Do you experience nuisance trips in circuit breakers? Have you found some motors running hotter than normal?
The study of harmonics gives engineers a way to analyze these problems.
Most electrical systems in your facility contain switching power supplies. Your computers, Uninterruptible Power Supply (UPS) devices, office copier machines and Variable Frequency Drives (VFDs) make up a major portion of the non-linear loads for your power system. These cause harmonic current distortion and voltage distortion.
The application of VFDs is identified as one of the key ways to reduce energy consumption in motor driven systems. (See the US Dept. of Energy’s website.)
There are many cutting edge technologies that integrate solutions in the newest drive technology reducing the effects of harmonics on your VFD applications.
How do you know if your system needs protection? Or, how do you know if your equipment will create problems for the rest of your plant, or possibly for your neighbors? Solving these problems can be difficult.
Call Brian Sorenson at Brithinee Electric 909-825-7971, ext.13, or Craig Slape at ext. 35. We’ll help you engineer the right package for your controls.
Depending on the application and the extent of the harmonic distortion to measure the extent of the distortion), the following devices/kits may help you solve the problem. Some of these are inexpensive.
- Input Line Reactor
When you have a drive/controller nuisance trip off, you might have power quality issues from within your facility causing this. Other equipment may cause harmonic distortion and affect your drives. You can try to put a simple device such as an input line reactor or an isolation transformer. These are low cost devices that can reduce the harmonic distortion and protect your expensive drives. They also reduce harmonic voltage and currents that come back onto the distribution system.
- Output Load Reactor
If your motor is controlled by a VFD, the voltage and current delivered to your motor is not a purely sinusoidal wave. Far from it! This is especially the case when the leads run hundreds of feet from the VFD to the motor. Harmonics can cause an increased temperature rise, and the motor might have premature failure because of that. The output load reactor used between the drive and the motor (< 300 ft) can absorb the harmonic surges and spikes. There will be a slight voltage drop at the motor. However, your motor will run cooler with reduced heat losses of the core iron.
- DC Link Choke
A “choke” is the name given to an inductor that is used as a power supply filter element. It can be used individually on the positive DC bus before the inverter to reduce AC input line current harmonic distortion while absorbing DC bus voltage spikes. Although DC link chokes increase the internal filtering and have the ability to absorb spikes, they should not be considered a direct alternative to reactors because they do not offer protection for the input bridge rectifier and the inverter output circuit due to their location on the DC bus.
- dV/dT Filter
A dV/dT filter is designed to reduce voltage spikes to motors fed from a wide variety of pulse width modulation (PWM) inverters. When the distance between the VFD and motor is less than 1000 feet, a dV/dT filter can usually smooth the motor terminal voltage so that it will not exceed 1.5 times the drives bus voltage.
- Passive Filter kit
A passive filter is simply a filter that is made up of passive components (resistors, capacitors, and inductors) that use no amplifying elements (transistors, operational amplifiers (op amps), etc.). Applications with long leads above 1000 ft (< 3000 ft) will need a passive filter kit to prevent the voltage overshoots at the motor causing degradation of insulation systems.
- Active Filter kit
Active filters use amplifying elements, especially op amps with resistors and capacitors in their feedback loops, to synthesize the desired filter characteristics. When the cable length goes beyond 3000 ft, you might want to consider an active filter kit as an option to protect your drive and motor.
- Dynamic breaking using a 7th “giant transistor” GTR
For high inertia applications that require quickly reducing the speed (such as slowing down a large fan driven by a motor and PWM drive), dynamic breaking is needed. The 7th GTR kit can help to protect the drive from the high peak voltage coming back to the drive when the speed changes rapidly from high speed to low speed. Also, when incoming line voltage is on the high-side of acceptable voltage, and when that voltage is added to the voltage coming back from the motor trying to slow a load, the DC bus voltage can reach a level that causes the drive to trip off with an “overvoltage trip”.
The above is not all inclusive, but should give you an idea of typical solutions you need. There are many cutting edge technologies which integrate those solutions in their newest drive technology. These carry such names as 18 pulse drive, or drives with active front ends.
How do you know if your system needs protection? Or, how do you know if your equipment will create problems for the rest of your plant, or possibly for your neighbors?
The IEEE Standard 519 is the recommended practice which describes requirements for harmonic control in electrical power systems. Here is a FREE tool that might help you make your decisions. http://www.transcoil.com/Applications/Tools/Analyzer.htm
All of these devices, and others, are available with Brithinee Electric built control systems and panels. Call Brian Sorenson at Brithinee Electric 909-825-7971, ext.13, or Craig Slape at ext. 35.