Electronic AC fuse. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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The AC electronic fuse circuit shown in the figure protects the circuit in which the power is controlled by the triac (or even just the triac operates in the "connect - disconnect" mode) by removing control signals when the current exceeds the set value (emergency mode).
If the current exceeds the limit value, contacts 3 and 4 (normally closed) break the triac control circuit. When the current in the load circuit does not exceed the set level, relay K1 is de-energized, LED HL3 (green) and LED HL1 are lit. When the current has exceeded a predetermined level, the Zener diode VD5 gives a command and relay K1 is activated, self-caught through normally open contacts 6, 7.
Contacts 3, 4 open: contacts 7, 8 also open. HL3 (green) stops shining and red HL2 lights up. After eliminating the cause of abnormal operation in the load circuit, the SA1 button is pressed and the protection circuit is again ready for operation.
When the triac that regulates the current in the load is controlled by a pulse transformer, then contacts 3, 4 are connected to the break in the primary winding of this transformer. Naturally, the presented fuse works in any AC circuit, even if it is not regulated by a power triac.
To set up the fuse circuit, a T1 transformer of the TPP-287-220-50K type was used. By connecting PEV resistors ranging in size from fractions to several ohms as a load, it is convenient and safe to receive various currents. A small transformer at hand was used as the current transformer T2. Leaving only the primary winding in it (2740 turns, PETV-2 diameter 0,125), removed the secondary windings and wound 8 turns with MGSHV-2,5 wire (the numbers indicate the wire diameter in mm). These 8 turns made up the winding of the current transformer. Its power is several watts (iron Ш20х20). Transformer TZ is the same as T2, but left the secondary winding giving 15 V to power relay K1 when it catches itself. Button SA1 - type KM-1 (its contacts 1 - 3 are used). LEDs HL1, HL2 - AL307 (with any last letter) red. НL3 - green color (type is unknown to me - the marking is erased).
The R1C1 chain provides "comfort" to the VS1 triac when switching off and on. Capacitor C1 - type MBG4-1 (0,5 microns x 250 V). Relay K1 - type RES9 RS4.524.200 (15 V, actuation current 30 mA, release current 6 mA, u=2,58). Capacitors C2, C3 - type K50-12 (200 microns x 50 V).
Anyone who wants to use the proposed idea of a fuse should use the literature [1].
Literature
- R. Thomas. Small-sized DC relays. Radio No. 1, 1973 (p. 56 ... 58, 61).
Author: S.Levchenko
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