Analysis and effect of large synchronous motors on power systems

Abstract

Large synchronous machines are frequently utilised in industry and have several advantages and disadvantages. Although a synchronous motor is more efficient than an induction motor, it is also far more complex and sensitive in terms of starting and voltage dips respectively. It is therefore important to understand the impact and sensitivities of a synchronous motor. The impact that a large synchronous motor has on a power system network can be significant. The impact of the quality of supply of the power system on a large synchronous motor can also impact negatively on the operational availability of the motor and should be well understood. A synchronous motor will be installed in a production facility and as such, this investigation is in the form of a case study. This document entails the detailed study, modelling and simulation of the impact of a large low-speed synchronous motor on a power system network, as well as the impact of the power system network on the motor (in terms of voltage dips). Detailed machine and system parameters were gathered from the motor supplier and utility. The effect that the motor has on the network and the effect of the network on the motor were analysed with detailed actual system and motor data. These analyses included load flows, short circuits, motor starting and a transient stability. A comparison of the supplier-suggested stability limits was made with the outcome of an undervoltage stability study. The study revealed that the supplier was over-pessimistic about the voltage dip ride-through capability. Graph 3.28: Voltage dip scatter plot indicating different tripping areas indicates a significant improvement from what was initially offered by the supplier. The dip ride-through capability was increased almost threefold after the interaction of the motor with the power system was studied in detail. This increased dip ride-through capability will have a significant impact on the plant performance. This however must be achieved without any damage to the motor or the associated equipment of this machine. Proper control with a thorough understanding of the synchronous motor's behaviour will lead to an increase in the machine's operational availability (on-line time for a continuous process)