MODEL PC-252 Transformer Temperature Indicator Oil & Winding Temperature Indicator (with Micro Switches)

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1 1. Description: PC 252 is a Liquid-in-Metal expansion type Self powered Oil/ Winding Temperature Indicator for Power & Distribution transformers. PC 252 is Approved & Used by all reputed customers in India & Globally including NTPC, Power Grid Corp., Nuclear Power Corp of India, BARC, various State Electrical utilities & SEBs etc. 2. Features: Can be used as Oil Temperature Indicator and Winding Temperature Indicator Specially designed to protect power & distribution transformers Proven Reliability in field for over 35 years. Liquid-in-metal expansion type Self Powered operation Ergonomically designed 60 segmental scale No periodic site adjustments Up to four electrically isolated heavy duty MICRO SWITCHES Winding temperature indication by thermal image device Various Remote Signal transmission options for Display, SCADA etc RS 485- MODBUS RTU Protocol Digital Communications option. Integrated Signal Transmitter design option with/without Input/output isolation Complete ambient temperature and head compensation for bellows & capillary line Switch & Circuit testing facility from outside the case All circuits to ground tested at 2500 Volts a.c. 50 Hz for 60 seconds. Maximum temperature indicating pointer Suitable for mounting directly on the transformer. Ventilated weather-proof case (Protective Class IP 55 of IEC 529) Air vent is provided 3. Measuring System When heated, volumetric expansion of a liquid will be proportional to the rise in temperature. A sensing bulb, measuring bellows and a small bore capillary tube connecting the two form the measuring system which is filled with liquid. 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. 4. 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. 5. 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. 1

2 6. 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. 7. Switching Electrically isolated heavy duty Micro switches which are independently adjustable to operate at pre-set temperature are provided to actuate Control Circuits. 8. Quality Components Bulb: Brass with silver joints-natural finish. Bellows: Phosphor Bronze Capillary : Copper with stainless steel armour sheathing. Case: Die Cast Aluminium housing with Powder coated Siemens grey or Polyurethane finish painted. Viewing Window: Clear transparent polycarbonate. Switch: Snap action Micro switches. Other Parts: ONLY Non ferrous metals or other non-corrosive materials are used. 9. Technical Specification: Dial: 60 segmental scale 114 mm (4.5 Inches) long finished matt white with bold black markings for rapid reading with 2 C division. Control Switches: Upto 4 numbers, electrically isolated Normally Open SPST Standard (Miniature) microswitches which are independently adjustable to make contacts at preset temperature. Capillary: Standard lengths 5m, 6m, 10m and 12m stainless steel armour sheathed. Case Mountings: Weather-Proof case (Protective class IP55 of IEC529) is suitable for directly mounting on transformer. However, a canopy type weather shield will improve visibility under tropical conditions. Capillary entry: Bottom or Top of case vertical. Electrical Entry: Bottom of case vertical through 2 holes (19mm or 26mm) Maximum Pointer: Resettable from outside by means of screwdriver is fitted to the instrument window. A special damping device ensures accuracy of readings even under operating conditions. Switch Testing : A switch testing knob is fitted on the instrument lid to facilitate checking of the switch settings from outside, without removing the instrument lid. Electrical Connections are made to the terminal blocks, suitable for 2.5 Sq mm Wire, inside the instrument case. Approved insulating material are used and all circuits to ground tested at 2500 Volts, ac 50 Hz for 60 seconds. A wiring diagram is fixed inside the instrument case. 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 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. 2

