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Modeling and generating power quality disturbances

Monitoring power quality (PQ) in the distribution system is an important task for energy suppliers and their customers. In a distribution system, various types of faults cause power quality disturbances. Power supply operation can be improved and maintained by systematically analyzing power quality disturbances.
The power supply is designed to operate with a sinusoidal voltage at a constant frequency. Power quality disturbances occur when the magnitude of the voltage, frequency, and/or waveform deviation change significantly due to various types of faults such as nonlinear loads, switching of loads, weather conditions, etc.
The effects of poor power quality depend on the duration, magnitude, and sensitivity of the connected equipment. Poor power quality can lead to process interruptions, loss of data, malfunction of computer-controlled equipment and overheating of electrical equipment.
It is important to detect and classify power quality disturbances. A variety of waveforms can be generated by simulations and be useful for disturbance detection and classification.
The waveforms of the possible disturbances are created in this description by mathematical models. The EPOS 360 three-phase signal generator and EPOS operating software are available for modeling and generating signals to analyze the events in the power system.

The mathematical models of the power quality signals can be implemented in the EPOS operating software by means of the "Signal Editor" module and generated with the EPOS 360 signal generator. The use of equations offers advantages as it is possible to vary signal parameters in a wide range and in a controlled way.
The following pictures show the different power quality signals which have been defined via the Signal Generator module.

Ideal voltage/current source
An ideal AC voltage source generates a continuous, smooth sinusoidal voltage.

Voltage fluctuations
A drop (undervoltage, voltage dips) or rise (overvoltage, swell) of the mains voltage of at least ½ cycle up to several seconds.

Voltage interruptions
A significant or complete voltage interruption. The interruption can be short-term but also permanent.
 

Harmonics
Distortion of voltage and current waveforms caused, for example, by operation of nonlinear loads.

Transients
A sudden disturbance in the line voltage that typically lasts less than one period and consequently the waveform becomes discontinuous.

In this description, the basis for generating typical power quality disturbances was presented. This signal generation solution includes the EPOS 360 signal generator supported by a PC with the EPOS operating software. The software includes the Signal Editor module, through which parameters such as amplitude, phase angle and frequency can be adjusted for signal generation. Furthermore, the Signal Editor module provides many other functions for adjusting the basic parameters, such as offsets, overlays and harmonics.
The hardware and software functionality makes it very easy to perform the generation of diverse waveforms. The generation of the previously defined waveforms is provided by four voltage and three current output channels of the EPOS 360. The signal generator can thus be used in procedures for testing instruments and devices for power quality measurement and analysis.

For more information, please refer to the following application notes:

  1. Signal generator EPOS 360 - A laboratory for power quality
  2. Three-phase signal generator for precise power network simulations

Do you have any questions about our measuring devices?
Then contact us via the comment function here on the blog or by mail to info(at)kocos.com.

Voltage transformer VT2 – Extension for ARTES test systems

Testing of protection devices with rated voltages up to 690 VLL

With the steady increase in decentralized power generation, the requirements for power distribution are also becoming more complex. Due to the increasing plant power, these are often connected directly to the medium-voltage distribution grid, but the individual generation units of a plant are interconnected at the low-voltage level. This is raised to medium-voltage at the grid connection point by means of a transformer.

The low-voltage used within a generation plant results in a high current load on the cables for long distances between the individual generation units. In order to minimize the associated power losses, the nominal voltage on the low-voltage side is increasingly being raised to up to 690 VLL, in deviation from the widely used 400 VLL.

With an appropriate configuration, many protection systems can also measure this increased voltage directly without additional voltage transformers. This automatically results in new requirement for the test systems. These are largely designed for testing voltage protection functions up to a nominal voltage of 400 VLL. In order that these systems can also be used for testing with higher voltages, an extension is offered with the VT2 to also meet the new requirements.

During the development of the VT2, care was taken to incorporate the advantages of the ARTES RC3 relay test system. Therefore, the VT2 was also fully integrated into a hard shell case and is thus also ideally suited for use under harsh conditions.

Do you have any questions about the voltage transformer VT2? Then contact us by mail to info(at)kocos.com

When testing electrical components, such as motors, accurate, reliable and powerful power supplies are required. Furthermore, in production, many processes are automated where time is an important factor in testing.

The voltage sources of the EPOS CV series are designed for above mentioned requirements, where adjustable output voltages up to 270 VAC / 300 VDC are needed.

A special feature of the EPOS CV voltage sources is the variable transformer with a fast motor drive that controls the AC/DC output voltage. A variable transformer is used because it enables a continuously adjustable voltage and is insensitive to current peaks. With the EPOS CV voltage sources, the output voltage can thus be steplessly adjusted to the respective requirements automatically and manually. 
The voltage sources are provided with internal voltage and current measurements via a controller, which significantly increases the efficiency of the system. The internal measurement electronics permanently control and regulate the values and ensure function monitoring. Among other things, the voltage sources are overload-protected with a circuit breaker that disconnects the output circuits in the event of a short circuit, for example. 
The series has been equipped with a convenient operating unit with touchscreen, jog wheel and function keys. The system is easy to operate and extremely user-friendly due to the control unit and display.
The output voltage can be set in stand-alone mode via the rotary knob. In automatic mode, the EPOS CV voltage sources can be easily integrated into own applications via an Ethernet interface.
The voltage sources of the EPOS CV series are available in different power classes. They are used wherever continuously adjustable DC and AC voltages in the range up to 270 VAC or 300 VDC are used. All models are suitable for connection in the frequency range 50 Hz / 60 Hz. 

