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Which material for split-core current transformers: Ferrite, FeSi or FeNi ?

The choice of magnetic material used in a current transducer impacts the cost, size, weight as well as performance aspects such as linearity, phase-shift and stability over temperature. Consequently, the choice of material depends on the application. Split-core current transducers usually use either ferrite, FeSi or FeNi.

FeSi split-core current transformers

FeSi current transformers are relatively low cost but suffer from poor linearity and drift, mainly due to the air gaps induced by the split-core architecture. They are also heavy and bulky – thus, not very suitable for environments with limited space. Poor linearity, especially at low currents, and large phase shift limits the use of FeSI to low cost applications not requiring a high degree of accuracy. A typical application is branch current monitoring in panel boards to detect overload risk and trigger an alarm or load balancing.

FeNi split-core current transformers

FeNi has been the best material for split-core current transformers for a long time, offering good performance, but at a relatively high cost. FeNi offers a good alternative to the FeSi material when accuracy and phase shift are important, or when transformers need to measure small currents. Apart from the price, FeNi current transformers have some other limitations.

Ferrite split-core current transformers

Although ferrite materials have been well known for years, their poor performance in terms of saturation level and magnetic permeability did not allow their use at frequencies as low as 50/60Hz. However, new types of ferrite have significantly improved permeability and can be implemented in 50/60Hz current transformers as a substitute for FeSi or FeNi cores, despite the low magnetic saturation level. Split-core current transformers implementing these new types of ferrite can perform accurate measurement of AC signals in an extended frequency range that includes the 50/60 Hz application domain.

Ferrite provides high accuracy and excellent linearity even at very low current levels. The material also offers low phase-shift between input and output currents. The hard and dense core allows for the minimization of air gaps and, in contrast to FeSi or FeNi, is virtually insensitive to ageing and temperature changes. Ferrite is also available at low cost, which makes high performance split-core ferrite current transformers an attractive choice. However, the large ferrite cores required for higher currents are not easy to manufacture. Consequently, for higher currents FeNi transformers or Rogowski Coils are typically a more appropriate choice.

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PPM Power at the Low Carbon Vehicle Show: Sept 12-13

Millbrook – Wednesday 12th and Thursday 13th September

As usual, PPM Power exhibited at the Low Carbon Vehicle LCV2018 show at Millbrook Proving Ground, run by Cenex. This year’s show took place on Wednesday 12th and Thursday 13th September 2018, attending by thousands of attendees, conference delegates, speakers, VIPs and press.

PPM Power C4-200

PPM Power were in hall 4 with Ray Goodenough, Phil Surman, and Paul Salter present to engage with anybody on the subject of power electronics. On the stand was a running demo of PLECS power simulation software with HIL (Hardware In the Loop) as well as integrated semiconductor modules, film capacitors, advanced programmable power supplies, resistors and high voltage connectors.

See you next year?

If you went to LCV2018 and you didnt manage to see us then please give us a call on 01793 784389, email sales@ppm.co.uk or maybe we’ll just see you next time in 2019!

 

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Kanthal improves already outstanding BA series bulk ceramic resistors

Kanthal has released the BA series of ceramic resistor series into bulk production. The BA series offers a maximum resistance of 1MΩ and voltages up to 20kV.  The series now also includes the new 100 and 200 axial lead resistors.

Excellent performance with bulk construction

Kanthal’s non-inductive ceramic resistors are designed for use in applications requiring high voltage, high energy and high peak current resistors. An inherently non-inductive resistor is produced through the bulk construction, rather than meanders or turns. This enables the uniform distribution of energy throughout the whole ceramic resistor body. The resistors offer the best performance when high peak power and high energy pulses must be managed in a limited volume.

“BA material extends the pulse energy capability of Kanthal’s products into applications requiring high ohmic values, up to 1MΩ”, says Phil Surman – Sales Director at PPM Power. “Space and weight are saved by specifying energy absorption, rather than average power in low-duty applications like inrush current limiting in drive systems.”

