Qualitrol T/Guard 408 Fibre Optic Temperature Monitor

Qualitrol T/Guard 408 Fibre Optic Temperature Monitor


The Qualitrol T/Guard 408 & 408XT are rugged, real-time, multi-channel fibre optic hot spot monitoring systems for dry-type and oil-filled transformers.

Used in conjunction with the Qualitrol T2 fibre optic temperature probes, the provide high accuracy, real time temperature monitoring of transformer hot spots.

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A multichannel fibre optic temperature monitor for transformer hot spot measurements

The 408 & 408XT monitoring systems have been developed with long-term performance and stability in mind. They provide the accuracy of fibre optic measurement with the toughness and long-term resistance to failure required in transformer applications.

Coupled with the 408 system, the Qualitrol® T2 fibre-optic temperature probes provide accurate and direct temperature monitoring of transformer windings. This solution provides a realistic, real-time view of winding conditions that is quicker and more accurate than top oil thermocouple measurements, and greatly complements indirect measurements based on thermal models.


The Qualitrol T2 Fibre-Optic Probe

This temperature probe is designed to withstand initial manufacturing conditions, including kerosene desorption and heat runs, as well as long term oil immersion and vibration.

The T2 probe consists of a 300-microns OD solid-state crystal and optical fibre sheathed with an oil permeable protective PTFE Teflon tube. Only chemical resistant dielectric materials are used for these temperature probes. The temperature range is -80 °C to +250 °C. The probes can be embedded in a standard spacer or attached directly onto any other location inside power transformer copper windings.

All T2 optical temperature probes are available in custom length from 1 to 25 meters.

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Tank wall optical feedthrough


Specifically designed for transformer tank walls, this feedthrough has a simple design that provides both toughness and long-term leak-free operation. It is made from 316 stainless steel and relies on proven glass-to-metal bonding techniques.

The feedthrough uses 1/4” NPT ANSI threads and can be installed directly into the tank wall or on a tank wall mounting plate. No O-rings are used.

External fibre-optic extension cables


These cables are made with a polyurethane jacket reinforced with Kevlar threads and are designed to withstand the harshest conditions. External fibre-optic extension cables come in standard 5 or 10 metre lengths. Custom lengths are also available from 1 metre to 1 kilometre.

The temperature range is -50 °C to +85 °C. Cables should be routed into protective conduits or tracks.


Tank wall mounting plate & JBox2


Up to 24 feedthroughs can be mounted on a tank wall mounting plate. The plate is made with carbon or stainless steel 316. Tank wall mounting plates can be customised in size or material according to customer specifications, with larger plates allowing more feedthroughs.

The mounting plate comes with the JBox2 protective enclosure.


NEMA-4 Enclosure


The T/Guard system can be mounted in a NEMA-4 enclosure that houses and protects the instrument for long-term exterior use.

All fiber-optic extension cables are connected inside this enclosure. The NEMA-4 enclosure includes a clear polycarbonate window-door and is compliant with NEMA/EEMAC Type 4 and 12 standards.


Download Qualitrol 408 Brochure

Fibre Optic Monitoring System


Qualitrol 408, 408XT Features

  • Provide essential data during transformer heat run

  • Maximise cooling efficiency with accurate hot spot temperature measurement

  • Optimise loading dynamically without compromising transformer life

  • Complements predictive hot-spot algorithm simulations

  • Compatible with Qualitrol Q-Link™ for Apple® iPhone®, OptiLink and OptiLink-II

  • Available with 4, 6, 8, 10, 12 or 16 channels

  • 408XT - Ethernet and Smart grid ready, and incorporates, among others, IEC-61850 protocol

408 Options

  • Number of channels – 4, 6, 8, 10, 12 or 16 optical channels



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