How to maintain your OTI/WTI Winding Temperature Indicator

Keeping your OTI/WTI performing reliably

Capillary based mechanical transformer oil and winding temperature indicators are all but bulletproof. They've been designed and built for a long life in outdoor conditions. And they've done this for many decades, performing reliably across the world in every environment imaginable.

As such, there's not a whole lot of maintenance required to keep an OTI/WTI in peak condition. However, to secure maintenance-free operation, the installation on the transformer must be made with care. And there are some key checks to take into account for transformer asset management and regular transformer maintenance checks.



1. Pre-Installation Considerations

The best way to achieve correct operation and maximise longevity of your OTI/WTI is to ensure that the device is correctly installed in the first place. This begins with performing some pre-installation checks and following correct handling procedures.

DAMAGES CHECK:  Before installing an OTI/WTI, check for possible damage from transport handling. If you notice anything, contact Insulect, your local agent or the manufacturer.

CORRECT HANDLING:  Do not carry the instrument by the capillary. Do not twist the capillary when unwinding it, or bend too sharply – minimum radius is 25 mm. Clamp it along its entire length at approximately 400 mm intervals. Excess capillary can be wound in a spiral with minimum diameter of 100 mm.

THERMAL EXPANSION:  Leave at least 15% thermal expansion space in oil filled pockets.

ANTI-VIBRATION MOUNTING:  The non-vibration mountings included with the OTI/WTI must be used to prevent mechanical wear out caused by transformer vibrations.

OPERATING TEMPERATURE: Consider positioning the device to avoid long exposure to direct sunlight where ambient conditions are high. Installation shall prevent instrument casing temperatures over +70°C for standard OTI/WTI types.

Thermal Expansion allowance

Thermal Expansion allowance

Anti-Vibration mounting

Anti-Vibration mounting


2. Calibration check

Each OTI/WTI instrument is factory calibrated. Hence no further calibration is required for the life of the device, however a pre-installation calibration check should be performed to ensure that the device calibration is within tolerance limits, as follows.

Device calibration would be checked at 100 degrees Celsius, using a Dry Block Calibration Device or customer approved methodology. 

3. OTI/WTI Maintenance

Once your device is correctly installed and commissioned, there are only a couple of recommended checks from the manufacturer, shown below. For these, a regular control is suggested as part of transformer asset management schedules, and where required, certain maintenance carried out.

Protection Class IP 65

To eliminate the potential condensation build up inside the instrument, the OTI/WTI is provided with two desiccant capsules. These can get saturated after a time in operation and a replacement will become necessary. The colour of the gel will change from pink (when new) into white (after saturation). If condensation is occurring inside the instrument, replacement of the capsules will be necessary.

Mountings with Rubber Dampers - Seismic Type and Universal Type

The vibration dampers on these mountings are made of Natural Rubber, NR, (also called Isopren). The expected life time of these parts is estimated to be a minimum of eight years. Since Natural Rubber will age faster when exposed to direct sunlight, high ambient temperatures or corrosive environments, we recommend a regular check of these parts. When the rubber dampers become old they should be replaced. Please also note that it is important to mount these parts without any torsional stress.

More information can be found in the manufacturer's Instruction manual. You can download a copy of the Qualitrol OTI/WTI (AKM 345) Gen2 Instruction Manual below.

That's all the manufacturer recommendations for installing, commissioning and maintaining your OTI/WTI devices. If you follow these, you can expect your OTI/WTIs to perform as they have for so many others - as expected from a world class, CE approved, fully weather-proofed transformer temperature indicator for.

If you require any further information on OTI/WTIs, visit our product page, or contact our team.