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# 3 phase voltage calculation formula

Assume a voltage drop, say 2 %, Base voltage 230V, 1∅ vd = .02(230) 2. The relationship between kVA and kW is the power factor (pf): Single phase system - this is the easiest to deal with. I would treat these as three separate single phase problems. Any help greatly appreciated! ... Voltage drops are phase-to-phase, for three-phase, three-wire or three-phase, four-wire 60 Hz circuits. The current is simply the kVA divided by the voltage. three phase power is 36 kW,  single phase power = 36/3 = 12 kW   S 1ph = P 1ph pf = P 3×pf, Phase current I (A) is the single phase apparent power divided by the phase to neutral voltage (and given VLN=VLL / √3):      In a single phase system you would only have one winding, giving you a single phase (live and neutral). The voltage measured between any line and neutral is called phase voltage. Back to basic, below are the simple Electric Power formulas for Single Phase AC Circuit, Three Phase AC Circuits and DC Circuits. Phasor Diagrams of Three Phase Circuits..... 22 4D. To protect the windings of a transformer against overcurrent, use the percentages listed in Table 450.3(B) and its applicable notes. Current I = kVA per phase / phase voltage You need to be cognisant of what you are supplying and if this will affect the sizing (for example if the load is non-linear). Since a 3-phase supply has a fixed voltage and frequency it can be used by a rectification circuit to produce a fixed voltage DC power which can then be filtered resulting in an output DC voltage with less ripple compared to a single-phase rectifying circuit. For example, for a 208/120 volt service, the line voltage is 208 Volts, and the phase voltage is 120 Volts. The power P in kilowatts (kW) is equal to 3 times the power factor PF times the phase current I in amps (A), times the line to neutral RMS voltage V L-N in volts (V) divided by 1000: P (kW) = 3 × PF × I (A) × V L-N (V) / 1000.

54,611, This story has been shared 34,261 times. The 3 phase Induction motor is popular for its efficiency and is … The corresponding AC power demand is equal to the sum of the fixed power loss and the DC power demand. KVA is calculated by multiplying the line to line maximum voltage & maximum phase current; then multiplying this value with 1.732 in case of three phase ; lastly dividing the final value by 1000 for KVA and 100,000 for MVA . The phase order is 1‑2‑3. AddThis use cookies for handling links to social media. Cheers, Nathan. If remembering is formulae more easy, just go with that. In Delta connection, phase sides are connected in a cyclical arrangement in order to make a closed loop as shown in figure 1. 21,000 / 230 = 91 A. In a three phase system we have the line to line voltage (VLL)  and the phase voltage (VLN), related by: or alternatively as: We have a lot of loads that are connected line-neutral and figuring out those loads is easy. I've always been bad a remembering formulae, so I prefer to remember concepts/methods. Hopefully it may prove useful to someone else. Would it be possible for you to ask this in our question section. If you know the kVA and voltage, it is very easy to work out the current. KW, KVA KW is real consumed power turned into heat, and is the product of volts x current x power factor. Let’s see two most common methods for calculation of voltage drop – approximate and exact methods: 1. Calculation of Power in a Balanced Three Phase Circuit ..... 20 4C. Formulas Used: Three phase = I x V x 1.732 / 1000 One / single phase = I x V / 1000 Where, I = Amps V = Volts Example: Calculate kVA value for three phase voltage of 5 v and 8 amps. That 60A is total rms current for a single phase, not the peak current, correct? I believe that as you lower the voltage across the lamp, the current would reduce and the brightness (think of the lamp as a resistance). While some colleagues prefer to remember formulas or factors, I prefer to resolve the problem step by step using basic principles. I = Amps. The product of the voltage and current is the apparent power and measured in VA (or kVA) . The power taken by a circuit (single or three  phase) is measured in watts W (or  kW). It is important that calculations be carried... A lot of our members work in countries where PPE (personal protective equipment) is regulated or they work for companies/organizations which take employee... Modelica is an open source (free) software language for modelling complex systems. phase 1 apparent power = 80 x 230 = 18,400 VA = 18.4 kVA      The above method relies on remembering a few simple principals and manipulating the problem to give the answer. dilan, the kVA would be ( 642.24 + 651.85 + 651.84) * 220 = 428102 VA = 428.1 kVA the kW would be 428.1 x 0.86 = 368.2 kW For the breaker, I would likely be looking at 800 A (posibly something like a MasterPact NT or NW, depending