Fuse Failure Relay Block VAPM31

Type : VAPM31

Features and technical specifications:

1.  High speed operation
2. Compact and robust construction
3.  Positive action                                                                                                                                                                   Technical data : –                                                                                                                                                           Coil Rating – 110V, 50 Hz phase to phase, phase to neutral series impedance of the distance or other relays in series with the fuse failure relay should not exceed 1000 ohms i.e. the voltage circuit burden should be
   greater than 4VA per phase.                                                                                                                               Operating time – Time between failure or removal of voltage transformer secondary fuses and opening of normally closed contact is less than 7m seconds. Refer Figure 1 for time/voltage curve.                               Thermal Rating – 110% of rated voltage continuously. Burden –  3.5VA per phase at rated voltage during operation. Operation indicator Hand reset operation indicator provided. Contacts One make, one break self reset contact. Break contact is faster in operation than make contact. Insulation The relay meets the requirements of IS3231:1965/IEC 255-5 Series C-2 KV for 1 minute.                                                                                                                                                                                                                                                               Type VAPM 31 relay consists of a static rectifier circuit with a long core hinged armature output unit. Three coils for the three phases are wound over a single core producing in effect a common relay for the three phases. Each coil is connected across one of the voltage transformer secondary fuses and under healthy
   conditions, this coil is short circuited by the fuse and cannot be energised. When one or more fuses blow or are removed, the appropriate coil(s) is energised and the relay operates immediately to open the trip circuit.
   Successful prevention of false tripping relies on the high speed of the VAPM 31 relay, which operates faster than most schemes of protection but cannot begin to function until the fuse is completely blown. In practice, however, most VT fuse failures are caused by deterioration or accidental removal and fuse blowing time is not important.