Cabinet equipment operation and maintenance, maintenance problems lead to fever
1. High voltage switchgear outlet room floor heating lead to cable failure
A llOkV substation only one main transformer. One day, the report "35kV bus grounding" signal, check for phase A fault; then 35kV outlet PD line and PW line at the same time by the overcurrent I segment protection tripping action. On-site inspection of the equipment revealed that black smoke appeared at the lower door of the PD line switchgear, opened the cabinet door and found that the terminal of the A-phase cable was severely burned. The insulation of the cable terminal was almost completely fused by the electric arc to expose the inner conductor of the cable ). Check the line by the user, PW line C-phase ground fault occurred.
Professionals to check the PD line switch cabinet equipment, in addition to see A-phase cable terminal serious burnout, the rest no exception. Arc-free cabinet short-circuit signs, cable terminal clamp without burning phenomenon.
In the cable tunnel under the switchgear cabinet, PD cable A phase cable wear board, check the arc burned hole. It is found that the PD line switchgear outlet room floor is iron plate, PD line cable phase through the cable hole, there is no gap between the two iron plates at the bottom of the cabinet, pressed together to form a closed magnetic circuit side). When the A-phase cable terminal flows through a large load current, an induced current flows on the iron plate forming a closed magnetic circuit, and heat generation poses a serious threat to the outer insulation of the cable terminal.
Based on the above analysis, PD cable A phase cable terminal, at the wear plate Department of heat damage, the formation of weak points of insulation, and gradually developed to the perforation of iron insulation is burned through, A-phase cable terminal on the bottom iron arc discharge to form Single-phase ground fault. When a fault occurs, due to the system B, C relative voltage increases, PW line C-phase weak insulation breakdown through the formation of two different lines of short circuit to ground, the two line protection devices trip simultaneously trip.
PD line A-phase cable insulation weakness, may be the laying of the cable construction quality or maintenance of quality problems.
(1) Standard cable terminal production process, improve the quality of cable terminal production, eliminate "barbaric construction." Cable phase split through the laying of the floor, switch cabinet outlet room at the bottom of the iron plate is not allowed to form a closed magnetic circuit.
(2) Switch cabinet outlet room floor should be non-magnetic materials.
(3) When the bottom plate of outlet cabinet of switchgear is made of iron plate, the iron plate must be fixedly installed to prevent the gap caused by the change to form a closed magnetic circuit.