The micro programmable controller in the application of the main transformer cooler control circuit

1, the application background one of three of the main transformer is hydropower equipment, its main function is to change the voltage grade, transmission ac electricity. Because of reasons of structure and working principle, the transformer runtime will inevitably produce iron loss, copper loss, and translated into heat transformer temperature rise. High temperature reduce transformer work ability and efficiency, insulation aging, reduce the service life. As a result, the reliable operation of the transformer cooling device for transformer normal work important, such as my company 'operation rules' regulation: transformer loading process, such as all cooler lose power, allow to continue running 20 min, but the longest must not exceed 1 h ( Depending on the oil temperature) 。 Our company has four main transformer, the capacity is 90 - 150 MVA, # 2, # 3 and # 4 main transformer cooler are forced oil circulation wind cooling way. Cooler original automatic control circuit is mainly composed of conventional relays, the main problems are as follows: operation and maintenance equipment travel-weary, low insulation, circuit components of complex number, wiring, poor universality and high failure rate, due to the use fixed number of year for a long time at the same time, the lack of spare parts, still exist some circuit parasitics, caused some difficulties to overhaul maintenance, also cannot meet the needs of the company running unattended 'less'. Therefore, the company related department to control circuit of main transformer cooler technical improvement scheme was proposed, the new circuit mainly adopts new type of micro programmable controller of the programmer ( PLC) Replace most of the relay, the control circuit is simple, reliable, strong adaptability and abundant functions, etc. With # 2 main transformer cooler under the transformation of control circuit as an example to illustrate the application of programmable controller. 2, cooler start-stop control and monitoring functions to achieve 2 operation. 1 cooler automatic control target codes specified number of sets of various operation conditions must be into coolers are shown in table 1. Table 1 under various running state inspection procedure must be in note: the cooling 1) According to the main transformer cooler in no-load or loading condition in the cooler groups 'working location'; 2) When the set values for the main transformer oil temperature is reached, 55℃) Or load current is greater than 70% is again in the 'auxiliary' cooler group; 3) When in the 'job' or 'auxiliary' cooler set is malfunction can't normal operation, in the 'standby' cooler set. 2. 2 cooler condition # 2 main transformer cooler 8 groups, divided into the following four state run: state 1: light 1, 2 groups; Load l, 2, 3, 4, 5, and 6 groups; Auxiliary 7 groups; Standby 8 group status 2: light group 3, 4; Load 3, 4, 5, 6, 7, 8 group; 1 set of auxiliary; Standby 2 group status 3: light group 5, 6; Load 5, 6, 7, 8, l, 2 groups; Three groups; Standby state of four groups of 4: light 7, 8 group; Load 7, 8, 1, 2, 3, 4 group; Secondary 5 groups; Standby state 6 groups of 4 kinds of q switch once every 15 days, by the switch 'time' or 'artificial set' implementation. 'In the' artificial set, assigned by operation personnel in the touch screen to set the cooler set describes the state; When in the 'timing switch' way, the programmable controller set automatic switching process. 2. Three block diagram for the reasonable design of PLC process is the normal work of the circuit and the key factor for stable operation. According to the cooler operating characteristics and control objectives, set series programmable controller block diagram as shown in figure 1. Control circuit diagram (figure 1 cooler The PLC part) 3, and simplicity of operation maintenance for process design is reasonable, after # 2 main transformer cooler control loop was put into operation, stable and reliable running, at the same time, PLC controller and touch screen, friendly man-machine interface, make routine maintenance simple and convenient. The example below. 3. 1 contact changes such as # 2 main transformer 22 o2 original access switch auxiliary contacts are closed contact, after changed to open contact, only need to modify the PLC process. 3. 2 to eliminate the influence of the main transformer at the critical temperature for process set up the cooler set start-stop related to main transformer temperature in the operation of the found that when the temperature of the main transformer thermometer in cooler start jumping up and down, which are in a critical state, will lead to the cooler moment, stop, extremely easy to cause the motor damage, in reaction to the phenomenon, we set a time delay in the process of PLC circuit, problem be solved immediately. 3. 3 before 'time switch' function transform, cooler into groups and the operation mode by artificial periodic switching operation personnel, both cumbersome and inconvenient ( Main transformer platform and operation is designed. the farther apart) Now, inside the PLC process Settings can be realized automatically switch 'time', at the same time period can be arbitrary choice, simple and convenient, reducing the workload of operators. 3. 4 external loop exception alarm function because the PLC has high reliability, so most of the faults in the PLC controller control circuit comes not from the PLC itself, but rather due to external components failure, such as common button or relay contact welding and oxidation circuit short circuit or open circuit fault; Operation safety fuse making control circuit and electricity; Thermal element operation, etc. , once the PLC automatic detected components failure, not only has alarm function, and the fault status through the touch screen can display immediately, make the maintenance personnel can quickly determine the cause of the problem.
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