The per unit system allows engineers to analyze a single phase network where. Power system analysisper unit reactance diagram youtube. Another approach to solve circuits containing transformers is the perunit system. Also, machine and transformer impedances fall within fairly narrow ranges for each type and construction of device while the perunit system is employed. Calculate lateral loads continued in the additional information provided in the description of the house, the top of footing is 24 in. Watch this video to see jim phillips explain how to use the positive, negative and zero sequence impedances in a per unit format to calculate the three phase and. The elements have to be converted to an mva value and then the circuit is converted to admittance values. Its important to remember any time we do calculations we must have our measures in the same system and in the same sized units. Handout page 1 of 6 dosage calculations this unit looks at drug calculations. These become useful when performing calculations across a power system where multiple voltage levels and different equipment sizes occur.
Dosage calculations dosage calculations include calculating the number of doses, dispensing quantities, and ingredient quantities. This is a useful method to obtain an estimated value of fault current. For each system parameter, per unit value is equal to the actual value divided by a base value. Every time you cross the transformers, the currents and voltages change.
Singlephase per unit system advantages of the per unit system. One kilowatt hour is the amount of energy that would be converted by a one thousand watt appliance when used for one hour example a consumer uses a 6 kw immersion heater, a 4 kw electric stove and three 100 watt lamps for 10 hours. Short circuit current calculations threephase short circuits basic pointtopoint calculation procedure step 1. The kva and voltage bases used in the per unit calculations. Calculations are simplified because quantities expressed as per unit do not change when they are referred from one side of. The per unit system also makes the calculation easier as all the values are taken in the same unit. Vin per unit vin kvv base in kv where the base value is a reference value for magnitude. Per unit fault calculations is a method whereby system impedances and quantities are normalised across different voltage levels to a common base. Short circuit calculations only one calculation needs to be done for most 3 phase systems. Per unit calculations a key problem in analyzing power systems is the large number of transformers. Short circuit calculations per unit and symmetrical. As you can see there are a lot of things to factor in.
Fault current calculations the base current of the generator can be computed as, 0 4 0 e e e s ia v the subtransient, transient, and steadystate currents are per unit and amps 1. Calculations the following controls are part of the calculations section. Power system analysis per unit reactance diagram abhishek maurya. The pharmacy technician must have a full working knowledge of how to perform these calculations. Heat conduction and thermal resistance for steady state conditions and one dimensional heat transfer, the heat q conducted through a plane wall is given by. Hvac rule of thumb calculator engineering pro guides. The machine hour rate is similar to the labour hour rate method and is used where the work is performed primarily on machines.
Electric utility data is also often provided in terms of per unit and symmetrical components. Shortcircuit current calculations cooper industries. Per unit analysis for single and three phase systems udemy. The basic equation for calculating a per unit value is shown below. Convert the per unit currents and voltages from step 4 into volts and ohms. Per unit system and symmetrical components are used for many short circuit calculations. Select rated values as base values, usually rated power in mva and rated phase voltage in kv. For example, a motor with a 100 horsepower hp nameplate rating which delivers 90 hp to a dynamic load is said to be 90% loaded or 0. By removing the impact of varying voltages, the necessary calculations are simplified. On the second day, jim builds upon the per unit system and takes you to the next level with symmetrical components and unbalanced power system calculations. In per unit, base conversion is a normal part of the calculation method while in ohmic method, complex entities conversion. In parts 2 and 3 april 1996 issue, well describe the per unit method of performing shortcircuit calculations.
Sample calculations 1 you need to spread a crabgrass herbicideyou need to spread a crabgrass herbicide over 2400 sq. The determination of per unit values is not the end objective of a study. These calculations are made to assure that the service equipment will clear a fault in case of short circuit. Impedance and voltagelevel conversions are avoided. Parameters calculation this section is to enter the. Transformers can be replaced by their equivalent series impedances.
Short circuit fault calculations as required to be performed on all electrical service entrances by national electrical code 1109, 11010. The label states that the contents of the b ill 5 000 ftbag will cover 5,000 sq. This allows the removal of the complexity of transformer ratios in the fault calculations. Singlephase per unit system university of texas at. The easy way to do hand calculation is the mva method.