Typical data of the motor-driven EPOS CV voltage sources are:

EPOS CV 821

  1. one phase
  2. 1 x 15..270 VAC
  3. 1 x 15..300 VDC
  4. 1 x 30 AAC
  5. 1 x 20 ADC
  6. 8,1 kVA

EPOS CV 831

  1. one phase
  2. 1 x 15..270 VAC
  3. 1 x 15..300 VDC
  4. 1 x 40 AAC
  5. 1 x 30 AAC
  6. 11,5 kVA

EPOS CV 753

  1. three phase
  2. 3 x 15..300 VACPN
  3. 3 x 15..520 VACPP
  4. 1 x 15..300 VDC
  5. 3 x 25 AAC
  6. 1 x 32 ADC
  7. 22,5 kVA

EPOS CV voltage sources provide both a high output voltage and a high output current. Especially when operating motors, large starting currents occur when the full rated voltage is applied, which can be many times the rated currents. The voltage sources are capable of supplying these current peaks up to 10 times the rated current of the load during the switch-on process.

Testing is the only way to ensure that electrical components function correctly. By analyzing the curve signatures of the actuating and operating currents and the resulting characteristics, it is possible to make accurate statements about the behavior of components and thus draw conclusions about their electrical and mechanical condition. For such analyses, KoCoS provides powerful AC/DC sources in the form of the EPOS CV series of voltage sources.

Would you like to find out more? You can find more information at the following link or contact us by mail at info(at)kocos.com.

In the real power supply environment, it is difficult to generate power quality events in order to analyze their characteristics and effects. Therefore, a system is needed with the ability to generate and output diverse three-phase signal waveforms.

With the software-based signal generator system EPOS 360, it is possible to realize an overall system with which three-phase power quality events can be simulated in a simple way.
Three-phase voltage and current signals with different signal disturbances can be generated with the EPOS operating software, such as voltage dips or interruptions, transient pulses and distortion of the voltage or current signal caused by the influence of higher order harmonic components.

Different monitors are available in the software for parameterization and the output of signals and test sequences.

TRANSIG-Monitor

The TRANSIG-Monitor module can be used to check the function of a DUT under real conditions. The TRANSIG-Monitor enables the graphical display and output of recordings and signal curves. Signal curves can be, for example, recordings of fault value acquisition systems or digital protection relays, which are available in the standardized COMTRADE format, or SigDef files with self-defined signals.

The functions of the TRANSIG monitor are:

  1. Loading of recordings in COMTRADE format or SigDef files.
  2. Assignment of the signals of the recording to the EPOS output signals.
  3. Scaling of the signals of the recordings.
  4. Transfer of the defined TRANSIG functions into a test plan.

Signal Editor

Another component of the EPOS operating software is the signal editor. The signal editor enables the definition, parameterization and calculation of any signal characteristics. The parameterization of the signals is done interactively on the screen. A signal duration can be set for each channel and each channel can in turn be divided into any number of time windows of different lengths. Within the time windows different function curves can be synthesized. It is possible to synthesize the function curves from a basic function, such as

  1. sine, 
  2. rectangle, 
  3. sawtooth,
  4. triangle, 
  5. DC

and their additive or multiplicative superposition with one or more superposition functions.

Superpositions can be functions, such as

  1. sine,
  2. exponential functions,
  3. ramps,
  4. DC,
  5. impulse,
  6. harmonics,
  7. mathematical expressions.

In particular, the mathematical expressions in the overlays should be pointed out, since the creation of formulas offers a wide range of possibilities for signal generation. The overlay function "Expression" is used to create a curve using mathematical inputs.

Conclusion

The three-phase signal generator EPOS 360 offers the possibility to create different signal waveforms, to apply them to the test object and to analyze the effects. The overall EPOS 360 system with the EPOS operating software thus provides a useful mechanism to understand and explain network phenomena without much effort.

Do you have questions about the EPOS 360 three-phase signal generator? We have the answers!
Contact us via the comment function here on the blog or by mail to info(at)kocos.com.

Multifunctional three-phase signal generator

With the EPOS 360 current and voltage source, KoCoS Messtechnik AG offers a signal generator that is recommended wherever maximum performance and the highest signal precision are required.

EPOS 360 has four voltage and three current signal sources. The signal curves are output via electronic power amplifiers. The parameters amplitude, phase angle and frequency can be varied over a wide range during the output.

Intelligent amplifier technology and synthetic signal generation make it possible to output any signal forms over a wide frequency range or even to play complex transient signals.

The TRANSIG monitor, included in the scope of delivery of the EPOS operating software, enables the graphical display and output of recordings that are available in SigDef format or in the standardized COMTRADE format. The corresponding signals are "played back" by EPOS as a transient sequence during tests.

In addition, the EPOS operating software contains a signal editor which enables the parameterization and calculation of any signal characteristics. These can be generated from a basic function, e.g. a sine and its superposition with one or more superposition functions, such as a DC component, exponential functions, harmonics, etc.

For special requirements, such as use in test benches, there is also a simple programming interface. This can be used in COM/ActiveX-supporting as well as in .NET environments.

For more information on EPOS 360, please visit the homepage. Ask our sales department for a quote.