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Although single-phase electricity is used to supply common domestic and office electrical appliances, three-phase alternating current ac systems are almost universally used to distribute electrical power and to supply electricity directly to higher power equipment.
This technical article describes the basic principles of three-phase systems and the difference between the different measurement connections that are possible.
Three-phase electricity consists of three AC voltages of identical frequency and similar amplitude. This system can be represented diagrammatically by both waveforms and a vector diagram Figure 2.
Consider three single-phase systems each supplying W to a load Figure 3. To supply the power, 1 amp flows through 6 wires, and there are thus 6 units of loss. Alternatively, the three supplies can be connected to a common return, as shown in Figure 4. When the load current in each phase is the same, the load is said to be balanced. One-half of the copper is required, and the wire transmission losses will be halved. The common point is called the neutral point.
This point is often grounded at the supply for safety reasons. In practice, loads are not perfectly balanced, and a fourth neutral wire is used to carry the resultant current. The neutral conductor may be considerably smaller than the three main conductors if allowed by local codes and standards.
The three single-phase supplies discussed earlier could also be connected in series. If the sum is zero, then both end points are at the same potential and may be joined together. The Wye configuration is used to distribute power to everyday single-phase appliances found in the home and office.
Single-phase loads are connected to one leg of the wye between line and neutral. The total load on each phase is shared out as much as possible to present a balanced load to the primary three-phase supply.
The wye configuration can also supply single- or three-phase power to higher power loads at a higher voltage. The single-phase voltages are phase-to-neutral voltages.
A higher phase-to-phase voltage is also available as shown by the black vector in Figure 8. The delta configuration is most often used to supply higher power three-phase industrial loads. In the US, for example, a V delta system may have a split-phase or center-tapped winding to provide two V supplies Figure 9.Although single-phase electricity is used to supply common domestic and office electrical appliances, three phase alternating current a.
This technical article describes the basic principles of three phase systems and the difference between the different measurement connections that are possible. This can be represented diagrammatically by both waveforms and a vector diagram Figure 2.
Consider three single-phase systems each supplying W to a load Figure 3. To supply the power, 1 amp flows through 6 wires and there are thus 6 units of loss. Alternatively, the three supplies can be connected to a common return, as shown in Figure 4. When the load current in each phase is the same the load is said to be balanced.
One half of the copper is required and the wire transmission losses will be halved. The common point is called the neutral point. This point is often grounded at the supply for safety reasons. The three single-phase supplies discussed earlier could also be connected in series. If the sum is zero, then both end points are at the same potential and may be joined together. The Wye configuration is used to distribute power to everyday single-phase appliances found in the home and office.
Single- phase loads are connected to one leg of the wye between line and neutral. The total load on each phase is shared out as much as possible to present a balanced load to the primary three phase supply. The wye configuration can also supply single or three phase power to higher power loads at a higher voltage. The single- phase voltages are phase to neutral voltages. A higher phase to phase voltage is also available as shown by the black vector in Figure 8.
The delta configuration is most often used to supply higher power three phase industrial loads.
The center-tap may be grounded at the transformer for safety reasons. Power is measured in ac systems using wattmeters. A modern digital sampling wattmeter, such as any of the Tektronix power analyzers, multiplies instantaneous samples of voltage and current together to calculate instantaneous watts and then takes an average of the instantaneous watts over one cycle to display the true power. Only one wattmeter is requiredas shown in Figure The system connection to the voltage and current terminals of the wattmeter is straightforward.
The voltage terminals of the wattmeter are connected in parallel across the load and the current is passed through the current terminals which are in series with the load. In this system, shown in Figure 11, the voltages are produced from one center-tapped transformer winding and all voltages are in phase. To measure the total power and other quantities, connect two wattmeters as shown in Figure 11 below.
Where three wires are presenttwo wattmeters are required to measure total power. Connect the wattmeters as shown in Figure In Power Generating Stations, the cumulative reading of such energy meters are used for the calculation of total Million Units MUs of energy exported.
On the basis of MUs, total revenue generated by the Station is calculated. Thus reading of Energy Meter is quite important to be recorded, accounted and audited. As we know that. Therefore, an Energy Meter shall take current and voltage as an input. Let us take an example. Assume power factor to be unity for the sake of easy understanding of Multiplication Factor. So, the current and voltage input to meter will be 1 A phase to neutral current and V phase to phase.
How to read a 3 Phase Bi-Directional Meter?
Let us convert the input current and voltage to phase to neutral value. Per phase power calculated by the Energy Meter assuming power factor to be unity. Hence, energy displayed by meter assuming Is this the actual power?
Definitely not. This discrepancy in the actual power and power displayed in energy meter is due to the fact that meter is taking CT and PT secondary value as input for its calculation. To overcome this discrepancy, we need to have a Multiplication Factor of Energy Meter.
Multiplication Factor of Energy Meter is calculated as below. You can find the meter CT and PT ratio in the manufacturer manual. Usually both the ratios are 1. Let us calculate the Multiplication Factor for our example. Let this difference in meter reading is n Wh for the given period. Supposing my CT ratio is same but the PT ratio differs. Then how should i calculate the M. High light on it please. One meter will only have one CT and one PT input.