on other parameters) and setting the overload protection in the range of 710 A (this is plus 10%). It converts instantaneous three-phase AC voltages to DC voltage and DC power demand to three-phase AC power demand. Just try to balance your single phase loads as much as possible across all three phases. If it is star connected than the phase voltage is 240/sqrt(3) = 138 V and the current is 56,000/138 = 400 A. ... To better understand three phase power, a person would be well advised to first review and understand the principles applicable to single phase power. The Three-Phase Voltage System Three-phase voltage systems are composed of … I am calculating the current in a 3 phase 380 V balanced Y system with a single motor load of 746 watts with a power factor of 0.72 and am getting different results when using the approaches suggested above. Similarly for phase B (1/2AB + 1/2BC) and phase C (1/2BC + 1/2AC). 3-Phase Calculations. Line and Phase currents are related to each other as: I_line=square_root(3)*I_phase Which means that whatever supply current we have, we need a wire cross-section for 1/ square_root(3) times line current only. I = kW / ( √3 x pf x VLL ), in kA The power factor is the ratio of the real work to the apparent power. Calculate three-phase motor power consumption by multiplying amps by volts by the square root of three (W = AV(sqrt 3). one more question. Ignoring efficiency and assuming single phase 230 V, the VA would be 184 (230 V x 0.8 A) and power factor 110/184 = 0.6. Open 3-Phase Circuit Formulas: Open Delta Watts = 2 / 3 W DELTA Open Wye Watts = 1 / 2 W WYE Open 4-wire Wye Watts = 2 / 3 W WYE. This is done all the time (fridge or toilet extract fan in your house for example). For example, take a 400 V (VLL) three phase system with the following loads: phase 1 = 80 A, phase 2 = 70 A, phase 3 = 82 A, the line to neutral (phase) voltage VLN = 400/√3 = 230 V How can I calculate power factor(pf) if I know the kW, V, Hz and reactive power?For a three phase AC generator.Thanks. Which brings up another question. In addition the voltage would be increase the torque and current for which the motor is likely not designed. John, line voltage is dependant on country (and varies within countries). I just don't know how to go about it. The rpm does not affect it. Similarly given the power in each phase you could easily find the phase currents. Google use cookies for serving our ads and handling visitor statistics. Now the calculation you gave me gives me the total amps on A-B but it doesn't tell me how many amps I'm pulling on A and how many amps I'm pulling on B. I know when you are dealing with loads connected across phases figuring out the current isn't as straight forward as using ohms law. That is the current in each phase is the same and each phase delivers or consumes the same amount of power. Enter the rated volts, amps, power, and efficiency to find the current flowing through the motor. Not directly related to the post, but this is a great question. The relationship between kVA and kW is the power factor (pf):Single phase system - this is the easiest to deal with. But a different result when using L = Length of the circuit from power supply to load. Turns Ratio = N 1 / N 2 = V 1 / V 2 = I 2 / I 1. If you wanted to do all your calculations in kW, you could - but you would need to include the power factor as well in any calculation. Generally there are two phases - Single phase or three phase. This formula can help you determine voltage drop across a circuit, as well as the size wire gauge you will need for your circuit based on the maximum desired voltage drop. Formula for Voltage | How to calculate Potential Difference. When selecting a cable, the performance of the cable under fault conditions is an important consideration. Pip, sorry for the delay – busy relocating countries/jobs at the moment. Does Power Factors plays any role? I understand a little more now (perhaps not fully). In a three phase system, the amount of current going through one of the phases is not a fraction of the amount of current going through all three? You give the worse case as 80.6A. To make the situation confusing, the contractor got the confirmation from the manufacturere. In general when connecting in delta you have a higher voltage on each leg, so I would say you consume more power. V Line-Line = 380 V Steven, let me give you a few more details. or need modification on the motor. Please share. Add up the three phases = 48720 VA (or 48.72 kVA). By measuring voltages from Line 1 to Line 2, Line 2 to Line 3, and Line 3 to Line 1, and performing a few simple calculations, a technician can determine if there is a voltage unbalance problem. With single-phase AC power there is only one single sinusoidal voltage. my question is do i need to multiply 80.6a to 1.732 to convert in 3 phase? 