SPEED REGULATORS
The engines represent a very important part of electricity consumption and even more in the industrial sector. Although machines are reliable enough, there is always the risk of occurrence of any damage or anomalies appear in the voltage. Why not simply connect a motor to the network to use it properly, but there are several elements that help ensure safe operation.
Let's see if when the need is starting an engine, the option will choose between the traditional methods electromechanical power (directly or as star-delta reduced voltage autotransformer motor cage rotor resistance or rotor winding engine, etc.), and a progressive electronic starter.
If the application needs are of varying speed and torque control, the options are to use a mechanical solution, a special motor (dc, servo, etc.), Or a squirrel cage induction motor with frequency .
2 .- SCOPE
inverters are power converters to modulate the energy charge to the engine or other definition would variable speed drives are devices that vary the speed and the coupling of three-phase asynchronous motors, turning the magnitdes fixed frequency and voltage in varying magnitude.
control of electric motors by switching sets of "All or Nothing" is a solution well suited for driving a wide range of machines. However, poses constraints that may be inconvenient in certain applications:
- The current spike at startup can disrupt the operation of other devices connected to the network,
- The mechanical shocks that occur during starts and stops can be unacceptable machine and for the safety and convenience of users,
- constant speed operation.
starters and electronic speed controllers eliminate these drawbacks. Engines suitable for AC or DC power, ensuring progressive acceleration and deceleration and to tailor the speed to the operating conditions very accurately. Depending on the type of motor, used various controlled rectifier type, frequency converter or voltage regulator.
3 .-. REGULATIONS
* CEI 61800-3: EN 61 to 800 -3, UNE In - 61800-3, electric power drives and variable speed.
* IEC-EN: 61800-5-1 Level of Protection
Variable speed drives are electronic devices that allow for change speed and torque of three phase asynchronous motors, converting fixed magnitudes of voltage frequency and in varying magnitude.
these teams are used when the needs of the application are:
* Domain
torque and speed regulation without mechanical shock *
* * Mechanical Movements
sensitive complex
Motor Drive controllers are trained to deal with three-phase asynchronous motor rotor cage. The motor voltage can not be larger than the mains. A voltage and frequency of motor plate behaves according to the following graph:
The motor dimensions must be such that tough braked load does not exceed the rated motor braked, and the difference between one and another provides the accelerator and esacelerante braked enough to meet the start and stop times.
The drive
thus are called variable speed drives rectifying the alternating voltage network (single or three phase), and by six transistors working in pulse width modulation to generate a three-phase variable frequency and voltage. A further transistor, called the braking energy can address returned by the engine (during regenerative braking) to an external resistor. Below is a typical electronic diagram:
shot strategy of the inverter transistors is performed by a microprocessor, for maximum engine performance within the entire speed range, using an algorithm flux vector control.
This algorithm by using knowledge of motor parameters and operating variables (voltage, current, frequency, etc.) Performs precise control of magnetic flux in the motor keeping it constant regardless of frequency. As the steady flow, the torque provided by the engine will be also.
The chart shows that from 1 Hz to 50 Hz nominal motor torque is available for permanent use, 170% of rated torque is available for 60 seconds and 200% of rated torque is available for 0.2 sec.
4.2 .- METHODOLOGY
Any device to be used in a electrical installation has a specific selection methodology, which we rely below
4.2.1 .- SELECTION OF A DRIVE CONTROLLER
To define the most appropriate equipment to meet a variable speed application must taken into account the following aspects:
Load Type: Constant torque, variable torque, constant power pulsed loads.
Engine Type: Induction squirrel cage rotor winding, current and power rating, service factor, voltage range.
Operating Ranges: maximum and minimum speeds. Verify need for forced ventilation of the engine. Par
startup: Check not exceeding those permitted by the drive. If you exceed 170% of rated torque should overestimate the drive. Regenerative braking
: high inertia loads, cycle times and vertical movements require external braking resistor.
Environmental: temperature, humidity, altitude, type of enclosure and ventilation.
mono or multi Application: Provide individual thermal protection for each motor. The total power of all motors will be the rating.
Network Considerations: microswitching, voltage fluctuations, harmonics, power factor, line current available, isolation transformers.
Application Considerations: motor overtemperature protection and / or overload, isolation contactor, bypass, automatic restart, automatic speed control.
Special Applications: Electromagnetic Compatibility , audible motor noise, pumps, fans and blowers, hoist, motors in parallel, etc. 4.2.2 .-
RECOMMENDED CIRCUIT
circuit to use a drive must recorded with some of the following elements:
Breaker: His choice is determined by considerations seen in the course of Electrical Measurement and Electrical Installations II I.
The current line corresponds to the current drawn by the drive at rated power utilization.
Line Contactor: This feature ensures automatic switching circuit in case of emergency shutdowns or failures. Use in conjunction with the circuit breaker type 2 is responsible for coordinating the output and facilitates implementation tasks, operation and maintenance.
Selection is based on rated power and the rated engine in S1 and job category AC1
choke line: These inductances can be improved surge protection network, and reduce the rate of current harmonics produced the drive, improving the distortion of the voltage at the connection point.
