Libratherm Instruments Private Limited

Libratherm offers Thyristor Switch Module for capacitor Bank, specially designed for Automatic Power Factor Correction (APFC) applications. In APFC the capacitor banks of suitably rated KVAR are sequentially selected, based on the command from the automatic power factor relay module to maintain the desired power factor (Ratio of KW: KVA). In the conventional method, the number capacitor banks are selected by switching the contactors connected in series with each capacitor bank. This LTSM module allows the selection of such capacitor banks using thyristors (i.e. Solid state switch). Thyristors being solid state switch offers many advantages compared to electromechanical contactors.

 

Libratherm makes LTSM modules are available to switch single or 3 phase capacitor banks rated for 5, 10, 15, 25, 50 and 100 KVAR. Zero crosses over switching technique are used to turn on and turn off the thyristors connected in series with these capacitor banks. LTSM accepts direct potential free contact command and does not require any external 12 or 24 VDC auxiliary power supply for switching the capacitor banks.

Advantages of Thyristor switch module over conventional electromechanical contactor:

• Since there are no mechanical contacts involved, no arcing and sparking takes place and no audible switching noise is produced.

• Due to zero cross-over switching techniques, voltage transients can be controlled within the safe limits.

• Using LTSM it is possible to switch the capacitors at 100mS rate, thereby power factor close to unity can be maintained. Whereas, contactors cannot be switched that fast.

• There are no limitations in a number of switching operations for thyristor compared to the contactor.

These LTSM modules are safe to operate under the environment of maximum 70oC @ 90% RH – non-condensing.

 

These switching modules LTSM are easy to install and come with built in indications for normal function and faults, along with built-in protection circuits for fail-safe operations.

 

Generally, each of the real time power factor controllers (RPFC – relay module) gives 4 to 12 outputs, to select that many capacitor banks to maintain desired power factor and hence it will be required to use that many numbers of LTSM modules.