Ideal applications

• Electric drives
• Voltage balancing
• DC coupling and filter cap discharge

Even higher resistance levels

The BA resistor series expands Kanthal’s range to include higher resistance levels than are available through its SP and AS materials. BA resistors are designed for high energy and voltage pulse applications that require those higher resistance levels. Also, the maximum continuous operating temperature of 230°C is achieved through the choice of coatings. Kanthal have also produced the new 500BA non-inductive bulk ceramic slab resistor in the same range.

About Kanthal

Kanthal is a high-technology engineering group from Buffalo, USA. Now part of the Sandvik Group, Kanthal is an expert in industrial heating and materials technology. Kanthal has been part of the Sandvik Group for over 20 years and has since become a pioneering brand in the industry.

Useful Links

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LEM introduce 1000A fluxgate current transducer

LEM have introduced the IN 1000-S current transducer as an addition to the fluxgate technology range. The new transducer is operational at 1000A and a maximum temperature of 85ºC. The compact design uses digital domain signal processing for minimal interference and delivers excellent linearity, very low offset and a low noise level over the whole temperature range.

Streamlining design and increasing capabilities

The IN 1000-S combines two separate parts: the measuring head and the electronic treatment. Both parts are integrated into a singular design which allows vertical or flat mounting.

High performance from -40 to +85ºC

The new range of high accuracy current transducers operates with strong performance at a temperature range of -40 to +85ºC. Additionally, the wide operating range also allows for applications including labs, medical equipment, test equipment and for energy measurement.

max measuring resistance versus primary current and temperature – Uc = ±14.25V

Key features

• Accurate to 0.0018%
• Temperature range: -40 to +85ºC
• Operational with DC, AC and pulsed currents
• Vertical or flat mounting

Digital signal processing eradicates interference

Digital signal processing eliminates temperature effects, interference and supply voltage variation. The amplitude and phase are adjusted through calibration of each transducer, so any further interference is eliminated. The IN 1000-S operates with better than 3 ppm linearity over the whole temperature range.

About LEM

LEM are a Swiss power electronics company, in their 47th year of operation. LEM focus on current and voltage transducers.

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ABB announces enhanced IGBTs with up to 30% more current

ABB has announced two new enhanced IGBT modules in a HiPak package, with up to 30% more current. The Trench 3300V and Planar 6500V IGBT modules offer exceptionally high current density and robustness.

SPT+ and Trench technologies combined

Usually, ABB’s Enhanced Planar (SPT+) technology competes with Trench cell IGBTs. However, ABB has combined the two to create a new generation of IGBT cell technology. The results are (1) the Enhanced Trench TSPT+ and (2) the Enhanced Planar SPT++ IGBTs. These devices represent the latest generation of IGBT cell technology, further loss reduction and, as a result, the possibility to increase current density.

These new HiPaks are expected to be released for sale during Q4 of 2018.

SPT++ 6500V 1000A HiPak

The SPT++ technology boosts the rating of the 6500V IGBT from 750A to 1000A and  allows the IGBT module to function with an operating junction temperature of 150°C, with unrivalled robustness. For improved performance in regenerative mode, the diode area has been increased by 20%. This allows a system designer to use a smaller module or eliminate the parallel connection of modules.

TSPT+ 3300V 1800A HiPak

The combination of the very low loss and ultra-rugged SPT+ technology with the latest trench cell design further reduces losses and increases current density. The new device allows for a 20% increase in rated current compared with the previous 1500A generation in the same package. In addition, the new 1800A 3300V HiPak is designed to cope with increased stray inductance.

About ABB

ABB is a global leader in manufacturing high-power semiconductors with over 100 years of experience in power electronics. These key components are found at the heart of many leading ABB technologies, such as high voltage direct current (HVDC) transmission systems, flexible alternating current transmission systems (FACTS) and variable speed drives. Power semiconductors are also central to the development of a more reliable, smarter and greener grid.