This reduction of harmonics in a decrease of the rms value of current drawn from the power supply, and reduced rms current value taken by the components of the input stage inverter (rectifier, preload contactor, capacitors). The use of inductances line is particularly recommended for the following cases
:
- Red very disturbed by other receivers (parasitic, surges)
- Mains with voltage imbalance between phases> 1.8% of nominal voltage.
- fed by a line drive very low impedance (near power transformers of more than 10 times the drive rating.) The minimum line inductance corresponds to a short circuit current Icc of 22000 A
- Installing a large number of drives in the same line.
- Reduced overhead condensers fp improved, if the installation includes a battery compensation of power factor.
Selection is based on the nominal drive current and switching frequency. There are standard inductors for each type of drive.
radio interference filter: these filters can limit the spread of parasites that produce drives for driving, which could disturb certain receptors located in the vicinity of the device (radio, television, audio systems, etc.). .
These filters only be used in TN type networks (Update neutral) and TT (neutral ground). There
standard filters for each type of drive. Some drives bring them home built.
braking resistor: Its function is to dissipate the energy of braking, allowing the use of the drive in quadrants 2 and 4 of the torque-speed diagram. This will make best use of engine torque during the braking time and is known as dynamic braking. It is usually an option as it is only necessary in applications that require high braking torques.
The installation of this resistance is very simple: should be located outside the cabinet to allow proper dissipation, and the drive has a terminal block where it connects directly. According to the factor of the motor power is determined should dispel resistance.
tables exist for this selection. The ohmic value of resistance is characteristic of the drive and should not be modified
5 .- APPLICATION
Now we'll see how to operate the drive controller, with its own circuit recommended for proper operation and protection same, and the operator.
Installation Frequency Converter
Installation Recommendations
Wiring:
- In the control cables, use shielded twisted cable circuits slogan.
- There must be a physical separation between power circuits and circuits for low-level signals.
- The land must be of good quality and low impedance connections.
- cables as short as possible.
- The drive must be as close as possible to the motor.
- Ensure that power cables are away from cable television antennas, radio, cable television and computer networks.
Cabinet: Metallic or at least on a metal tray attached to the ground bar. In the user manuals for the drives are making recommendations as to size.
Ventilation: You must agree to the heat dissipated by the equipment at nominal power. Are supplied as optional extra fans and mounting kits ventilation and to ensure IP54 protection without losing the possibility of dissipation.
Grounding: The land must be of good quality and low impedance connections. We should make the ground connection of all bodies of the facility, and the housings of electric motors. The grounding system must have a resistance value that ensures a contact voltage 24V or less permanently.
Applications of frequency inverters
frequency inverters have their main applications in the following types of machines
:
Conveyors: control and synchronize the production rate for the type of product being transported to dose, to prevent noise and shock in transportation of bottles and packaging, to boot smoothly and prevent the fall of the product that is transported, etc.
centrifugal pumps and fans: control the flow, pressure systems use constant and variable volume. In this case you get a great energy savings because consumption varies with the cube of speed, or half that speed,
consumption is the eighth of the nominal.
Positive displacement pumps: Flow Control and dosage accurately controlling the speed. For example, screw pumps, gear pumps. Transport of fruit pulp, pulp, mining concentrates, chemical additives, chocolates, honey, mud, etc..
Lifts and elevators: For soft start and stop maintaining constant engine braked, and different speeds for different applications.
Extruders: You get a wide variation in speed and total control of the motor braked.
Centrifuges: soft start is achieved by preventing spikes and resonance speeds.
mechanical presses and dipper: soft start is achieved by low speeds and at the beginning of the task, avoiding the waste of materials. Textile machinery
: For different types of materials, including fabric that does not have a symmetrical tissue can attain speeds of random type to get special fabrics.
air compressors: soft starts are obtained with maximum braked and lower power consumption at startup. Oil wells
: pumps are used for extraction rates according to the needs of the well.
Other applications Elevators bucket, screw conveyors, continuous paper, machine tools, welding machines, pantographs, machines for glass, fulones tanneries, snuff dryers, fruit sorting shapers of cables, extruded pipes, rolling mills, mixers, extruded profiles aluminum cable, etc, mineral crusher, sugar cane mills, balancers, flour mills, cement rotary kilns, ovens, food industries, bridge crane, test stands, industrial dryers, capping containers, wells for refrigerators, mixers , cardeadoras, dispensers, dispensers, reactors, kettles, washing machines, polishers, rotary grinders, polishers, cutters, wrappers and esbobinadoras, sanding machines, separators, vibrators, screens, trains, electric vehicles, escalators, air conditioning, automatic doors, moving platforms, worm screws, rotary valves, calenders, knitters, CHIP, pumps, positioning, etc.
6 .- RESULTS
7 .- RECOMMENDATIONS
These characteristics, both technological (power electronics) and motor performance associated with a drive, showing the need to provide suitable safeguards for the proper operation of this equipment.
Obviously, these protections do not replace those required at the beginning of each circuit, according to installation regulations, which are "outside" the drives.
8 .- CONCLUSIONS
- Variable speed drives provide greater security to the other, both starting with the stop, but the cost is higher than a drive system without long-term results very beneficial both in cost savings as in the period of engine life.
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