3 10. Measuring Range, Accuracy table: Indicator Switching Range Accuracy Type Range (to close) Accuracy Differential (close to open) C ±3 C between Standard C ±4 C 6-8 C Fixed C (Miniature) 11. Micro switch Rating: Switch Type Rated Voltage Rated Current (Non- inductive) Standard (Miniature) 12. Additional options: 125V ac 250 V ac 125 V dc 250 V dc 15 A 10 A 0.50 A 0.25 A Precision Potentiometer: A precision potentiometer (2800Ω or 440Ω), mounted inside the instrument case converts the movement into a resistance signal corresponding to the measured temperature. Integrated Transmitter Monitor ITM909 / ITM369 / ITM639 / ITM27 Model PC-252 can be fitted with a rugged reliable integrated transmitter that produces a standard 2 wire, 4-20mA dc output corresponding to the measured temperature. The various combinations of digital indicators that can be used with ITM for remote display are tabulated below: Model No Analog Output User configurable Alarms Digital Communication Mounting Data Sheet Reference idisp ma Two alarms RS 485 MODBUS RTU Panel 252ITM909 idisp 369 Nil Two Alarms Nil Panel 252ITM369 idisp ma Two Alarms RS 485 MODBUS RTU DIN Rail 252ITM639 Mounting itd 27 Dual 4-20 ma Nil RS 485 MODBUS RTU Panel 252ITM27 Integrated Transmitter with Input / Output Isolation IST909 / IST369 / IST639 / IST27 Model PC-252 can be fitted with a rugged reliable integrated transmitter with Input to Output Electrical Isolation that produces a standard 2 wire 4-20mA dc output corresponding to the measured temperature. The various combinations of digital indicators that can be used with IST for remote display are tabulated below: Model No Analog Output User configurable Alarms Digital Communication Mounting Data Sheet Reference idisp ma Two alarms RS 485 MODBUS RTU Panel 252IST909 idisp 369 Nil Two Alarms Nil Panel 252IST369 idisp ma Two Alarms RS 485 MODBUS RTU DIN Rail 252IST639 Mounting itd 27 Dual 4-20 ma Nil RS 485 MODBUS RTU Panel 252IST27 3

4 Resistance to Current Converter The resistance signal from the precision potentiometer is converted into a robust standard 4-20mA dc single or dual output that is reliable and less prone to Electromagnetic Interference (EMC) compared to a Voltage mode measurement (refer our data sheet RCXT or RT36) Temperature Transmitter The resistance signal from the precision potentiometer can also be connected to our compact (17.5mm width) DIN Rail mounted Programmable Universal Temperature / Signal Transmitter models as listed below. These models provide Input to Output Electrical Isolation apart from a full 3-port High Voltage electrical isolation between Input/output/power supply. This prevents ground loops and other signal noise interference caused by grounded sensors or cables. Model No Type Power Supply Isolation Data sheet Reference itt108 1 Input/ 1 Output 24 V dc 3 port Input Output itt108-d-001 itt207 1 Input/ 2 Output 24 V dc 3 port Input Output itt207-d-001 itt405 1 Input/1 Output V ac/dc 3 port Input Output itt405-d-001 itt504 1 Input/2 Output V ac/dc 3 port Input Output itt504-d-001 These models also have various other very Unique features as listed in the respective data sheets of itt108 or itt207 or itt405 or itt504. Digital Indicator The 4-20mA dc output signal from Resistance to Current converter or Temperature Transmitter can be connected to a remotely mounted Digital Indicator Model idisp909 for display, 4-20mA retransmission output, with 2 user configurable Alarms and RS485/MODBUS RTU Digital communication interface (or) idisp369 for remote display of measured temperature with 2 user configurable Alarms The various unique features are listed in their respective data sheets. (refer our data sheet idisp909 or idisp369-d-002) Digital Repeater The resistance signal from the precision potentiometer fitted inside PC-252 can be directly connected to remotely mounted idisp369 for remote display of measured temperature with 2 user configurable Alarms (or) idisp909 for display, 4-20mA retransmission output, with 2 user configurable Alarms and RS485/MODBUS RTU Digital communication interface (or) DI36 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 (refer our data sheet idisp909-d-004 or idisp369-d-004 or DI36-D-001) 4

5 13. Case Dimensions and Fixing Details: 5

6 ORDER FORM 252 Instrument Type OTI only OTI WTI only WTI OTP OTI with Potentiometer WTP WTI with Potentiometer OTR OTI with Repeater WTR WTI with Repeater Temperature Range to 150 C to 140 C to 150 C Other range on special order No of Switches 2 2 switches 4 4 switches Switch Type ZS SPST Miniature Micro switch ZD SPDT Miniature Micro switch Case finish S- Powder coated Siemens grey L- Painted - Polyurethene light grey Capillary Entry B Bottom of Case Vertical T Top of Case Vertical Transmitter (Optional) P Ω P4 440 Ω Bellows Heater Graph for WTI only Specify your C.T.secondary current at transformer rated load and the corresponding winding gradient. Sensing Bulb Type (F) (M) Other as specified. Length of the Capillary 03-3 mtrs 05 5 mtrs 06 6 mtrs mtrs mtrs xx - upto 25 mtrs 6 Subject to Change without Notice