Instruction Manual
Table Of Contents
- Major Features and Benefits
- Functional Overview
- System Overview
- Application Examples
- Collect Fault Information From Remote Branches
- Improve Fuse Coordination
- Fuse-Blowing Scheme Shortcomings
- Improve Fuse-Blowing Schemes With the Fault Transmitter and Receiver System
- Fuse-Saving Combined With Fuse-Blowing Schemes
- Improve Feeder Cable First-Span Protection
- Implement a Low-Cost Fast Bus-Tripping Scheme
- Tripping the Right Recloser Faster
- Safety Information
- Network Deployment Overview
- Device Installation
- Dimensions
- Specifications
- Appendix A: Manual Versions
- Appendix B: Two-Branch Application
- Appendix C: Link Budget Analysis
- Appendix D: SEL-RP50 Fault Repeater Detailed Implementation
- Technical Support
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SEL-FT50/SEL-FR12 Fault Transmitter and Receiver System Instruction Manual Date Code 20210405
Appendix C: Link Budget Analysis
Appendix C: Link Budget Analysis
Overview
A radio link budget accounts for all losses and gains in a radio link from the
transmitter to the receiver. Link budget calculations are used to determine the
amount of link margin available for a given radio link. The link budget includes
five components: radio transmit power, antenna gains, cable and path losses,
interference margin, and radio receiver sensitivity. For a reliable link, the receive
power must be greater than the effective receive sensitivity. The link margin is the
difference between received power and effective receive sensitivity. The goal of
link budget calculation is to account for all of the system and path gains and
losses to determine if an adequate link margin is available (see Figure 31).
Transmitted and Radiated Power Requirements
FCC and IC regulations for 900 MHz ISM (industrial, scientific, and medical)
band radios such as those used by the SEL-FT50 place limits of +30 dBm on
maximum radio transmit power and +36 dBm on maximum Effective Isotropic
Radiated Power (EIRP). EIRP is a measure of the amount of power radiated from
the main lobe of the transmitter antenna, and is calculated by using Equation 1.
Equation 1
The specified transmit power for radio embedded in the SEL-FT50 includes the
antenna gain. Because there is no method of connecting an SEL-FT50 to an
external antenna, you do not need to be concerned with violating EIRP require-
ments if you do not modify the device.
Figure 31 Sample Link Budget
EIRP
TX Power Cable Loss
Attenuation
Antenna
Gain
Free-Space Path Loss
Clutter/Obstruction Loss
Polarization Mismatch
Fading Loss
Antenna
Gain
Cable Loss
Attenuation
RX Power
Interference
Margin
Link Margin
Effective
RX Sensitivity
Specified
RX Sensitivity
Signal
Power
(dBm)
Component Radio RadioFeed FeedAntenna AntennaPath Loss
EIRP (dBm) TX Power (dBm) Line Loss (dB)
Attenuation (dB)
–
Antenna Gain (dBi)+
–=