Application of intelligent relay in the control system of technical water supply pump in hydropower station

1 Introduction

The technical water supply system of a hydropower station uses volute water intake as the main water supply, and uses top cover water intake and tailwater water intake as backup water supply. Tailwater water intake is used as backup technical water supply for several units. It is not used at ordinary times and requires a simple control process. Therefore, PLC control was not used at the beginning of the design, but the traditional relay control method was selected. The control principle is shown in Figure 1.

During the start-stop test of the standby technical water supply pump, it was found that relay 4K kept sparking, and the "run" and "fault" indicators of the water pump were on at the same time. After checking and analyzing the original control circuit: after a certain period of time after starting the pump, the soft starter sent a normal operation signal, so the "water pump running" indicator lighted; 40s after starting the pump, the "water pump fault" signal was reported because the water pump control valve travel switch did not move (the control valve was not opened), and at this time the water pump control handle was still in the "start pump" position, requiring to continue

The pump is started (because the water pump fault signal does not lock the pump start circuit), so some abnormal conditions occur, such as the relay 4K coil is constantly energized and de-energized, sparking occurs, and the "Run" and "Fault" indicator lights are on at the same time.

In view of this, it is necessary to carry out technical transformation of the backup technical water supply control circuit. If the original traditional relay control method is improved, the circuit will become more complicated, increasing the difficulty of maintenance, and the intermediate relay and time relay are prone to logical errors in time coordination. If it is changed to PLC (such as other auxiliary machine monitoring systems) control, the circuit will become simpler, and the water pump control process and logic will be easy to implement, but the cost is high. At the same time, a switching power supply must be installed to provide 24V DC power to the PLC. The subsequent maintenance involves the PLC program and needs to be carried out by a dedicated person.

After consulting the data and consulting the manufacturer and supplier, we considered changing the control of the standby technical water supply pump to the intelligent relay control mode. In this way, the control loop is relatively simple, and the cost of the intelligent relay is relatively low. It can be equivalent to a micro PLC device to realize self-holding, clock, delay and other functions. After comparison, it is recommended to use the EASY-619-AC-RC intelligent relay produced by German Moeller Company. "EASY" is a low-cost compact control relay used for simple control projects. "EASY" has a wide range of applications and has user-friendly intelligent operation functions and LCD display functions. Using "EASY" can be programmed directly on its display screen by keystroke. Through programming, you can quickly learn and master the various functions of "EASY", such as counting relays, real-time clocks, analog comparators, intermediate relays, text displays, etc.

2 Renovation plan

2.1 Backup technical water supply pump control requirements

When the pump is in the start position, it starts (soft start is required to be fault-free and the main power is closed); when the pump is in the stop position, the pump stops and the fault signal is reset. When stopping the pump, first issue an order to close the pump control valve and then issue an order to stop the pump (if there is no stroke feedback signal after closing the valve for 40 seconds, stop it by force); 20 seconds after the start command is issued, the soft starter has no running signal feedback to report a fault and automatically holds and stops the pump. Within 20 seconds after the soft start running signal is fed back, the pump control pump stroke signal does not feedback to report a fault and automatically holds and stops the pump. The signals sent to the remote include the pump running signal, fault signal, pressure signal, and the control handle, voltage measurement display, etc. remain unchanged. Based on the above control requirements, a control flow chart for the public technical water supply pump is drawn (see Figure 2).

2.2 Signal Description

(1) Switch input signal: pump start, pump stop, water pump control valve open, power supply, soft start operation signal, soft start fault signal, water pump control valve closed;

(2) Switch output: start the water pump, the water pump runs, the water pump fails, and the water pump control valve is closed;

(3) Upward signal: water pump running, water pump failure, water pump outlet pressure, water pump stop.

According to the data sheet of the intelligent relay EASY-619-AC-RC and the control process and requirements of the public technical water supply pump, the schematic diagram of the public technical water supply control box is drawn (see Figure 3).

According to the control principle diagram of the standby technical water supply pump, the control requirements and the technical parameters of the intelligent relay "EASY", a program is compiled using a ladder logic diagram (see Figure 4).

3 Conclusion

After technical transformation, the control system has overcome the shortcomings of the original system, eliminated abnormal phenomena, achieved the effect of micro PLC control, and has a good operating effect.

Summarizing this technical transformation, there are the following experiences:

(1) The intelligent relay is small in size and can be installed on a standard rail. The wiring is simple and there is no need to replace the original control box.

(2) The external circuit is simple and clear, and maintenance and troubleshooting are simple. It only requires checking the connected signal (DI) and the controlled element (DO), reducing many intermediate components and thus reducing the source of faults.

(3) Intelligent relays are practical, with simple logic control and convenient on-site programming, which can be directly realized using the device's own buttons;

(4) On the basis of the original equipment, only a few devices were added (including intelligent relays), but the effect of micro PLC control was achieved. It can be said that while adopting new processes and new equipment, a high cost-effectiveness was achieved.