TS – Temperature Supervisor for Oil-immersed Transformers

Thermal monitoring of oil-immersed transformers is essential for their safe operation.  This is the case not only for large-scale equipment, but also for medium-sized transformers and distribution transformers, thus achieving maximum return from the investment in these assets without jeopardizing their life cycle.

The Temperature Supervisor’s competitive cost allows the inclusion of thermal monitoring for small and medium size transformers. The advantage of digital temperature monitoring is no longer reserved for higher power transformers only.  The TS eliminates the need for manual readings taken using electro-mechanical equipment, with significant increase in the level of accuracy, reliability and more efficient use of cooling both in operations and maintenance areas.   The monitor features an input for an RTD sensor for measuring the temperature at the top of the oil, and an input for external CT of the clip-on type (optional), for measuring load current, performing the calculation of the temperature of the winding by thermal imaging. Optionally, the TS can be equipped with two additional temperature sensor inputs for measuring, for example, ambient temperature, or the on load tap changer or others.

Main Features:

• IED (Intelligent Electronic Device) designed specifically for substation yard conditions (interference, extreme temperatures);

• Real time temperature reading on display, with programmable display mode: indication of highest temperature, automatic screen roll or fixed channel reading indication;

• High-glow LED type display for easy visualization; and operation in extreme temperatures;

• Serial communication port RS485 (optional) for integration into supervision or remote monitoring systemsallowing the establishment of a temperature monitoring network covering the entire facility. Open communication protocols   Modbus   RTU or DNP3.0;

• Self-calibrating Input for Pt100W at 0ºC RTD type temperature sensors, ensuring high-level accuracy and stability throughout the entire ambient temperature range;

• Programmable analog output (optional) for remote temperature readings, user selectable for display of highest temperature or a pre- defined temperature. Programmable output range: 0…1, 0…5, 0…10, 0…20 or 4…20mA;

• Output relays for alarm indications, transformer trip, self-diagnostic and command of two-stage forced cooling with Automatic/Manual selection. Forced activation of cooling in case of lack of auxiliary power, internal fault or fault in temperature sensor (NC relays);

• Internal clock with date and time and non-volatile memory for storage of readings (optional);

• Self-diagnostic for internal fault detection. Total absence of mechanical parts for parameter setting and calibration.

• Additional inputs for measuring of up to two additional   temperatures (for sensor Pt100W at 0ºC), allowing measuring of the temperature of the on load tap changer, ambient temperature or other;

• Non-volatile memory for storage of temperature  readings  and alarm events, trips and activation of forced cooling, based on internal clock with day, month,  year, hour, minute  and second. A memory recording can be started by:

– User defined time interval between recordings, or;

– Variation of any temperature monitored higher than the dead band selected by users, in ºC, or;

– State change in any output relay (control of cooling, alarms, trips or self-diagnostic).

• Pre-cooling can prolong the life cycle of insulation ontransformers subject to overloads, by activating cooling groups whenever previously user selected load levels are reached. Taking advantage of the high thermal inertia of oil, the forced cooling system is activated even before the increase in temperature occurs, this increases the times required to achieve high temperatures, which would cause an accelerated loss of lifetime for the insulation.  The following are user programmed:

– Load percentage for activation of the first forced cooling group;

– Load percentage for activation of second forced cooling group;

– Hysteresis for shut down of forced cooling when load level drops.

• The Fan Exercising function keeps fans from remaining inactive for long periods of time on transformers operating at low load levels or during periods of low ambient temperatures.  This prevents axle blockage from accumulation of dirt or grease dry out and bird nesting.  Fans are activated daily, in accordance with the equipment’s internal clock and dependent on the selections made by users:

– Time and minute for switching fans on;

– Total daily fan operation, between 0 and 100 minutes.

Pt100W at 0ºC Temperature Sensor

The measurement of the top oil temperature in transformers is usually performed through temperature sensors installed in a “thermal- well” found on the cover of the transformer.  Sensors used must be of the Pt100W at 0ºC type. If necessary, Treetech offers a sensor suited for installing in thermal-well, (special dimensions by consultation), supplied as optional accessory.

External Clip-on CTs

The use of external clip-on CTs allows the installation of the Temperature Monitors without the direct connection of a bushing CT to the instruments. This eliminates   the risk of accidentally opening the CT secondary, besides simplifying the installation with the transformer energized.

Cubicles

The Temperature Supervisors   TS must be installed protected from the weather, and for this reason, it is usually installed inside control cabinet or building.  For those cases where this is not convenient, such as for example in refurbishing older transformers, the TS can be supplied in easy-to-install weatherproof cubicles.

Ambient Temperature Sensor

The Temperature Supervisors   TS can have two additional inputs (optional) for temperature sensors, which can be used in measuring ambient temperature, load tap changer temperature, etc.

If used for ambient temperature, it is measured by way of Pt100W at 0ºC type temperature sensor installed in thermal shelter, minimizing errors caused by sun, rain, wind, etc. on the readings.  If required, Treetech has sensors and thermal shelters suited for this type of reading, supplied as optional accessories.