Measurement of power, HR Management

Assignment Help:

Q. Measurement of poweri

A wattmeter is an instrument with a potential coil and a current coil so arranged that its defiection is proportional to VI cos θ, where V is the voltage (rms value) applied across the potential coil, I is the current (rms value) passing through the current coil, and θ is the angle between ¯V and ¯I. By inserting such a single-phase wattmeter to measure the average real power in each phase (with its current coil in series with one phase of the load and its potential coil across the phase of the load), the total real power in a three-phase system can be determined by the sum of the wattmeter readings. However, in practice, this may not be possible due to the nonaccessibility of either the neutral of the wye connection, or the individual phases of the delta connection. Hence it is more desirable to have a method for measuring the total real power drawn by a three-phase load while we have access to only three line terminals.

The three-phase power can bemeasured by three single-phasewattmeters having current coils in each line and potential coils connected across the given line and any common junction. Since this common junction is completely arbitrary, it may be placed on any one of the three lines, in which case the wattmeter connected in that line will indicate zero power because its potential coil has no voltage across it. Hence, that wattmeter may be dispensed with, and three-phase power can be measured by means of only two single-phase wattmeters having a common potential junction on any of the three lines in which there is no current coil. This is known as the two-wattmeter method of measuring three-phase power. In general, m-phase power can be measured by means of m - 1 wattmeters. The method is valid for both balanced and unbalanced circuits with either the load or the source unbalanced.

Figure shows the connection diagramfor the two-wattmetermethod ofmeasuring three-phase power. The total real power delivered to the load is given by the algebraic sum of the two wattmeter readings,

P = WA + WC

The significance of the algebraic sumwill be realized in the paragraphs that follow.Twowattmeters can be connected with their current coils in any two lines, while their potential coils are connected to the third line, as shown in Figure. The wattmeter readings are given by

2165_MEASUREMENT OF POWER.png

The two-wattmeter method, when applied to the balanced loads, yields interesting results. Considering either balanced wye- or delta-connected loads, with the aid of the corresponding phasor diagrams drawn earlier for the phase sequence A-B-C, it can be seen that the angle between ¯ VAB and ¯ IA is (30° + φ) and that between ¯VCB and ¯IC is (30 - φ), where φ is the load power factor angle, or the angle associated with the load impedance. Thus, we have

954_Measurement of power1.png


Related Discussions:- Measurement of power

Organizational structure, Work-flow is a highly dynamic process. A well-des...

Work-flow is a highly dynamic process. A well-designed organizational structure will ensure that work is performed efficiently and produces a high quality product or service. Chapt

Cross-functional groups and teams, One type of organic, decentralised organ...

One type of organic, decentralised organisational structure are work groups that integrate different disciplines and types of expertise, such as multidisciplinary teams in hospital

Selection criteria applied in the selection of a manager, Question 1 What ...

Question 1 What is the selection criteria applied in the selection of a Project Manager? Question 2 As a project manager, you will always have projects for which you must

Delegation, with the aid of a diagram, discuss the process of delegation

with the aid of a diagram, discuss the process of delegation

International human resource management, International Human Resource Manag...

International Human Resource Management ACN Inc is a UK based company who wishes to expand in other markets. The company offers wide range of products. Presently it is central

HRM, “Effective Human Resources Management depends upon sound reward system...

“Effective Human Resources Management depends upon sound reward system”. Comment.

Explain the term interview, Question 1 (a). Explain the term "interview...

Question 1 (a). Explain the term "interview" and discuss the following: i. What an interviewer needs to do before / during and after an interview? ii. What an interview

Advantages of the selection tests, Advantages of the selection tests: ...

Advantages of the selection tests: 1. Selection tests are standardized & unbiased methods of soliciting information about the prospective employees. 2. Selection tests can

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd