Power System Performance - Short answer questions from AMIE exam (Winter 2021)

What arc the applications of Y-bus and Z-bus matrix?

Y bus is bus admittance matrix which is used (generally) in Load flow analysis. This matrix helps in finding values of P, Q, |V| & delta. The elements of matrix are the admittances of transmission lines between buses. Z bus is bus impedance matrix which is used in Fault analysis.

What is restructure power system?

Power restructuring, a systematic running of modifying the rules and instructions that control the power market to impart consumers for the option of power producing, those are may be traders and allowing rivalry within the traders. Deregulation improves the stock rate and usage. Due to gain in the electric market, the power rates are likely to come down which welfare the consumers.

What is off nominal transformer ratio?

Transformers with voltage ratios different from the nominal (expected) voltage ratios of their associated network sections are identified as off-nominal transformers. The Off-nominal Turns Ratio indicates the voltage transformation. It determines the additional transformation relative to the nominal transformation.

Define primitive network?

A set of non-connected elements of a given system is defined as a primitive Network and an element in it is a fundamental element that is not connected to any other element.

Give the methods available for forming bus impedance matrix.

  • Form bus admittance matrix and take the inverse to get bus impedance matrix.
  • Using bus building algorithm.
  • Using L-U factorization of Y-bus matrix.

Why bus admittance matrix is preferred in load flow?

The following are the advantages of the bus admittance matrix.

  • The data preparation of the bus admittance matrix is very simple.
  • The formation of the bus admittance matrix and its modification is easy.
  • The bus admittance matrix is a sparse matrix thus the computer memory requirement is less.

Draw the single phase equivalent circuit of three winding transformer.

The transformers may also be constructed with a third winding in addition to the primary and secondary windings. This third winding is known as tertiary winding. The primary winding has the highest voltage rating, the tertiary winding has the lowest voltage rating and the secondary winding has the intermediate voltage rating. Its equivalent diagram is given below:

What are the approximations made in impedance diagram.

  • The neutral reactances are neglected. 
  • The shunt branches in equivalent circuit of transformers are neglected.

How is generator in transient analysis represented. 


The study material for AMIE/Junior Engineer exams is available at https://amiestudycircle.com