Transformer Protection Devices Explained | Buchholz Relay, REF, Differential, OTI, WTI Working

99% of electricians fail the interview because they are asked a question about how many protective devices are connected to the transformer and what types of protective devices are provided. If you are going to give an interview, or if you are going to give an interview in the future and you are asked this question at that time, then you can answer it properly. Also, you should know all the protective devices in the transformer. For that, watch this video until the end. You are going to receive a lot of information throughout this class. First of all, we understand here what kind of fault we are likely to observe in our transformer. If you count the fault in this, then there are 14 faults in total. You can read this video by pausing it once. We will get to see so many flaws here. Now, if we are encountering 14 faults here, under this condition, we cannot protect everyone by connecting just one protective device. For this transformer, we will have to install different protective devices. Now the first protective device here is our Buchholz relay. The Buchholz relay is installed between the transformer tank and the conservator tank. This means that the oil flowing from the conservator tank to the main tank of our transformer is located in the middle of the same pipeline. And with this Buchholz relay, two cables are connected here. This cable is used to trip the circuit breaker of our transformer. So first of all, you understood that the Buchholz relay is located between the conservator tank and the main tank. And the function of this Buchholz relay is that if the winding in the transformer becomes weak, if any sparking is generated in the transformer, if there is a core fault in the winding of our transformer, or if there is a turn-to-turn fault, or if a large amount of heat is generated in the oil, Then the Buchholz relay will provide us with protection under these conditions. You can understand that the Buchholz relay detects gas and oil surges in the transformer. If there is any kind of gas or oil surge in our transformer, Then it will detect it. And after detecting it, it will recognize that there is an internal fault. And because of that, it will offer us protection here. It means that it will send us a signal to protect the transformer. Now let's understand how it sends a signal. Look, in the Buchholz relay, you will get to see something like this, where you get two contacts. One contact is used for alarm. The other is used to cause a trip here. What will happen next in this Buchholz relay? When the heat inside the transformer starts getting very high, or when sparking occurs, bubbles are generated as a result. Whatever the bubbles may be, they will enter this Buchholz relay. The gas will come inside it. And after coming inside, these two contacts will be operated. But it is not the case that both contacts will be operated simultaneously. First of all, if our gas is very low, not much, less, then in this condition, our first switch here, It has a mercury switch here. The first mercury switch will be operated. And this is used for alarm. We connect it in such a way that if this cable is operated, Then we get an alarm under this condition. The whistle starts ringing. And we discover that heat is being generated inside the transformer, due to which we have received an alarm signal from our transformer. Here, our Buchholz relay, the second contact in this relay, It is operated when our gas, That gas flows very high, very fast. If there is a very large fault inside the transformer, then under these conditions, the gas will be very high, The bubbles will be very high, due to which our trip contact here will be operated. And by its operation, Our breaker will be shut down. Now how do we trip the breaker? So simply, you understand that the Buchholz relay, the contact of this relay, We will reach that contact. And with that, our master trip relay here, The signal will be sent to this trip relay from here. When this master trip relay receives the signal, then it will understand that the Buchholz relay has sent me a signal here, That means there is a fault inside the transformer. Now this master trip relay will generate a command. to trip the BCB breaker, That means it will send a signal to trip the BCB breaker. due to which our BCB breaker will be shut down. And we will cut off the power supply to this transformer, with which our transformer will be protected. So our first protection is the Buchholz relay. And this Buchholz relay, the gas generated inside the oil due to heating and sparking, detects it and provides us with protection. Now let's move on to the second protective device. Our second protection device is the oil temperature indicator. The oil temperature indicator tells us the temperature. What is the final temperature inside the oil? As you can see here, in our OTI, We can see two needles here. In which one needle is here, at the position of 20 And the other needle is here at 60. That means at the present time, The temperature of the oil in our transformer is 20 degrees Celsius. And inside this transformer, the highest temperature that has occurred so far has risen to 60 degrees Celsius. So a meter of this type is installed, That meter tells us the temperature of the oil. Now many electricians think That this meter only tells us the temperature. But it's not like that. In many of your meters, You will also receive contact information, NONC through which we also seek protection. For example, in your transformer, if the temperature is very high, Then we have to turn off the transformer. We won't come here right away and check. If the temperature of the transformer has become high. So if the transformer's temperature is high, then under these conditions, The breaker also has to be turned off. The breaker will have to be tripped. The power to the transformer will have to be cut. So to cut the power to the transformer, your