Although the dry / cast resin transformers are safer than oil cooled ones from fire hazards, they can also cause disasters, if they exceed the rated temperature limits. 

Depending upon their insulation class, the upper temperature limit for operation will be between 120 to 180 ^OC. For economic reasons now a days the transformers are operated at “near limits” of temperature ratings. If suitable temperature monitoring system is not installed on the transformer then there is a very high risk of failure of insulation leading to transformer failure and associated hazards and loss. Hence there is a need for specialized and reliable temperature surveillance system.

As dry type / cast resin transformers are usually installed at utilities where large unbalanced load is a normal condition, it is necessary to monitor all the three phase windings of the transformer.

WTS are built specially for transformer application. The features provided in this series of scanners are in line with the requirements of transformer industry. Also these scanners are designed specially keeping in mind, the environment they would be subjected to. Normal temperature scanners are built keeping in mind that they will be installed in a control room.

The operating conditions are more severe for equipments meant for transformer application. The design for these scanners is more focused towards reliability, vibration handling, noise immunity, mounting ease etc. Designs of normal scanners are more focused on control room requirements for environmental conditions, which are much less severe than that are expected for transformer winding temperature scanners.

That is the reason we call these winding temperature scanners as Transformer Protection Relays.

At PECON, we manufacture products for both transformer as well as for control room application. We therefore insist and suggest to use appropriate equipment for specific need and application.

For the safety, reliability and long operational life of the transformer, a good temperature surveillance system is necessary.

A good temperature surveillance system should provide the following features:

•       Accurate temperature measurement for atleast three windings and core.
•       Capability of warning the user of excessive transformer temperature
•      Capable of switching off and isolating the transformer from line in case the transformer reaches a limiting temperature level.
•       Cooling fan control.
•      Alarm, trip and fan controls fully settable over operating range.
•       Sensor Fault monitoring and indication.
•       Maximum temperature registering.
•       Should be suitable for switchyard environmental conditions.

All PECON winding temperature scanners (Transformer protection relays) are designed to meet these basic requirements. Most of them will have many more added features incorporated.

Resistance Temperature Detector or RTD for short, is a wire wound device whose resistance changes with the temperature. Higher the temperature more the resistance. This change in resistance of these sensors allow us to measure the temperature.

The main reasons which make RTD based instruments the only choice for transformer winding temperature measurements are:

• Long life
• Very good stability
• Very good linearity
• Fully interchangeable
• High operating temperature range
• Reasonable cost and ease of availability.

Thermistors are mostly used in consumer goods. Their industrial use is limited to, where no indication is required and where fixed temperature cut offs with no settability is acceptable.

S-02 can easily be checked with ordinary multimeter. Sensor S-02 being a simple resistance, will show about 110 to 115 Ohms corresponding to ambient temperature between White and Red lead. Further, both the RED leads should show near zero ohms of resistance.

All S-02s coming to you from PECON are checked and calibrated to international standards and traceable to national standards.

Yes, this is necessary to minimize errors in temperature measurement due to lead resistance of the sensor S-02.

Field cable (copper cable) of 1.5 or 2.5 sq. mm. can be used for RTD lead connections. Keep extension leads as small as possible and try to avoid intermediate joints and terminations.

It is recommended to keep RTD wire lead length as small as possible to keep lead resistance errors minimum. However, this distance in some installations can be large upto few hundred meters. With three wire lead extension, 200 meters of 1.5 sq. mm extention leads will cause less than 1^OC error. 2.5 sq. mm wire would cause even lower errors.

Please refer our application note AN-202a (Installation of RTDs on CRT) and AN-205 (Installation of RTD in cast resin windings).

Alarm is a warning signal (either in the form of visual or audio) to indicate that winding temperature of the transformer has reached the alarming temperature limit.

Sometimes, the alarm condition may prevail for long time. In such condition, the alarm (buzzer) will sound for long time. Normally available buzzers in market may not run continuously for such long times as they are low duty type. Hence, ensure to use continuous duty type of buzzers / hooters.

Operating Environmental conditions for PECON WTI / WTS are specified as follows:

• Operating Temperature: 0 °C to 50 °C
• Humidity: 95% R.H. max. (non-condensing)

Some of our controllers are also available in extended operating temperature ranges, like

•  –20 Deg C to upto 70 Deg. C.
•   –40 Deg C to upto 70 Deg. C.

WTS is designed for marshalling box application. However, WTS can be mounted on the transformer enclosure directly, if the transformer is installed in a covered area.