Draw the system impedance diagram using the per unit values. Per unit systems is an important concept in power system analysis. Per unit calculations transformer electrical impedance. Easy and simple methods for calculating short circuit curr. Calculation of intravenous drip rates in these types of calculations, for a given volume, time period, and drop factor gttsml, the required iv flow rate in drops per minute gttsmin is calculated. You purchase a 25 lb bag of the herbicideyou purchase a 25 lb bag of the herbicide. Per unit notation in per unit notation, the physical quantity isin per unit notation, the physical quantity is expressed as a fraction of the reference vava ue.
Per unit representation results in a more meaningful and correlated data. Equations used for finding base quantities of impedance, current, and power are shown in table 1, where. The per unit system of calculation is a method whereby system impedances and quantities are normalized across different voltage levels to a common base. So onethird of your ml per hour 150ml should be your answer i. These hand calculations are very prone to errors due to so many conversion required. Selection of base quantities the most fundamental requirement of a per unit system is that all formulas and calculations must. Calculations are simplified because quantities expressed as per unit do not change when they are referred from one side of a transformer to the other. In part 1 of this article, which was featured in the june 1995 issue, we discussed the types of networks to calculate shortcircuit current i.
The three systems available in this calculator are the 1 split system, packaged ac, 2 air cooled chilled water and 3 water cooled chilled water. Short circuit current calculations cooper industries. Since a fraction of a drop is not possible to give to a patient, it is usual to round the answers to the nearest whole number. Thank you for showing interest in buying our book technical calculation and estimators manhours manual you can buy the electronic v ersion of the manual containing all the figurest and other relat ed data at the following prices. How many units kwh of electrical energy have been converted. Per unit system for the analysis of electrical machines or electrical machine system, different values are required, thus, per unit system provides the value for voltage, current, power, impendence, and admittance. Per unit pu systems are used by engineers to quantify equipment parameters in terms of their nameplate ratings. In the most common usage for per unit calculation, the analysis of an entire power system, the nominal or nameplate voltage rating for each.
Define four quantities in per unit of their respective base values. Rather determined per unit values serve to assist in the calculation of other system values. Perform the circuit analysis to determine the current magnitudes in per unit. Learn how to more easily use positive, negative and zero sequence components and draw zero sequence diagrams. All p and q quantities are three phase voltage magnitudes are represented as a fractional part of their standard or base value all phase angles are represented in the same units as normally used advantages 1. Per unit system in power system with problem solution of finding reactance duration.
The generators per unit voltage is the transmission lines per unit impedance is the other base quantities are 10 0 41. Per unit and primarysecondary calculations per unit basics a per unit value is the actual value of some quantity divided by the base value of that quantity. In this course you will learn exactly what per unit analysis is, the main advantages of using it, how manufacturers of equipment use and rate their products and the technique of converting to and. Per unit identities university of minnesota duluth. To use the per unit method, we normalise all the system impedances and admittances within the network under. Imagine a 3phase system with a generator, a transformer, a tline, another transformer, and a load.
This class is loaded with many in class examples and problems for a hands on. Jirutitijaroen 2 20012012 threephase circuit analysis. To perform the fault calculations the following information must be obtained. Per unit impedances of transformers are the same whether they are referred to the primary or secondary side, which makes calculations much simpler in multiple voltage level power systems. Fault calculation methods university of new south wales.
There is no need to convert to an mva base or worry about voltage levels. Equipment impedances can be easily estimated since their per unit impedances lie within a relatively narrow range. It would be very difficult to continually have to refer impedances to the different sides of the transformers thi bl i id d b li i f ll energy systems research laboratory, fiu this problem is. The per unit and ohmic method are very tedious manual calculation. It would be very difficult to continually have to refer impedances to the different sides of the transformers thi bl i id d b li i f ll energy systems research laboratory, fiu this problem is avoided by a normalization of all variables. These values are computed as distributed per unit of distance, lumped or total for a specific line distance, and in per unit. In the power systems analysis field of electrical engineering, a perunit system is the expression of system quantities as fractions of a defined base unit quantity. The reason the per unit system is employed is because it simplifies calculation of currents. Performing shortcircuit calculations requires an understanding of various system components and their interaction. So much so, it shows up in all exams pertaining to power. Fault calculations are simplified very substantially if they are performed using the per unit system and normalising all electrical quantities relating to the fault in per unit values for the fault analysis.