To use the per unit method, we normalize all the system impedances and admittances. Equations used for finding base quantities of impedance, current, and power are shown in table 1, where. Lecture notes on fault detection and location in distribution systems, 2010. The basic equation for calculating a per unit value is shown below. Perunit 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. Singlephase per unit system university of texas at. Power factor per unit calculations is the property of its rightful owner. This article, part of a series of articles, will explain step by step how to calculate these parameters for any component anywhere in the power system. Shortcircuit current calculations cooper industries. The determination of per unit values is not the end objective of a study. 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. Explain the requirements of planning the operation of a power system. The application of the perunit method simplifies these c. Per unit fault calculations is a method whereby system impedances and quantities are normalised across different voltage levels to a common base.
The handbook contains a wide array of topics and each topic is written by an authority on the subject. Source impedance for fault analysis is furnished in per unit. The eqn 1 show that the per unit impedance is directly proportional to base. Introduction to per unit calculations pages 1 11 text. This video explains the complications created by transformers and turns ratios in circuit analysis. For each system parameter, perunit value is equal to the actual value divided by a base value. Besides being taught in higher education, it is quite commonly used by engineers in the power industry. Rather determined per unit values serve to assist in the calculation of other system values. Table a1 provides definitions of base values for the perunit system, in which the rat ed values of the wind generator or power converter are selected as the base. These become useful when performing calculations across a power system where multiple voltage. In such analysis, the power base is often chosen as 100 mva and bases for current and impedance are calculated using the power and voltage base. Equipment impedances can be easily estimated since their per unit impedances lie within a. Select rated values as base values, usually rated power in mva and rated phase voltage in kv.
The treatment throughout the handbook is practical with very little emphasis on theory. Energy, power, and photons energy in a light wave why we can often neglect the magnetic field poynting vector and irradiance the quantum nature of light photon energy and photon momentum. Electrical pe exam perunit an introduction youtube. The manufacturers usually provide the impedance values in per unit. Therefore, the perunit power on the load is the actual power on the load is d the perunit power lost in the transmission line is the actual power lost in the transmission line. I1 ereqt, where i1 total line current,e line voltage powersupply voltage, and reqt line resistance or total equivalent resistance seen by power supply. 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. The direction of flow will be from the higher voltage bus to the lower voltage bus. Handbook of electric power calculations pdf drive electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit.
In the most common usage for per unit calculation, the analysis of an entire power system, the nominal or nameplate voltage rating for each voltage level of the system is chosen as base voltage. Perunit and primarysecondary calculations perunit basics a perunit value is the actual value of some quantity divided by the base value of that quantity. In the above steadystate equation, time does not appear explicitly. The perunit system was developed to make manual analysis of power systems easier.
Power factor 1 for resistive loads such as resistance heaters, incandescant lights, stoves or other nonmotorized equipment. Transformers can be replaced by their equivalent series impedances. The situation is the same here, except that we also must deal with speed or. 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 system explaination with solved example electrical. The per unit system of calculation is a method whereby system impedances and quantities are normalized across different voltage levels to a common base. Perunit and primarysecondary calculations power eng. It is necessary that the proper impedance be used to represent the primary system. With transformers, we need to convert the voltage magnitudes,impedances, currents, etc. V, i, z, and s, and then the base quantities for the other two are computed. Singlephase per unit system advantages of the per unit system.
The motor is to be started by a manual starter, shown in fig. Vin per unit vin kvv base in kv where the base value is a reference value for magnitude. Now consider the real power flow equation from eqs. Per unit identities university of minnesota duluth. The generators perunit voltage is the transmission lines perunit impedance is the other base quantities are 10 0 41. In order to calculate the hydraulic pump flow rate q lmin, you must enter the following figures. A single line diagram is diagrammatic representation of power system in which the components are represented by their. Experiment 6 per unit calculations, impedance diagrams. In the per unit representation, the equivalentin the per unit representation, the equivalent circuit of a transformer is a simple winding impedapeda cence z pu ww t e c tat o b a cith excitation branch ignored i i v v 2 pu 1 pu 2 pu z pu 1 pu.
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. Per unit analysis for single and three phase systems udemy. Fundamental to any power system analysis is the knowhow of per unit systems. Then press p to calculate, this will be shown in the result box. Per unit system explaination with solved example free download as powerpoint. By using per unit calculations that different voltage bases but the same powerbase are used in different transformer sections. The handbook of electric power calculations provides detailed stepbystep calculation. By removing the impact of varying voltages, the necessary calculations are simplified. Impedance and its expression in perunit pu symmetrical fault current calculation systematic fault calculation with bus matrix asymmetrical. Fault calculations are simplified very substantially if they are performed using the perunit system and normalising all electrical quantities relating to the fault in per. For each system parameter, per unit value is equal to the actual value divided by a base value.
When only one device transformer or motor is analyzed, its own ratings are used as the basis for perunit system. Calculations are simplified because quantities expressed as perunit do not change when they are referred from one side of. The calculations using the perunit system are simplified. So much so, it shows up in all exams pertaining to power. Calculations are simplified because quantities expressed as perunit do not change when they are referred from one side of a transformer to the other. Calculate the per unit impedance for transformer t1. Include base values for all data given in per unit. Agitation scaleup calculation does the scaleup from smaller to larger scale based on criteria like equal tip speed, power per unit volume, equal reynolds number, equal shaft speed. The per unit system is a method of normalizing system and equipment. If so, share your ppt presentation slides online with.
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