ABB’s vast range of power semiconductors will be expanded with the following new products for:

  • Traction
  • Power transmission and distribution
  • Renewable energy
  • Industrial markets.

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MNPC or NPC – best topology for a multi-level inverter?

Mixed-voltage Neutral Point Clamped (MNPC) and Neutral Point Clamped (NPC) modules are power module topologies used in high power applications such as three-phase solar/photovoltaic (PV) inverters and uninterruptible power supplies (UPS). The choice between the two topologies is mainly a question of switching frequency. NPC delivers at higher switching frequencies, while MNPC delivers at lower switching frequencies. However, the threshold frequency between the two is always getting lower and there are other factors to consider…

Advantages of MNPC and NPC power semiconductor modules

MNPC and NPC semiconductor modules have significant advantages when used as as multilevel inverters:

  • Low EMI caused by dv/dt issues
  • High efficiency
  • Reduced stress caused by multiple voltage levels on the DC bus.
  • Low-disturbance input current
  • Lower common state voltage

How MNPC and NPC modules work

When MNPC and NPC modules are used as inverters, the DC voltage can be converted into a variable alternating voltage and variable frequency. Unlike a half-bridge or sixpack topology, these topologies offer an additional voltage level at the output. The potential can also have a status of 0, as well as DC+ and DC-.
At real or active power, these are switched at just 50Hz; therefore, they correspond to the positive or negative sinusoidal half-wave. Usually operated at 8kHz for MNPC and 16kHZ for NPC, the outer switches generate the sine wave so they require only half the blocking voltage capability required for conventional topologies. This is significant because semiconductors with a high blocking voltage capability are slower at switching. MNPC and NPC modules with 600V or 650V components can be operated at higher switching frequencies than, for example, 1200V half-bridges.

MNPC topology

The classic MNPC stage comprises four IGBTs and four diodes. The topology is also known as T-type, or NPC2. The blocking voltage is 600V or 650V for the horizontal (neutral point) switches and 1200V for the outer switches. Some modules come with 1200V and 1700V components. Modules are typically equipped with an NTC or PTC alongside the semiconductors.

NPC topology

Historically called a three-level module (though, confusingly, the MNPC topology also has three levels), the classic NPC stage uses four IGBTs and six diodes. The blocking voltage is 600V, 650V or 1200V.

 

classic MNPC topology (left) and classic NPC topology (right)

So, which is better – MNPC or NPC?

The choice between the two is largely based on the switching frequency of the application, though there are other factors (see the list below). Each topology has better loss characteristics at different frequencies.

NPC allows higher switching frequencies. NPC enables faster switching than MNPC. So above a certain frequency, it makes sense to choose NPC. This depends on the IGBTs used, but as a rule of thumb it was traditionally 16kHz. However, this is getting ever lower and now it is more like 10kHz. Manufacturers have considered discontinuing MNPC but some designers prefer to stick with this topology because they are familiar with it.

NPC allows a little more power. A higher current range due to smaller switches means an NPC can have a higher nominal current rating inside the module. Consequently, NPC allows a little more power.

MNPC makes emergency switch-off easier. Emergency switch-off is easier with MNPC because the switching order is not important. In the case of NPC, the IGBTs must be switched in a particular order – typically the outer IGBTs followed by the inner ones to avoid too much voltage across one of the 600V/650V-rated IGBTs.

It depends (indirectly) on the application power rating. Manufacturers typically offer both types for each power rating. However, higher power applications tend to operate at lower switching frequencies, and vice versa. Therefore, while there is a power rating correlation this is more directly related to switching frequency. For high power ratings such as 500kW or above (e.g. solar inverters), MNPC tends to be the better choice because the switching frequencies are usually quite low (e.g. 4kHz or 8kHz). For lower power applications, NPC makes more sense because the switching frequency is likely to be higher. Higher switching frequencies mean smaller passive components, which save cost, weight and size.

