Scaling Examples - Allen-Bradley Rockwell Automation 857 User Manual

4-18
Supporting Functions
857-UM001A-EN-P – July 2009

Scaling Examples

Example 1
Average active exported power is 250 MW.
Peak active exported power is 400 MW.
Pulse size is 250 kWh.
The average pulse frequency will be 250/0.250 = 1000 pulses/h.
The peak pulse frequency will be 400/0.250 = 1600 pulses/h.
Set pulse length to 3600/1600 – 0.2 = 2.0 s or less.
The lifetime of the mechanical output relay will be
This is not a practical scaling example unless an output relay lifetime
of about six years is accepted.
Example 2
Average active exported power is 100 MW.
Peak active exported power is 800 MW.
Pulse size is 400 kWh.
The average pulse frequency will be 100/0.400 = 250 pulses/h.
The peak pulse frequency will be 800/0.400 = 2000 pulses/h.
Set pulse length to 3600/2000 – 0.2 = 1.6 s or less.
The lifetime of the mechanical output relay will be
Example 3
Average active exported power is 20 MW.
Peak active exported power is 70 MW.
Pulse size is 60 kWh.
The average pulse frequency will be 25/0.060 = 416.7 pulses/h.
The peak pulse frequency will be 70/0.060 = 1166.7 pulses/h.
Set pulse length to 3600/1167 – 0.2 = 2.8 s or less.
The lifetime of the mechanical output relay will be
Example 4
Average active exported power is 1900 kW.
Peak active exported power is 50 MW.
Pulse size is 10 kWh.
The average pulse frequency will be 1900/10 = 190 pulses/h.
The peak pulse frequency will be 50000/10 = 5000 pulses/h.
Set pulse length to 3600/5000 – 0.2 = 0.5 s or less.
The lifetime of the mechanical output relay will be
6
50x10 /1000 h = 6 a.
6
50x10 /250 h = 23 a.
6
50x10 /417 h = 14 a.
6
50x10 /190 h = 30 a.