Three-Phase Transformers Lecture

sponsored by madx this is a three-phase Transformer it has a Delta primary and a y secondary and it's rated for 2 KVA confused well don't worry I will explain all of that the Transformer basically just takes an ac voltage and converts it into another voltage we can get one two or even three different voltages out of the secondary side but there are no moving parts inside and there are no wires connecting from one side to the other you've likely seen these big green boxes at the side of the road inside is a three-phase Transformer these Supply power to commercial buildings because they have a lot of lighting and Equipment inside your home has much less stuff so you only get a singlephase Transformer this might be pole mounted or pad mounted we can see there are three wires going to the home but this is not a three-phase Transformer the typically connect to just a single phase and the neutral of the distribution grid it then reduces this voltage to a much safer level inside we basically have a primary coil which connects across the phase and the neutral then we have another completely separate coil called a secondary and the two hot wires connect to the ends of this coil and the neutral connects to the center these wires run into the property to your electrical panel the primary side has a singlephase AC Supply the secondary side is also a single phase between the two hot wires giving us 240 volts the current and voltage are flowing forwards and backwards between these two as it is alternating current but if we connect from the neutral to one of the hot bus bars we get 120 volts because we're using just half of the secondary coil the other side is also providing 120 volts and it uses the other half of the coil if we plug an oscilloscope into the outlet we would see a sine wave this sine wave has a positive and negative half of the AC sine wave if we connect to each bus bar and the neutral we see one side is positive 120 Vol while the other side is negative 120 volt the difference between these gives us 240 volt so this is just a single phase that they split into two however you'll often see Banks of two or three Transformers which do provide three-phase Power to commercial buildings but where did the three phases even come from well the power station generates three-phase AC electricity the generator basically just spins a magnet past a coil of wire the magnetic field pushes and pulls electrons in the coil forwards and backwards as the strongest part of the nor North and South Pole passes through the coil this creates the sine wave with a positive half and a negative half and this is a single phase the generator spins the magnet fast enough that the sine wave repeats 60 times per second and that gives us 60 htz frequency but notice the output power is not constant with single phase we could add another coil which adds another phase and helps to improve this or or we can add a third coil giving us three phases and we see a much better constant output power notice we have three phases but six wires also notice the current is always flowing forwards in one coil and backwards in another so we can combine the coils and the current will share the wires only using them when they need to we could try sending this power directly to the property but it's very far away so the resistance of the wire means we will lose a lot of power just trying to get it there however if we increase the voltage we can send the same amount of Power with less current so we lose almost nothing the power station feeds into a Step up Transformer this increases the voltage to hundreds of thousands of volts and this will keep the current low over the long distance then when it reaches the city it enters a sub station and the voltage is reduced in a Step Down Transformer this continues on the sub transmission lines and it might feed some larger industrial or commercial sites with their own dedicated substations but it otherwise continues to the distribution substation where the voltage is again reduced and then distributed out along the streets to the properties homes will then connect to one of the phases while commercial properties will connect to all three phases now if you need to buy a Transformer keep madx in mind they're basically like a Transformer Superstore they have Transformers of all sizes in stock and ready to ship all across the US from 15 KVA up to 15 MVA they have both dry type and oil filled if you need a Transformer quick call madox Transformer you can also check out their channel for some great tips and tutorials too I'll leave a link for you down below do check them out three-phase Transformers come in many designs but inside we basically just have three singlephase Transformers joined together a Transformer is simply two separate coils of wire placed around a steel core when current flows through a wire it produces an electromagnetic field around the wire when the current changes Direction the magnetic field also changes Direction when we wrap the wire into a coil the magnetic field joins together and forms a larger stronger magnetic field when AC current passes through the coil the magnetic field will increase and decrease as well as change polarity as the current alternates direction if we place another coil in close proximity the magnetic field will interact with the electrons in the second coil and the magnetic field induces a voltage into that coil if the path is complete