Description
The bench is designed for conducting labs in “Electrical machines”.
Structurally the bench consists of two parts:
housing, in which part of electrical equipment, electronic boards, front panel, power module and tabletop of integrated desktop are installed;
machine assembly, which includes DC motor, asynchronous motor with wound rotor, one asynchronous motor with squirrel-cage rotor, as well as an optical speed sensor with the definition of the direction of rotation.
The bench can be supplemented with electrical machinery unit on the basis of electric motors of small (90 W) or large (0.55 kW) power.
The bench housing contains:
Frequency converter for generating variable frequency three-phase AC network and voltage of asynchronous motor and three-phase transformers power supply. The converter is based on a microcontroller MB90F562 (Fujitsu) and power intelligent module PS11033 (Mitsubishi). The controller is used for calculating input data (specifying voltage and frequency) and output (current, voltage) signals, for data exchange with PC (RS-485), and displaying the measured values on the bench front panel. The power module includes power circuits of three-phase bridge rectifier, three-phase bridge inverter on IGBT transistors, as well as drivers and protection circuits (short circuit, insufficient supply voltage drivers, improper control signals input). The frequency converter allows the user to explore the asynchronous motor in all the four quadrants of the mechanical characteristics.
Pulse-width converter for the armature circuit and the DC motor excitation winding power supply, as well as power supply of rotor circuit of three-phase asynchronous motor with wound rotor in the mode of synchronous motor and generator. The pulse-width converter is implemented on the basis of the power element of the frequency converter. Two of its arms are used for obtaining reversible symmetric PWC, and the third arm is used as an irreversible PWC for three-phase asynchronous motor rotor. Winding power supply is implemented on a single International Rectifier MOSFET transistor. The control system is based on a microcontroller AT Mega163 (Atmel) and implements the calculation of input (specifies voltage, frequency, and current for dynamic braking) and output (currents of anchor, excitation, rotor) signals, provides data exchange with PC (RS-485), the displaying of measured values on the bench front panel. The pulse-width converter of DC motor armature circuit is supplemented with a closed system mode (current or speed control), as well as generator mode.
Measurement unit is based on digital measuring devices. In addition to direct current and voltage measurements, each channel can calculate:
effective value of alternating current and voltage;
shift angle between current and voltage, as well as calculate cos(φ);
active power.
Relay-contactor control, which allows the user to:
switch the circuit of asynchronous motor with squirrel-cage rotor (star / delta);
change the value of the load resistor in three-phase circuit;
connect asynchronous motors to 3 ~ 380/220 V 50 Hz network or frequency converter;
Resistors in excitation winding circuit (two stages);
Load resistors in three-phase circuit (three stages);
Overvoltage dump resistors on intelligent modules.
Frequency converter and pulse-width converter are switched on for internal network operation (recovery mode) in order to reduce power consumption from the network.
Three two-winding transformers;
Relay subsystem power contactors.
The wiring diagrams of the studied objects are depicted on the front panel. All the diagrams are divided into groups in accordance with the lab theme. The panel contains switching sockets, indicators of digital devices, switchgear, and controls that allow the user to change parameters of the elements during the laboratory work.
Controls on the bench front panel:
setpoint potentiometer to control the reverse pulse-width converter, the reference signal of the closed system;
setpoint potentiometers of pulse-width converters of power supply for DC motor excitation windings and asynchronous motor wound rotor in synchronous machine mode;
setpoint potentiometers of frequency converter, which allow for the smooth change of output frequency (0 ÷ 163 Hz) and the output voltage settings (0 ÷ 220 V);
relay subsystem controls.
To carry out the lab it’s necessary to assemble the circuit of the studied object, using standardized jumpers, which allow the user to assemble the circuit without loss of clarity.
Software and a set of methodological and technical documentation intended for academic staff are supplemented to the laboratory bench.
The bench provides the conduction of the following labs:
1. Study of two winding power transformer with the use of open circuit and short circuit methods.
Investigation of single-phase transformer in various modes, the determination of the equivalent circuit parameters and rating the transformer external characteristics.
2. Experimental determination of three-phase two-winding transformer connection groups.
Study of vector diagrams of voltage for different connection patterns and experimental determination of three-phase transformer connection group.
3. Study of three-phase asynchronous motor with squirrel-cage rotor.
Study of construction and characterization of three-phase asynchronous motor with squirrel-cage rotor using methods of open circuit, short circuit and immediate loading.
4. Study of methods of three-phase asynchronous motors with squirrel-cage rotor start-up.
Study of three-phase asynchronous motors startabilities, circuit assembly and rating static and dynamic characteristics of motor start-up.
5. Study of DC generator with parallel excitation.
Study of the operating principle and characterization of DC generator with parallel excitation.
6. Study of DC generator with separate excitation.
Study of the operating principle and characterization of DC generator with separate excitation.
Study of the operating principle and characterization of DC motor with parallel excitation.
Measuring system technical characteristics:
Number of parameters displayed on the bench 15 pcs. (12 indicators)
Voltmeters 4 pcs.
Ammeters 6 pcs.
Phase meters 1 pc.
Velocity meters 1 pc.
Wattmeters 2 pcs.
Frequency meters 1 pc.
Range of measured voltage from ±1 V to ±750 V
Range of measured current from ±1 mА to ±5 А
Range of measured velocity from ±1 rad/s to ±314 rad/s
Range of measured frequency from 0 Hz to 163 Hz
Measurement accuracy, up to 1%
Pulse-width converter technical characteristics:
Rated current ±5 А
DC link voltage 300 V
Converter frequency 8 kHz
Current overload ±7 А
Frequency converter technical characteristics:
Motor power:0,4 kW / 1.5 kWt
Rated current:7 А
Output voltage operating range 3~ 220 V
Control method:sinusoidal PWM (control U/f, independent)
Frequency control range:from 0 to 163 Hz
Frequency resolution:0,3 Hz
Overload margin:150% of rated output current during 1 minute (integral dependence)
Complete set of equipment "Electrical machines":
laboratory bench "Electrical machines";
one machine assembly;
set of jumpers;
cable AM-BM USB 2.0;
CD-R with accompanying documents and software.
