DESIGN OF DC MACHINES AND TRANSFORMER [ ] ACTIVE LEARNING ASSIGNMENT: TOPIC : VARIOUS PROTECTIVE AND INDICATIVE INSTRUMENTS. UNIVERSITY : GUJARAT TECHNOLOGICAL UNIVERSITY. COLLEGE : VADODARA INSTITUTE OF ENGINEERING. DEPARTMENT : ELECTRICAL ENGINEERING [E.E.– I]. SEMESTER : VI. PREPERED BY : [ JOBIN ABRAHAM ] [ SAGAR KALAL ] [ DENISH I. KHATRI ] [ KRISHNA SURYA ] GUIDED BY : ASST. PROF. PARTH M. SHAH. [ELECTRICAL DEPARTMENT] [ELECTRICAL DEPARTMENT] ACTIVE LEARNING ASSIGNMENT 1

 CONTENTS  Introduction Introduction  Buchholz Relay Buchholz Relay Buchholz Relay  Oil Temperature Indicator or OTI Oil Temperature Indicator or OTI Oil Temperature Indicator or OTI  Winding Temperature Indicator or WTI Winding Temperature Indicator or WTI Winding Temperature Indicator or WTI  Remote Temperature Indicator Remote Temperature Indicator Remote Temperature Indicator  Magnetic Oil Gauge or MOG Magnetic Oil Gauge or MOG Magnetic Oil Gauge or MOG  References References ACTIVE LEARNING ASSIGNMENT 2

 Introduction  Transformer Protection  There are different kinds of transformers such as two winding or three winding electrical power transformers, auto transformer, regulating transformers, earthing transformers, rectifier transformers etc.  Different transformers demand different schemes of transformer protection depending upon their importance, winding connections, earthing methods and mode of operation etc. ACTIVE LEARNING ASSIGNMENT 3

 Buchholz Relay  The relay was first developed by Max Buchholz (1875– 1956) in  In the field of electric power distribution and transmission, a Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a "conservator".  The Buchholz relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment. ACTIVE LEARNING ASSIGNMENT 4

 Buchholz Relay Operation  Depending on the model, the relay has multiple methods to detect a failing transformer.  On a slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition of insulating oil accumulates in the top of the relay and forces the oil level down.  A float switch in the relay is used to initiate an alarm signal.  Depending on design, a second float may also serve to detect slow oil leaks. ACTIVE LEARNING ASSIGNMENT 5

 If an electrical arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator.  This flow of oil operates a switch attached to a vane located in the path of the moving oil.  This switch normally will operate a circuit breaker to isolate the apparatus before the fault causes additional damage.  Buchholz relays have a test port to allow the accumulated gas to be withdrawn for testing.  Flammable gas found in the relay indicates some internal fault such as overheating or arcing, whereas air found in the relay may only indicate low oil level or a leak. ACTIVE LEARNING ASSIGNMENT 6

 Temperature Indicator of Transformer  These are generally precision instruments. A temperature indicator of power transformer is specially designed for protection of transformer in addition to its temperature indication and cooling control features. That means, this device performs these functions:  These instruments indicate instantaneous temperature of oil and windings of transformer.  These also record maximum temperature rise of oil and windings. ACTIVE LEARNING ASSIGNMENT 7

 Temperature Indicator of Transformer {cont.}  These instruments operate high temperature alarm at a predetermined value of allowable temperature limit.  Temperature indicators of transformer can also trip the circuit breakers associated with the power transformer when the temperature of oil or winding reaches a predetermined limit.  These devices also control the cooling system of transformer. Switch on the cooling equipment when the winding attains a preset high temperature and switch it off when the temperature drops by an established differential. ACTIVE LEARNING ASSIGNMENT 8

 Types of Temperature Indicator of Transformer  There are mainly two types of temperature indicators used in transformer. Principally both of the instruments are the same but, one is used for oil temperature and the other is used for winding temperature. There is another type of temperature indicator often used in power transformer, which is little bit different principally and this is remote temperature indicator.  The types of temperature indicator of transformer are  Oil temperature indicator (OTI)  Winding temperature indicator (WTI)  Remote temperature indicator (RTI) ACTIVE LEARNING ASSIGNMENT 9

 Construction of Temperature Indicator of Transformer  These indicators are provided with a sensing bulb.  This sensing bulb is placed in a pocket on the roof of transformer tank.  The pocket is filled with transformer oil.  The bulb is connected to the instrument housing by means of flexible connecting tubing consisting of two capillary tubes.  One capillary tube is connected to the operating bellow of the instrument and other to a compensating bellow.  Compensating bellow compensates variation of ambient temperature.  The pointer is fixed with a steel carriage on which normally four mercury switches are mounted. ACTIVE LEARNING ASSIGNMENT 10

 Construction of Temperature Indicator of Transformer {cont.}  The make and break temperature of these mercury switches can be adjusted separately.  One mercury switch is use to operate cooling fans, one mercury switch is used to switch on oil pumps, one mercury switch is for high temperature alarm and last switch is used to inter trip the transformer in extremely high temperature condition.  In addition to these the dial of oil temperature indicator is also provided with dummy pointer which is pushed by main pointer when temperature rises.  When main pointer moves back due to decreasing temperature, the dummy pointer stays at maximum temperature position of the main pointer.  This indicates maximum temperature rise of transformer during a preset period of time. ACTIVE LEARNING ASSIGNMENT 11

