power transformer Temp Measurement indicators

Temperature indicator

1. POWER TRANSFORMER TEMPERATURE MEASUREMENT

2. OIL/WINDING TEMPERATURE INDICATURE (OTI/WTI) In Transformer, an  OTI (Oil Temperature Indicator)  is a temperature indicating instrument used for monitoring and displaying the temperature of dielectric oil filled in the Transformer tank. The dielectric oil filled in the tank of a transformer plays a crucial role in insulation and cooling of the Transformer. This oil maintains the temperature of the Transformer within a safe limit and improves the energy efficiency. Therefore, it is important to continuously monitor the temperature of the oil to ensure that it is within the specified limit. The Winding Temperature is an important parameter that significantly affects the efficiency and performance of the Transformer. For desired efficiency, the Winding Temperature must be within a specified limit. If the temperature of the Transformer windings goes beyond a specified limit, it can cause insulation breakdown and burning of the windings. Therefore, it is desirable to continuously monitor the winding temperature and keep it within the specified limit for the safe and reliable operation of the Transformer. For this purpose, the Winding Temperature Indicator (WTI) is equipped with the Transformer.

3. OIL/WINDING TEMPERATURE INDICATURE (OTI/WTI) Measuring System: A sensing bulb, measuring bellows and a small-bore capillary tube connecting the two form the measuring system which is filled with liquid. When heated, volumetric expansion of a liquid will be proportional to the rise in temperature. When the bulb is exposed to a rise in temperature, the liquid inside the measuring system expands proportionately causing corresponding volumetric changes in the bellows. Since one end of the bellows is anchored, it will move linearly in proportion to the measured temperature. Temperature Compensation: A second bellows (compensating bellows) and capillary terminated at the head of the bulb provide complete compensation of ambient temperature changes on the measuring bellows and capillary. The volume changes are identical in the twin systems for any ambient temperature change. The two bellows are linked in such a manner that these volume changes are cancelled out. Thus, the measuring bellows output is related directly to the temperature being measured by the bulb. Head Compensation The head pressure will have no effect on the bellows since the systems are sealed under initial pressure which is greater than the head pressure.

4. PRINCIPLE OF OPERATION: The Sensor assembly comprising PT100 Sensor, Heater Coil and shunt is mounted in the oil filled pocket located in the hottest oil of the Transformer. The Heater is fed with current from a CT Placed in the Transformer load Circuit. The Heater simulates the hotspot Temperature rise of the winding over the top oil Temperature corresponding to the Transformer Load current. The PT100 Sensor assembly reacts to this simulated temperature rise in addition to the top oil temperature. To obtain precise thermal image, a portion of the current through the heater is shunted through calibrating Shunt Resistor. The thermal time constant of the heater is nearly the same as that of the Transformer winding. Hence, the Sensor Assembly simulates closely the Actual hotspot temperature of winding in relation to Time. Operating Mechanism : Link and Lever mechanism amplifies the movement of the measuring bellows and drives directly a rotating disc actuating the controls switches. An Indicating pointer mounted on the same disc moves over a calibrated dial. OIL/WINDING TEMPERATURE INDICATURE (OTI/WTI)

5. OIL/WINDING TEMPERATURE INDICATURE (OTI/WTI) Switching: Electrically isolated heavy duty Micro switches which are independently adjustable to operate at pre-set temperature are provided to actuate Control Circuits. Thermal Image Device for WTI: An electrical heater coil, fitted around the measuring bellows, simulates the winding to top oil temperature differential in addition to the top oil temperature being measured by the instrument bulb. The temperature in the hottest part of the winding or hotspot temperature is displayed directly by the instrument. Thus, the instrument functions as a winding temperature indicator. Precise thermal image is obtained by shunting a portion of the heater coil current (WTI CT Current) through an adjustable shunt resistor mounded inside the instrument case. Since the thermal time constant of the heater coil is nearly the same as the transformer winding, the instrument simulates closely the actual temperature of the winding in relation to time. Precision Potentiometer: A precision potentiometer (2800 or 4400), mounted inside the instrument case converts the movement into a resistance signal corresponding to the measured temperature.