Therefore the method for calculation of multiplication factor will remain same. For Multifunctional meter it is not required. Yes u r right Mr. Aurel made the calculation with 6. That should be Then the answer would be Thank you Aurel for asking.
Yes, you need to multiply the energy meter reading by for kWh or Unit conversion for getting the actual energy consumption by auxiliaries. You can download Multiplication Factor Calculator for Energy Meters for your future use and reference.
Please share the post if you like it. Thank you for asking.Click Here! To save energy!
3 Phase Energy Meter Working,Construction,Uses
One of the questions that I get most from commercial and industrial customers is, what is demand and what is a demand meter? They want to know what demand is and why they have it on their bill. Customers want to know what demand meters are and why they are on their buildings. They also want to know if the demand meter can be removed.
I am going to attempt to break this down so that it is easy to understand. I want any commercial or industrial customer who comes across this website and has a demand meter to understand demand meters and how to calculate demand. In addition I hope they develop some tools on how to reduce their demand. The first question is, what is demand? When commercial and industrial customers, and even some residential customers now, get their bill they typically notice two types of charges.
The KWH portion of the bill is the total amount of energy that has been consumed for the billing cycle for which the bill was calculated.
In most cases, this is somewhere around thirty days. So, think of KWH as the usage over time. Demand on the other hand is the rate at which the energy is consumed. Again, the unit of measurement is KW. Suppose that one customer has 10, watt light bulbs and another has only one, watt light bulb. Suppose that the second customer, with his one, watt light bulb has baby chickens and does not turn the light off all month because it is required to keep his baby chickens warm all month.
That is all well and good but where does the demand come into play. The first customer in the example would require a larger transformer than the second customer.
His demand would be 1 KW. The demand for the second customer would be 0. If we convert this to amps, we can see that it takes more amps to run 10 bulbs for one hour than it does for 1 bulb. Why does this matter? This matters, and the reason that these demand charges are there is to help the utility offset its cost for the infrastructure that has been built to supply each customer. If the first customer, who requires larger equipment to serve his needs only comes in once per month as in the example, it will take the utility a very long time to recoup its investment.
Another reason the utility has demand charges is because the utility pays higher demand charges when it purchases electricity. It also causes them to run their generation plants more to keep up with the demand.
When a blackout happens, this is what is going on. The demand of the customers exceeds the generation capacity of the utility. How can a customer get around these demand charges? The best way is to know the electric rates that are offered by the utility who serves you. There may be time of use rates, or coincident peak rates that may help out. These could also hurt if they are not understood. Also, some companies base who goes on a demand rate based on their KWH consumption.Three phase meter reading - 3 ഫേസ് മീറ്റർ റീഡിങ് പഠിക്കാം
A standard for many utilities is about 3, KWH. Once a customer goes past this many KWH in one month or in a certain number of months in a twelve month period, they will get a demand meter and be placed on a demand rate.
Some companies require any customer who has three phase power to be on a demand rate. Some rates are also based off of the demand. For instance, if you are already on a demand rate and you buy more equipment and your demand goes beyond a certain threshold, you could be placed on a higher rate.Again, with this meter I was going for simplicity. This meter measures the supply current through each phase using a CT current transformer and then does a few calculations to give you the current, power, maximum power and kilowatt hours consumed for each phase.
With a few changes to the code, you can also add your local tariffs and display the cost of electricity used to date. This instructable assumes you know the basics of Arduino programming, otherwise read my guide on getting started with Arduino. You also need to know how to connect an LCD screen to an Arduino although you can use an LCD screen shield which does most of the work for you.
First you need to start by assembling your components onto the CTs to create the current sensors which produce a signal which your Arduino can understand. An Arduino only has analogue voltage inputs which measure VDC, so you need to convert the current output from the CT into a voltage reference and then scale it into the V input range.
If you are going to be installing your power meter somewhere permanently then you may want to solder the resistors and capacitor directly onto each CT so that they cannot come loose. If you are simply trying this project for fun then a breadboard is perfect. The basic circuit for the connection of the CTs to the Arduino is shown in the attached circuit diagram. The LCD screen shield already picks up on the analogue inputs but only A0 is used by the shield for the button inputs.
Simply solder the five leads from your current sensors onto the pin headers on the shield and use A1 to A3 as your sensor inputs as shown in the attached image. Once you have connected all of your components, you need to connect your sensors onto the supply you want to monitor. For connection to a typical 3 phase mains supply, connect one CT around each of the phases as shown in the attached connection diagram.
NB — Be careful when connecting the CTs to your mains and make sure that the power to your board is switched off before doing anything in the mains box. Do not remove any wires or remove any screws before checking your local regulations with your local authority, you may require a certified electrician to install the CT for you. There are essentially four components which need to be chosen or correctly sized for your energy meter.