on the secondary side then a current will also flow however a lot of the magnetic field is currently being wasted so we use a steel core to concentrate and direct the magnetic field making it stronger and more efficient the magnetic field will move around the core this will induce an eddy current within the core material this wastes energy and it also generates heat and we don't want that so we use lots of thin laminated steel sheets to build the core this helps keep the Eddie currents as small as possible so when we apply a voltage to the primary side we get a voltage on the secondary output side and the frequency will remain the same if both coils have the same number of turns then the output voltage and current is the same as the input voltage if the secondary side has fewer turns than the primary we get a lower output voltage but a higher current and this is a Step Down Transformer if the secondary side has more turns than the primary then we get a higher output voltage but a lower current and this is a Step up Transformer in each case the power transferred is the same value for example if this Step Down Transformer was supplying 200 volt and 10 amps to the load then we have 2,000 volt ampers on the secondary side the primary side would see 5 amps and 400 volt which is also 2,000 Vol ampers or 2 KVA so the power transferred is the same but the voltage and current change now we could have three separate Transformers but to save cost material and space we often combine them the three coils on the primary are connected to the phases in either Delta or Y configuration the secondary side coils can also be Delta or Y so we can have a Delta Delta a y y a y Delta or a Delta y Transformer the name plate on the side of the Transformer will tell you how it's configured for y configurations we connect one end of each coil together the other end connects to a phase notice it looks like the letter Y so it's easy to remember from the central point of the coils we can connect a neutral wire and also a ground connection this allows us to connect to a single phase or all three phases we can see with this Transformer that one side of each coil connects to a dedicated terminal for each phase but the other end of each coil connects into the same point using four terminals so we know this is a y connection with the Delta all the coils are connected end to end with the phases connecting between the coils this forms a triangle that looks like the Greek symbol for delta there isn't a neutral with this design so it's only for three phase loads however there are some variations like the high leg and the open Delta but I'll explain those later in the video with this Transformer we can see each coil connects to a terminal but the other end of each coil connects to a different terminal so we know that this is a Delta connection the coils could be on either side of the core but we usually find them placed concentrically with one surrounding the other so maybe we have a pad mounted Transformer powering a small commercial building the stickers and name plate tell us it's a 12,470 volt Delta primary and a 20820 volt y secondary and the Transformer is rated for 150 KVA so we have three phases and three wires entering the Transformer's primary side with 12,470 volts between each phase the secondary side is wire connected with four wires leaving the Transformer it's a Step Down Transformer with 208 volts between any two phases or 120 volts between any phase and the neutral it can handle up to 150,000 volt ampers in total so that's 50,000 per phase or per coil set which means we can supply up to 416 amps on each phasee and through each coil on the secondary and that would cause four amps to flow through the primary coils and that causes 6.9 amps to flow through each line that is our maximum limit for the Transformer the actual KVA transferred depends on how much equipment you connect and power we just can't exceed the Transformers limit otherwise it will overheat cause a short circuit and it will simply burn out our next EX example is this larger commercial building which might need to power 480 volt 3-phase Motors 277 volt fluorescent lighting 28 volt appliances and 120 volt Outlets outside the building we find a pad mounted Transformer rated 12,470 g/ 7,200 and that's on the primary side and on the secondary side we have 480 v/ 277 Vol and the Transformer is rated for 500 KVA and this is supplying the building we know it's a y yre Transformer with four wires entering the primary side and four wires leaving and entering the building it also tells us that the primary side is grounded so there's 12,470 volt from Line to Line or 7,200 volt from line to neutal on the primary side and there's 480 volt Line to Line or 2 277 volts line to neutral on the secondary side now this might enter the building and Connect into a switchboard and from here it might feed a panel which feeds a motor 480 volt 3phase and maybe it feeds a panel which supplies a smaller step down dry type Transformer and that Transformer fees a 208/120 volt panel this smaller Transformer is 480 volt Delta primary and 28 Vol 120 volt y secondary and the Transformer is rated for say 30 KVA so this provides 28 volt 3phase or 120 volt phase to neutral inside this Transformer we have three coils and the terminals labeled H1 H2 and H3 this is our high voltage side where the phases connect for the Delta connection then we have X1 X2 and X3 along the bottom this provides our