Wireless Temperature Sensing Solution for Switchgear

Problem: Continuously and Cost-effectively Monitoring Switchgear Temperature

Nov 1st, 2010
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Problem: Continuously and Cost-effectively Monitoring Switchgear Temperature

Switchgear, which serve as important points of control within power distribution systems, transformers and other transmission and distribution components, are susceptible to failure if not closely monitored and controlled. Increased loads can greatly stress switchgear. The resulting increases in temperatures of critical switchgear components can cause significant degradation of metal contacts and insulation. In turn, this increases the probability of internal short-circuits or increases in contact resistance, which, if unchecked, can lead to system failure and possibly cause personal harm to system operators. The problem is especially relevant in emerging economies where the burgeoning need for power greatly stresses outdated legacy electric power infrastructure. Conventional methods of monitoring switchgear temperature are expensive and not entirely effective. Surface acoustic wave (SAW) technology can provide a passive (no battery or energy harvesting), wirelessly-interrogated temperature measurement solution that is ideally suited for switchgear.

Situation: Conventional Methods are Expensive and Provide Sporadic Coverage.

Hot spots within switchgear are readily identified by taking thermal images of cable connections, insulators and bus bar connections. Non-contact testing with infrared (IR) cameras addresses a variety of safety concerns when operating in a high voltage/high current environment. Thermal images, however, have distinct disadvantages:

  • Spot assessments,
  • Cost,
  • Reference images in winter and spring,
  • Images distorted by dust, and
  • Absence of real-time data.

Other traditional temperature measurement methods, including battery powered sensors, also have distinct disadvantages:

  • Burden of battery replacement,
  • Restricted access to equipment compounding battery replacement burden,
  • Environmental impact, and
  • Time consuming installation.

Solution: SAW-based Switchgear Temperature Sensing

A SAW-based temperature measurement solution for switchgear includes SAW temperature sensors mounted at critical contact points within the switchgear box and a reader capable of interrogating multiple SAW temperature sensors in rapid sequence. The reader antenna is mounted within the box, offering radio frequency shielding of the interrogation process by the box itself. The locally powered reader sends short radio frequency (RF) pulses into the switchgear, and if the pulses are at the frequency of the sensor the sensor receives, modifies and passively returns the pulses. Returned pulses contain information related to sensor temperature.

SAW-based temperature sensors take advantage of the controlled change in material properties of a crystal, automatically converted to an electrical signal via the piezoelectric effect. The sensing mechanism involves electrically inducing a surface acoustic wave into a piezoelectric material and then reconverting the energy of the wave-influenced by the temperature the sensing element is exposed to-back into an electrical signal for temperature measurement.

One significant advantage of SAW devices is their passive operation, which makes them very amenable to operation in harsh environments via wireless interrogation and inherently have low maintenance requirements. A wireless SAW-based temperature sensing solution consists of a reader-RF Transceiver-electromagnetically linked to a SAW sensing element.

Solution Differentiators

A SAW-based temperature measurement system addresses many of the disadvantages associated with other means of temperature monitoring:

  • Continuous monitoring: A SAW-based temperature measurement solution allows continuous monitoring of temperature and thereby provides the ability to continuously monitor the switchgear for adverse events or the prelude to adverse events.
  • Cost: The cost of a SAW-based temperature monitoring system is much lower than traditional methods of temperature monitoring, including IR thermography.
  • No seasonal effects: Calibration consists of a one-time adjustment to a software parameter that accounts for manufacturing variations of the sensing elements. The sensors can be calibrated at any known temperature within their stated operating range, so seasonal effects do not affect a SAW-based temperature monitoring solution. Calibration to a reference temperature allows accuracy over the entire operating range. The sensor typically is calibrated once at installation and remains calibrated for years of reliable operation.
  • Dust: SAW-based temperature measurement solutions are immune to the effects of dust accumulation.
  • Environmentally friendly: SAW wireless sensors are passive-do not require batteries-and thereby provide an environmentally friendly temperature measurement solution.

SenGenuity's TempTrackr system is a key solution differentiator that measures temperature at the source of expected failure: the bus bar connection, the cable connection and the circuit breaker connection. Unlike other solutions that measure the ambient temperature of the air within the switchgear box, the TempTrackr system measures the temperature at the most vulnerable points within the switch. The core value of the system lies in its ability to provide early warning signs of expected failure by continuously monitoring the temperature of critical switchgear components.

Key attributes:

  • Enhanced operator and asset safety,
  • Wireless temperature sensors (SAW based),
  • Passive (no batteries and no energy harvesting),
  • RS232 communication protocol, and
  • Control room software with alarm capability.

TempTrackr SAW Sensor System

SenGenuity's TempTrackr SAW-based temperature sensing solution fully addresses the unique needs of transmission and distribution infrastructure temperature monitoring. The TempTrackr SAW sensor system is capable of wirelessly monitoring up to 18 passive SAW temperature sensors per breaker box. Temperature data is obtained from the sensor via a wireless reader-connected to an antenna-that is located within the switchgear cabinet. The wireless reader can generate temperature data on demand or on a continuous basis. For switchgear original equipment manufacturers interested in integrating the TempTrackr system into the switchgear control architecture, SenGenuity can provide wireless readers capable of communication via RS232. For end-users of legacy switchgear or end-users interested in monitoring switchgear temperature remotely, SenGenuity can provide control room software with alarm capabilities.

The various components of the TempTrackr system have undergone certification tests and are in compliance with European conformity (CE) and Federal Communications Commission (FCC) requirements.

Key features:

  • Wireless passive temperature sensors,
  • -40C to +220C operating temperature range,
  • 428 mHz to 439 mHz RF operating range, and
  • Scalable system configurations:
  • Six-sensor system-basic configuration,
  • Twelve-sensor system-with sensors partitioned into two isolated sub-compartments, and
  • Eighteen-sensor system-with sensors partitioned into three isolated sub-compartments.

About SenGenuity, a division of Vectron International: SenGenuity, an operating division of Vectron International, is a provider of sensor solutions for performance and reliability in critical data gathering applications. Coupling its precision sensor solutions with Vectron's surface and bulk acoustic wave technology, SenGenuity delivers innovative solutions for measuring the condition of fluids in challenging, embedded environments.

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