Such system processes the decision-making parameters and the signals representative of the individual components technical condition (indicators of degradation). Through appropriate engineering models and appropriate decision logic defined by Terna long experience, the system shows the technicians the appropriate action to be carried out at the right time, allowing them to switch from periodic maintenance policy to a condition based maintenance and therefore to standardize their behaviour.
In 2003 Terna also started looking for on-line asset monitoring systems for diagnosis of installed HV critical components, in order to detect the parameters evaluated to be significant by means of sensors mounted on these components, and to locally process them to possibly generate an alarm signal (“summary information”), which has to be sent to the MBI system. Preliminary monitoring experiences were then carried out on autotransformers, HVDC Circuit Breaker (DCCB), surge arresters, SF6 insulated substations.
In 2006 Terna introduced a new system (called MRE: Electrical Grid Monitoring) that makes information about the disturbances and network events available on remote monitoring devices. This system can also transmit the monitoring data of HV components in order to make them available for MBI and for the Operation & Maintenance Support Platform (PSE).
Based on the above-described experiences Terna in 2007 concluded that, in order to have a reliable monitoring system, applicable to all types of equipment (regardless of manufacturer and model) it was necessary to design and implement an "ad hoc" system able to provide an early detection of quick degradation phenomena and to optimize the “on-condition” maintenance actions.
The following specifications have been defined for this system:
HV equipment that should be considered for continuous monitoring,
equipment parameters to be monitored,
diagnostic criteria that should be applied, and
Based on such specifications the diagnostics systems were manufactured. According to the system project criteria, components of high reliability and minimum invasiveness towards equipment, monitored device and control system were employed.
Then the on-line monitoring systems were installed in different cases, which are now in service:
As for the AIS system in Lacchiarella Substation, the monitoring system, called MCS, is characterized by a collection of peripherals dedicated to each device that needs to be monitored. The system architecture is shown below.
By means of fiber optics, the monitoring devices send the measurements to a central unit that will analyze them, detect alarms and predict long-term trend for some of them. Every central unit is connected to the MRE supervision system by IEC 60870-5-101 communication protocol.
The system peripherals are related to the following components/parameters:
SF6 Current Transformer
The figure below shows the surge zinc oxide arrester peripheral as an example.
For such equipment the following parameters are being measured:
The measurements are acquired by three units: one central unit and two peripheral ones. Each unit includes:
a device which is capable of measuring very low currents (few tens of µA) to verify the correct operation of the equipment according to the standards defined by IEC 60099-5 A1. Both the peak value of the whole conduction current and the effective value of its third harmonic component are measured;
a device for measuring the discharge current pulse with 8/20 µs waveform, with peak values of several kA. This device also acts as a “discharge counter”, providing the number of interventions operated by the surge arrester.
Since 2004 the MBI-Substation implementation has been increasingly applied and now takes care of more than 450 substations including more than 5000 bays and about 50.000 primary equipment.
After the experiences of this period it could be concluded that the new on-line diagnostic systems are very flexible, since they allow to monitor a variety of substation equipment and can be applied both to new plants and to existing equipment already in service.
The remote monitoring units are independent of any component manufacturer and the feeder of the central unit can handle different protocols to communicate with the Protection and Control System SPCC.
The installation of the monitoring systems minimally impact on the existing equipment and circuits. The systems can be implemented in a short time and, if they are applied on a large scale, they constitute valuable instruments to shift from a preventive maintenance to a condition-based maintenance, thus reducing the outage times and the related costs, enhancing the asset security and increasing the component and apparatus lifespans.