Medium-voltage frequency inverter HERCULES

Description

Medium-voltage frequency inverter HERCULES, depending on version, is meant for frequency scalar or sensorless vector speed control of one or more asynchronous or synchronous motors with capacity from 185kWto 7100kWeach with 3kV, 6Kvor 10kV network, connectedtooutput of the motor. In special cases device might be used for the soft start of the motor, which provides starting current decreasing up to target normalized value. If required, might be implemented the motor reversing function.

Complete specification

Medium-voltage frequency inverters HERCULES – automatic systems of new generations, which control the motor speed through generation of electric tension with preset amplitude and frequency at the output of inverter.

Core of the system, which was developed and is now produced by our company, is the direct medium-voltage frequency-changing circuit, which provides form output signal receiving close to sinusoidal. It is achieved through the chain of inverter power cells usage, which makes system operation with medium-voltage asynchronous and synchronous motors without extra voltage increasing and without extra electric filter possible.

Operation of inverter is based on high-efficiency frequency rotation sensorless vector control mode and U/f control mode. The advantages of our system are low distortion of input and output voltage, high-capacity factor, high control accuracy, rapid response to rotational moment dynamic change and high value of rotational moment at low speed.

Medium-voltage frequency inverters HERCULES might be used with three-phase electric motors of alternating current when voltage value is following – 3, 3,3, 4,16, 6, 6.6, 10 and 11 kV. Main distinctive characteristics are listed below.

Slight input voltage and current distortion

Voltage and current waveform distortion factor value meets the strictest requirements of IEEE 519-1992 standard, regarding frequency content of power electric systems. It is achieved by secondary winding phase pushing of phase-shifting transformer and usage of multi-pulse converter rectifier (30-pulse for 6 kV, 48-pulse for 10 kV). Phase-shifting transformer usage provides power units electrical isolation realization from power supply, which disposes the majority of current sinusoidal components, provided by inverter power units operation.

High-capacity factor

Medium-voltage frequency inverters HERCULES are based on phase controlling multi-level pulse-width modulation (PWM), which provides keeping the phase factor with value over 0,97 at any motor speed. All that decreases the problem of low phase factor during inductive load.

Low level of output sinusoidal components

The usage of PWM technology provides output sinusoidal components decreasing (refer to fig. 2.2 and 2.3) without output filter using. It has the following advantages:

• low noise level of electric motor during operation;

• rated motor parameters overstating not required;

• almost no motor heating caused by sinusoidal components;

• reduced torsionals, even in conditions of low speed;

• minimized correlation dU/dt, which has positive effect on cable and motor insulation;

• no limitation of cable length owing to arising overvoltage at the end of cable line.

It all decreases excessive ware of motor and device, reduces expenses on maintenance.

High-efficiency mode of sensorless vector control

Efficiency of this control mode is comparable to efficiency of sensor vector control. In this case high accuracy of control and dynamic response are provided. Moreover, maximum output torque is achieved even at low level of voltage.

U/f vector mode control

There was accomplished an optimization of common U/f control for quick dynamic response, torque automatic increasing and high torque achievement at low frequencies.

Excellent low-frequency equalization

Type of medium-voltage frequency inverters output current used to be unstable at low frequencies, especially at frequencies lower than 10 Hz. Moreover, there used to be mechanical oscillations at low frequencies, caused by current sinusoidal components. In vector frequency inverters HERCULES an algorithm of pulsatory current compensation and low-frequency vibrations cancellation is used, which provides qualitative output signal in vector and scalar control modes.

Excellent voltage adaptability

There is possibility of frequency inverter adaptation to long range of input voltage, which provides stability of performance in case of electric line voltage variation within -15%~+10%. Function of automatic voltage control is meant for output voltage automatic control in accordance with line voltage fluctuation. Medium-voltage frequency inverters HERCULES are adapted for continuous operation in short-term voltage slump conditions up to 85%~65% level from rating value or in case of its exceeding up to 110% ~120% from rating value.

