Abstract: By analyzing the cause of the accident, that there is a large transformer cooler control circuit of major design flaws, and specific rehabilitation programs for design, manufacture, installation, operation and other departments.

Currently, large transformers commonly used forced oil circulation cooling air cooling, and extensive use of strong winds forced oil circulation cooler main accessories of such transformers, despite the many manufacturers to improve, but in actual operation and maintenance process of discovery, cooler control loop design, there are still many defects. Without timely transformation of the control loop, it will affect the reliability of cooling systems, to speed up the aging rate of transformer insulating oil, and even threaten security and stability of the grid.

Following the latest design and production of the plant XKWFP-6-type strong winds forced oil circulation cooler master control box, for example for analysis.

1 to prevent the replacement of contactors and short-circuit caused by the air switch

Transformer cooler during operation, then a small bus on power in the cooler and the air switch contacts easily damaged. Not because of the small bus power, we can only replace the damaged equipment live. Given that the control box space, power and white from the past, so replace the equipment very vulnerable to phase short circuit, even the small bus blown, two power supplies are not on the cast, causing the transformer forced outage.

Shown in Figure 1, the factory design is only a small bus, if the small bus segment, according to the diagram shown in dotted line, the installation of sub-switch DK, you can effectively avoid the occurrence of short circuit. Normal operation, close the DK, when a contact device (such as 1JC) or an air switch (such as 1ZK) is damaged, disconnect the power supply of this paragraph (Ⅰ segment power supply), and then opened the DK, you can make the damaged equipment and Power supply isolation, can not live in the case to be replaced. This will effectively prevent accidents, but also to ensure that half of the cooler to continue normal operation. Select the DK should check their capacity.

2 Power Supply AC contactor to prevent loss of field trip caused by the main transformer switch

September 27, 1997, the Bureau Fei Shan 220 kV substation main transformer cooler 1, total control of the power supply box (Ⅰ segment) AC coil contactor 1JC burned. Manufacturers are not designed to burn AC contactor coil (or circuit break) the possibility, so the main control room without any signal, the cooler will not automatically switch to standby power (Ⅱ), the resulting loss of cooling power. Cooler full stop after 20min, the main transformer top oil temperature does not reach 75 ℃, the main transformer cooler so there is no full stop to protect exports. 60min after the stop delay trip circuit cooler full export, so that three sides of the main transformer No. 1 switch tripping. Shown in Figure 2, time relay 1BSJ setting as 20 min, 2BSJ be set to 60 min.

Figure 2 shows the current relay BLJ is the response phase of the power supply off, power off when the work phase, moving together contact BLJ1 closed, 6ZJ excitation, the cooler can automatically put into standby power supply (automatic input circuit in figure not shown).

The cause of this trip cause of the accident, the loss of the power supply AC magnetic contactor, not only does not automatically put into standby power cooler, and cooler can not start the central signal. For the cause of the accident, it is suggested in Figure 2 (dashed line) for cooler control circuit transformer to transform. Full-stop trip in the cooler time of the relay coil in parallel at both ends of an intermediate relay 7ZJ, then moving together contact 7ZJ1 start 6ZJ, the cooler can be achieved using 6ZJ power switch. In addition, moving together and linked together at both ends of contact BLJ1 contact 6ZJ3 aim is to achieve 6ZJ self-sustaining. Moving together contact 6ZJ2 start using the central signal, call duty officers to run cooler control loop and process defects. Through the switch 2K, can 6ZJ reversion.

 Figure 2 cooler control circuit to stop the transformation of the whole

3 to prevent the air cooler work after the switch can not jump start back cooler

November 16, 1996, the Bureau Jingling 220kV substation main transformer No. 1 for light load and low temperatures, only 1 cooler to work, failure due to short-circuit transformer oil pump, the air switch 1ZK rapid removal of the fault , shown in Figure 3. Because manufacturers design unreasonable, 1ZK trip, 1 lost power control circuit cooler and therefore can not start backup cooler, can not start the central signal, resulting in a cooler full stop.

In response to this major flaw, it is recommended to power the cooler control circuit wiring in Figure 3 (dashed line) for the transformation, that is, points in the cooler to install a fuse in the control box, change the air before taking control of the power switch . After the transformation, when the transformer cooler pump or fan fault, the failure by the rapid removal of the air switch, and the cooler control circuit power supply will not disappear, you can automatically put the cooler back guarantee.

   Figure on the 31st cooler control circuit power transformation

4 to prevent the auxiliary transformer cooler frequent load fluctuations start

Auxiliary transformer cooler starting in two ways, first by starting the transformer top oil temperature; the second is starting the transformer load current.