three output phases and there is also an x0 terminal for the neutral notice on the coil these black jump leads and the Seven connection points on each phase these are called Taps we can move the jump leads to increase or decrease the length of the coil let's say we have 84 turns on the primary with five Taps and 20 turns on the secondary we measure the supply side and have 480 volts so the data sheet says to use tap three on All Phase coils this has 80 turns and provides the designed 120 Vol output however if we measured 54 volts on the supply side we would get 126 volts on the secondary so we need to increase the coil and we use tap one with 84 turns to reduce the output voltage back to 120 volt but if we had only the 456 volts on the primary then we' need to use tap 5 with 76 turns to get the 120 volt output so we can compensate for Supply voltage variations using these Taps we usually find the primary coil on the outside because we can easily change the connections the large pad mounted Transformers also have tap changes but the coils are submerged in oil for cooling so we can't access them the the coils therefore connect to different points of the tap changer and the dial changes which parts of the coil are connected across we often find smaller commercial buildings supplied by three pole mounted Transformers connected in Delta y this provides three phase 208 Volt or singlephase 120 volts or it could be 480 volts and 277 volts sometimes they are connected Delta Delta usually providing 480 volt 3phase only sometimes only two Transformers are used forming an open Delta it typically provides 240 volt 3phase and 120 volt single phase with a high leg of 28 volts however this design is missing a coil so it has a reduced capacity I'll explain why in just a moment I've made these three phase Transformer mugs with the formulas and diagrams on to make it very easy to remember and you can grab my PDF sheets too links down below for that if you'd like one for y connections we have all three coils joined at the center at this point we normally ground the Transformer and we run a neutral wire from here so we have a three-phase four wire system this gives us a line voltage or line to line voltage and also our phase voltage which is often called the line to neutral voltage in this example we have a 208 120 volt secondary so we have 208 volts between any two lines or we have 120 volts between any line and the neutral now it's the coil that's producing the 120 volts and that just depends on how many turns the coil has and the primary applied voltage the simple reason we get 208 volts is because we are connecting across two coils but these coils are not in phase one is in the positive while the other is in the negative cycle at the widest point roughly 120° rotation phase a will be 104 Vol RMS while phase c will be negative4 Vol RMS so the difference is 208 Vol or we can solve using trigonometry we have three coils which are all 120 volts and they are 120° rotation apart so all we need to know is the length of the side of the triangle from trigonometry we use this formula and drop in our values and that gives us 208 volts between two phases now no one wants to write that out every time but notice the ratio between the two voltages it's around 1732 etc etc etc this number just goes on and on so Engineers just say 1732 or they use the square Ro T of three because it's even easier we get that because if we Square this ratio meaning we just multiply it by itself then we get three so to undo that to find the original or the root number that was used to make this square number we just take the square root so the square root of three is 1732 Etc therefore if we know the phase voltage we multiply this by the square root of three to find the line voltage and if we know the line voltage then we divide that by the sare < TK of 3 to find the phase voltage luckily the current in the Y configuration is super easy the phase current is the same as the line current so if we had 100 amps on the line we would also read 100 amps through the coil in the Delta connection each coil is joined end to end the phase wires connect to the intersections between two coils this gives us a three-phase three wire system there is no neutral so we only have line voltages in this example we have 480 volts between any two phases the line voltage is the same as the voltage across the coil or the phase voltage because we only have one coil between any two phases but the current is split between two coils and we know that they are flowing at different times so the line current will be larger than the phase current if we know there's 43.3 amps flowing on the line then we divide this by the square < TK of 3 to get 25 amps on the coil and if we know the coil current is 25 amps then we multiply by the square < TK of 3 to get 43.3 amps on the line a fairly quick way to mathematically see that is to simply draw each of our coil currents 120° apart to find line a current we have coil C to a and coil A to B connected to it so we reverse coil C to a which would sit 60 de apart from the other two coil currents then we slide that line to the end of the ab coil current line and really we're just making a parallelogram but we're going to skip that step we know that this angle must be 180° total so 180° minus the 60° we already have means this remaining angle is 120° so our line current will be the resultant line between these two points so now we just have a triangle