Make sure that the surrounding ambient conditions are within the specified limits. Never mount WTS inside the transformer enclosure, as the temperature inside the enclosure is likely to be more than the permissible maximum ambient temperature limit.  

Fault relay is provided to indicate abnormal  / fault condition in WTI / WTS. These include the following

• No power to the scanner (controllers supplied with Electrical Fail fault)
• Sensor RTD open or short circuited

Please refer the engineering manual of the controller for exact fault relay specifications for that particular model.

This is very important feature as it can prevent a condition where transformer is operating in unprotected condition.

This relay control can be used either as a permissive contact in interlocks or may be wired to alarm annunciator circuitry.

As a standard engineering practice, relay contacts are shown as in “Un-energized” state.

During working of the equipment, the actual relay state may be different than that shown on the label / in the diagram. Therefore, it is necessary to confirm this from the engineering manual while making the wring diagrams.

This is particularly important in understanding the Fault relay contact conditions in some of our models.

RC snubbers are provided across normally open contacts to reduce generation of Electrical noise while switching external loads. These components are not shown in relay diagrams.

PECON winding temperature indicators / scanners and surveillance system are in operation across the world for past over twenty five years. Substation and switchyard condition are extremely critical and extremely high reliability is necessary.

Efforts are taken to make PECON products more reliable and this is an ongoing process at PECON.

We design our products keeping in mind at least 15 years of service life. In an unlikely event, the product might fail for some reason or the other. One of our policies that our customers appreciate the most is that “we do not try to make money out of servicing our products”. We provide free service for our products even if they have crossed their warranty period. In case our products require any repairs (not including the breakages or controllers that have damaged beyond repairs), the equipment can be sent to us on Freight Paid basis. We will do the required repairs and send back the equipment on Freight To Pay basis. All other statutory expenses also have to be borne by the user.

Our Standard Guarantee Clause is:

•  All equipments manufactured by us are guaranteed against manufacturing defects for a period of full twelve month in service or eighteen months from the date of dispatch, whichever is earlier.

This guarantee is subject to :

•  Equipments are operated strictly according to the detailed instruction given in instruction manual or if Instruction manual is not given then, when the equipment is operated within specified operational conditions and limits.
• Equipments are not tampered with.

Under this guaranteed the repairing or replacing of defective parts or equipments will be at our discretion and this will be either at our works or at the place of delivery depending upon nature of the problem and as decided by us.

DAS stands for data acquisition system. It is computerized plant / system monitoring system where signals of metering / current / temperature / level / vibration / flow etc etc from various places in plant are collected and monitored by supervisor staff in control room.

RS-232 is the most popular serial communication protocol but has its own limitations.

•  the distance of cable cannot be larger than 10-12 feet.
•  Only one equipment can be connected with each port

RS-485 is the most popular serial communication protocol for industrial environments. It has many advantages above the conventional RS-232 protocol

• the distance of cable can be as large as 1 km.
• Its 2 wire connection and many instruments (atleast 32) can be connected on the same two lines.
• The distance and no of instruments can be increased by using repeaters.

Most of our Winding temperature scanners are provided with a current signal for indication of temperature at remote location. This current signal corresponds to the measured temperature. Say for example, TR-7544 gives output signal of 4 ma for 0^OC, 12 ma for 100^OC and 20 mA for 200^OC.

Current signal facilitates error free temperature signal over long lead between the scanner and the temperature indicator (Remote winding temperature indicator – RWTI) mounted at remote place / in control room. This current signal is also used on many occasions for DAS application. However, it is advisable and suggested to use signal isolators for this signal while connecting it to DAS. This is important for safe and reliable operation for overall DAS system.

Yes, you get a copy of internal test report with each and every scanner manufactured by us. The test report also shows calibration status. All scanners are calibrated against standards traceable to the national standards.

All the RTDs are tested and are calibrated to standards traceable to national standards. The TCs can be provided on specific requests.

Yes, we do provide such facility at our works.

Most of the PECON WTIs manufactured today are with auxillary power input of 90-270VAC/DC. Therefore, you really donot have to worry on this matter and can safely use these without any consideration or difficulty. For older units, please check up with the works citing the serial number of the scanner for suitability or remedy.

Most of the PECON WTIs manufactured today are with auxillary power input of 90-270VAC/DC. Further, they can accept any supply frequency from 40 Hz to 400Hz. Therefore, you really donot have to worry on this matter and can safely use these without any consideration or difficulty.

Even for older units, 120VAC, 60 Hz is no problem.