6. COMPONENTS OF OTI/WTI Sensor Bulb  − It is the component provided for measuring the temperature directly by placing it into the oil. Capillary Tube  − It is provided to connect the sensor bulb with the temperature gauge. Temperature Gauge/Dial  − Its function is to show the reading of oil temperature. It is generally calibrated in °C or °F. Micro Switches S1 and S2  − Mercury switches being banned; hence Micro switches are being Utilised. PT100 Sensor - Embedded PT-100 sensor in the sensing bulb of the local OTI provide for a master indication at control room and Scada compatibility. Heating Element (Only for WTI)  − It is a heating coil which is wrapped around the Capillary Tube/sensor bulb and the WTI CT is connected to Heating element . Its function is to simulate the change of winding temperature more accurately. Current Conversion Unit (CCU) –  To transmit the measured temperature as a 4-20mA dc current signal for use in SCADA and data acquisition systems. Hybrid Model – CCU is Part of Dial type Temp Meter. For CCU working either External PSU or DTI. Remote Indicator (DTI) - Oil Temperature Indicator inbuilt with an Integrated Signal Transmitter that converts the measured temperature to a robust 2 wire 4-20mA dc current O/P for reliable transmission to a remotely mounted Digital Temperature Indicator (DTI). Power Supply Unit (PSU) – PSU can be installed at marshaling box instead of DTI for dual 4-20mA signal output to SCADA / Display purpose. DTI or PSU – It provides 24 V dc Power Supply to the Integrated Signal Transmitter and receives the 4-20mA signal input on the same 2 wires. Outputs - 4 to 20 mA Single or Dual or & RS485 Modbus Port as per Customer Requirement. Only 2 wires are required for 24 V dc power supply as well as 4-20mA dc current O/P.

7. PT100 SENSOR PT100 Sensor  Platinum 100 or PT100 are Resistance Temperature Detectors (RTD) R esistance  t emperature  d etectors or RTDs, are a class of sensors that change resistance when the temperature of the medium they are inserted into changes. This change of resistance is proportional to temperature and varies in a somewhat  linear  fashion with temperature. This means that as the temperature increases, the resistance of the RTD also increases. So, if we can measure the RTD’s resistance, we can determine the temperature. While RTDs can be manufactured from many metals including  nickel  and  copper ,  platinum  exhibits physical properties that make it ideal for use in RTD. Platinum is a basic element, with the chemical symbol  Pt . That is the first part of the designation of the PT100 RTD. Platinum exhibits an electrical resistance that varies in a nearly linear fashion with temperature and has a resistance of exactly  100.00  ohms at zero degrees Celsius. Another property of platinum that makes it highly valuable to temperature measurement is that it is quite inert. It does not react with other compounds to any great extent. The most common PT100 RTD used in industry is one that changes resistance at the rate of about  0.385 ohms  for every degree Celsius rise in temperature. We know the resistance of a P T 100 sensor at zero degrees Celsius is 100 ohms, so the resistance we would expect at 100 degrees Celsius would be 138.5 ohms.

8. PT100 SENSOR  Pt100 RTD, we have been describing if we substitute the resistance values of the Pt100 RTD at zero and at 100 degrees Celsius, we find that the value of alpha is  0.00385 . Knowing alpha, we can calculate the approximate resistance the RTD will exhibit at any temperature within its range. The Pt100 RTD is often referred to as the  Pt100 (385)  RTD. There are platinum RTD’s that exhibit different values of alpha, and those would be designated with their respective alpha values, such as with the  Pt100 (391)  sensor. In industrial applications, RTDs are commonly placed inside protective metal tubes called  thermowell . PT100 RTDs can be constructed from a single platinum wire, giving a sensor with two leads.

