SYNOPSIS

The talk begins with a survey of the following:
• Constant impedance, constant power and constant current loads
• Why a power supply has an internal impedance, which limits its fault current contribution
• When the shunt admittance Y of a cable or line may be significant
• The measurement and significance of the %Z of a power transformer
• The 16 reactances of a generator which include combinations of saturated and unsaturated direct- and quadrature axis data – which five data are to be used for the different types of power system studies

When a current I flows through an impedance Z, is the voltage drop V = IZ? The answer may surprise you!

The talk will show that it is possible to transform the classical voltage drop equation  V = I (r cos φ + x sin φ)  into a more elegant and meaningful equation. Using a simplification, it is a relatively easy task to estimate the motor starting voltage dip in transformers and generators.

The talk will then use per unit data to show that the highest impedances in a power system are the loads, transformers and generators. Using a software, the talk then continues with examples of load flow and motor starting studies.

Does power in an AC system always flow from a higher voltage to a lower voltage? A combination of the simplified voltage drop formula, phasor diagrams and computer simulation is then used to show the Ferranti effect, i.e. under certain load conditions in a transmission system, it is possible to have a receiving end voltage which is higher than the source voltage.


BIODATA OF SPEAKER

Ir. Lee Chong Kiow is currently a director of VI Power, which specialises in providing technical training on electrical equipment and performing power system studies. He holds a BSc (Hons) (Electrical & Electronic Engineering – 1974) and an MSc (Power System Engineering –  1977), both from the University of Strathclyde, Glasgow. He was previously the Engineering Manager of a company manufacturing indoor MV and LV switchgear. Prior to that, he spent more than five years as an Associate Director in a large consultancy practice and another 15 years working as a protection engineer in the former National Electricity Board. He is also a Suruhanjaya Tenaga competent/services engineer up to 275kV. Over the last 19 years, he has trained more than 5,500 technical staff from utilities, petro-chemical, multi-national and other industrial companies throughout Malaysia and South-East Asia. China, India & Oman as well as Mauritius, Zimbabwe and Botswana on a variety of power engineering topics.