OTI, which we call the Oil Temperature Indicator, also sends a signal. Where will the signal be detected? A sensor will be installed inside the transformer's oil. The sensor will detect the oil's temperature here. And after detection, It will tell you the temperature here. And the temperature that will be set, if the temperature goes above that level, Then it will provide you with two types of signals here. The first contact will be with the alarm here. And the second will be to trip. Means if our temperature is low, It hasn't gone much. then under these conditions, The contact with the alarm will be operated. And this signal will activate a relay. And after starting this relay, Through this, we send a signal to a horn. So that we get an alarm here that our temperature has risen significantly. But under these conditions, The power of our transformer will not be cut. But this temperature increases slightly more. So in this condition, There is another contact inside it. the one on the trip It will be operated here. So OTI means Oil Temperature Indicator. if the trip signal comes here, then in this condition, We will start a relay here. And from this relay, We will send a signal to the master trip relay. So the master trip relay here, We will send a signal to that relay. And that relay will generate a power supply here and turn off our VCB breaker. That means it will cut off the power to the transformer. Our transformer will be completely shut down. Now after the oil temperature, The next protective device here is our WTI. Means Winding Temperature Indicator. This WTI protection device, It also works like our OTI. The only difference here is that the sensor of OTI, inside the oil tank Where is the upper layer of the oil tank? We keep it there. But our WTI here, What do we do with WTI? We keep the winding with the winding so that it can measure the temperature of the winding. So WTI tells us the temperature of the winding. Along with that, if the temperature of the winding increases, Then it also offers us protection here. Along with the WTI, You will also have to use a CT here. It must be connected to the CT. No CT will be used in OTI. So our WTI here, A CT will be used with it. which is connected with the boosting. And what do we do with it? The WTI meter here, The signal is given to that meter. Plus the temperature here, The signal for that temperature is also provided. So this signal will read that signal. After reading, It will show you on the display. What is the current temperature? Now we are understanding OTI and WTI. So understand one more thing here, which will often be asked in the interview. The question will be that in that transformer, What is the setting of OTI? And what is the setting of WTI? It is a simple question. But many people are unable to answer. The answer to this question is written here. Just read it and understand. First of all, you will have to understand that the OTI here, What is this? It is measuring the oil temperature. And WTI is measuring the temperature of our winding. So the fault lies in the winding itself, due to which the oil is heated. That is, where will you observe the highest temperature? In the winding. And the oil temperature will be low here. Now how much protection setting should we apply here? First of all, The temperature of our oil is the lowest. And who will be the first to leave? Alarm contact. So for the alarm, The temperature we set here is 85 degrees Celsius. Now after this, We have to make the oil trip in the fault. So we will set the temperature to 95 degrees Celsius. That means 85 plus 10 plus 95. 85, 95. Remember this. For oil, 85 and 95. 85 is the alarm and 95 is the trip. The second thing here is the winding. So in the winding, if we have to generate the alarm here, Then the alarm will be 105. 85 plus 10. 95 plus 10. 105 So here you will set the temperature to 105 degrees Celsius. for the alarm of the winding. Now you have to make the trip. To make the trip, if you add 10 here, It will be 115. But we didn't set it to 115. We set it a little more than that. 120 degrees Celsius So you just have to remember this thing here. You are often asked questions in interviews. Now we must understand here How WTI completely halts our transfer. You will have the WTI alarm signal here. We will start the relay with that signal. We will trigger an alarm from the relay. That is, we will generate an alarm. from the NONC contact of this relay. In the same way, if the trip signal comes, Then a relay will be initiated through it. From the relay, We will send the signal to the master trip relay. And the master trip relay will provide the power to our 20V breaker to halt our transfer and stop the transfer. Okay, understand one more thing here. In WTI, in many transformers You will get to see two things. One will receive the LV side, One will get the high-voltage side. The low-voltage side will be different. and the high-voltage side will be different. Because to measure the temperature here, CT is also used. That is, how much current is flowing, It is used to detect temperature. So, the high-voltage side and the low-voltage side, The temperatures on both sides are measured. So, if it's a large transformer, then you will get to see the temperature separately for the LV side and HV side. Okay, remember this thing. Now let's move on to the next frame. The next protective device here Is our MOG here? Magnetic Oil Gauge Magnetic Oil Gauge Understand it simply. Here is our conservation tank. How much oil is inside that tank? It is used to see. What is the oil level? Is our oil tank full? Is it empty? Is it half? How much is it? It is used to detect it. Where will it be installed? In the conservator tank. Now in our MOG, There is such a float switch. which is according to the oil level, Up and down. And through that, we get to know here, at this place through the indication How high is the oil level in our case? What is the oil level? We get to see it here. And after this, We have