Closed busbarWhat are the common problems? Let's take a look together.

I. Cause Analysis

1. Due to the fully connectedClosed busbarThe skin effect and proximity effect of the shell circulating current, the ratio of the additional resistance of the middle phase to the average additional resistance of the three phases in the parallel arrangement of the circular tube current-carrying conductors is close to2 times, so the middle phaseClosed busbarThe temperature rise of the shell is generally higher than that of the side phase.

2. Unit 5 generator of the power plantClosed busbarHidden in the expansion joint12 pieces of 120×10 mm cross-section jumper aluminum bars, which can be consideredClosed busbarThe shell loop current generated by electromagnetic induction is also uniformly distributed, that is, under normal circumstances, the loop current passing through each jumper aluminum bar is approximately1/12 of the generator load current.

3. Although the jumper aluminum bars at the expansion joint are hidden, the manufacturer of Kexu busbar troughs, it can be preliminarily judged that there is poor contact phenomenon in the hidden jumper aluminum bars at the overheating area. According to the fully connectedClosed busbarCalculation formula of shell circulating current lossPc=I2krkoKf. In the formula, Ik is the shell circulating current; rko is the DC resistance of the shell; Kf is the skin effect loss coefficient of the shell, which can be taken as 1 when the thickness is not greater than 8mm.

Obviously, the DC resistance in the overheating areaRKO increases with poor contact, thus causing the circulating current loss PC in the overheating area to increase proportionally, thus inevitably leading to local overheating. With the change of unit load, the shell circulating current Ik changes accordingly, the circulating current loss Pc is proportional to the square of the shell circulating current (effective value), and the temperature rise must change accordingly.

Determination of the on-line processing technical scheme

1. Contact the provincial dispatching center to appropriately reduce the active and reactive power load of unit 5, the electrical operation duty officer strengthens the inspection, does the continuous temperature measurement work, Zhaotong air type busbar trough production, installs a temporary exhaust fan, external wind cooling, and tries to control the temperature of the overheating area.

2. There are 24 bolts fixing one bolt on each side flange of the soft junction box at both ends of the expansion joint. It is proposed to add equipment connecting small aluminum bars one by one between each pair of bolts, so as to reduce the patient's fever by implementing education diversion for the hidden jumper aluminum bars.

3. BecauseClosed busbarThe shell is a three-phase short circuit and grounded, and the axial electromotive force induced on the aluminum shell is equipotential with the ground, so the installation and connection of small aluminum bars can be implemented without shutdown.

Post-shutdown processing process

1. Remove the rubber sleeve of the expansion joint, but the aluminum bar fixing bolts have no serious loosening phenomenon. However, some of the tightened screws have obvious traces of electrochemical corrosion environment causing poor contact and leading to overheating, especially the fixing screws corresponding to the overheating area. Unscrew the 12 rows of bridge aluminum, grind the overheating and galvanized corrosion parts, apply conductive and antioxidant enhanced electrical lubricating grease, and eliminate the heat generated by excessive contact resistance.

2. Considering that unit 5 has been in operation for many years, in order to enhance the B-phaseClosed busbarThe carrying capacity of the expansion joint connection, still according to the above processing scheme, in24 connecting small aluminum bars with a cross section of 50mm×5mm are added between the outer flanges of the soft junction boxes at both ends of the B-phase expansion joint.