How understanding the type of reactive energy(Inductive, capacitance and harmonics)is critical, for saving on capital expenditure (CAPEX)
With the advent of automation and technological transformation of Electronic equipment like UPS, drives and digital Lighting has altered from being an inductive load to capacitive.
Multilevel Inverters with Input Power Factor Improvement in UPS and employing Advanced switching devices Like the silicon control rectifiers (SIC IGBT/ Mosfet) with the capability of switching at higher frequencies with Low ripple, and switching in such a way that it does not distort the input waveform. However, the flip side is that these switching may cause higher-order harmonics beyond the PQ range of 2500HZ, which is not in the range of normal power quality analyzers.
These higher-order harmonics beyond 2500Hz to 150kz do interact with the electrical network harmonics and sometimes pull down the Power factor (leading Power factor), which the Automatic Power factor Control Panels are unable to handle, and thus become redundant.
Leading MNC Brand UPS current waveforms
Leading MNC Brand UPS individual harmonics
The issue now is that most designers assume the loads to be inductive and some go by the thumb rule of assuming a 0.6 lag Power factor and recommend 500KVAR APFC panels for a load of 1000KVA and then find that these APFCs do not turn on the capacitor Banks. In some cases Detuned Automatic Power factor Panels are installed, thereby increasing the Capital expenditure a 500KVAR detuned filter will normally cost Rs 10 Lacs. Moreover, they occupy valuable space. It must be noted that these detuned APFCs do not mitigate harmonics, they are only tuned away from the System frequency, hence they only block the Harmonics and prevent resonance.
There is another serious problem encountered when operating with generators.
In one case we found the generators trip when the generators start, this is due to the capacitance of Power factor Improved with the Input filter capacitor. When the generator starts and builds up due to the mismatch of the low current and higher capacitance of UPS the UPS trips. Thought the generator is sized 2X and the UPS load just 120 KVA. This was however solved by installing a suitably sized shunt Inductor connected in Parallel to the network.
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Leading Power Factor
The generator is physically unable to absorb despite the generator of 550KVA. The reactive capacitive KVAR power, the reverse KVAR load presented a leading Power factor of UPS which drives the alternator into an overvoltage condition, thus destabilizing and tripping ultimately.
While filters provide positive impacts on the overall power system, they can be very disruptive to generator operation. Input filters are often sized to operate at the expected maximum load there may be excess filter capacitance, causing a leading Power factor.
On the contrary, a utility supply absorbs the reactive power output because it is extremely large relative to the filter system as it has many loads to consume the reactive energy.
A generator with a rising voltage from the leading Power factor causes the Voltage Regulator (AVR) to turn down and reduce alternator field strength. If the AVR turns all the way off it loses control of the system voltage. The increase in voltage may also damage the load.
Conclusion:
A power system study and thoughtful study is very critical to decide what is required, whether what is an important issue to address, Power factor, or harmonic mitigation. Optimizing energy usage and ensuring power quality is the key to a safe, reliable, efficient, and resilient network.
Ultimately it is about ensuring the voltage waveform and current waveform are not displaced or distorted and reactive energy is minimum. An Ideal electrical system is reached when KWAH= KVAH, and that should be the benchmark.
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2 年Great work John. The most neglected and yet the most harmful electrical effect on any equipment that we may be using today. Every facility today self generates third, fifth and seventh harmonics by the very nature of loads that are being connected to the electrical distribution systems. The third world countries where power cut is a regular practice and the business owners are forced to use DG sets will inherit another uncalled for problem called breaking actions to reduce the engine RPM leading to higher fuel consumption and less power generation only because of the fifth harmonics being the negative harmonics. Harmonics and its various aspects must be discussed and awareness must be created about the negative impacts of the same on the business as a whole. Once again thank you Jon for raising this very important topic.
Power Quality and Industry 4.0
2 年Great work, the power factor -1.015 is an erraneous PF reading from that meter. I also have a question, can we consider harmonics as reactive energy?