silica gel here. You know, if the transformer is heated, Then the oil expands. It spreads. What will happen because of this? The oil stored in the conservator tank, Its level increases. But when the temperature of the transformer oil is low, Then the oil contracts. It goes down. And when it comes down, Then the transformer breathes. It draws air in. And the air that goes, Moisture can also get inside it. If moisture enters the transformer oil, then in this condition, the level of oil's insulation will decrease. The breakdown voltage will decrease. Because the level of oil's insulation the transformer's is weak, in between 100 circuits of sparking can start generating in the transformer. So, to maintain the insulating value of the oil, Moisture should never get inside it. So, so that moisture does not enter the transformer, A type of silica gel is applied. which we also refer to as a breeder. What is silica gel? So, this blue part you are seeing, This is our silica gel. Air enters the transformer from inside it. And it breathes. Then, when the temperature of the transformer is high, It will come out from there. So, This is our breeder. in which silica gel is applied. Now, The pressure relief valve is also used in the transformer. The pressure relief valve It works like this. If there is high pressure inside the transformer, for some reason There is a fault inside the transformer. Due to that fault, There is so much gas inside the transformer. That gas can blast the transformer. So, to save the transformer from being blasted, above the transformer you will see that A PRB is installed here. whose full form is the pressure relief valve. This will work. What will happen when it is operated? The oil pressure will cause it to open. When it opens, The oil will come out from here. And the transformer will be saved from being blown apart. So, What is the work of PRB? You have understood. If the pressure of the oil increases inside the transformer, then to provide protection against it, This type of PRB is used. as soon as the pressure of the PRB is high, It will release the oil outside. For this reason, The pressure inside the transformer will be reduced. Now, Let's move on to the next part. Now, Differential protection comes here. It is very important. Normally, You will never mention its name in the interview. Because you know that along with the transformer, PRB is installed. MOG is installed. Our breather is installed. Our OTI, WTI is installed. You will only tell this thing. But, It will never occur to you for the protection of the transformer, We use differential protection. Now, this differential protection detects very serious electrical faults. For example, if there is a fault in the phase-to-phase, a fault in the phase-to-earth, if there is a fault in the winding, if the internal source circuit begins to occur, then under these conditions, the differential protection relay, like this relay, This relay will provide us with protection. So, this relay, We won't get this relay. above the transformer Where will we get this? In our electrical panel. It is installed in the electrical panel. And there, We detect the protection and use it to close the circuit breaker. So, this differential protection relay, What is its function? How does it provide protection? I will explain that. See, Here you will see, I have made a simple Diagram of differential protection. In which you can see that This is our power transformer. In power transformers, Here we have delta side and star side. Suppose, This is our primary side. And this is our secondary side. That means, incoming power supply is given on this side and from this side, The power supply goes to the load. Wherever we want to provide power supply. Output power supply has been completed. Now, the power supply that comes It will come from a busbar. So, along with the busbar We put three whistles here. And in the same way, the output power that will go, There will also be three whistles installed. Now, Here you know that the current that flows here, That current will also flow to this side. We leave this. Let's assume a simple example. That we have a breaker here. With this, Power is moving forward. Now, You know that. before the breaker here, the current here, that current It will be the same here as well. That means, if 10 ampere current is flowing from here, then here as well you will get to see 10-ampere current. Now, this current should be exactly the same in both But, if these two currents are not the same as each other, then in this condition, We have to turn it off. that breaker Why do we have to turn it off? Because, if the current difference comes here, 10 amperes came from here, 10 amperes did not reach here, It means that somewhere in the middle The fault has come, which is grounding. Which we can understand that earth fault has happened here. So, for its protection we use differential protection relay here. In that, we use 6 CTs In total. 3 CTs will be used on the primary side 3 CTs will be used on the secondary side And, these 6 CTs are connected in this type. So that, the current detected here, assume that current flow from here 10 amperes. And, current from this side is also 10 amperes. So, after coming here, after coming to our protective relay, What will happen? In these two? 10 minus 10 Will be here. So, 0 ampere current Will be here. But, assume that current here is 10 amperes. But, through these 3 CTs, currently detected is only 8 amperes. So, if I Subtract 10 from 8, 2-ampere current will be left here. This current will operate our relay And, through this relay, we will Trip the breaker. So, this relay, Who is this relay? This is our differential protection relay Means, if there is Any difference in current, we use differential protection relay OK. Let's move ahead. Now, our next protective device is REF protection. REF full form restricted earth fault And, Its ANSI code is 64H. For REF protection, we use this type of relay Through this relay We trip. breaker