What are the electrical parameters?
Selecting measurement system
Single parameter,Multi function, analogue or digital instrument
Sizing the system,choosing the CT
Sizing the measuring system starts with knowing the main parameters of the plant;in particular,starting from the characteristics of the protection switch,the type of distribution system,rated current,rated voltage and bar type can be known.
After the type of instrument has been defined that is most suitable for requirements,if the measurement is conducted through indirect insertion,the accessories of the measuring system such as current and voltage transformers must be chosen carefully.
Cabling and wiring diagrams
Connecting analogue instrument is very simple,it in fact suffices to connect the phase and neutral cables to the instrument terminal.Two cables for the auxiliary supply must always be connected for digital instruments.
Protecting the instrument
In order to ensure that the instrument is properly protected fuses must always be fitted to the supply cables of digital instruments and to the voltmeter measuring inputs.
Setting digital instruments
Before digital instruments start operating they must be set with the parameters of the measuring system and the communication parameters. The main measuring parameters are the transformation ratio of the CTs and of the VTs,which are defined as the mathematical ratio between the nominal value and the value of secondary.
Troubleshooting during final testing
The main problems that arise during the test phase may be due to incorrect installation of the instruments and the accessories. Always check that the wiring complies with the instruction manual.
Error during installation
The following errors are those that are most frequently committed when installing a measuring instrument.
Inverting the secondaries of the CTs
Inverting the phase of the current and voltage measuring inputs
Failure to eliminate the short circuit of the secondaries of the CTs
Setting an incorrect transformer ratio