Dual constant pressure water supply system for domestic water and fire water
With the development of urbanization in China, the problem of water supply in urban communities has become increasingly prominent. On the one hand, it is required to improve the quality of water supply, not to cause water supply problems due to pressure fluctuations, and on the other hand, to ensure the reliability and safety of water supply, and to provide reliable water supply in the event of a fire. In response to these two requirements, a new water supply method and control system should be born. This is the PLC+VFD-controlled dual constant pressure water supply system for domestic water and fire water. In order to facilitate monitoring, it is necessary to add a host computer. And monitoring configuration software to form a SCADA system.
The following figure is a schematic diagram of a three-pump live/fire-fighting double tower constant pressure water supply system. Tap water from the urban pipe network enters the reservoir via the inlet valve. As long as the water level is lower than the high water level, the water inlet valve automatically opens and fills the reservoir. The water level is higher than the high water level and the water inlet valve closes automatically. The high/low water level signal from the pool is sent directly to the PLC as a control inlet valve and alarm. There are three pumps for domestic water and fire fighting water. The solenoid valve of the main water outlet pipe is used to control the switching of domestic water and fire fighting water. The solenoid valve is normally closed, the fire pipe network is closed, and the effluent can only flow into the domestic water pipe network. Three pumps are used. According to the amount of domestic water, it operates in accordance with a certain control logic to make the pressure of domestic water constant; when there is a fire, the solenoid valve opens, the domestic water pipe network is closed, the fire water pipe network is opened, and three pumps are used for fire fighting water. And according to the amount of water used, the fire fighting water maintains high pressure and operates constantly. After the fire was over, the three pumps were changed to use for domestic water.
Control process requirements for the three-pump life/fire control dual constant pressure water supply system:
1. When supplying water for living, the system shall be operated at a low constant pressure value. When used for fire fighting water, the system shall operate at a higher constant pressure value;
2. The three pumps adopt the principle of first opening and stopping first according to the setting of pressure;
3. It can implement automatic on-time rotation switch pump to prevent a certain pump from running for a long time and burn out and prevent a certain pump from rusting for a long time without running;
4. The current, voltage, power and status of each motor can be monitored on the screen of the host computer;
5. Must have protection and alarm functions;
6. For ease of maintenance, set the manual function;
7. The anti-evacuation function of the pool should be set;
8. In order to prevent the system from transmitting power to the inverter and causing the inverter to burn down, the power frequency contactor and frequency conversion contactor of each pump must be mechanically interlocked.
Selection:
1. PLC: using Siemens S7-200 series of CPU224;
2. Converter: Fuling DZB200-P, 30KW.
working principle:
1. Make use of the two programmable output breaks MO1 and MO2 of the inverter to set the function. When the inverter reaches the upper limit frequency, MO1-MCM is closed. When the inverter reaches the lower limit frequency, MO2-MCM is closed. These two contacts are used as the PLC. The input signal to determine whether to add or reduce the pump;
2. PID regulation is accomplished by an external PID regulator;
3. The operation of the inverter shall be determined according to whether the output of the PLC Q0.6 (S1-DCM) is closed or not. The reset of the inverter shall be determined according to whether the output of the PLC Q0.7 (S2-DCM) is closed.
Inverter parameter setting table
(Fuling DZB200 inverter)
Code
Features
Setting value
F0.00
Speed ​​control mode (V/F control)
1
F0.01
Run command channel (terminal control)
1
F0.03
Frequency command selection (analog CI setting)
2
F0.05
Operating frequency upper limit (50Hz)
50
F0.06
Operating frequency lower limit (15Hz)
15
F0.08
Acceleration time (30s)
30
F2.01
S1 terminal function selection (forward operation)
1
F2.02
S2 terminal function selection (free stop)
6
F2.07
Terminal control operating mode (two-wire control 1)
0
F2.19
MO1 output (upper limit frequency arrival)
7
F2.20
MO2 output (low limit frequency arrival)
8
F2.21
Relay output selection (failure normally open output)
3
PLC I/O and Register Allocation Table
(SIEMENS S7-200)
I/O address and function
enter
Features
Output
Features
I0.0
Inverter high frequency arrival
Q0.0
KM1 (1 # motor connected inverter)
I0.1
Inverter low frequency arrival
Q0.1
KM2 (1# motor frequency)
I0.2
Fire signal
Q0.2
KM3 (2 # motor connected inverter)
I0.3
Live/Central Control Switch
Q0.3
KM4 (2# motor frequency)
I0.4
Pool water level signal
Q0.4
KM5 (3 # motor connected inverter)
I0.5
Q0.5
KM6 (3# motor frequency)
I0.6
Inverter fault signal
Q0.6
S1-DCM (converter started)
I0.7
Pool water level lower limit signal
Q0.7
S2-DCM (inverter reset)
AIW0
1# motor current
Q1.0
Life / fire water supply conversion solenoid valve
AIW2
2# motor current
Q1.1
Fire alarm buzzer
AIW4
3# motor current
AQW0
Inverter given signal
AIW6
Outlet pressure
Internal register address and function
Register address
Features
Register address
Features
VB200
Frequency pump pump number
M0.0
Initialize from manual to automatic
VB201
The total number of industrial frequency pump operation
M0.1
Increase pump signal
VD260
Pumping time
M0.2
Reduce pump signal
T56
Upper limit frequency reaches filter time
M0.3
Pump signal
T57
The lower limit frequency reaches the filter time
M0.4
Disconnect current inverter pump contactor signal
T34
Frequency conversion pump contactor disconnected, switching to industrial frequency contactor time
M0.5
Switch to power frequency pump contactor switch-on signal
T53
After the frequency conversion pump is switched to the industrial frequency pump, the time for the next frequency conversion pump contactor is switched on
M0.6
New frequency conversion pump contactor switching signal
T55
After the inverter stops, disconnect the current inverter pump contactor
M2.0
Stop frequency converter signal
M2.1
Switch to industrial pump signal
M2.2
Start signal after inverter switching