9. PT100 SENSOR – 2 WIRE RTD In order to determine the resistance of the RTD, a special bridge circuit is used, called a  Wheatstone bridge . In this diagram, there are four resistors. Resistors A, B, and C are of equal value. The fourth resistor is the RTD itself and its resistance can be deduced from the voltage measured across the two legs of the bridge. This 2-wire RTD design is not very accurate , because the platinum leads themselves have an electrical resistance due to the length of the wire and the connection points, in addition to the resistance from the temperature detected at the point of measurement.

10. PT100 SENSOR – 3 WIRE RTD To compensate for this added resistance, a second platinum wire is added to the sensor at a third lead. This third lead is used to determine the resistance of the lead itself, and the resistance is subtracted from the overall measure resistance to give the true resistance due to the change in temperature alone. These 3-wire RTDs are the most widely used in the industry. Although more expensive than a 2-wire RTD, the added stability and accuracy are well worth the added cost. A Pt100 RTD is typically constructed by winding a thin platinum wire around a non-conductive core which helps support the thin wire. The entire assembly is encased in a sheath to protect the sensor and to give it stability.

11. PT100 SENSOR & THERMOMETER POCKET

12. PT100 RESISTANCE TEMPARATURE VS RESISTANCE Temp ºC RESISTANCE (OHMS) Ω OUTPUT SIGNAL (4 – 20 mA) OUTPUT SIGNAL (4 – 20 mA) Precimeasure Perfect Controls LOW NOMINAL HIGH LOW NOMINAL HIGH LOW NOMINAL HIGH 99.88 100.00 100.12 3.84 4.00 4.16 3.800 4.000 4.200 10 103.76 103.90 104.04 4.90 5.07 5.23 4.867 5.067 5.267 20 107.63 107.79 107.95 5.97 6.13 6.29 5.933 6.133 6.333 30 111.49 111.67 111.85 7.04 7.20 7.36 7.000 7.200 7.400 40 115.35 115.54 115.73 8.11 8.27 8.43 8.066 8.266 8.466 50 119.19 119.40 119.61 9.17 9.33 9.49 9.133 9.333 9.533 60 123.01 123.24 123.47 10.24 10.40 10.56 10.200 10.400 10.600 70 126.82 127.07 127.32 11.31 11.47 11.63 11.266 11.466 11.666 80 130.62 130.89 131.16 12.37 12.53 12.69 12.333 12.533 12.733 90 134.42 134.70 134.98 13.44 13.60 13.76 13.399 13.599 13.799 100 138.20 138.50 138.80 14.51 14.67 14.83 14.466 14.666 14.866 110 141.97 142.29 142.61 15.57 15.73 15.89 15.533 15.733 15.933 120 145.72 146.06 146.40 16.64 16.80 16.96 16.599 16.799 16.999 130 149.46 149.82 150.18 17.71 17.87 18.03 17.666 17.866 18.066 140 153.21 153.58 153.95 18.77 18.93 19.09 18.732 18.932 19.132 150 156.92 157.31 157.70 19.84 20.00 20.16 19.800 20.000 20.200

13. DC CURRENT (4 -20mA) MEASUREMENT METHOD

14. OTI & WTI METERS IN FCC/CCC/MCC PRECIMEASURE PERFECT CONTROLS THERMOMAX

15. CURRENT CONVERTION UNITS IN FCC/CCC/MCC

16. PERFECT CONTROL ACCESSORIES Resistance to Current Converter (RCXT): The Resistance to Current Converter Unit measures the variations in the sensor resistance (corresponding to top oil plus simulated winding hot spot temperature) and produces a directly proportionate single output signal of robust standard 4-20mA dc single Output. The output is reliable and less prone to Electromagnetic Interference (EMC) compared to a Voltage mode measurement. Current to Current Converter (CCXT): The above 4 to 20 mA DC Signal is transmitted to a remote point and fed in to a Current Converter to obtain two independent channels of 4 – 20 mA DC current output signals. ºC Ω Ω Ω I 4-20 mA DC Signal I I Channel-1: 4-20 mA DC Channel-2: 4-20 mA DC To Indication To DAS/SAS 1. SENSOR 2. RCXT 3. CCXT PT100 RWTT – SINGLE SYSTEM TWO OUTPUT CHANNELS