It depends on the input voltage. Even at high power ratings the choice still depends on input voltage. A solar inverter might typically have an input of 1000V, so MNPC is an option. But many designers want up to 1500V, which requires 1700V-rated chips. Since the performance of MNPC semiconductor dies are not as good as NPC dies at 1700V, the NPC topology is a better choice.

Summary of advantages – MNPC v NPC

MNPC

  • Easier emergency switch-off
  • Familiarity (more traditional topology)
  • Best for switching at <10kHz

NPC

  • Allows a little more power (higher current range)
  • Best for switching at >10kHz

 

 

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PPM Power in Electronics Weekly: The pros and cons of Silicon Carbide

Last month Electronics Weekly published an article written by PPM Power colleagues Paul Salter and Joe Petrie on the advantages and disadvantages of silicon carbide (SiC) modules.

Specifically, the article points out:

  • SiC devices offer dramatic improvements over silicon IGBTs in power conversion applications above 600V.
  • SiC-specific packaging is required to facilitate operation at higher frequencies in order to minimise loop inductance and poor performance due to wave propagation effects.
  • SiC-specific gate drivers are needed because silicon IGBTs will not support the switching speed of an SiC device or the rapid fault response time needed to protect an SiC device in the event of a short circuit. Specifically, soft or augmented turn-off is required to reduce spiking and ringing problems.
  • Because of these considerations, SiC is a good choice for new system designs – as opposed to upgrades to existing designs, where the advantages of the technology are less realisable.

You can read the full article on Electronics Weekly’s website here.

Paul Salter – Business Development Manager

Joe Petrie – Marketing Manager

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10kV power resistors delivering 5ppm over temperature


Austrian manufacturer of power resistors EBG has developed new material combinations and processing methods to achieve a thermal coefficient of resistance (TCR) of +/- 5 ppm while maintaining the minimal voltage coefficient of resistance (VCR).

Leading-edge capability with resistive inks and sintering

The SHP series is a new generation of high-precision and high-stability resistors that have already been implemented in applications such as medical power supply units. “To produce such ultra-high precision HV resistors requires leading-edge capability in the use of resistive inks in combination with the sintering process,” says Louis Klein of EBG.

From 100MΩ to 250MΩ

The non-inductive SHP series of power resistors currently includes SHP39, SHP52 and SHP78. The series offers a 10kV operating voltage with a tolerance range from ± 1% to ± 0.1%. The ohmic range is from 100MΩ to 250MΩ, though other ranges are possible on request. The overall stability is ± 5ppm/°C from +25°C to +65°C (including TCR and VCR).

“Achieving a stability of 5ppm over temperature including the TCR and VCR is a big deal at 10kV,” says Phil Surman, sales director at PPM Power, “and every resistor comes with stability data collected in 10-degree steps.”

Typical applications

Typical applications for the SHP series include medical power supplies, motor drives and controls, X-rays, converters and energy regeneration.

Next generation

The next generation promises broader thermal application areas and even higher thermal stability. This is currently in development.

About EBG

EBG is based in Kirchbach-Zerlach.

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Resistor modules: save space, increase reliability and reduce cost

ULX800

Integrating power semiconductors components is standard industry practice to reduce size, reduce cost and improve reliability. A similar approach is now possible with power resistors, courtesy of Austrian resistor manufacturer EBG.

Multiple resistors of similar or differing values

Thick-film power resistor modules from EBG allow multiple power resistors, of similar or differing ohmic values, to be integrated into a single package, reducing size, increasing reliability and reducing cost. Increasing the level of package integration reduces the overall solution size. Reducing the number of solder joints and thermal interfaces increases reliability.

