Design of temperature controller for dry-type transformers

Introduction to Transformer Temperature Controller Design

The transformer temperature controller adopts LPC1768 as the main CPU chip technology, which can use PT100 platinum thermistor embedded in the temperature measurement hole of the dry-type transformer winding to measure the winding temperature of the dry-type transformer; And it can make users constantly pay attention to the temperature parameter values of the transformer operation through the measured temperature values. It can also automatically start and stop the fan according to the set temperature value, effectively improving the safety and reliability performance of the transformer operation and extending its service life. At the same time, the product has RS485 communication function, which can be easily connected to the monitoring system.

Introduction to the Functions of Transformer Temperature Controller System

(1) Display function. After the device is powered on, it directly enters the normal display mode. When there is keyboard operation or an alarm interface is pushed out or in other interfaces, it automatically enters the normal display mode after more than 1 minute of keyboard operation is not performed. This mode detects and displays the temperature of the three-phase winding in real-time, with a refresh time of 1 second.

(2) Description of over temperature trip function. When the temperature of any phase in the three-phase circuit exceeds the set over temperature trip temperature value, the temperature controller will light up the trip indicator light and send a signal to the remote control cabinet through the over temperature trip output terminal, and the trip circuit will start.

(3) Analysis of the implementation of the alarm function in case of over temperature. When the temperature of any phase in the three-phase temperature reaches the set over temperature alarm temperature value, the temperature controller will activate the alarm indicator light and simultaneously connect the over temperature alarm output terminal signal, which will send an action message to the remote control cabinet to supply the sound and light alarm system of the control cabinet to achieve protection in case of over temperature.

(4) A brief description of the implementation of the fan start stop function. When the temperature of any phase in the three-phase circuit exceeds the set starting temperature value of the fan, drive the corresponding fan relay to act. When any phase of the three-phase temperature drops to the set fan stop temperature, reset the corresponding phase of the fan to start the corresponding relay.

(5) Introduction to the Function of Relay Transmission Experiment. Transmission experiments can be conducted on the output relay of this device through the human-machine interface or a remote computer.

(6) Analysis and explanation of the number setting function. All parameter values can be set directly on the operation panel through the keyboard to set the start and stop of fan temperature, over temperature alarm temperature, over temperature trip temperature, function on/off, and set data not to be lost after power outage.

(7) The event report recording function enables analysis. It can record events such as overheating fan startup, alarm or trip of the temperature controller, providing users with a basis for judgment.

(8) A brief description of the implementation of communication functions. Equipped with an RS-485 serial communication interface, it can communicate with a computer through an RS232 or RS485 converter, or directly with a communication management machine with an RS485 interface.

Introduction to Circuit Design of Transformer Temperature Controller

Hardware circuit design implementation diagram

Selection and application explanation of components used in transformer temperature controller

Introduction and description of the usage method of the main control chip of the transformer temperature controller.

The external components of the LPC1768 microcontroller include up to 512KB of Flash memory, 64KB of data EPROM memory, Ethernet MAC, USB host slave OTG interface, 8-channel universal DMA controller, 4 UARTs, 2 CAN channel interfaces, 2 SP interfaces, 3 I2C interfaces, 8-channel 12 bit analog-to-digital converter, 10 bit analog-to-digital converter, motor control PWM, orthogonal encoder interface circuit, plus 4 universal timer circuits, 6 output universal PWM controllers, RTC with independent battery power supply, and over 70 universal I/O pins.

Brief instructions for using the power module of the transformer temperature controller.

Select LH10-10D0524 produced by MORNSUN, input AC or DC 220V, output 5V and 24V. The 5V power supply supplies power to the integrated chip, and the 24V power supply supplies power to the relay.

Introduction to other peripheral chips. A LM1117 low-voltage differential linear regulator can be used to convert a 5V power supply to a 3.3V power supply, which is used for the power supply of a 3.3V integrated chip.

Choose to use two LM358 chips to convert the resistance signal of the three temperature sensors PT100 into a small voltage signal input by the ADC conversion module inside LPC1768. LM358 is an operational amplifier that includes two independent high gain and internal frequency automatic compensation, suitable for use with a wide range of single power sources, and also suitable for the working modes of both power sources.

The AT24C16 chip is selected for storing set parameters and event report records, and it exchanges data with LPC1768 through the I2C bus. AT24C16 is a 16K bit serial COM EEPROM, which contains 2K 8-bit bytes inside. The device needs to be operated through the I2C bus interface. The I2C bus with a dedicated write protection function only occupies two input/output ports, allowing multiple devices to share one bus, making it easy to use and the system simple.

EL2501 optocoupler is selected for isolation and driving of LPC1768 and relays. The DSP2a-24V high capacity and polarity relay produced by Panasonic is selected as the relay, which is used for driving output in case of over temperature alarm, trip and trip, and when starting the fan.

The driving of the digital tube is achieved by using the ZLG72128 chip, which can directly drive 12 bit common cathode digital tubes (or 96 independent LEDs). The communication adopts the I2C bus method, and the interface with the microcontroller LPC1768 only requires two signal lines. This chip is an industrial grade chip with strong anti-interference ability. Reset RST is a response to low-level pulses, which is connected to the pin IO of the LPC1768 chip and reset by LPC1768.

The human-machine exchange interface keyboard adopts a four key type button, which can be recognized by the IO port cable of LPC1768 for pressing or releasing.

The communication interface chip adopts a low-power half duplex MAX485 transceiver, which has a driver and a receiver inside. The driver has a current protection function in the event of a short circuit fault in the circuit, and can set the output of the driver to a high resistance state through a thermal shutdown circuit to prevent excessive power consumption loss. The receiver input has a failure protection feature, which ensures a high-level output of logic when the input is open circuit.

Transformer temperature controller anti-interference

In order to improve anti-interference ability, a dual channel isolator ADu M1201 chip is used between the LPC1768 and MAX485 chips. The ADu M1201 chip is a dual channel digital isolator using ADI's i Coupler magnetic isolation technology. Adopting CMOS technology and chip level transformer technology, it has optoelectronic isolation in various aspects such as performance, power consumption, and volume that cannot be achieved by devices.

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