The first is the CT or current transformer. At VAC, it can theoretically sense up to To calculate how many amps yours needs to sense, take the maximum continuous power your are expecting to sense and divide that by your voltage usually V or V depending on your country.
Next you need to size your burden resistor R3, this converts your CT current into a voltage reference. This should be around to 1. This article worked on 42A with a turns ratio of giving a secondary current of 0. Your analogue reference voltage to the Arduino is 2.
For a list of some options on different CTs and their ideal burden resistors, visit this link. Finally you need two dividing resistors to get the 2. Here is the link to download the 3 phase meter code.
Because your setup, CTsresistors and input voltages may be different, there is a scaling factor in the sketch which you will need to change before you will get accurate results, see below for calibration. If your LCD is connected to the same pins as used here and your CTs are connected to the same input pins, you should at least get the screens populated with some figures although these will most likely be incorrect and some may be negative.
For those of you who have read that the millis function goes into overflow after about 49 days, the code deals with the rollover automatically by making use of the unsigned long variable. As mentioned above, because your setup, CTsresistors and input voltages may be different, there is a scaling factor in the sketch for each CT which you will need to change before you will get accurate results.
To calibrate your energy meter, your need to be sure that the current that your meter says is being drawn on each phase is what you expect is actually being drawn. In order to do this accurately, you need to find a calibrated load.
These are not easy to come by in a normal household so you will need to find something which uses an established and consistent amount of power. I used a couple of incandescent light bulbs and spot lights, these come in a range of sizes and their consumption is fairly close to what is stated on the label, ie a W light bulb uses very close to W of real power as it is almost entirely a purely resistive load. Plug in a small light bulb W or so on each phase and see what load is displayed.
You will now need to adjust the scaling factors defined in line 8 accordingly:.Below is the most common inner connection of of 3-Phase energy meter. Here is another live example of a a three phase energy meter which has been installed on the main pole of source supply. Warning : This example shows the most common used arrangement in the world, but there are variations as well in some areas. The setting may be different in other type of kWh or energy meter in different locations around the world.
For safety. Please contact to the supply and service provider to confirm the connection type before installation. You may also interested to read in. How to control one lamp from six different places by using two, 2-way switches and four intermediate switches? Everything is a very clear explanation of concerns. Detailed actually. The site is really useful, thank you very much for sharing.
Thx u for such connection. Thx for such 3phase connection. Thanks for sharing, I will bookmark and be back again.
How To Wire a 3-Phase kWh meter? Installation of 3-Phase Energy Meter.
Thank you for this posting. How can indicator lights can be wired to indicate the phases that has light close to the meter. Pls show the connection diagram. This will allow monitoring of which phase has electricity. Diar sar how to joind anarjy mitar in 3 phas line about Ampairs. Plis simpal daiyagaram.
Help mi sar.The calculation of current in a three phase system has been brought up on our site feedback and is a discussion I seem to get involved in every now and again. While some colleagues prefer to remember formulas or factors, I prefer to resolve the problem step by step using basic principles. I thought it would be good to write how I do these calculations. Hopefully it may prove useful to someone else. The product of the voltage and current is the apparent power and measured in VA or kVA.
The relationship between kVA and kW is the power factor pf :. Single phase system - this is the easiest to deal with. Given the kW and power factor the kVA can be easily worked out. The current is simply the kVA divided by the voltage. As an example, consider a load consuming 23 kW of power at V and a power factor of 0.
To convert from VA to kVA just divide by Three phase system - The main difference between a three phase system and a single phase system is the voltage.
To me the easiest way to solve three phase problems is to convert them to a single phase problem. Take a three phase motor with three windings, each identical consuming a given kW. The kW per winding single phase has to be the total divided by 3. Similarly a transformer with three windings, each identical supplying a given kVA will have each winding supplying a third of the total power.
Easy enough. 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. As a rule I remember the method not formulae and rework it every time I do the calculation. When I try to remember formulae I always forget them soon or become unsure if I am remembering them correctly. My advice would be to always try remember the method and not simply memorize formula. Of course if you do have some super ability at remembering formula, you can always keep to this approach.
The above method relies on remembering a few simple principals and manipulating the problem to give the answer. More traditionally formulas may be used to give the same result. These can be easily derived from the above, giving for example:. The above deals with balanced three phase systems. That is the current in each phase is the same and each phase delivers or consumes the same amount of power. This is typical of power transmission systems, electrical motors and similar types of equipment.
Often where single phase loads are involved, residential and commercial premises for example, the system can be unbalanced with each phase have a different current and delivering or consuming a differing amount of power. Luckily in practice voltages tend to be fixed or very by only small amounts. In this situation and with a little thought it is possible to extend the above type of calculation to unbalanced current three phase systems. The key to doing this is that the sum of power in each phase is equal to the total power of the system.
Similarly given the power in each phase you could easily find the phase currents. If you also know the power factor you can convert between kVA and kW as shown earlier. If the voltages become unbalanced or there are other considerations i. System voltages and currents can be found by drawing out the circuit in full detail and using Kirchhoff's laws and other network theorems.