2 thoughts on “ Cable Sizing & Voltage Drop Calculations Formula ” Brian July 19, 2019. I'm just holding off on posting as the upgrading of site is going really well. To avoid any misunderstanding, the following post may also help you: http://myelectrical.com/notes/entryid/172/three-phase-power-simplified. Answer: Applying the three-phase formula for voltage drop, where: K = 21.2 ohms-cmil/ft for aluminum; I = 100 amps; D = 80 ft; cmil = 83,690 cmil. With single-phase AC power there is only one single sinusoidal voltage. You can easily find electric power in watts by using the following electric power formulas in electric circuits. Voltage Drop : Calculate Another Variables Used-Things that need to be taken into consideration before computing the cable size and voltage drop. Single phase to 3 phase power calculation input requirement = The square root of 3 (1.732) x 10 amps = 1.732 x 10 amps = 17.32 Amps.   I= S 1ph V LN = P 3×pf 3 V LL, Simplifying (and with 3 = √3 x √3):      Power & Amp - The amount of voltage running through the lines is related to the power and amp. I pretty sure the formula given is correct. To convert from VA to kVA just divide by 1000. 208/120 is the voltage for a delta (208) / star (120), connected system. Voltage Drop Calculation and Formulas for Three Phase system. now simply follow the above single phase method. You can't divide the current by three (power kW or kVA - yes). Mathematical calculation for KVA and MVA for transformer. A higher phase to phase voltage is also available as shown by the black vector in Figure 8. thank you very much. I = 249/(1.73*0.72*380) = 0.52 A 3 phase system, if 1 phase out ( fuse cut0ff burn ) for meter kwh, can make the electricity bill increase..?? If your looking for more detailed information... IEC 60947 is the circuit breaker standard and covers the marking of breakers in detail. Generally there are two phases - Single phase or three phase. The 3 phase load current amps formula is explain with a three phase load voltage induction motor nameplate data. When I try to remember formulae I always forget them soon or become unsure if I am remembering them correctly. Once you know the kVA, you can calculate the power factor form pf=kW/kVA. I know this probably is easy to understand, but I got myself to a completely confused state. If you want to promote your products or services in the Engineering ToolBox - please use Google Adwords. Approximate method. Steven has over twenty five years experience working on some of the largest construction projects. From All About Circuits: In balanced “Y” circuits, line voltage is equal to phase voltage times the square root of 3 In balanced “Δ” circuits, line voltage is equal to phase voltage: *ignore Iline and Iphase I would say you cannot use the motor at 50Hz, 380V. The new posting/commenting system is way better than the current one and I'm now just waiting to use it. Assuming delta connected, the line voltage is across each phase and the current is 56,000/240 = 230 A. And now I would like to know how does the calculation works when a generator has to be used? By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community. Voltage Drop Calculations shall be provided in accordance with the NEC, regardless of where the cable was manufactured. 746/3 = 249 watts per phase If you create a fault the current will increase (you have reduced the circuit impedance with the fault). so that i can assign suitable cable and breaker? The following formula calculates total power in a three-phase system based on KW and KVAr or voltage and current. If  I have a system having Amperes on each phase as 80A, 70A, 82A and VLL is 400V and VLN is 210 V. Kindly share how to calculate its power consumption in KVA. thanks :), Hi, I believe your equation I = kW / ( √3 x pf x VLL ), in kA Should VLL not be VLN here? 80x210 = 1680 VA). Typical 3-Phase Wiring Diagrams and Equations for Resistive Heaters. Each phase is a sine wave. Project management and team collaboration, with clear easy to read calculations and reports. Real Power. 345/219 = 1.57 A per Phase = Line I know that it is right but how can i used it to find the value of complex power?? Most AC power today is produced and distributed as three-phase power where three sinusoidal voltages are generated out of phase with each other. And three-phase voltage drop formula is given as. What normally happens in star is that because the voltage is less across each winding, you end up delivering less power then you would in delta (less power is less current). Because you have an unbalanced system, you will have some current in the neural line. For the red phase, assuming a power factor of 0.95, the kVA is 20 kW / 0.95 = 21 kVA. Secondary voltage, Tap arrangement. By remembering that a three phase power (kW or kVA) is simply three  times the single phase power, any three phase problem can be simplified. On the Star Delta. Hope this makes sense. 