Manholes

Slide1: 

Combustible Gas Monitoring in Underground Electric Utility Manholes and Vaults A Low Cost Gas Sensor System EPRI August 30, 2001

Slide2: 

Underground power utility vault Manhole fires & explosions are becoming commonplace in major cities with aging underground infrastructures. Problem: No sensor systems are in place to early detect build up of gases that cause manhole fires and explosions.

POTENTIAL SOURCES OF EXPLOSIVE GASES: 

POTENTIAL SOURCES OF EXPLOSIVE GASES • Thermal decomposition of cable insulation resulting from electric arcing or I2R heat: methane, ethylene, acetylene, carbon monoxide • Hydrolysis of water due to arcing with carbon present: hydrogen, carbon monoxide, methane (secondary) • Pipeline leaks of natural gas: methane, ethane • Leaks of sewer gas: methane, ethane • Leaks from underground storage tanks: gasoline vapors

Combustible Gas Mixtures: 

Combustible Gas Mixtures • Gases like hydrogen, carbon monoxide, methane/ethane, and other hydrocarbons will form mixtures that can reach concentrations equal or above the LEL. • Ignition will occur at the proper combination of oxygen with the combustible gases and high temperature. • At low oxygen levels resulting from air displacement by increased concentrations of combustible gases, explosive conditions may not occur (smoking manhole). • The production rate of combustible gases is a key factor in establishing the type of manhole event.

Slide5: 

Design Criteria Functionality (I.D., Sensor OK, thresholds, comm.) Simple Operation (Unattended) Extended Time Interval Between Calibrations Rugged Waterproof (Sensors and Electronics) Easy Field Deployment Low Cost

Slide6: 

Low Cost Combustible Gas Monitor Concept Sketch Indicator Lights Red Yellow Green MOS Sensor Flame Arrestor Gas Permeable- Water Rejecting Membrane Power Connection PC Board Electronics - + - + Communication Port Powerline Communications Cellular Modem Communication Wireless Communications

Slide7: 

Why MOS Sensors? Low Cost Long Life Selective and Sensitive enough for this application Fast enough for this application Able to function in the underground utility vault’s nasty environment

Slide8: 

Advances in Technology Commercial Gas Sensors New planar MOS sensors with high stability, low sensitivity to humidity, long life and low cost are now available. GALAI knowledge of MOS sensors Effect of temperature on sensor sensitivity Effect of oxygen on sensor baseline Effect of humidity on sensor stability Effect of long term drift on threshold levels

Slide9: 

Electronics for Sensor Operation Factory pre-programmed powerful and low cost microprocessor chips are now available; also compact power supplies and sensor temperature controllers. Advances in Technology Microcomputer board Power supply

Slide10: 

Communications Advances in Technology

Itron Wireless Communications Network Communicating to Galai Vault Monitors : 

Itron Wireless Communications Network Communicating to Galai Vault Monitors

System Hardware: The Box: 

System Hardware: The Box

Slide13: 

System Hardware: The Board

Slide14: 

System Hardware: Sensor Head

Concluding Remarks: 

A gas monitor has been designed and built that could: 1) help utilities to diagnose an incipient problem in underground lines and 2) aide in the prevention of fatal accidents caused by manhole explosions Advances in sensors and electronics support a low cost device Input from utilities are required for final product design (e.g. communication protocols) Concluding Remarks

Slide16: 

• Prevent outages and lost revenue • Reduce system damage and repair costs • Improve customer and crew safety • Enhance corporate image • Reduce lawsuits from gas, explosion, fires Expected Benefits