Cau chi:

1.Dn: cau chi la loai kcd bao ve mach,tu ngat nguon dien khi su co qua tai va ngan mach(chu yeu la ngan mach)

2. dac diem: cau tao don gian,kick thuoc nho gon,kha nang cat lon,gia thanh thap

3.Yeu cau: Dac tinh bao ve A-s cua cau chi phai nam thap hon dac tinh cua thiet bi duoc bao ve,bao ve co chon loc,dac tinh bao ve phai on dinh,kha nang cat lon,de sua chua thay the

4. Nguyen ly:

Dua vao qua trinh phat nong nhiet cua day chay(bo phan chinh cua cau chi)Khi I chay qua day chay->nhiet do day chay tang len.Khi I < Ith(dong toi han)->nhiet do day chay<nhiet do nong chay cua day chay->cau chi ko tac dong.

Khi I>Ith-> nhiet do day chay>nhiet do nc cua day chay->day chay dut->cau chi tac dong

Ith:tri so dong dien ma tai do day chay bat dau chay dut.