Blog

Any non-linear load (such as a computer, a microwave oven, some refrigerators and electric stoves, or a variable frequency drive) will generate harmonics to some extent. Motors and generators themselves - because of inherent dissymmetries in the manufacture - can create some as well. The variable frequency drives that are referred to as "active front end" topologies are probably the worst, since their whole approach is to introduc ...

Variable frequency drive (VFD) operation with voltage and frequency control of the induction motor was acceptable for most applications. There were certain machines that DC motor control had some technical advantage. The VFD needed more intelligence to know the true load of the motor. An AC machine requires a magnetizing current to operate at no load. This current is not actually a lot of power, but looks like the induction motor always has 20 to 30% load. The DC machine load on the armature ...

HVDC has been in existence for a long time but has become so popular these days with weighing advantages for the traditional HVAC transmission technology. HVDC system uses direct current for the bulk transmission. There are different configuration, types and topologies to include HVDC back to back, classical HVDC, etc.

The advantages lies in the fact HVDC links are able to connect to two asynchronous network, a typical example is a 60Hz and 50Hz ...

Variable Frequency Drive, in short VFD, it can be called VVVF drive, variable voltage and variable frequency to change this from sinusoidal AC, the VFD changes the AC to DC first then DC to AC by using IGBT, this is done by firing IGBT very fast (carrier frequency), so this output is not sinusoidal.

If you want to know how does a VFD work, you should hit up Wikipedia or Google it, lots of articles out there. If you're wondering about how to use a VFD, there are numerous considerati ...

You can find a simple explanation of what an induction generator can do. It is totally self-synchronizing with the grid it is feeding power into. It stays in sync and delivers energy as long as it is driven at an rpm higher than its synchronous speed. If it is feeding a 50 Hz power supply it must be driven 2% to 5% above ts sync speed. Sync speed is 120 X frequency / number of poles thus a 4 pole machine ...

Required or not, ground ring provides a better (lower impedance) grounding system. It really depends on what the specifications of the project call for. Here, ground rings are typically only used for sensitive electrical equipment installations - such as computer/data/network server rooms. For industrial/motor control/general light and power applications, a properly sized equipment grounding conductor (green wire), sized in relationship to the overcurrent protective device, is installed in th ...

I would certainly say that thyristors are indeed extremely robust. Many IGBTs are designed to deliberealy limit the max current they can supply to limit short circuit currents and then allow a slower ("soft") turn off within the 5-10us s/c withstand time. So if you want very high peak to average current rating it may be this deliberate thing that is working against you.

Thyristors are 4-layer devices with two sources of carriers in difference with IGBTs. They operate at higher pla ...

Lot of literature can be found in French since France and Quebec are the countries where the HVDC transmission is very developed and already mature technology.
Why it is used? The answer is to avoid corona effect which is a source of energy losses, which are between 5-8% of the nominal installed power (huge if you compare with the power of a single transmission line). For this reason almost all of the long distance transmission lines from Siberia to European part of Russia are HVDC whic ...

An Active Front End (AFE) Drive installation where shutting off the filter would also shutoff the variable frequency drive (VFD). This is truly a serious and widespread problem that the AFE Drive manufacturers don't want anyone to know about. In fact, they actively promote their AFE 'low harmonic drives' as the ultimate solution. I chuckle when I watch one elaborate video produced by an AFE drive manufacturer that properly highlig ...

Why is it so difficult to have high switching frequencies at high wattage power converters..viz., at 1 MW - Frequency is 1 MHz, 1 KW - 100 KHz, 10 W - 1 MHz. What will be the issues if we go for 1 MW - 1 MHz?

The switching losses are related between the current and voltage on the switching device. Some loss occurs on every switching and if the switching occurs very frequent (depending on the switching frequency.) the total losses will be so much that heat sink will not be able to d ...

If the variable frequency drive (VFD) has a load of 1000KW, then the low frequency impedance must be fairly low to prevent excessive voltage drop. The problem is what the high frequency impedance looks like and whether there are any local supply resonances in the KHz range.

We see a lot of problems on the power supply with common mode, often coming from the output of poorly installed VFDs. Issues due to active front end and actives filters can be so much worse. It is both equipmen ...

Reactive power means Voltage and Current are not in phase and therefore during a cycle (say 20ms for 50 Hz), the power flow reverses during a part of the cycle. You can simply draw a voltage sine wave, a current sine wave 45 degrees lagging and instantaneous power wave (product of V & A instantaneous values every 1ms) to visualize the phenomena. You will realize that power loops exist above and below the X axis; these would be equal for 90 degrees phase difference, when power factor is 0. ...

The resistor breaking in an AC motor variable frequency drive (VFD) consists of a switching power converter where the back EMF of the motor acts as the voltage source and the converter is controlled by the duty-cycle to produce a variable voltage across the breaking resistor. The voltage is increased to the breaking resistor by increasing the control duty-cycle and this produces an increasing armature current with a torque that resists the mechanical shaft torque resulting in breaking. The me ...

Most modern motors are built to standards and frame sizes, efficiencies, power factor are very close from manufacturer to manufacturer. The definition depends on what you mean by "Heavy Duty". Examples would be "Punch Press" or a "Rock Crusher", anything with a high inertia or heavy intermittent load. If the load is a high inertia load the first thing to look as is the design letter of the motor. The standard motor is Design "B" and a motor for a high inertial load should be Design "C". A mot ...

I have involved with a soft starter study recently which was about a 750 kW motor had failed to start. In the investigation, we found that there were many flaweds in the system configuration as follows:

* The power supply was slightly weak to handle the full starting current this is why a soft starter was deployed - of course - but again with the soft starter there was some voltage dip during the operation.

* The cables were laid flat rather than in trefoil. This caused ...

At frequencies below radiation, ground currents must obey Kirchhoffs' current law and return to the source.

Say you have a Dyn1 distribution transformer that is serving multiple distribution feeders. When one of the feeders has a ground fault at a remote location, 100% of the ground current will return to the transformer neutral point when it is connected to ground (earthed). The return current may take many different paths depending on the configuration of the distribution system ...

In a simple definition, motor stalling means that the electric motor has more load on it than it is designed for and it can no longer supply enough torque to keep it spinning. In general this could happen at all types of motors. The main thing is when the load torque has increased more and more (which is above the characteristic of the main torque of the motor) so called "overload region" where the motor develops its maximum torque. At this point if the load torque is further increased the sp ...

Once a time one of our customers ask to install three numbers of 150HP capacity soft starters (with auxiliary I/O's) to build an intelligent motor control center. Their main goal is to limit the high starting current of the chillers compressors. They do not need an expensive variable frequency drive (VFD) as the system is designed to operate at full capacity most of the times. They need a AC motor soft starter with Modbus RTU communication ...

If the induction motor is lightly loaded it will continue to run. As it nears its rated power, the current will rise because the power will be 2 x Iph x Vph x Cos Theta instead of 3. with V constant, I must rise. Add to this you mess up all the magnetic circuit and the efficiency goes for a ball of chalk. The induction motor will pulse as it goes through the rotation where it is not being driven. This may be small but it is there and will affect gearboxes and vee belts. If the motor is star c ...

First of all think of a DC Motor. If it is an 8-pole motor is will have 8 field coils evenly spaced all the way around it. Now, in an AC Motor with 3-phases you will have the 8-poles 3 times. That means you would have 24-groups of coils. If the motor has 48 slots and 48 coils you would wind the stator with 24 groups of 2 coils. If you were to go round the 24 groups of coils and number them 1, 2, 3 repeat all the way around you would have 8 number 1's, 8 number 2's and 8 number 3's. All the nu ...