SDG&E, in the USA, deploys Treetech Sensors and IEDs for On-Line Monitoring and Control of Transformers and Reactors

Since 2003, the company San Diego Gas & Electric (SDG&E), in San Diego, California, has used Treetech on-line transformer monitoring and control systems with a view to increasing operating safety for two single-phase 525/230kV 1120MVA auto-transformer banks (GE and Siemens) and one bank of single-phase 525kV reactors (Siemens) at SS Miguel.

Parameters Monitored
Treetech’s on-line monitoring and control solutions in operation in the substation include the following equipment and intelligent sensors – IEDs:

– Bank 80, GE auto-transformers:

• BM – Capacitance and Tangent Delta of GE 525kV and 230kV bushings;
• GMM – Gas Dissolved in oil (H2);
• GMM – Oil in Water Content (ppm) and Saturation of Water (%)
• TM1 and TM2 – Primary, secondary and tertiary winding and oil temperature;
• MBR – Membrane Rupture in conservation tank;
• SPS – Position of TAP on Load, Control and Parallelism between phases and between banks.

– Bank 81, Siemens auto-transformers:

• BM – Capacitance and Tangent Delta of HSP 525kV and ABB 230kV bushings;
• GMM – Gas Dissolved in oil (H2);
• GMM – Oil in Water Content (ppm) and Saturation of Water (%)
• TM1 e TM2 – Primary, secondary and tertiary winding and oil temperature;
• MBR – Membrane Rupture in conservation tank;
• SPS – Position of Tap on Load, Control and Parallelism between phases and between banks.

– Reactor Bank, manufactured by Siemens:

• BM – Capacitance and Tangent Delta of HSP 525kV bushings;
• TM1 – Oil and winding temperature;
• MBR – Membrane Rupture in conservation tank.

Architectures for Integration
Since SS Miguel is unassisted, it is essential that these sensors and equipment be linked to the company’s remote systems. The decentralized architecture adopted by Treetech for its IEDs presupposes that these IEDs operate totally autonomously and independently, carrying out their functions and making on the spot decisions, with several outputs being available affording integration in different levels.

At a first level, the IEDs can be integrated with the company supervision system through:

• Dry contact outputs for alarms and event annunciators signals and the substation’s RTUs, alerting the operating center of possible events. In this case a maintenance team is actuated to go the site and check on the occurrence.
• IED dry contact inputs connected to the RTU outputs, allowing commands to sent remotely, for example, raise or lower OLTC.
• Connection of analog outputs of IEDs to RTU, allowing remote reading of variables.

At the Miguel substation, currently, alarm contacts and dry inputs of IEDs for connection with the event annunciator and the substation’s RTU are in use. Analog outputs are not used, since a serial communication network is currently being set up in the substation in order to take integration to the next level, as described below.

At the next level of integration, IEDs maintain their autonomy feature, but are connected to digitizing or remote monitoring systems through their serial communication ports. This allows acquisition of every variable measured and the occurrence of events, without exception, as well as query and changes to any parameter setting in the equipment, plus access to the internal memory for readings and events. Treetech’s Smart Trafo previously supplied to SDG&E, can be used to perform these functions.

Field experience
It has been shown that the objective for installing monitoring IEDs – increasing operating safety and reliability for auto-transformers and reactors – was achieved when, in late 2004, the BM bushing monitor issued a high capacitance alert for one of the GE 525kV bushings, thus avoiding a possible failure for that equipment, a fact that was later proven by performing off-line measurements.

In order to obtain the most recent functionalities available for their bushing monitoring system, SDG&E contracted Treetech’s Retrofit Program for up-dating of the existing equipment. To this end, Eng. Marcos Alves and engineering trainee Daniel Santos, from Treetech, visited substation Miguel between February 13 and 15, 2007 to commission the new system and deliver operation training to users.

Among the many new and different functionalities afforded by the system up-date is the new algorithm for detection of loss of signal from the bushing tap, which allows auto-transformers and reactors to be shut-down without unnecessary warnings. This functionality is particularly important for the bank of reactors, which is switched on and off frequently during regular operation of the power system.

The Retrofit Program also included the up-date of temperature measurement equipment on autotransformers and reactors, by installing the new TM1 and TM2 temperature monitors. This way, the forced ventilation systems, previously controlled by mechanical thermometers, started to operate more accurately, thus ensuring lower operating temperatures for the machines, in addition to affording more reliable over heating protection.

Treetech Supply

1) IED Sensors on auto-transformers, reactors and control room:

• 05 BM-MM – Bushing Monitors – Measurement Module
• 03 BM-HMI – Bushing Monitors – Interface Module
• 06 GMM-Sensor – Gas and Moisture Monitor – Sensor Module
• 06 GMM-MMI – Gas and Moisture Monitor – Interface Module
• 10 MBR –Membrane/Bag Rupture Monitor
• 10 TM1 – One winding and oil temperature monitor.
• 07 TM2 – Two windings Temperature Monitor.
• 06 SPS – Parallelism Supervisors.

2) Smart Trafo Digitizing Software:

Modular and scalable digitizing system that allows:

• Safe Access via commercial browser.
• on-line visualizing of readings and events.
• Data base, reporting on chart or table capability.
• Alarm indication system and sending of notices by email or SMS.
• Other IT functions.

3) Engineering Services:

• Support to project adaptations for equipment retrofit purposes.
• Commissioning of IEDs at substation Miguel.
• Training for SDG&E technicians and engineers in installing, operating and parameter setting for IEDs.