Drive technology is the largest sub-sector in mechanical engineering. Drive technology ‘made in Germany’ is in heavy demand and can hold its ground on the global market despite high cost pressures as a result of the synergy of premium quality, intelligent design, and efficiency.
Integration of power electronics systems in drive technology and therefore in the production process and in building services technology has risen disproportionately. Applications of this kind are particularly energy-efficient and flexible. More use needs to be made of frequency inverter-controlled drive systems in future, for instance, in order to achieve global climate policy targets.
The requirements and complexity of modern systems and plants have also risen in line with the increase in power and microelectronics components. BLOCK has an extensive range of reactors and filters which guarantee that the drive technology works reliably, efficiently, and failure-free, including within the scope of Industry 4.0.
A power electronics drive system consists of more than a frequency inverter, motor cable and motor. Additional Power Quality components also need to be integrated into the system in order to ensure safe and failure-free operation for the mechanical system. This is because system and plant manufacturers are required to guarantee the electromagnetic compatibility (EMC) of the drive system and of the entire plant and provide evidence of this through the CE mark.
“EMC” relates to the ability not to disturb other devices through unwanted electrical or electromagnetic effects, or to be disturbed by other devices and systems. We speak of EMC problems if this does occur.
Frequency inverters can be the source of various EMC effects. By transforming the mains frequency and the mains AC voltage, firstly into DC voltage and then into pulse-width-modulated voltage (PWM), a large part of the plant’s overall power is transferred to a motor (in most cases an electric motor).
Frequency inverters consist of an input rectifier circuit which converts the mains AC voltage into DC voltage. The downstream intermediate circuit capacitor smooths the DC voltage further and also serves as an energy storage system. The intermediate circuit capacitor is charged temporarily via the rectifier circuit (1~ B2-/3~ B6 bridge rectification). Spikes arise in the mains power signal as a result of this. Aside from the fundamental frequency of the mains, these also feature superimposed frequency components and are known as “harmonics” or “harmonic vibrations”. Harmonics can be presented and evaluated in a magnitude spectrum via the Fourier Transform. These harmonics result in non-linear voltage drops across the impedance in the upstream mains and therefore to voltage distortions in the network range supplied by the same transformer. This circuit feedback causes damage or impairs the operation of the transformer and of further consumers. A high degree of harmonic currents means high additional reactive power at the same time, which is also known as distortion reactive power. This reactive power must be provided by the energy supplier and may be charged. The applicable standards such as IEC 61000-3-2 / -3-12 or IEEE 519 stipulate limit values for harmonic currents.
Line reactors reduce low-frequency disturbances (harmonics) and reduce the strain on the mains supply by compensating for the distortion reactive power. Limiting the start-up current protects the connected consumers and thereby also increases their lifetime. The standard product range includes series with short circuit voltages of 3%, 4% and 5%.
Passive harmonic filters
Passive harmonic filters from BLOCK reduce harmonic currents and thereby also reduce the distortion reactive power because they are precisely aligned with the main harmonics frequencies. The quality of the power signal is stated as a percentage with the THDi value (Total Harmonic Distortion). While a THDi of 30 – 40% is achieved with a line reactor in standard industrial applications, BLOCK harmonic filters can reduce the THDi to <= 7%. In this way, in addition to improving the Power Quality, BLOCK harmonic filters also contribute towards mains stabilization.
Currents and voltages deviating from the sinusoidal shape feature components with higher frequencies. In the frequency range between 0-2000 Hz, they are known as harmonics, while in the frequency range over 150 kHz, they are known as radio interference. Radio interference is subdivided into conducted interference (150 kHz to 30 MHz) and radiated interference (greater than 30 MHz). High-frequency switching operations (cycle frequencies) featuring high edge steepness in the kHz range at the output of the frequency inverter cause these types of radio interference. The higher the frequency and steeper the rising edge (hard switching), the greater the potential for radio interference. There are standards and limit values which must be complied with and which relate to the operational environment for the device or for the system in the residential or industrial area. Radio interference can only be effectively reduced by radio interference filters.
Passive EMI filters are used to suppress electromagnetic interference between the mains network and frequency inverter in the frequency range between 150 kHz and 30 MHz. They are used for compliance with the limit values required by the standards for the residential or industrial area. We offer a comprehensive range of filters as well as measurements on-site or at our in-house accredited EMC Lab. When designed as a line filter, the passive EMI filter can also be combined with a line reactor. This also reduces low-frequency interference (harmonics).
