Static relay

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The conventional relay type of electromagnet relays can be replaced by static relay which essentially consists of electronic circuitry to develop all those characteristics which are achieved by moving parts in an electro-magnetic relay.

For example, in an induction type relay operating time can be adjusted by adjusting the distance travelled by disc where as in a static relay it can be achieved by adjusting the value of resistance in R-C time delay circuit. In other words static relay are capable of performing the same functions with the use of electronic circuit control which an electro-magnetic relay perform with te use of moving parts or elements.

Static relays are superior to electro-magnetic relays in the following aspects:

  1. The moving parts and the contats are largely eleimineted. The only moving element in static relay is final tripping contact.
  2. C.T.s and P.T.s employed are of lesser VA rating as static relays require a very little volt-ampere for their operation.
  3. More accurate and high speed operation.

[edit] Structure

Static relay consists of following units for operation:

  1. Auxiliary Voltage Supply:24 V D.C. supply is required for energizining the circuitry of the static relay. This obtained by converting 230V a.c. to 24V d.c. and in some cases station battery voltage of 110V to 24V d.c.
  2. Comprator:It compares the actual quantity with the pre-set quantity. For example in an over-current relay it will compare the actual current supplied by CT with the pre-determined set current over which tripping is required.
  3. Time delay Elements:The required operation time is achieved here by adjusting the values of R and C.
  4. Logic Circuit:By using the gate circuits conditions of operation of relays are set and relay can only be operated when these conditions are satisfied.
  5. Output Device:The actual tripping of relay can be achieved by firing the SCR or operating the attracted armature type relay by feeding the signal coming from logic circuit output.