TXU ERCOT Metering Project

Background:

Due to deregulation of the Texas Utility Market, TXU Electric was forced to split into TXU Generation and TXU Transmission (now known as Oncor). ERCOT (the Texas ISO) enacted requirements to introduce revenue metering at every generating and startup / standby transformer unit. On the TXU system, no revenue metering existed at any power plants. TXU engaged MSE to provide this metering on an Engineer / Procure / Construct (turn-key) basis. The scope of the project was to install high voltage (69 kV – 345 kV) metering, complete with ERCOT approved telemetry at 110 units at 23 different locations throughout the state. The deadline for meeting this requirement was December 1, 2001.

Critical Timing:

MSE was awarded the project in mid-November of 2000. In January, 2001 – the Texas state legislature instituted an additional mandate that all power plant locations have revenue grade metering installed with at least dial-up telephone access no later than May 1, 2001. The interim systems did not necessarily have to comply with the full set of ERCOT requirements required by December 1, 2001.

The MSE Project Team:

MSE set up a project office at TXU’s Fort Worth, Texas T&D Headquarters. The entire project team was resident in this office, including design engineers, drafting personnel, project scheduling / coordination personnel (managing personnel, construction equipment, vendor shipments, testing, and coordinating with outage requirements for 110 units), construction supervisors, and test engineers. MSE hired a contractor to provide qualified labor for the installations.

MSE Design Innovations:

A recurring series of problems was encountered at most of the generating units these included: low voltage metering was impractical due to iso-phase bus connections and there was very limited space available on the high voltage sides of the GSU transformer; traditional current transformer accuracy ranges would not be effective for both generation and back-feed conditions, since the disparity in the amount of current flowing under these conditions was very different (a traditional 0.3 ANSI accuracy class CT maintains rated accuracy from 10 – 100 % of rated primary current, but during back-feed, the current flowing was 2 – 3 % of full generation current). MSE worked with a major manufacturer of instrument transformers to provide an extended range, slip-on bushing current transformer to be installed on the HV bushings of the GSU and Start-up / Standby Transformers. This saved a significant amount of space and cut outage time required for the installation in half. The extended range CT’s were rated for 0.3 ANSI accuracy from 1 – 150 % of nameplate primary current on a continuous basis. This allowed TXU to maintain ERCOT required metering accuracy without having to resort to optical CT’s (which cost over 4 times as much as the ERCT’s). In addition, MSE and TXU worked to develop an interface from the meters to the TXU fiber optic communications network to allow ERCOT and TXU to access all metering data via the TXU computer network. This solution also provided realtime generator output data to TXU generation to assist with unit operation.

Results:

MSE completed both phases of the project on schedule and within budget. TXU claims that they were the only major investor owned utility in Texas to comply with both deadlines.