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December 2, 2020
The main specifications that are considered in design of overall system determine the requirements for planning of mechanical and civil works, and plant management and operation. The picture of established micro hydro system is shown in Fig. 1. The micro hydro system can be divided into three main segments: civil works, hydro-mechanical works and electricity generation. The schematic of overall system structure is depicted.
1) Civil work:
Reinforced reservoir with volume of 150m3 stores the required water.
Water storage tower with 3m diameter and 16m height cylindrical steel structure. Attached to which is a lighting protection system. A pipe line with 12m height is fitted vertically inside the tower to reject disturbances of water flow at the entrance to the turbine
Steal pipelines with 500mm diameter and 6m lenght at supplementary side and 600mm diameter and 8m lenght at exit side
Power house: To maintain the safety and quality of electricity supply within defined limits, the small plant must be operated in such a way that the utility is able to fulfill its operating requirements.Therefore various associated electrical devices are required within the powerhouse for the safety and protection of the generator and other related equipment.
Artesian well: used for water requirement.
2) Hydro-mechanical equipment and accessories
Centrifugal Pumps: Total power output of 180kW are activated by five induction motors. Three are 20kWs drivenby AC drivers the remaining two are 50kWs driven by soft starters.
Turbines: Two different sized cross flow type Micro hydro turbines 20 kW and 40 kW were specifically designed for this project.
Control panel-1: equipped with starters, protection relays, fuses, two AC soft starters and three AC drivers for pumps control.
Flow meter: acoustic type Mag 5000 with a 400mm diameter ( Siemens) measures the turbine water flow.
Measurement of water level: pressure sensors: to measure atmospheric pressure in storage tower, a capacitive sensor Keller PA21Y with upper limit pressure of 4 bars is mounted within tank. Water level tracking task within the storage tower is enabled by a water buoy sending an on/off signal to the data acquisition card.
Data acquisition card: NI USB 6009 hardwired to PC collects signals from the sensors. These signals are used to keep water levels within parameters and to protect the storage tower from environmental abnormalities.
Control devices: PLC s7 200, CPU 222 (Siemens) which communicates with a host PC via PPI/PC cable, automatically activates the water pumps according to pressure and turbine water flow.
Coupling aparatus: A gear box with ratio of 4:1 inserted between the turbine and generator increases turbine revolutions.
Valves: A valve at both the entrance and exit of the storage tower are fitted for fill and discharge operations.
A pump: Draws required water from artesian well and fills the reservoir.
Lightning arrestor: one arrestor is mounted on top of water storage tower to protect the system against lightning strikes.
3) Electrical and other equipments:
Generators: There are two choices of generator: One is a18kW power, star connected asynchronous (squirrel cage type induction motor) generator (GAMAK) which can be utilized either for grid connected (over synchronous speed mode) or stand alone operations. Second option is a selfexcited (brushless), 20kVA synchronous generator (GENSAN) which is already installed to the turbine shaft with direct coupling through a gear box and can be utilized for islanding and/or grid connected generation mode. The synchronous generator has an onboard automatic voltage regulator (AVR) which can be used to adjust generator voltage and reactive power.Control panel-2: Contains necessary equipment needed for energy monitoring, recording and metering, for the safe operation of the power generation system. Moreover switches and breakers for manual on/off operation and interconnection, emergency stop buttons, voltage check switch, indicators for mains generator supply and breaker position. Manual switches and contactors for synchronizing controls.
Metering devices: These devices are mounted on panel-2: three ammeters (A) for each phase current, voltmeter (V) with voltage selector switch (VS) for line to line voltage measurements, frequency meter (f), active power meter (kW), meters of reactive power (kVAr), apparent power (S), active energy kWh and reactive energy kVArh. Monitoring device: To perform energy monitoring and recording tasks using device UMG507 (Jenitza), which is capable of measuring voltage, current, power, both harmonic contents of voltage and current, power factors, frequency and energy consumption etc. and also capable to communicate with other devices through the Profi-bus, RS 432 or Ethernet card. Synchronizing relay: in order to provide automatic synchronization to connect a generator to grid the SELCO T4000 auto-synchronizer is used.
Protections: Two seperate earthing points are provided one for the generator neutral point, and one for body of the generator and control panel. Earthing protection is performed by the relays installed on control panel 2. Each of these relays sends a trip signal to the associated devices to interrupt generation system if an electrical fault occurs. These relays are: Over voltage relay (OVR) and under voltage relay (UVR): responsible to protect consumer load against over voltage and under voltage respectively. Normally automatic voltage regulator (AVR) maintains generator terminal voltage within certain limits. If terminal voltage is out of these limits then OVR and/or UVR provides trips. Over current relay (OCR) protects the generator against excessive current due to faults such as short circuits or overloads.
Mains loss protection: with the removal of grid supply generator is automatically disconnected by an auxiliary relay energized by mains.