 Oil Temperature Indicator or OTI  This device is used to measure the top oil temperature. An oil temperature indicator or OTI is also used for protection of transformer. ACTIVE LEARNING ASSIGNMENT 12

 Oil Temperature Indicator or OTI {cont.}  Operating Principle of Oil Temperature Indicator  This device measures top oil temperature with the help of sensing bulb immersed in the pocket by using liquid expansion in the bulb through a capillary line to operating mechanism. A link and lever mechanism amplifies this movement to the disc carrying pointer and mercury switches. When volume of the liquid in operating mechanism changes, the bellow attached to end of capillary tube expands and contracts. This movement of bellow is transmitted to the pointer in temperature indicator of transformer through a lever linkage mechanism. ACTIVE LEARNING ASSIGNMENT 13

 Winding Temperature Indicator or WTI  This device measures the LV and HV winding temperature. A winding temperature indicator or WTI is also used as protection of transformer. ACTIVE LEARNING ASSIGNMENT 14

 Winding Temperature Indicator or WTI {cont.}  Operating Principle of Winding Temperature Indicator  The basic operating principle of WTI is same as OTI. But only difference is that the sensing bulb pocket on transformer top cover is heated by a heater coil surrounded it. This heater coil is fed by secondary of current transformers associated with transformer winding. Hence the current through the heater coil is directly proportional to the current flowing through transformer winding. This is because there is no scope of direct measuring of temperature inside a winding. When load of transformer increases, the winding temperature is also increased and this increased temperature is sensed by sensing bulb as the heater coil surrounds it. Rest of the working principle of winding temperature indicator is same as principle of oil temperature indicator. ACTIVE LEARNING ASSIGNMENT 15

 Remote Temperature Indicator  A precision potentiometer mounted inside the instrument case functions as a transmitter and operates an electrical repeater for remote reading of measured temperature.  In one scheme the transmitter is directly connected to the repeaters and alternative scheme is to connect the transmitter to a resistance transducer, which will supply direct current for operating repeater. ACTIVE LEARNING ASSIGNMENT 16

 Magnetic Oil Gauge or MOG  This device is used to indicate the position of transformer insulating oil level in conservator of transformer. This is a mechanical device.  Magnetic oil level indicator of transformer consists of mainly three parts-  One float,  Bevel gear arrangement and  An indicating dial. ACTIVE LEARNING ASSIGNMENT 17

 MOG{cont.}  Working Principle of Magnetic Oil Gauge or MOG  All oil immersed distribution and electrical power transformers are provided with expansion vessel which is known as conservator of transformer.  This vessel takes care of oil expansion due to temperature rise. When transformer insulating oil is expanded, the oil level in the conservator tank goes up. ACTIVE LEARNING ASSIGNMENT 18

 MOG{cont.}  Again when oil volume is reduced due to fall in oil temperature, the oil level in the conservator goes down. But it is essential to maintain a minimum oil level in the conservator tank of transformer even at lowest possible temperature.  All large electrical power transformers are therefore provided with a magnetic oil level indicator or magnetic oil gauge.  In conventional conservator tank, a light weight hollow ball or drum floats on the transformer insulating oil. The float arm is attached with bevel gear as we already explained during the discussion on the construction of magnetic oil gauge.  Naturally the position of the float goes up and down depending upon the oil level in the conservator and consequently the alignment of float arm changes. ACTIVE LEARNING ASSIGNMENT 19

 MOG{cont.}  Consequently, the bevel gear rotates. This movement of bevel gear is transmitted to the pointer outside the conservator, as this pointer is magnetically coupled with the bevel gear.  The pointer of magnetic oil level indicator is also incorporated with a mercury switch.  So it is need not say, when oil level in the conservator goes up and down, the pointer moves on the MOG dial to indicate the actual level of transformer insulating oil in conservator tank.  As the alignment of mercury switch changes along with the pointer, this switch closes and actuates an audible alarm when pointer reaches near empty position on the dial of magnetic oil gauge.  This event alerts us for topping up oil in electrical power transformer. ACTIVE LEARNING ASSIGNMENT 20

 References 1. A Course in ELECTRICAL MACHINE DESIGN – Sixth Edition, 2014 Reprint [A.K. SAWHNEY] {DHANPAT RAI & Co. Pvt. Ltd.} (2014). 2. PRINCIPLES OF ELECTRICAL MACHINE DESIGN – Fourth Edition, [ R.K. AGARWAL ] {S.K. KATARIA & SONS PUBLISHERS} (2015). 3. Theory & Performance of ELECTRICAL MACHINES – Fourteenth Edition, 2013 Reprint [J.B. Gupta] {S.K. KATARIA & SONS PUBLISHERS} (2013) transformer/ transformer/ transformer/ ACTIVE LEARNING ASSIGNMENT 21

 References {cont.} 6. Video of Buchholz relay : Video of Buchholz relay : Video of Buchholz relay : remotetemperature-indicator-of-transformer/ remotetemperature-indicator-of-transformer/ remotetemperature-indicator-of-transformer/ 8. mog-magnetic-oil-level-indicator-of-transformer/ mog-magnetic-oil-level-indicator-of-transformer/ mog-magnetic-oil-level-indicator-of-transformer/ ACTIVE LEARNING ASSIGNMENT 22

ANY QUESTIONS? ACTIVE LEARNING ASSIGNMENT 23