Functional leakage currents can result in downtime
Leakage currents can arise through damaged insulation (fault current). They then flow via the equipotential bonding system (ground). An upstream fault current circuit breaker is able to switch off these leakage currents safely. This safety system protects people and provides protection against fire. On the other hand, leakage currents also occur through grounded capacitors for suppression of radio interference, and through unwanted/parasite capacitors in the system. Functional leakage currents result in system downtimes as they trigger the upstream safety systems (FI circuit breaker). In the case of frequency inverter-controlled drive systems, parasite capacitors produce switching frequency-dependent leakage currents in the kilohertz range via the motor cable and at the motor itself. The intermediate circuit capacitor is the source here. Radio interference suppression capacitors in the EMI filter and frequency inverter produce low-frequency leakage currents with the mains network as the source. BLOCK has experts with specific expertise in solving the problems caused by excessively high leakage currents or frequent false tripping of the FI circuit breakers. They also carry out measurements on-site or at our in-house EMC Lab.
Motor reactors protect the drive from high voltage spikes and enable safe operation
Frequency inverters used for three-phase motor drives are a source of differential mode (symmetrical) and common mode (asymmetrical) interference. Controlling the rotating field frequency, torque, as well as the start-up and braking behavior of the connected motor works through variation of the pulse and pause times of the pulse-width modulated voltage at the output of the frequency inverter. This voltage signal rises via the capacity-based motor cable. This can damage the motor insulation and thereby reduce the motor’s lifetime. Longer motor cables in particular make operation of large drive systems more difficult. This is because leakage currents, bearing currents, and EMC problems impair the drive system’s operational reliability.
Motor reactors protect the motor from high edge steepness of the frequency inverter output voltage. High edge steepness at the motor occurs through an upswing in the pulse width modulated voltage at the output of the frequency inverter via the capacitance per unit length of the connected motor cable. The longer the motor cable the higher the capacitance per unit length – and therefore the higher the expected edge steepness at the motor. This is stated as a dv/dt value and results in a gradual increase in voltage. A dv/dt value of >2 kV/µS is achieved if no filters are used. This can cause insulation damage and even total failure, particularly with older motors or motors with efficiency classes IE1 and IE2. Motor reactors reduce the dv/dt value to up to <500V/µs for motor cable lengths of up to 100 meters. A dv/dt value of <250V/µs is also feasible with long cable lengths >100 m when a dv/dt filter is used with additional filter components, such as small capacitors and resistors.
Sine filters produce a sinusoidal voltage featuring low distortion from the switched frequency inverter output voltage. The sine filter achieves a very high filter effect through precise low-pass tuning to the switching frequency of the frequency inverter. The useful signal (motor operating frequency) passes through the sine filter with a minor effective drop in voltage, while the switching frequency is reduced by approx. 90%. Switching frequency harmonics are almost entirely filtered out. The use of sine filters enables the use of long shielded motor cables and ensures low noise motor operation.
Sensors and process data acquisition have long been part of connected plant and drive systems. Interfaces in the inverter enable communication via fieldbus systems for status monitoring as well as plant management and control. Bearing currents, leakage currents, and EMC problems caused by common-mode voltages impair a drive system’s operational reliability. High-frequency parasitic currents of this type couple into the grounding system via the stray capacitance of the motor cable and of the motor itself. They can spread throughout the entire plant area via fieldbus cables and encoder cables as well as on the wire paths for the voltage supply and the equipotential bonding. The galvanic coupling of the disturbance is one of the principal causes of EMC problems in electrical plants. Disrupted communication signals in the data transmission process can result in undefined plant statuses and downtimes. Control and electronics components installed within the system can also be damaged. All-pole sine filters from BLOCK provide a comprehensive solution for ensuring operational reliability in the production process in plant networks according to Industry 4.0.
All-pole sine filters
All-pole sine filters combine the benefits of a regular sine filter with additional filtering of the common-mode components which cause bearing currents at the motor, excessively high leakage currents, and EMC problems in the plant. BLOCK’s concept for all-pole sine filters provides for an additional connection to the intermediate circuit of the frequency inverter. This means that common-mode currents are returned directly to the source, i.e. the intermediate circuit of the frequency inverter. Further benefits:
◼︎ Reduction in bearing currents
◼︎ Very long, unshielded motor cables can be used
◼︎ EMC optimization
◼︎ Reduction in filter components on the mains
◼︎ Reduction in leakage currents
◼︎ Flawless operation on FI circuit breakers
BLOCK: Longstanding development partner for more Power Quality in industry
As one of the world’s leading manufacturers of inductive winding goods, BLOCK began working on the EMC of frequency inverter-controlled drive systems at an early stage. We have demonstrated our capacity for innovation in supporting this development over the last 40 years, together with manufacturers of drive systems and machine constructors. Our EMC solutions are geared towards these drive systems. Extensive vertical integration and our expertise in filtering frequency inverter-controlled drive systems in our in-house Fundamental Research and Innovation Center ensure that customers achieve the best practice EMC solution for their application. Aside from EMC checks and tests for the most adverse environmental conditions, we also carry out shock and vibration tests in our in-house laboratory.
At BLOCK, we develop a closely aligned solution whenever customers are planning particularly challenging projects. We benefit here from our many years of experience and constantly gain innovative ideas from the requirements from a wide range of industries, such as railway technology or wind power. In this way, we develop the perfect voltage solution for our customers’ products.