Name of the College : Kings College Of Engineering
Department : Electrical & Electronics Engineering
Subject : Power System Analysis
Document Type : Question Bank
Website : https://www.kingsengg.edu.in/
Kings Power System Analysis Question Bank
NAME OF THE SUBJECT: EE 1351 POWER SYSTEM ANALYSIS
YEAR / SEM : III / VI
Related / Similar Posts :
Kings College EE1451 Renewable Energy Sources Question Bank
Unit – 1 The Power System
Part – A : [2 Marks]
1. What is single line diagram? :
A Single line diagram is diagrammatic representation of power system in which the components are represented by their symbols and the interconnections between them are shown by a single straight line (even though the system is 3- phase system).
The ratings and the impedances of the components are also marked on the single line diagram..
2. What are the components of power system? :
The components of power system are Generators, power Transformers, Transmission lines, Substation Transformers, Distribution Transformers and Loads.
3. Define per unit value.
The per unit value of any quantity is defined as the ratio of the actual value of the quantity to the base value expressed as a decimal. The base value is an arbitrary chosen value of the quantity..
Actual Value
Per unit Value = —————-
Base Value
4. What is the need for base values? :
The components or various sections of power system may operate at different voltage and power levels.
It will be convenient for analysis of power system if the voltage power, current and impedance ratings of components of power system are expressed with reference to a common value called base value.
Hence for analysis purpose a base value is chosen for voltage, power, current and impedance. Then all the voltage power, current and impedance ratings of the components are expressed as a percent or per unit of the base value.
5. What are the advantages of per-unit computations? :
(i) Manufacturers usually specify the impedance of a device or machine in per unit on the base of the name plate rating.
(ii) The p.u values of widely different rating machines lie within a narrow range, even though the ohmic values has a very large range.
(iii) The p.u. impedance of circuit element connected by transformers expressed on a proper base will be same if it is referred to either side of a transformer.
(iv) The p.u. impedance of a 3-phase transformer is independent of the type of winding connection (Y or ).
6. What is impedance and reactance diagram? :
The impedance diagram is the equivalent circuit of power system in which the various components of power system are represented by their approximate or simplified equivalent circuits.
The impedance diagram is used for load flow studies. The reactance diagram is the simplified equivalent circuit of power system in which the various components are represented by their reactance.
The reactance diagram can be obtained form impedance diagram if all the resistive components are neglected. The reactance diagram is used for fault calculations.
7.What are the factors that need to be omitted for an impedance diagram to reduce it to a reactance diagram? :
(or)
What are the approximations made in reactance diagram? :
The following approximations are made in reactance diagram.
1. The neutral reactances are neglected.
2. Shunt branches in the equivalent circuits of transformer are neglected
3. The resistances are neglected.
4. All static loads and induction motors are neglected.
5. The capacitances of the transmission lines are neglected..
8. What is a bus? :
The meeting point of various components in a power system is called a bus. The bus is a conductor made of copper or aluminum having negligible resistance. The buses are considered as points of constant voltage in a power system.
9. What is bus admittance matrix? :
The matrix consisting of the self and mutual admittances of the network of a power system is called bus admittance matrix. It is given by the admittance matrix Y in the node basis matrix equation of a power system and it is denoted as Ybus. The bus admittance matrix is symmetrical.
10. What is bus impedance matrix? :
The matrix consisting of driving point impedances and impedances of the network of a power system is called bus impedance matrix. It is given by the inverse of bus admittance matrix and it is denoted as Zbus. The bus impedance matrix is symmetrical.
11. Write the four ways of adding an impedance to an existing system so as to modify bus impedance matrix.
To modify a bus impedance matrix, a branch of impedance Zb can be added to original system in the following four different ways.
Case 1 : Adding a branch of impedance Zb from a new bus-p to the reference bus.
Case 2 : Adding a branch of impedance Zb from a new bus-p to the existing bus-q.
Case 3 : Adding a branch of impedance Zb from an existing bus-q to the reference bus.
Case 4 : Adding a branch of impedance Zb between two existing buses h and q.
12. How the Zbus is modified when a branch of impedance Zb is added from a new bus-p to the reference bus? :
When a branch of impedance Zb is added from a new bus-p to the reference bus, the order of the bus impedance matrix increases by one. Let the original bus impedance matrix have an order of n and so the new bus impedance matrix have an order of (n+1).
The first n x n sub matrix of new bus impedance matrix is the original bus impedance matrix. The elements of (n+1)th column and row are all zeros except the diagonal. The (n+1) diagonal element is the added branch impedance Zb .
13. What are symmetrical components? :
An unbalanced system of N related vectors can be resolved into N systems of balanced vectors. The N – sets of balanced vectors are called symmetrical components.
Each set consists of N – vectors which are equal in length and having equal phase anglesbetween adjacent vectors.
14. What are sequence impedance and sequence networks? :
The sequence impedances are impedances offered by the devices or components for the like sequence component of the current .
The single phase equivalent circuit of a power system consisting of impedances to the current of any one sequence only is called sequence network.
Unit – 2 Power Flow Analysis
PART – A (2 MARKS) :
1. What is power flow study or load flow study?
The study of various methods of solution to power system network is referred to as load flow study. The solution provides the voltages at various buses, power flowing in various lines and line-losses.
2. What are the works involved in a load flow study? or How a load flow study is performed?
The following work has to be performed for a load flow study.
(i) Representation of the system by single line diagrams.
(ii) Determining the impedance diagram using the information in single line diagram.
(iii) Formulation of network equations.
(iv) Solution of network equations.
4. Define Voltage controlled bus.
A bus is called voltage controlled bus if the magnitude of voltage V and real power (P) are specified for it.
In a voltage controlled bus the magnitude of the voltage is not allowed to change. The other names for voltage controlled bus are generator bus and PV bus.
5. What is PQ-bus?
A bus is called PQ-bus or load bus when real and reactive components of power are specified for the bus. In a load bus the voltage is allowed to vary within permissible limits.
6. What is swing bus (or slack bus)?
A bus is called swing bus for (or slack bus) when the magnitude and phase for bus voltage are specified for it. The swing bus is the reference bus for load flow solution and it is required for accounting line losses. Usually one of the generator bus selected as the swing bus.
7. What is the need for slack bus?
The slack bus is needed to account for transmission line losses. In a power system the total power generated will be equal to sum of power consumed by loads and losses.
In a power system only the generated power and load power are specified for buses. The slack bus is assumed to generate the power required for losses.
Since the losses are unknown the real and reactive power are not specified for slack bus. They are estimated through the solution of load flow equations.
Download Model/Sample Question Paper :
https://www.pdfquestion.in/uploads/ki…20ANALYSIS.pdf