with an unknown side and we can use trigonometry to solve that so our line current is therefore 43.3 amps which is 1732 times larger than the coil current which is equivalent to the square < TK of 3 so if we had a Delta y Transformer with 80 turns on the primary and 20 on the secondary we have a ratio of 4:1 the primary side has 480 volts between two phases so there's 480 volt on the coil we calculate the voltage in our secondary coil is therefore 120 volt and that is our phase voltage so we can then easily find the line voltage of 208 volts the secondary side has 100 amps on each phase we find the primary winding current of 25 amps through each Cor oil the current on each line is therefore 43.3 amps so the primary side power is 36,000 Vol ampers the secondary side is also 36,000 amp so the power transferred is the same but the voltage and current are transformed in the high leg Delta we have three coils connected in delta in this case the voltage between any two phases is 240 volt the voltage across Ross the coil is also 240 Vol but one of the coils has a wire connected to the center of the coil this is also grounded the wire acts as a neutral so we can use half of the 240 volt coil to get 120 volts between phase a and neutral or between phase C and neutral however between phase b a neutral we get 208 volts because we are using one and and a half coils we can find that using trigonometry this is why the B phase will usually be orange in the panel to warn it's a higher voltage and that's because it will likely destroy any 120 volt Appliance if it's improperly connected the open Delta uses just two Transformer coils so it's missing one of the coils we get the same voltage in the coil so it's the same voltage between lines and the same voltage between the line and the neutral however the capacity is reduced if we had three Transformers each rated 20 KVA that gives us 60 KVA in total then the maximum coil current or phase current would be 83.33% 4.6 kba that's 57.7% in comparison or a reduction of 42.3% compared to the three Transformer Delta our rated capacity for this two Transformer design is now just 40 KVA but we can only handle 34.6 KVA meaning we can only use 86.6% of the stated capacity so this design is cheaper to install but it's not always practical however it is easy to increase at a later date hey I'd just like to give a huge shout out to our incredible patreon and channel members thank you so much for supporting us and if you'd like to see your name here along with Priority Access to our content and behind the scenes footage links down below for how to join

sponsored by madx this is a three-phase Transformer it has a Delta primary and a y secondary and it&#39;s rated for 2 KVA confused well don&#39;t worry I will explain all of that the Transformer basically just takes an ac voltage and converts it into another voltage we can get one two or even three different voltages out of the secondary side but there are no moving parts inside and there are no wires connecting from one side to the other you&#39;ve likely seen these big green boxes at the side of the road inside is a three-phase Transformer these Supply power to commercial buildings because they have a lot of lighting and Equipment inside your home has much less stuff so you only get a singlephase Transformer this might be pole mounted or pad mounted we can see there are three wires going to the home but this is not a three-phase Transformer the typically connect to just a single phase and the neutral of the distribution grid it then reduces this voltage to a much safer level inside we basically have a primary coil which connects across the phase and the neutral then we have another completely separate coil called a secondary and the two hot wires connect to the ends of this coil and the neutral connects to the center these wires run into the property to your electrical panel the primary side has a singlephase AC Supply the secondary side is also a single phase between the two hot wires giving us 240 volts the current and voltage are flowing forwards and backwards between these two as it is alternating current but if we connect from the neutral to one of the hot bus bars we get 120 volts because we&#39;re using just half of the secondary coil the other side is also providing 120 volts and it uses the other half of the coil if we plug an oscilloscope into the outlet we would see a sine wave this sine wave has a positive and negative half of the AC sine wave if we connect to each bus bar and the neutral we see one side is positive 120 Vol while the other side is negative 120 volt the difference between these gives us 240 volt so this is just a single phase that they split into two however you&#39;ll often see Banks of two or three Transformers which do provide three-phase Power to commercial buildings but where did the three phases even come from well the power station generates three-phase AC electricity the generator basically just spins a magnet past a coil of wire the magnetic field pushes and pulls electrons in the coil forwards and backwards as the strongest part of the nor North and South Pole passes through the coil this creates the sine wave with a positive half and a negative half and this is a single phase the generator spins the magnet fast enough that the sine wave repeats 60 times per second and that gives us 60 htz frequency but notice the output power is not constant with single phase we could add another coil which adds another phase and helps to improve this or or we can add a third coil giving us three phases and we see a much better constant output power notice we have three phases but six wires also notice the current is always flowing forwards in one coil and backwards in another so we can combine the coils and the current will share the wires only using them when they need to we could try sending this power directly to the property but it&#39;s very far away so the resistance of the wire means we will lose a lot of power just trying to get it there however if we increase the voltage we can send the same amount of Power with less current so we lose almost nothing the power station feeds into a Step up Transformer this increases the voltage to hundreds of thousands of volts and this will keep the current low over the long distance then when it reaches the city it enters a sub station and the voltage is reduced in a Step Down Transformer this continues on the sub transmission lines and it might feed some larger industrial or commercial sites with their own dedicated substations but it otherwise continues to the distribution substation where the voltage is again reduced and then distributed out along the streets to the properties homes will then connect to one of the phases while commercial properties will connect to all three phases now if you need to buy a Transformer keep madx in mind they&#39;re basically like a Transformer Superstore they have Transformers of all sizes in stock and ready to ship all across the US from 15 KVA up to 15 MVA they have both dry type and oil filled if you need a Transformer quick call madox Transformer you can also check out their channel for some great tips and tutorials too I&#39;ll leave a link for you down below do check them out three-phase Transformers come in many designs but inside we basically just have three singlephase Transformers joined together a Transformer is simply two separate coils of wire placed around a steel core when current flows through a wire it produces an electromagnetic field around the wire when the current changes Direction the magnetic field also changes Direction when we wrap the wire into a coil the magnetic field joins together and forms a larger stronger magnetic field when AC current passes through the coil the magnetic field will increase and decrease as well as change polarity as the current alternates direction if we place another coil in close proximity the magnetic field will interact with the electrons in the second coil and the magnetic field induces a voltage into that coil if the path is complete on the secondary side then a current will also flow however a lot of the magnetic field is currently being wasted so we use a steel core to concentrate and direct the magnetic field making it stronger and more efficient the magnetic field will move around the core this will induce an eddy current within the core material this wastes energy and it also generates heat and we don&#39;t want that so we use lots of thin laminated steel sheets to build the core this helps keep the Eddie currents as small as possible so when we apply a voltage to the primary side we get a voltage on the secondary output side and the frequency will remain the same if both coils have the same number of turns then the output voltage and current is the same as the input voltage if the secondary side has fewer turns than the primary we get a lower output voltage but a higher current and this is a Step Down Transformer if the secondary side has more turns than the primary then we get a higher output voltage but a lower current and this is a Step up Transformer in each case the power transferred is the same value for example if this Step Down Transformer was supplying 200 volt and 10 amps to the load then we have 2,000 volt ampers on the secondary side the primary side would see 5 amps and 400 volt which is also 2,000 Vol ampers or 2 KVA so the power transferred is the same but the voltage and current change now we could have three separate Transformers but to save cost material and space we often combine them the three coils on the primary are connected to the phases in either Delta or Y configuration the secondary side coils can also be Delta or Y so we can have a Delta Delta a y y a y Delta or a Delta y Transformer the name plate on the side of the Transformer will tell you how it&#39;s configured for y configurations we connect one end of each coil together the other end connects to a phase notice it looks like the letter Y so it&#39;s easy to remember from the central point of the coils we can connect a neutral wire and also a ground connection this allows us to connect to a single phase or all three phases we can see with this Transformer that one side of each coil connects to a dedicated terminal for each phase but the other end of each coil connects into the same point using four terminals so we know this is a y connection with the Delta all the coils are connected end to end with the phases connecting between the coils this forms a triangle that looks like the Greek symbol for delta there isn&#39;t a neutral with this design so it&#39;s only for three phase loads however there are some variations like the high leg and the open Delta but I&#39;ll explain those later in the video with this Transformer we can see each coil connects to a terminal but the other end of each coil connects to a different terminal so we know that this is a Delta connection the