3 Phase Induction Motor current calculator is used to calculate the rated and full load amperes of the motor. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. = (kW x √3) / (3 x pf x VLL) This configuration of voltage sources is characterized by a common connection point joining one side of each source. 572.1A). 345/380 = 0.90 I Phase However, if you prefer you can write, manage... GE's latest thinking on product manufacturing is he Shingijutsu philosophy or Lean production system. Example 3: The transformer of a small building is 25000VA single-phase, with a voltage of 240V and an impedance of 3%, which will be the short-circuit level of the transformer. Figure 8 – Voltage (phase-phase) The delta configuration is most often used to supply higher power three phase industrial loads. 380/1.73 = 219 V Line-Neutral (Phase Voltage) Current won't flow through the fault to the load (or very little will). Also, thanks again for posting and all of your help. More traditionally formulas may be used to give the same result. Network analysis is not the intent of this note. Power factor (cosΦ). alternating-current-circuits Have a read of the note and if you are still unclear, you can add a comment to post. THREE-PHASE CIRCUIT CALCULATIONS In the following examples, values of line and phase voltage, line and phase current, … Total three phase power = 18.4 + 16.1 + 18.86 = 53.36 kVA. In the second formula, the phase values of voltage and current are multiplied by 3. Figure 1 illustrates real-time cosine functionality and associated phasor notation for a 3-phase line-to-line voltage system with line voltage V12 as reference. In this post, we’ll detail how to calculate the required KVA for a 3 phase transformer. Please read AddThis Privacy for more information. In your example where you break down a 3-phase problem to a single phase problem with the 36kW load, you get 60A. Voltage Drop - Generally we take the percentage of voltage drop and the most common percentage of voltage drop is 3 percent and 5 percent. A-N, B-N and C-N). Phase Selection - The first thing you want is the type of circuit phase you are going to use. I thought it would be good to write how I do these calculations. = kW / (√3 x pf x VLL) - your formulae 249/0.72 = 345 VA per phase Actually, The calculation of KVA capacity for a Three Phase Transformer is based on Winding Voltage and Amperage information. Line to line voltage: W applied = 3 1/2 U ll I cos Φ = 3 1/2 U ll I PF (1) where. Businesses that require three-phase power need to add an extra component in the formula to arrive at the correct transformer size, i.e., square root of 3 (√3) or 1.732. For 3-phase systems, we use the following equation: kW = (V × I × PF × 1.732) ÷ 1,000. Formulas to calculate single phase AC power in HP, Watts, Kilo-Watts & Kilo-watts-hour Formulas to calculate three phase AC power in HP, Watts, Kilo-Watts & Kilo-watts-hour When Wire length is in meters. Calculation with line to neutral voltage. Luckily in practice voltages tend to be fixed or very by only small amounts. Here is a 3 phase generator output voltage formula to calculate the three phase generator output voltage. If you have a 50A 3 phase MCB, that's 50 per phase - when calculating voltage drop using the tables do you calculate using 50A or 150A? Easy enough. Any ideas where I'm going wrong? Some of our calculators and applications let you save application data to your local computer. Initially, we explored the idea of three-phase power systems by connecting three voltage sources together in what is commonly known as the “Y” (or “star”) configuration. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected. Robert, I make the line current as 33.6 A. Each phase is a sine wave. In this situation and with a little thought it is possible to extend the above type of calculation to unbalanced current three phase systems. I have now changed it to show kVA. To find the kVA you can use sqrt(kW^2 + kWr^2), where kWr is the reactive power. KVA is apparent power, is always greater than or equal to KW and is the product of volts x amps 1 phase, volts x amps x , √3, 3 phase. Is this wrong? To find the power given current, multiply by the voltage and then the power factor to convert to W.  For a three phase system multiply by three to get the total power.    