Telemetric System of Intermediate Pumping Stations Control (STSP)
Telemetric System of Intermediate Pumping Stations Control (STSP) is designed for remote monitoring and controlling of unmanned intermediate pumping stations working on main lines in Łódź heating system, from central dispatching room. The intermediate pumping stations are located in the range of 4-6 km from the central dispatching room. Their task is to maintain proper pressure distribution in previously chosen points of the heating net. The task is fulfilled by adaptive control of efficiency and selection of the number of working pumps. Basic system functions are as follows:
- automatic pumping station start,
- automatic planned and emergency pumping station shutdown,
- automatic pressure control - selection of the number and efficiency of pumps,
- automatic and planned turning on of backup main supply,
- protection of buildings against burglary or fire,
- eakage detection in sets of pump units and monitoring of building flooding,
- fittings control for main line protection in case of any pumping station emergency shutdown,
- emergency shutdown of pump units in case of increased vibrations or temperature,
- providing of redundant radio-communication with the central dispatching room,
- ensuring of an alternative remote control,
- local and distant monitoring of pumping station work (of hydraulic and electric systems),
- recording of all-important occurrences and changes of selected work parameters.
For their strategic importance to the city heating system, the pumping stations should be reliable and their smooth running should be controlled permanently. Realization of this requirement is possible only when the reliability of the communication system is also up to these requirements. A radio system with an additional backup communication channel was selected as a solution, which met the mentioned requirements best. Two paths of data transmission were used, i.e.:
- main and redundant paths - radiomodems operating on licensed frequency in 400MHz band
The figure shows the structure of Telemetric System of Intermediate Pumping Stations Control (STSP). Following elements are exposed:
- central dispatching room for Heating Network Plant (ZSC),
- intermediate pumping stations (SOC_D, SOC_P).
Specialized radiomodems MDS 4710 were applied to communication lines.
The system includes two data concentrator stations (KD) located in the intermediate pumping stations and the central point of data acquisition - base station (SB) enabling communication with pumping stations by means of two additional operator stations SCADA (SO).
Tasks of an operator station (SO) are:
- visualization of acquired data describing the present state of technological process,
- remote manual or parametric automatic control of the object,
- data archiving.
Operator stations are located in the central dispatching room and they enable remote control of the pumping station in one of the following modes:
- emergency manual (OPERATOR MODE) - in case of emergency situation or repair and maintenance work,
- parametric (AUTOMATIC MODE) - enables setting of selected parameters for the autonomic system of local automatic regulation.
Operator stations (SO) read independently actual data from the base station (SB). Data are read by means of a serial interface. Because commonly used standards are utilized, connection of the base stations (SB) to any visualization and control systems is possible.
As it has been mentioned, the base station (SB) is responsible for reading data from data concentrators (KD) using one of available communication channels. An adaptable configuration of the base station and data concentrators allows future development of the system. The figure shows the configuration where intermediate pumping stations are equipped with a digital radio link working on licensed frequency (main and redundant links). Both paths use radiomodems MDS 4710E.
Base station (SB) enables connecting additional data concentrators and other monitoring and controlling units to the system, as for example DGH intelligent modules, SAIA PLC controllers etc. Adding more concentrators is realized by software reconfiguration in the base station. Base stations (SB) are equipped with 8 channels for serial data transmission. Two channels are used to communicate with SO station (operator) and 2 for transmitting data to data concentrators.
Their task is to ensure reliable data transmission with redundancy. Independent transmission paths increase the reliability in case of maintenance works or malfunction of one of them. Any data concentrator acquires data from primary controller and controllers of local units connected to the network and transmits them to the base station (SB) through one of the communication paths. Transmitted data are protected against accidental interference; data flow is monitored and data are retransmitted in case of error detection. Software for controllers does not contain any dedicated elements connected with communication i.e. the built-in operating system is harnessed to the maximum degree. Smooth running of the telemetry and controlling systems is independent of mains continuous work, which is ensured by using uninterruptible power supply (UPS).
Primary controllers (SP) perform most control and regulation functions. Local controllers connected to a common bus perform remaining functions. Controllers are connected with one another with RS485 interface. To encourage redundancy, important signals meaning malfunction are sent through independent additional signal lines. Any primary controller is responsible for the performance of the following functions:
- automatic control of all working devices of the pumping station hydraulic system,
- control and monitoring of pumping station power supply, including the control of automatic start of stand-by power supply,
- control and monitoring of the access control system, fire protection system and flooding control system,
- monitoring of the access to remote control functions.
Primary controllers and local controllers are designed so as to be capable of performing all autonomic functions without the necessity of communicating with dispatching room stations.
Function of monitoring of the smooth run of pump units is partly performed by programmable local controllers adjacent to these units and partly by the primary controller (a diagram below). The tasks of these controllers are:
- performing of algorithms of units correct work monitoring,
- local measuring of selected parameters,
- adjustment of selected parameters,
- detection of possible leakage in pump units.
They are responsible for measuring signals from sensors of vibration, temperature, dampers positioning, signal filtering and for comparing of the measured values with the maximum ones. There is one local controller installed for each pump unit. The primary controller cyclically reads monitored parameters by the serial interface and it shuts down the unit if set limit values are overshot. As an additional protection, independent binary signals come into the master primary controller (SPM), informing about overshooting of limit vibration and temperature values in individual units and forcing an immediate shutdown of the unit. This way the system reliability is increased in case of communication loss with a given controller.
Communication between primary and local controllers is performed by means of a serial interface. Because of the RS485 standard in which the local controllers work, an RS485/RS232 converter is used, which enables connecting to the primary controller. To ensure a proper redundancy level, two additional binary signals are provided independently from each controller (SP) to the master primary controller (SPM). They signalize:
- the state of overshooting maximum temperature of unit bearings,
- the state of overshooting permissible value of vibration level.
Appearing of one of these signals runs emergency pump shutdown algorithm independently of correct work of the transmission cable. Engine bearings are equipped with temperature sensors PT100 and piezoelectric vibration sensors. Specialized amplifiers converting low-voltage signals to current signals were placed in measurement lines to properly form the converter performance. To ensure possibility of unmanned operation of intermediate pumping stations it was necessary to create a system, which automatically detects planned and accidental leakage of water in the network. During normal work of pump units, small quantities of water from bearings cooling system and pump natural leakage are drained to waste water sumps nearby. Periodically, during normal operation, much larger quantities of water are drained to the sumps, e.g. water from venting system or bearings cooling installation. Therefore, some modifications in the design of waste water sumps were made and float sensors installed. Software of local controllers is adjusted to system properties and they react only when water getting out of the cooling system of bearings or any other large leakage causing the float sensor to work, lasts longer than 5 minutes. It allows monitoring leakages and reacting only when there is a real danger to the intermediate pumping station. Additionally, water-flooding sensors connected to anti-breaking system were installed in pipeline passages.
Radio Connection on a Licensed Frequency
In this line, the communication device - a radiomodem - is connected to a computer using RS232 serial interface and it transmits serial data to a distant data processing system by means of radio waves in 400MHz band. There is employed a "star" configuration here, in which the central station works with an omnidirectional antenna and communicates with distant stations (SOC_D and SOC_P) sequentially on one frequency. Distant stations are equipped with directional antennas in order to increase their range and decrease the effect of disturbances and interference from other transmitting devices. Such a system works on a leased frequency. Frequency was assigned basing on an application with project documentation of the radio network development, which included the network description, objectives, as well as propagation and disturbance analyses.