Fewer interfaces means reduced operational costs

Fewer interfaces, screwed or soldered, means less chance of reliability or manufacturing problems. Any thermal interface (i.e. a connection between the bottom of the resistor and the heat plate) requires thermal paste, which adds time, cost and complexity to manufacturing operations. Reducing the number of components by using integrated resistor modules means fewer components, reduced operational cost and time, and less manufacturing variability of the final product.

How it works

  1. EBG screen-prints resistive elements onto a substrate of aluminium oxide or, for high-performance applications, aluminium nitride.
  2. The resistive ink is baked to cure it.
  3. An additional dielectric layer is printed to cover the conductive ink.
  4. Connecting wires are soldered into place.
  5. The assembly is housed.

High power resistor modules from EBG

EBG offers baseplate-cooled packages, from 50W to 2000W, designed to house multiple resistive elements. The 50W rated AXP-50 series allows four connections, which equate to six different configurations of up to three resistors. In a similar fashion, the ULX-800 uses a slightly larger footprint to deliver a maximum rating of 800W.

AXP50

HXP600

Maximum rating – single vs multiple

When just one ohmic value is required, all the available surface area is used to fabricate the single resistor, which maximises the power rating all the active area is used. When multiple resistors are required, these are printed two or three separate areas on the substrate. The unused space between the layers, necessary to maintain isolation, reduces the maximum possible rating of the part. Therefore, multiple resistors have a lower maximum rating than a single one in the same package.

Simple and complex configurations

The simplest, single element, rated for the full power of the package, with just two terminals. If the application needs two resistors, with reduced power per element, the same package can be configured with two 20W elements. In larger packages like the ULX series, this can be two 300W elements or three 150W elements. The most complex configuration is three elements, which are either independent or form a div.

AXP-50 resistor configurations

ULX800 resistor configurations

Useful links

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New 600W aluminium nitride resistor from EBG

EBG has released a 600W version of the HXP thick film power resistor series. The HXP600 is capable of delivering 100% of its rated power at a bottom case temperature of 85°C. The non-inductive design makes the HXP series particularly well suited for high frequency and pulsed loading applications. Direct mounting on a heat sink means significant cost savings.

  • 1 x 600W, 2 x 240W or 3 x 135W operating power
  • Non-inductive design
  • Materials compliant with UL94 V-0

Specification

  • Resistance tolerance: +/- 5% to +/-10%
  • Temperature coefficient: +/-250ppm/°C (other on request)
  • Maximum working voltage: 500V DC (higher voltage on request)
  • Power rating: 600W at 85°C bottom case temperature
  • Electric strength voltage: Dielectric strength up to 4000V DC against ground
  • Isolation voltage between R1 and R2: 500V (1000V on special request)
  • Partial discharge: 2kVrms

Rated power (%) vs bottom case temperature (°C)

Applications

The main applications are speed drives, power supplies, control devices, telecoms, robotics, motor controls and other switching devices.

Multiple resistor configurations

A standard offering can include up to three resistors in the same package. Configurations of 4, 5 and 6 resistors are also available on special request. The maximum working voltage is 500V. The ohm values available are 0.15kΩ to 5kΩ with tolerances of +/- 10% to +/-5%.

About EBG

EBG is a leading international electronic components manufacturer supplying highly specialised resistive components. The company has a corporate HQ in Austria and operational facilities throughout Europe, the USA and East Asia. More than 85% of EBG production is exported to customers all over the world.

EBG delivers leading-edge resistive technology, including:

  • Very low/controlled temperature and voltage coefficients
  • High stability
  • High-temperature operations
  • Very tight tolerances.

All products meet applicable environmental requirements according to European and US military specifications. The different style options include:

  • Flats
  • Cylindricals
  • Dividers
  • Networks.

EBG’s research and evaluation capabilities include sophisticated X-ray facilities and thermal imaging.

Useful links

 

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More Information?

Telephone +44 (0)1793 784389 or email: sales@ppm.co.uk