coils could be on either side of the core but we usually find them placed concentrically with one surrounding the other so maybe we have a pad mounted Transformer powering a small commercial building the stickers and name plate tell us it&#39;s a 12,470 volt Delta primary and a 20820 volt y secondary and the Transformer is rated for 150 KVA so we have three phases and three wires entering the Transformer&#39;s primary side with 12,470 volts between each phase the secondary side is wire connected with four wires leaving the Transformer it&#39;s a Step Down Transformer with 208 volts between any two phases or 120 volts between any phase and the neutral it can handle up to 150,000 volt ampers in total so that&#39;s 50,000 per phase or per coil set which means we can supply up to 416 amps on each phasee and through each coil on the secondary and that would cause four amps to flow through the primary coils and that causes 6.9 amps to flow through each line that is our maximum limit for the Transformer the actual KVA transferred depends on how much equipment you connect and power we just can&#39;t exceed the Transformers limit otherwise it will overheat cause a short circuit and it will simply burn out our next EX example is this larger commercial building which might need to power 480 volt 3-phase Motors 277 volt fluorescent lighting 28 volt appliances and 120 volt Outlets outside the building we find a pad mounted Transformer rated 12,470 g/ 7,200 and that&#39;s on the primary side and on the secondary side we have 480 v/ 277 Vol and the Transformer is rated for 500 KVA and this is supplying the building we know it&#39;s a y yre Transformer with four wires entering the primary side and four wires leaving and entering the building it also tells us that the primary side is grounded so there&#39;s 12,470 volt from Line to Line or 7,200 volt from line to neutal on the primary side and there&#39;s 480 volt Line to Line or 2 277 volts line to neutral on the secondary side now this might enter the building and Connect into a switchboard and from here it might feed a panel which feeds a motor 480 volt 3phase and maybe it feeds a panel which supplies a smaller step down dry type Transformer and that Transformer fees a 208/120 volt panel this smaller Transformer is 480 volt Delta primary and 28 Vol 120 volt y secondary and the Transformer is rated for say 30 KVA so this provides 28 volt 3phase or 120 volt phase to neutral inside this Transformer we have three coils and the terminals labeled H1 H2 and H3 this is our high voltage side where the phases connect for the Delta connection then we have X1 X2 and X3 along the bottom this provides our three output phases and there is also an x0 terminal for the neutral notice on the coil these black jump leads and the Seven connection points on each phase these are called Taps we can move the jump leads to increase or decrease the length of the coil let&#39;s say we have 84 turns on the primary with five Taps and 20 turns on the secondary we measure the supply side and have 480 volts so the data sheet says to use tap three on All Phase coils this has 80 turns and provides the designed 120 Vol output however if we measured 54 volts on the supply side we would get 126 volts on the secondary so we need to increase the coil and we use tap one with 84 turns to reduce the output voltage back to 120 volt but if we had only the 456 volts on the primary then we&#39; need to use tap 5 with 76 turns to get the 120 volt output so we can compensate for Supply voltage variations using these Taps we usually find the primary coil on the outside because we can easily change the connections the large pad mounted Transformers also have tap changes but the coils are submerged in oil for cooling so we can&#39;t access them the the coils therefore connect to different points of the tap changer and the dial changes which parts of the coil are connected across we often find smaller commercial buildings supplied by three pole mounted Transformers connected in Delta y this provides three phase 208 Volt or singlephase 120 volts or it could be 480 volts and 277 volts sometimes they are connected Delta Delta usually providing 480 volt 3phase only sometimes only two Transformers are used forming an open Delta it typically provides 240 volt 3phase and 120 volt single phase with a high leg of 28 volts however this design is missing a coil so it has a reduced capacity I&#39;ll explain why in just a moment I&#39;ve made these three phase Transformer mugs with the formulas and diagrams on to make it very easy to remember and you can grab my PDF sheets too links down below for that if you&#39;d like one for y connections we have all three coils joined at the center at this point we normally ground the Transformer and we run a neutral wire from here so we have a three-phase four wire system this gives us a line voltage or line to line voltage and also our phase voltage which is often called the line to neutral voltage in this example we have a 208 120 volt secondary so we have 208 volts between any two lines or we have 120 volts between any line and the neutral now it&#39;s the coil that&#39;s producing the 120 volts and that just depends on how many turns the coil has and the primary applied voltage the simple reason we get 208 volts is because we are connecting across two coils but these coils are not in phase one is in the positive while the other is in the negative cycle at the widest point roughly 