Rotation frequency monitoring

Rotation frequency monitoring function is automatically activated after start of the motor from the frequency inverter, if there are set some definite parameters. There is automatically set rotation frequency following mode for the starting mode when the motor speed might be defined at all speed range. This provides starting dynamic overvoltage eluding.

Increased reliability

To guarantee reliability medium-voltage frequency inverter HERCULES is equipped with: 2 voltage inputs for power supply of control system, inverter power unit bypassing ability and automatic switching from variable frequency operation to power frequency operation.

Bypass inverter power units function

In case of power unit failure electric driver might continue its operation with defective power unit elimination from the circuit. In this case frequency inverter will operate at lower rated parameters. Users might choose between automatic and manual bypass inverter power unit modes by changing proper parameter.

Soft start without inrush current

Medium-voltage frequency inverters HERCULES have the function of the soft start without current exceeding. Start-up time is set by a user. Internal protection function limits runway speed in case of current exceeding and is meant for inrush current cancellation during the motor start. It provides operations security and lifetime extension, as well as start-up without negative effect on power network and electric motor. Moreover, this function prevents from short-circuit rotor of the motor breakdowns during the start and from failures connected with severe start-up conditions.

Gradual braking without overvoltage

Optimized breaking algorithm guarantees distribution of energy, which releases during braking, between all inverter power units, preventing overvoltage. Braking period is user set.

Diverse interfaces of user terminal

Standard frequency inverter HERCULES is equipped with plentitude of input/output terminals: 3 analog inputs, 4 analog outputs, 16 digital inputs, 20 relay outputs, 1 high frequency pulse input and 1 high frequency pulse output. All inputs and outputs are programmable, which enables creation personal user application system and guarantees opportunity of system extension.

Operation continuing after sudden power loss

Electric power supply might disappear because of shutdown, however electric motor might generate power to maintain system operation. Therefore, the system will be ready to continue operation after power-up. Frequency inverter HERCULES can continue operation after sudden power loss and return to normal operating conditions after power-up. Restart function helps to reset the inverter in case of outage period up to 5 seconds.

Diverse functions of operator interface

Interaction with operator in frequency inverters HERCULES is carried out through touch panel, which includes diversity of tuning functions and processes, which are displayed on-line and have user friendly interface. User can easily control condition of equipment during operation and control electric drive in accordance with technical process requirements. There are kept expenditure records of electric energy input.

Warning alarm and damage protection functions

Frequency inverters HERCULES provide different warning alarm and damage protection functions, which include 50 types of failure report regarding inverter power units. Operation of all these function might be checked by using P9 group parameters.

Steady control signal

Control signal of frequency inverter HERCULES is network isolated. For transmission of important signals is used fiber cable, which obtains interference protection and signal distant transmissibility.

Mode of one inverter and several electric motors

Medium-voltage frequency inverter HERCULES can operate with 4 bypass switching cabinets (optional supplying), which are connected to 4 electric motors. This function might be used for water-supply systems and for flexible start-up with soft changeover between variable frequency and network power frequency.

Master-slave device control

Master-slave device control distributes a load to several technologically (or mechanically) connected electric motors, provides rate speed synchronizing, operating as network with pilot circuit. For example, it is used to control several electric motors of belt conveyor.

High reliability and easy maintenance

IGBT block of medium-voltage frequency inverter HERCULES has a relatively large voltage and current built-in margin. For IGBT block protection in case of start-up and overcurrent special driver circuit is used (so-called driver), which provides high level of protection.

For control signal transmission in medium-voltage frequency inverter HERCULES is used fiber cable, in this case printed-circuit board is well protected by electromagnetic screening.

Frequency inverter HERCULES is based on modular concept. Inverter power units have the form of blocks of equal size, which are developed for easy and universal usage. In case of failure each block can be easily and quickly replaced within several minutes and using simple tools.

Front-mounted ventilation grids with filters are maintenance-friendly.

Synchronized motor changeover between mains-fed operation and operation from frequency inverter (optional)

Synchronized changeover function provides soft motor changeover between mains-fed operation and operation from frequency inverter (and conversely). That decreases effect on motor and electrical network.