The training laboratory system is designed to be used as educational equipment during laboratory works under the course “Electrical machines” in universities and specialized schools.
Structurally, the training system consists of:
- case with installed part of electrical equipment, electronic boards, front panel and countertop integrated desktop;
- electronic unit №1, which consists of one DC motor of independent excitation,one asynchronous electric motor with squirrel-cage rotor, one asynchronous electric motor with phase rotor, pulse speed sensor, determining the direction of rotation;
- electronic unit № 2, which consists of induction regulator with worm reduction gearbox. Shaft rotation is carried out via the handle through the gearbox. The angle of rotation of the shaft regulator is displayed on the scale between -180° to + 180°.
The training system is complected by the electric machine units, based on the low power electric motors (90 W).
The case of the training system includes:
- Frequency converter, which is used to form three-phase circuit of AC adjustable frequency and voltage. The converter is made on the base of microcontroller MB90F562 (Fujitsu) and smart power module PS11033 (Mitsubishi). The controller is used to input counts (voltage and frequent settings) and output signals (current, voltage), to organize data exchange with the PC (RS-485), to export measured values on the front panel of the training system. The power module consists of the power circuits of three-phase rectifier bridge, three-phase IGBT bridge inverter, the drivers’ circuits and the protection against short-circuit voltage, low driver power supply, incorrect control signals. The frequency converter allows to investigate asynchronous motor in all four quadrants of the mechanical characteristic.
- Three pulse width converters, which are used for power supply of anchor circuit and DC motor excitation windings, and for power supply of the rotor circuit of asynchronous motor with phase rotor in the mode of synchronous motor and generator. Two pulse width converters are located on the element base of the frequency converter. Its two arms are used to get reversible PWC, another arm is used as non-reversible PWC for power supply of phase-wound rotor induction motor in the mode of synchronous motor. The power supply of excitation winding is realized on the separate MOSFET transistor of International Rectifier company.
The control system is designed on the base of microcontroller ATMega (Atmel). It realizes input counts (voltage, frequency and dynamic braking current settings) and output signals (armature, frequency and rotor current), organization of data exchange with PC (RS-485), export measurement values on the front panel of the training system. Pulse width converter of the DC motor anchor circuits is added by the operating mode of the closed system (current or speed regulation), and generator operating mode.
- The measurement module is designed on the base of digital measurement equipment. Instead of current and voltage measurement, each channel can count:
o existing value of alternating current and voltage;
o phases shearing angle between current and voltage;
o active power.
The measured values can be displayed on the front panel of the training system or to be transferred to the computer.
- Relay contactor control, which allows:
o Switch connection scheme of asynchronous electrical motor with squirrel-cage rotor.
o Input inductances in the stator’s circuit of the asynchronous electrical motor with squirrel-cage rotor, in the circuit of parallel (second) three-phase transformator.
o Measure load resistance value in three-phase circuit.
o Connect asynchronous electric motors to the mains or frequency converter.
Resistors in the excitation winding circuit (two levels).
- Load resistors in three-phase circuit (four levels).
- Overvoltage energy drop resistors on the smart modules.
- Incandescent lamps for three-phase generator synchronization with network.
- Starters relay subsystem.
- Double winding transformers.
Frequency and pulse width converters are switched on intra-network collaboration (recuperation mode) to reduce power consumption from the network.
The electrical schemes of investigated objects are located on the front panel. The schemes, located on the panel, are split into groups, according to the theme of works. On the panel of the training system the following equipment is installed: switch sockets, indicators of digital units, switch gear apparatus and control units, allowing to change elements’ parameters during the laboratory works.
Control elements on the front panel of the training system:
- setting potentiometer to conduct a pulse width reversible converter;
- setting potentiometers of pulse width converters for power supply of DC motor excitation windings and the rotor of electric motor with phase rotor;
- setting potentiometers of frequency converter to allow smoothly change an imput frequency (0 ÷ 163 Hz), output voltage (0 ÷ 220 V);
- control elements of relay subsystem.
To carry out laboratory works, It’s necessary to collect the scheme of investigation object, using unified jumpers, which allow to show the scheme in visual form
It’s possible to carry out the laboratory works both in a manual mode, and in dialogue mode with PC.
The training system is supplied with:
- a set of technical and methodical documentation for teaching staff;
- a software to work with the training system. To carry the laboratory works, using «EM» software, is to collect the data in the background, to fill the data in the tables automatically and to construct the graphics in the real time mode, based on the received data, during the time of laboratory work.
The software also provides to conduct a complex laboratory work, in which a student is offered to pass the following steps:
- theoretical interview on the theme of the laboratory work;
- to collect, check and correct the schemes of conducted experiment on the digital panel of the training system;
- to carry out the laboratory work on the training unit.
If the theoretical or collecting steps are failed, a student can’t be allowed to the next step of the laboratory work.
Also for some works it’s used the variant to conduct the laboratory work automatically, under control of PC. It’s necessary to construct the scheme and to set correct parameters of the experiment, then the characteristics of investigated machines are measured automatically.
The results of the experiment are received in the form of tables, values and graphics in all variants of the laboratory works. There is an opportunity to export the tables in the clipboard or to MS Excel office application, to copy the graphics in the clipboard. Also it’s possible to change graphic’s scale display in a manual or automated mode, to configure the drawing options (color, thickness, line type), to smooth the data, graphic’s axis settings, etc.
The software can remotely control all the parts of the training system in a manual mode, which allows to check their workability and to conduct remotely the laboratory works.
During the work of the training system the software duplicates the training system’s panel on the computer screen. Thus all the measured values are displayed on the training system’s panel.