KONCAR - Electrical Engineering Institute Inc.

Protection Relay for Shaft Current and Voltage



The paper deals with the specific protection relay for all types of generators. The instrument, called Shaft Current and Voltage Protection Relay (SCVP) was developed at KONCAR – Electric Engineering Institute Inc. This instrument is a part of Institute's product line used for monitoring and diagnosis of rotating electrical machines.

The most important parts of every electric power system are electrical rotating machines, especially those involved in the production of electrical energy. Nowadays, electrical rotating machines must fulfill more complex requirements of electrical power system which are constantly increasing and at the same time the production of electrical energy must be optimized. On the other hand, long lifetime and increased reliability of the machines is expected. Various monitoring and protection systems represent solutions for owners of expensive electrical machines and they can enable better asset management. This can prolong the lifetime of the machines and reduce costs caused by unplanned downtimes and unnecessary maintenance.

Problems that can occur in electrical machines are shaft currents and voltages. Due to the asymmetry of the magnetic field in the machine, a voltage in the shaft can be induced, which, depending on the type of machine, its size and load, varies in amplitude and frequency composition. Low impedance of the circuit consisting of shaft, bearing, oil film and other structural components, can cause shaft current flow which leads to bearing destruction.

Continuous measurement and analysis of shaft currents and voltages can prevent major faults. Through detailed processing of the measured data the causes of occurrence of shaft currents and voltages can be identified. The main purpose of SCVP system is to detect shaft currents and voltages that may damage the generator bearing, and thus prevent greater economic damages.

The aim of this paper is to show how data obtained by SCVP system can extend the life-time of the machine and provide manufacturers and users of the machine insight to useful information during machine work period that can help in better asset management.

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