GE C70, Instruction Manual

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GE Multilin C70 Capacitor Bank Protection and Control System 5-265
5 SETTINGS 5.9 TRANSDUCER INPUTS AND OUTPUTS
5
The DCmA output settings are described below.
• DCMA OUTPUT F1 SOURCE : This setting specifies an internal analog value to drive the analog output. Actual values
(FlexAnalog parameters) such as power, current amplitude, voltage amplitude, power factor, etc. can be configured as
sources driving DCmA outputs. Refer to Appendix A for a complete list of FlexAnalog parameters.
• DCMA OUTPUT F1 RANGE : This setting allows selection of the output range. Each DCmA channel may be set inde-
pendently to work with different ranges. The three most commonly used output ranges are available.
• DCMA OUTPUT F1 MIN VAL : This setting allows setting the minimum limit for the signal that drives the output. This
setting is used to control the mapping between an internal analog value and the output current. The setting is entered
in per-unit values. The base units are defined in the same manner as the FlexElement base units.
• DCMA OUTPUT F1 MAX VAL : This setting allows setting the maximum limit for the signal that drives the output. This
setting is used to control the mapping between an internal analog value and the output current. The setting is entered
in per-unit values. The base units are defined in the same manner as the FlexElement base units.
The
DCMA OUTPUT F1 MIN VAL
and
DCMA OUTPUT F1 MAX VAL
settings are ignored for power factor base units (i.e. if
the
DCMA OUTPUT F1 SOURCE
is set to FlexAnalog value based on power factor measurement).
Three application examples are described below.
Example: power monitoring
A three phase active power on a 13.8 kV system measured via UR-series relay source 1 is to be monitored by the DCmA
H1 output of the range of –1 to 1 mA. The following settings are applied on the relay: CT ratio = 1200:5, VT secondary 115,
VT connection is delta, and VT ratio = 120. The nominal current is 800 A primary and the nominal power factor is 0.90. The
power is to be monitored in both importing and exporting directions and allow for 20% overload compared to the nominal.
The nominal three-phase power is:
(EQ 5.28)
The three-phase power with 20% overload margin is:
(EQ 5.29)
The base unit for power (refer to the FlexElements section in this chapter for additional details) is:
(EQ 5.30)
The minimum and maximum power values to be monitored (in pu) are:
(EQ 5.31)
The following settings should be entered:
DCMA OUTPUT H1 SOURCE
: “SRC 1 P”
DCMA OUTPUT H1 RANGE
: “–1 to 1 mA”
DCMA OUTPUT H1 MIN VAL
: “–1.247 pu”
DCMA OUTPUT H1 MAX VAL
: “1.247 pu”
With the above settings, the output will represent the power with the scale of 1 mA per 20.65 MW. The worst-case error for
this application can be calculated by superimposing the following two sources of error:
• ±0.5% of the full scale for the analog output module, or
• ±1% of reading error for the active power at power factor of 0.9
For example at the reading of 20 MW, the worst-case error is 0.01
×
20 MW + 0.207 MW = 0.407 MW.
Example: current monitoring
The phase A current (true RMS value) is to be monitored via the H2 current output working with the range from 4 to 20 mA.
The CT ratio is 5000:5 and the maximum load current is 4200 A. The current should be monitored from 0 A upwards, allow-
ing for 50% overload.
The phase current with the 50% overload margin is:
NOTE
P 3 13.8 kV 0.8 kA
×
0.9
× ×
17.21 MW
= =
P
max
1.2 17.21 MW × 20.65 MW
= =
P
BASE
115 V 120
×
1.2 kA
×
16.56 MW
= =
minimum power
20.65 MW
–
16.56 MW
------------------------------ 1.247 pu, maximum power
20.65 MW
16.56 MW
--------------------------- 1.247 pu
= = – = =
0.005
±
1 1
–
( )
–
( )
20.65 MW
× ×
0.207 MW
±
=