Automated Circuit Breaker Monitoring

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1. Introduction
This report presents work done on Automated Circuit Breaker Monitoring project during
the year of 2006. Previous work is described in annual reports for 2003 and 2005. During
year 2006, we have developed two CBM devices. Both devices are installed in
CenterPoint Energy 345kV substation Obrien in south Houston. The first CBM device -
CBM1 is installed a year ago. The second one, CBM 2, has implemented new features:
New signal conditioning board, communication protocol and time synchronization.
Detailed Functional Requirement Specification for Automated Circuit Breaker
Monitoring system is given in Appendix. Final reports for year 2003 and 2005 are also
provided in the Appendix.

2. CBM
Signal conditioning boar, communication protocol and time synchronization module have
been modified and upgraded during the 2006. These modifications are necessary to enable
I jmonitoring over the entire power system and to reduce cost of the device.

2.1 Signal Conditioning Module
New signal conditioning board with better over voltage protection on input side is
developed, tested in lab and installed as a part of CBM 2 device. It limits the maximum
voltage on the input amplifier to 220V, which is harmless for amplifiers. Functionality of
new signal conditioning board is shown in Figure 1.1. It has implemented two features:
over voltage protection and voltage level conditioning. Over voltage protection is realized
with high voltage suppression Zener diodes.



2.2 Communication Protocol
New communication protocol for CBM provides multipoint communication and time
synchronization enabling usage of several CBMs in one substation. We established pointto-
multipoint communication network. Considering the fact that concentrator has to
communicate with more than one DAU at the time, the main idea is that concentrator is
polling all of DAUs in a schedsuled way in order to determine if any of DAUs has a file
to send. If it has, the Master unit initiate file transfer. The Master unit communicates with
slaves using comands. Commands are divided in two parts. In the first part master sends
CBM ID and in the second part it sends command to be executed.



2.3 Time Synchronization
Time Synchronization is implemented in the CBMs using a GPS clock receiver and
wireless modems for time distribution to devices in a switchyard. The GPS
Synchronization signal (1PPS) is distributed from the master radio modem located in the
control house to the slave units at each CBM device. In this way only one GPS receiver
per substation is needed. Radio modems used for CBM have implemented the option for
1PPS distribution from master modem to several slave units.