KONCAR - Shaft Current and Voltage Protection System (SCVP)

Through detailed processing of the measured data the causes of occurrence of shaft currents and voltages can be identified. The main purpose of shaft current and voltage protection (SCVP) system is to detect shaft currents and voltages that may damage the generator bearing, and thus prevent greater economic damages.

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. These asymmetries can cause a potential difference between two points on the shaft which leads to shaft voltage and thus eventually shaft current flow.

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. 

The problem usually progresses with the following scenario:

• Bearing insulation and insulation stability of the bearing oil film deteriorate with usage
• The impedance of the circuit consisting of shaft, bearing, oil film and other structural components decrease
• Reduced impedance leads to current flow through the bearing
• The current flow causes serious damage to the bearing
• The proper and reliable work of the generator is jeopardized!!!!

Generator damage resulting from shaft currents depends on amplitude and duration of current flow. For larger generators currents less than 1A should not cause greater damage. However, monitoring of the smaller currents over a certain time period has proven that there are cases when shaft current flow causes problems to the generators.

Bearings damaged by shaft currents will eventually show increased vibrations which means that the damage is already done.  The main advantage of our SCVP system is that it indicates a problem before major bearing damage has occurred. This is the reason why SCVP is recommended as additional monitoring system along with the classic protection relay function.

Our solution in form of an easy-to-install protection relay provides measurement and analysis of shaft voltage and current which may damage the generator bearing. Monitoring of shaft currents and a quick response to increasing amplitude of these currents is an easy way to protect the expensive power generation equipment.

Easy Implementation

• sensor and system implementation performed with minimum interference in machine operation

Connectivity

• system can be integrated with other systems like SCADA using standard industrial communication
• integration of multiple user accounts into one user application
• Innovative technology which connects local HMI, database for long term archive and web server for a compact product

User Friendly

• intuitive data presentation and remote access to the system using standard Internet browsers
• automated report generation with all relevant information on machine status
• the system enables online analysis and real trending which is a more reliable form of predictive monitoring

Protection

• the system performs spectral analysis (FFT) using instrument transformer which can be used to set custom alarms for critical values
• long term archive of data and historical values are stored for detailed analysis and trends