Control panel at Kemijoki hydroelectric plant

CUSTOMER
Kemijoki hydroelectric plant, Finland

RELAY USED
SLO 24CR, SLI 250CR, SLO 24CRA 

MAIN SELECTION REASONS
Interference suppression on long signal cables, high voltage DC switching, infrequent switching.

Kemijoki renovated its Seitakorva hydroelectric generator. The control system was also renovated. Over the years poor experience with interface relays meant that the choice of new relays was carefully considered. Delcon's solid state interface relays were chosen for many reasons.

"Over the years we have tried several different types of electromechanical relay, and we have noticed that their reliability when using long signal cables is not sufficient. Relays may remain closed due to interference effects and give incorrect signals to the control system," says the system designer Heikki Kusmin. "Additionally some of the sensors and other equipment may switch only once in ten years. In this time frame, a mechanical relay's contact resistance may be so high due to oxidation that it will not give a reliable contact on the first switching action. In practice this problem does not exist with Delcon's solid state interface relays."

"In Seitakorva we are using 220 VDC which dramatically reduces the lifetime of mechanical relays. Delcon's product range also includes a solid state relay which can handle this voltage without derating."

Delcon's interface relays are connected to the Mitsubishi logic using relay mounting bases and flat cable.
"We saved considerably on installation time by using the flat cable system, and we avoided errors in connection," said the designer Jukka Kelloniemi. "We shall also be using Delcon's solid state interface relays in the coming Taivalkoski control system renovation."