120° rotation phase a will be 104 Vol RMS while phase c will be negative4 Vol RMS so the difference is 208 Vol or we can solve using trigonometry we have three coils which are all 120 volts and they are 120° rotation apart so all we need to know is the length of the side of the triangle from trigonometry we use this formula and drop in our values and that gives us 208 volts between two phases now no one wants to write that out every time but notice the ratio between the two voltages it&#39;s around 1732 etc etc etc this number just goes on and on so Engineers just say 1732 or they use the square Ro T of three because it&#39;s even easier we get that because if we Square this ratio meaning we just multiply it by itself then we get three so to undo that to find the original or the root number that was used to make this square number we just take the square root so the square root of three is 1732 Etc therefore if we know the phase voltage we multiply this by the square root of three to find the line voltage and if we know the line voltage then we divide that by the sare &lt; TK of 3 to find the phase voltage luckily the current in the Y configuration is super easy the phase current is the same as the line current so if we had 100 amps on the line we would also read 100 amps through the coil in the Delta connection each coil is joined end to end the phase wires connect to the intersections between two coils this gives us a three-phase three wire system there is no neutral so we only have line voltages in this example we have 480 volts between any two phases the line voltage is the same as the voltage across the coil or the phase voltage because we only have one coil between any two phases but the current is split between two coils and we know that they are flowing at different times so the line current will be larger than the phase current if we know there&#39;s 43.3 amps flowing on the line then we divide this by the square &lt; TK of 3 to get 25 amps on the coil and if we know the coil current is 25 amps then we multiply by the square &lt; TK of 3 to get 43.3 amps on the line a fairly quick way to mathematically see that is to simply draw each of our coil currents 120° apart to find line a current we have coil C to a and coil A to B connected to it so we reverse coil C to a which would sit 60 de apart from the other two coil currents then we slide that line to the end of the ab coil current line and really we&#39;re just making a parallelogram but we&#39;re going to skip that step we know that this angle must be 180° total so 180° minus the 60° we already have means this remaining angle is 120° so our line current will be the resultant line between these two points so now we just have a triangle with an unknown side and we can use trigonometry to solve that so our line current is therefore 43.3 amps which is 1732 times larger than the coil current which is equivalent to the square &lt; TK of 3 so if we had a Delta y Transformer with 80 turns on the primary and 20 on the secondary we have a ratio of 4:1 the primary side has 480 volts between two phases so there&#39;s 480 volt on the coil we calculate the voltage in our secondary coil is therefore 120 volt and that is our phase voltage so we can then easily find the line voltage of 208 volts the secondary side has 100 amps on each phase we find the primary winding current of 25 amps through each Cor oil the current on each line is therefore 43.3 amps so the primary side power is 36,000 Vol ampers the secondary side is also 36,000 amp so the power transferred is the same but the voltage and current are transformed in the high leg Delta we have three coils connected in delta in this case the voltage between any two phases is 240 volt the voltage across Ross the coil is also 240 Vol but one of the coils has a wire connected to the center of the coil this is also grounded the wire acts as a neutral so we can use half of the 240 volt coil to get 120 volts between phase a and neutral or between phase C and neutral however between phase b a neutral we get 208 volts because we are using one and and a half coils we can find that using trigonometry this is why the B phase will usually be orange in the panel to warn it&#39;s a higher voltage and that&#39;s because it will likely destroy any 120 volt Appliance if it&#39;s improperly connected the open Delta uses just two Transformer coils so it&#39;s missing one of the coils we get the same voltage in the coil so it&#39;s the same voltage between lines and the same voltage between the line and the neutral however the capacity is reduced if we had three Transformers each rated 20 KVA that gives us 60 KVA in total then the maximum coil current or phase current would be 83.33% 4.6 kba that&#39;s 57.7% in comparison or a reduction of 42.3% compared to the three Transformer Delta our rated capacity for this two Transformer design is now just 40 KVA but we can only handle 34.6 KVA meaning we can only use 86.6% of the stated capacity so this design is cheaper to install but it&#39;s not always practical however it is easy to increase at a later date hey I&#39;d just like to give a huge shout out to our incredible patreon and channel members thank you so much for supporting us and if you&#39;d like to see your name here along with Priority Access to our content and behind the scenes footage links down below for how to join

Transcript for:Three-Phase Transformers Lecture

Transcript for:
Three-Phase Transformers Lecture