Introduction：
The winter in northern China is long and cold, and heating methods such as heating and geothermal have become the main means for people here to keep out the cold in winter. The thermal power plant transports the superheated steam to each first heat exchange station through the steam transmission pipeline. In the first heat exchange station, the steam heats the heating hot water through the heat exchanger, and the circulating pump sends the hot water to the secondary network and the various heat exchangers through the heating pipeline. user. Shanghai Qidian's D71 inverter has been widely used in municipal fields, such as heating, HVAC, water works and sewage treatment plants. Our products and solutions have remarkable energy-saving effects, safe and reliable operation, and are the guarantee for the stable operation of the municipal system.
Features：
D71 is a wall-mounted inverter with a power range of 0.75KW-500KW, and the voltage level control mode of the incoming line voltage is 380V-480V, which is vector control without speed sensor. The speed sensorless vector control is especially suitable for fans and pumps. The speed sensorless vector control not only has a speed closed loop but also a current closed loop, and the steady-state current of the motor is more stable.
D71 has a wealth of client terminals, including 8 digital inputs (LI1-LI8), 2 analog inputs (AI), 2 relay outputs (TA), 2 analog outputs (AO), 5V auxiliary power supply for analog input Fixed input, 24V auxiliary power supply is used for digital input, all LI/TA, AI/AO can be freely programmed to define functions. MODBUS interface is standard configuration of D71, no option is required. The D71 can be connected to higher-level automation systems via MODBUS. D71 series inverter has built-in PID function, the operation is more flexible, and there are many ways to control the interface.
Advantage：
System Introduction：
In this system, a D71 110KW frequency converter is used to drive a 110KW heat network circulating pump. By collecting the temperature difference between the total output and return water temperature of the system, and comparing the temperature difference of the user system return water temperature in each area with the system design temperature difference, the speed of the circulating pump is automatically adjusted by the built-in PID function of the inverter to realize the adjustment of the total flow and temperature of the system.
Technical Parameter：
| Inverter technical parameters | Device configuration | |
 Model: D71-X | Output current: 215A | One D71 inverter |
| Input voltage: 3-phase, 380-480V | Frequency range: 0-400Hz | 110kW 1Heat network circulation pump and motor |
| Input frequency: 50/60Hz ±5% | Overload capacity: 150%, 60 seconds | temperature sensor |
| Output power: 110KW | Ambient temperature: -10-40°C | |
| Output voltage: 0-480V (the maximum value is determined by the input voltage) | Protection level: IP20 | |
On Site Usage：
According to the on-site space situation, a D71 series inverter is installed in the control cabinet, and the inverter installation and on-site motor are as shown in the figure
Running Result：
The heating network circulating water pump system using D71 inverter has been put into operation for more than three years, and has achieved good economic and social benefits:
The control device operates reliably and has a low failure rate;
Through PID automatic adjustment, the phenomenon of uneven heating and cooling of each station in the heating network is eliminated;
Realize unmanned operation of production, greatly reduce labor intensity and improve production efficiency;
The economic benefits are significant, and all the increased investment can be recovered in more than one year.
Customer Benefits：
The heating and cooling of each station in the heating network is uniform, which ensures the heating needs of the remote customers and avoids the overheating of the near-end customers.
Realize unmanned operation of production and improve production efficiency;
The mechanical impact is reduced, which greatly saves the maintenance cost;
The energy-saving effect is remarkable, and the increased investment can be fully recovered in more than one year.