I= P 3 ×pf× V LL. If the voltages become unbalanced or there are other considerations (i.e. I have electric motor from USA, 3 phase 230 Volt 60 Hz. For Example :- Each phase of 3 phase machine takes a load of 16 amps, So how do I calculate how many KVA generator is required ? Thanks. (Figure below) If we draw a circuit showing each voltage source to be a coil of wire (alternator or transformer winding) and do some slight rearranging, t… We previously studied that voltage is the basic property of electrical circuits . Consider the motor as a black box taking some power. Can we use in Asia (380 volt 50 Hz)? The 3 phase load current amps formula is explain with a three phase load voltage induction motor nameplate data. Thank you! The motor would be running faster due to the frequency. If sending end voltage and load PF are known. Hi Steven, Thanks for sharing your knowledge, it really helped me understanding the theory. The voltage drop formula for 3 phase systems is the following: where: VD = The voltage drop of the circuit, in volts. kindly correct my computation: I=1.732(80.6)+491.5A I=631.09. Also depends on if it is three phase or single phase and the voltage. By formula: Volt-Amps (VA) = √3 × V LINE × A LINE Your California Privacy Rights Sorry, your blog cannot share posts by email. This figure is a constant found in three phase, as the phases do not generate the same amount of power (simultaneously). Please check it .if u divide kw by p.f u will get kVA not KW. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. So, VD = 1.732 x 21.2 x 100 x 80/83,690 = 3.51 Voltage Drop Example 3 — Find the size of copper wire needed in a single-phase application to carry a load of 40 amperes at 240 volts a distance of 500 feet with a 2% voltage drop. Phase A starts at 0 at 0 degree phase angle, rises to 1 at 90 degrees, back to 0 at 180, to -1 at 270 degrees, and back to 1 at 360 degrees. *Line-to line voltage values to be considered. If you are looking at it on a phase by phase you may need to be a little careful. Dear Steven - I am a student and I've been struggling to understand something: if we have a balanced STAR connection with a certain apparent power consumption (VA), will this power change if we switch the connection to DELTA? Definitions For Both Wye and Delta (Balanced Loads) V P = Phase Voltage V L = Line Voltage I P = Phase Current I L = Line Current R = R1 = R2 = R3 = Resistance of each branch W = Wattage Wye and Delta Equivalent W DELTA = 3 W WYE. I have the same issue with our Contractor supplying pump motor 50hz, where-in our system here is 60 hz. We don't collect information from our users.   P 1ph = P 3, Single phase apparent power S1ph (VA):      The three phase current as you are trying to calculate it does not exist. The phase voltage is 400/ √(3) = 230 V. To convert kW to kVA you need the power factor (you could just use kW, but you would have some error). 3-Phase AC Calculations Revisited Preamble This application note is a continuation of Dataforth’s Application Note AN109, which contains AC system definitions and basic rules for calculations with examples. CM = Circular-Mils (conductor wire gauge) Notes: • The National Electric Code recommends a maximum 3% voltage drop for branch circuits. Only emails and answers are saved in our archive. The three phase power calculator calculates the active and reactive power current from the following parameters: Voltage (V): Enter the phase-to-phase ($$V_{LL}$$) voltage for a 3-phase AC supply in volts. Please check this and if you find any errors or mistakes let me know. So it is the second part of your reply that I don't understand. Calculating Currents in a Balanced Three Phase Delta Circuit –General ..... 23 4D.1 Resistive Loads ..... 23 4D.2 Capacitive Loads..... 27 4D.3 Inductive Loads..... 29 4D.4 Two or More Loads ..... 31 4E. kVA = kW / power factor = 12/0.86 = 13.9 kW (13900 W) Phase A - 1/2 56,000 + 1/2 17,00 = 36,500 W - divide by 120 V gives 304 A in the line conductor - similar for the other phases, giving B=329 A and C=167 A I have assumed the power factor =1 and W = VA. Exposure to time varying magnetic fields, from power frequencies to the gigahertz range can have harmful consequences. But if you don't mind, I would like to ask a few more question about the apparent power and complex power. VD = $$\frac{2 LRI}{ 1000 \times 0.866}$$ Here, L = refers to the length of the circuit R = refers to the resistance in Omega ($$\Omega$$) I = refers to the load current in amperes. to get the total current. VA is simply the current times the voltage, so knowing this and the voltage can give the current. Also be aware that if draw more power, you equipment may not have been designed for it. NEC 430-150, 10 HP @ 460V, 3 phase I = 14 Amp 3. I will also put together a proper answer when I get some time. Deliberately short, with the aim to provide a quick memory jog or overview. Voltage drop E VD = IR cosθ + IX sinθ where abbreviations are same as below “Exact Method”. Actually, The calculation of KVA capacity for a Three Phase Transformer is based on Winding Voltage and Amperage information. Wapplied = 3 Uln I cos Φ                    (2), For pure resistive load and power factor = 1 the real power in a 400/230 voltage (line to line / line to neutral) 20 amps circuit can be calculated as, WBHP = 31/2 U I PF μ / 746                       (3). The first formula is used more often because it is generally more convenient to obtain line values of volt- age and current, which can be measured with a voltmeter and clamp-on ammeter.