GE M60, Инструкция по эксплуатации

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5-340 M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
TRANSDUCER INPUTS/OUTPUTS CHAPTER 5: SETTINGS
5
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 is to be monitored from 0 A upwards, allowing
for 50% overload.
The phase current with the 50% overload margin is:
Eq. 5-65
The base unit for current (see the FlexElements section in this chapter for additional details) is:
Eq. 5-66
The minimum and maximum power values to be monitored (in pu) are:
Eq. 5-67
The following settings are entered:
DCMA OUTPUT H2 SOURCE
: “SRC 1 Ia RMS”
DCMA OUTPUT H2 RANGE
: “4 to 20 mA”
DCMA OUTPUT H2 MIN VAL
: “0.000 pu”
DCMA OUTPUT H2 MAX VAL
: “1.260 pu”
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 ±0.005 x (20 - 4) x 6.3 kA = ±0.504 kA
• ±0.25% of reading or ±0.1% of rated (whichever is greater) for currents between 0.1 and 2.0 of nominal
For example, at the reading of 4.2 kA, the worst-case error is max(0.0025 × 4.2 kA, 0.001 × 5 kA) + 0.504 kA = 0.515 kA.
Example: Voltage monitoring
A positive-sequence voltage on a 400 kV system measured via source 2 is to be monitored by the DCmA H3 output with a
range of 0 to 1 mA. The VT secondary setting is 66.4 V, the VT ratio setting is 6024, and the VT connection setting is “Delta.”
The voltage is to be monitored in the range from 70% to 110% of nominal.
The minimum and maximum positive-sequence voltages to be monitored are:
Eq. 5-68
The base unit for voltage (see the FlexElements section in this chapter for additional details) is:
Eq. 5-69
The minimum and maximum voltage values to be monitored (in pu) are:
Eq. 5-70
The following settings are entered:
DCMA OUTPUT H3 SOURCE
: “SRC 2 V_1 mag”
DCMA OUTPUT H3 RANGE
: “0 to 1 mA”
DCMA OUTPUT H3 MIN VAL
: “0.404 pu”
DCMA OUTPUT H3 MAX VAL
: “0.635 pu”
The limit settings differ from the expected 0.7 pu and 1.1 pu because the relay calculates the positive-sequence quantities
scaled to the phase-to-ground voltages, even if the VTs are connected in “Delta” (see the Metering Conventions section in
chapter 6), while at the same time the VT nominal voltage is 1 pu for the settings. Consequently the settings required in this
example differ from naturally expected by the factor of
.
The worst-case error for this application could be calculated by superimposing the following two sources of error: