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Power Fault RecordingHarmonic Monitoring of High-Voltage Power Lines
High-voltage DC lines are used for the transport of energy over long distances, sometimes for submarine cables or also for the connection of grids with different frequencies. Typically, we talk about 1 million volt and some thousand amperes. The latest project in which we were involved had a transmission rate of three GVA. The picture shows such a transformer station at the end of a 1.000 km long DC line.
Task
When we talk about HVDC then we mean semiconductors and converters. These converters are electronic switches that cannot utilize the whole sinus of the alternating voltage and thus produce harmonics. Some of these harmonics are also measurable on the side of the direct current of the converters. All harmonics must be limited and, if necessary, also filtered. Several coils and capacitors are necessary for this. When these filters are detuned it is important to receive an alarm message. Some parameters such as THD, THFF and EDC have to be monitored as well. All in all we talk of more than 200 measurement points. On each point 50 harmonics including DC values must be calculated every 200 milliseconds. As the measuring transformers are on various locations, the measuring systems have to be distributed and set up on various places as well. The measurement of the DC values requires a special solution as well. An interesting detail is the measuring of harmonics on the direct current side as in this case the fundamental oscillation is naturally not existent.
Solution
Hardware
Based on the DEWE-PFR series the hardware solution can easily be designed. The 19” rack systems are perfect for the whole equipment and the use of DAQP-HV, DAQP-LV and DAQP-LA modules respectively and allow any input configuration for such large-scale projects.
Software
As a basis the software package DEWESoft with its options POWER and DB (OMT report generator) are used. Special features such as THFF and EDC are added via a separate DC library as plugin. Communication with the central server is provided by the DB option. This is the system that stores all DEWESoft data on one central SQL server and that was developed for long-term analyses. The strong report generator (PMT) is used for the evaluation and presentation of data.
Some Details
Measuring AC Parameters on the DC Line
In order to be able to measure harmonics on DC lines, you have to know the exact frequency on the AC side. For that purpose, an AC instrument measures the frequency and provides this information as measuring channel to all other instruments via the LAN. This frequency channel serves as a basis for the calculation of the harmonics in DEWESoft POWER. The measurement of direct current is an interesting detail as well and is solved by a Rogowsky coil and fiber optic conductors for signal transmission. Due to these fiber optic conductors the galvanic isolation could be solved efficiently.
Advantages
- Flexibility of hardware and software
- Entire project management from one source
- Technical details of our technology:
- AAF
- Band width
- Precision
- Sampling rate
- Software functions
- Solution of the DC measurement and calculations
Customers
- Operators of transmission grids
- Plant manufacturers that install DC lines
Please check out our pre-configured standard models for power fault recording. Standard models meet approximately 80 % of all application requirements, are cost optimized and shipped faster.
Technologie AG