17. PERFECT CONTROL ACCESSORIES DIGITAL TEMPERATURE INDICATOR (DTI): The 4-20mA dc output signal from Resistance to Current Converter or Temperature Transmitter can be connected to a remotely mounted Digital Temp Indicator for display, 4-20mA retransmission output, with 2 user configurable Alarms and RS485/MODBUS RTU Digital communication interface for remote display of measured temperature with 2 user configurable Alarms. Digital Temperature Repeater: The resistance signal from the precision potentiometer can be directly connected to remotely mounted DTI for remote display of measured temperature with 2 user configurable Alarms for display, 4-20mA retransmission output, with 2 user configurable Alarms and RS485/ MODBUS RTU Digital communication interface for remote display with upto 2 Analog outputs. While this scheme saves cost, it is not as robust as the Resistance to Current Converter option listed above as signal transmission is by voltage mode which is more susceptible to Electromagnetic Interference.

18. OTI & WTI METERS WITH CCU & REMOTE METER

19. OTI & WTI METERS WITH CCU & REMOTE METER

20. OTI & WTI METERS WITH CCU & REMOTE METER

21. REMOTE TRANSMISSION & DISPLAY OF TEMP Optional one RS485 Modbus in place of Second 4-20mA DC O/P SCADA or DAS CCU INBUILT IN DIAL METER

22. REMOTE TRANSMISSION & DISPLAY OF TEMP Optional one RS485 Modbus in place of Second 4-20mA DC O/P SCADA or DAS CCU INBUILT IN DIAL METER

23. REMOTE TRANSMISSION & DISPLAY OF TEMP Optional one RS485 Modbus in place of Second 4-20mA DC O/P SCADA or DAS CCU INBUILT IN DIAL METER

24. 4 CHANNEL TEMPERATURE INDICAT0R CH1 - + G 1 2 3 CH2 - + G 1 2 3 CH3 - + G 1 2 3 CH4 - + G 1 2 3 4 – 20 mA Input 4 – 20 mA Output L N E AUX Supply 90-250 V 4-20 mA + - 4-20 mA + - 4-20 mA + - 4-20 mA + - RS 485 COM RL1 NO C NC COM RL2 NO C NC COM RL3 NO C NC COM RL4 NO C NC OTI WTI-HV WTI-IV WTI-LV DAS/SCADA OTI to BCU/87T WTI to BCU/87T WTI to BCU/87T WTI to BCU/87T BACK END FRONT END

25. 4 CHANNEL TEMPERATURE INDICAT0R Conversion of RS-485 MODBUS data into standard signals in 4 channels (current 4...20 mA). Possibility of connection via internal RS-485 port in order to increase no of analog outputs in other devices. Two independent communication ports (possibility to work as Master/Slave). Master Modbus function dedicated to read out data from other RS-485 devices and to scale analog value. Slave Modbus function to set the signal on analog outputs. Conversion of standard signals and temperature (4 to 20mA) into RS-485 / MODBUS in 4 channels Programmable measurement characteristic Mathematical functions realized between channels and on channels 2 programmable OC outputs

26. 4 CHANNEL TEMPERATURE INDICAT0R OTI WTI-HV WTI-IV WTI-LV OTI WTI-HV WTI-IV WTI-LV

27. YOUTUBE VIDEOs & DOCUMENTS https://www.youtube.com/watch?v=58kQBVN8Duk Working Principle of OTI/WTI of Power Transformer 2. https://www.youtube.com/watch?v=3qDL_ipZxLg Pt100 Sensor Detailed Explanation 3. https://www.youtube.com/watch?v=IJW_2xuqdJo What is Pt100 Sensor 4. https://www.youtube.com/watch?v=pDSUfqso_eA Measuring a 4 – 20mA Signal in your Meter 5. https://www.youtube.com/watch?v=mE9bODHvzQQ How to use Pt100 sensor with 4-20mA Transmitter 6. Precimeasure Dial Temperature Indicator 7. Perfect Controls Transformer Temperature Indicator 8. Perfect Controls  Pt100 Sensor Transmitter