Voltage dips due to direct connection of induction generators in low head hydro electric schemes

Abstract

This paper analyses phenomena which affect voltage dip due to direct connection of induction generators running close to synchronous speed to electrical distribution systems in low head hydro electric schemes. It is known that current transients and therefore voltage dips which, result from direct connection of induction generators to the system decay much faster when the speed of the generator on connection is close to synchronous speed. Current practice in determining whether the electrical transmission system must be strengthened to accommodate the generator is to evaluate the voltage dip for the induction generator connected at rest. The paper examines transient phenomena on connection of induction generators at close, to synchronous speed in determining whether costly system reinforcement may be avoided thus making many uneconomic developments viable while satisfying constraints of permissible voltage dip if the transient phenomena is taken duly into account. More use of renewable energy in electricity supply thus reducing greenhouse gas emissions from fossil plant will therefore result. Parameters of significance in evaluating voltage dip due to direct connection of induction generators running at close to synchronous speed which are studied include (i) effective resistance of stator together with system resistance and reactance of effective infinite supply, (ii) rotor circuit parameters, (iii) speed of generator on connection, and (iv) equivalent inertia of rotor and turbine. Results depicted in Tables and in Time Responses demonstrate relative importance of the parameters on voltage dip. It is concluded that costly system reinforcement may be avoided if detailed simulations are performed where dynamics and transients are fully modelled in assessing magnitude and duration of voltage dip. The analysis is based on a detailed induction generator model with single and double rotor bar simulation using Park's equations with simulation of rotor dynamics on connection of the generator to the electrical supply. © 1993 IEEE. All rights reserved.