Overheating is one of the largest single causes of failure of critical low-voltage switchgear, such as molded case circuit breakers (MCCB) and air circuit breakers (ACB). Modern circuit protection is provided by a microprocessor-based digital overcurrent relay that operates by measuring current rather than heat. Therefore, abnormal heating caused by loose connection bolts, ventilation failure, or contact wear is usually not detected by traditional circuit protection devices. This abnormal heating can cause premature failure of the switchgear and also constitute a potential fire hazard.

Many power-critical applications, such as data centers, hospitals, utilities, and mining sites, use technologies such as thermal imaging to help identify overheating in switchboards, but this method is only valid for a specific time "snapshot".

The latest development of microprocessor-based circuit breakers provides the option of continuously monitoring the temperature of the contacts and terminals, which can significantly reduce downtime and reduce the risk of fire.

If an abnormal situation is detected, this information will be transmitted to the building management system (BMS) so that facility managers can develop preventive maintenance plans before a serious power outage or fire accident occurs.

NHP is proud to bring a unique system to Terasaki ACB that offers condition-based temperature monitoring as an option.

This fully integrated temperature condition monitoring system continuously checks for overheating abnormalities that may be caused by main conductors, contacts, and connection problems-or this temperature monitoring concept as well known by the European electrical industry 3C.

The state and wear of the contacts are determined by temperature measurement using NTC (negative temperature coefficient) thermistors. Self-diagnosis is achieved by directly measuring physical characteristics. Each phase of the circuit breaker contacts is equipped with its own thermistor.

The thermistor will continuously analyze all three phases every 10 milliseconds. The thermistor used is a glass package package, a diode shape, and an axial tin-plated Dumet (copper-clad nickel-iron) wire.

It is important to distinguish between direct, continuous measurement and algorithmic modeling of contact wear indications. The latter is inherently less accurate, so it is more likely to cause false alarms or lower protection.

Direct continuous monitoring of contact temperature provides valuable input for preventive and predictive maintenance programs.

If an abnormal temperature occurs, the ACB's integrated protection relay will issue an overheating alarm on the LCD screen installed on the panel, close the non-voltage output contact and send a message to the Modbus network.

In order to supplement the over-temperature protection of the integrated circuit breaker and extend the monitoring level to other areas of the switchboard, such as the busbar area, an external 3C module can be used.

These external modules use non-conductive fiber optic probes, which can be directly fixed to the bus with special lugs. The temperature is measured by transmitting laser pulses along a fiber optic cable to a fluorescent spot located on the terminal lug.

The phosphor dots are excited by the laser and start to emit light. The module then measures the time for the phosphor to emit light (related to temperature), and then calculates the temperature that can be transmitted over the network.

This information enables facility managers to plan any necessary maintenance. The implementation of condition monitoring technology like this is equally applicable to both old and new installations.

When considering replacing or upgrading its protection and switchgear, end customers considering retrofitting solutions to replace aging switchgear can also take advantage of such new solutions. This partner content is brought to you by NHP. For more information, please visit contact your local NHP consultant or visit www.nhp.com.au.

Charlotte Pordage is the editor of Utility magazine, a position she has held since November 2018. She joined the team as the associate editor in October 2017, after improving her writing and editing skills in a series of print and digital publications. Charlotte graduated from Royal Holloway, University of London in 2011, with a joint honorary degree in English and Latin. When she does not organize Australia's only dedicated practical magazine, she usually sees her riding a horse or curled up in a good book.

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