TEİAŞ prepares a Communication Requirements document for switchyards connecting over 154–380 kV lines; the contractor is obliged to prepare the PAX communication before provisional acceptance of the switchyard.
What sets a PAX exchange apart: E&M support
A normal telephone call runs over 2 wires. In E&M (Ear and Mouth) communication this takes place over 4 or 6 wires. With the E lead, M lead, Tx and Rx pairs, signals are sent over the E and M leads to set up the call end to end, while voice is sent and received over Tx and Rx. In the system TEİAŞ uses there are 2 Tx and 2 Rx leads, providing communication over 6 wires together with E and M. The E&M channel provided by the PAX is carried to the opposite substation and to the load dispatch centre over the 64K leased line or the power line carrier.
Automatic redundant communication channel
One trunk of the PAX exchange installed at 154–380 kV sites runs over the leased line while the other runs over OPGW or the power line carrier. The system continuously monitors both outputs, routing calls over the leased line first and switching to the other channel if there is a problem. The PAX exchange performs this check automatically. A similar implementation can be found on the Turkish State Railways.
Brands used
In Turkey, KAREL is the brand most widely used as a PAX exchange. The Karel DS200, Karel DS200M and Karel IPG1000 models are available. Selta PAX and Telesis PAX are also used, though in smaller numbers.
Karel DS200Karel DS200MKarel IPG1000Selta PAXTelesis PAX
Remote subscriber solution
Apart from installing a PAX exchange, TEİAŞ requires PAX communication at some sites as a remote subscriber over the leased line or over OPGW. In such cases FXS-FXO modules are fitted to the leased line multiplexer, carrying one subscriber from the relevant load dispatch centre into the PAX system. To operate as a remote subscriber from neighbouring stations, the FXS-FXO ports on the SDH-MUX or the voice ports of the T40 power line carrier are used.