1 KΩ; for a
0 to 10 mA channel, this resistor would be 500 Ω; and for a 4 to 20 mA channel this
resistor would be 250 Ω.
FIGURE 3–15: Analog Output Connection
http://www.GEindustrial.com/multilin
V
FULL-SCALE
R
---------------------------------- -
=
LOAD
I
MAX
Typical Wiring
(EQ 3.1)
= 5 V /
LOAD
GE Multilin