Building Harmonic Filter
Building harmonic filter increases maintenance efficiency, asset & building value by eliminating nuisance tripping and failure with sensitive equipment like elevator maloperation, uneven floor landing, doors fail to open, HVAC and elevator's VFD drive failure and computer and server failures. In this Parry building, we have installed 2sets of harmonic filters following a notification from TNEB, a local utility company that has mandated to limit harmonic distortion for high voltage consumers, starting from the year 2012 for voltage and current harmonic dumping into the grid. It's in turn based on CEA 2007 regulation for grid connectivity which is devised to improve the quality of power supply and grid stability. It's for preventing the grid from a sudden collapse by relieving it together with the connected generating stations from the cascading effects of a possible built up of stressful power system condition. It's difficult to deconstruct the root cause of a grid collapse. Even after a decade of the American Grid Collapse, no convincing reason has emerged. It is however certain that the grid collapse when multiple reasons swell up, cascading one after the another, and reach at the threshold trigger point.
Power quality harmonic is one of the major elements that defines the stable grid. Power surge and voltage sag are the consequences of power quality harmonic. It's also the single most major cause which inflicts billions of dollars in damages in industrial equipment failure and productivity losses every year worldwide. In-addition, electrical harmonic is unpredictable and under a favorable power system impedance, it triggers harmonic resonance magnifying building harmonics and power and voltage fluctuations.
Building harmonic filter- Index Terms
Grid stability, IEEE-519 standard, CEA-2007 regulation, harmonic study, power quality analysis, harmonic resonance, passive harmonic filter, power quality engineering.
Building harmonic filter- Nomenclature
TNEB- Tamil Nadu Electricity Board, NLL- Non Linear Load, THDv- Total Harmonic Distortion voltage, THDi- Total Harmonic Distortion current, In- Individual current harmonic viz. I3 is 3rd harmonic current, I5 is 5th harmonic current, I7 is 7th harmonic current. Vn- Individual voltage harmonic viz. V11 is 11th harmonic voltage, V13 is 13th voltage harmonic.
Building harmonic filter- Introduction
EID Parry belongs to south India's largest conglomerate viz. Murugappa group which has diverse business activities in engineering, financial & leisure sectors namely automobile, abrasive, OEM component manufacturing, fertilizer, sugar, food, finance, insurance, travel and tourism. Its corporate head office is located in Chennai, which is also a 6-story heritage building. The first building block 'dare house' was built in the year 1932 and the second and third building blocks 'parry house' and 'dare house extensions' were built during the year 1950. Total built-up area of three building blocks together is 250,000SQF. It is the corporate head office of Murugappa conglomerate that accommodates 1300 head office employees.
The building's power source comprises of 2nos dry type indoor transformers each of 1250kKVA, 11/0.415kV capacity and 3nos DG of 750KVA, 550KVA and 500KVA capacities. The building's main power distribution system comprises of a 415V LT PCC with a double bas bar configuration which further is sub divided into two bus sections. Each outgoing feeder from the LT PCC as well as its incoming power sources are interlocked in a foolproof manner using conventional castle-key interlock system so as to accommodate all diverse incoming power sources safely and provide required flexibility for operation and maintenance. The Single Line Diagram of the LT PCC of the grid incomer is shown in Annexure-I.
Building harmonic filter- Problem Statement
The following harmonic problem and failure have been reported and verified both in qualitative & quantitative terms, during the onsite harmonic study.
415V capacitor failure: The building's main LT PCC has 4nos capacitor banks each of 195KVAR capacity out of which a set of 2nos each are connected at each of the two LT PCC bus sections. These capacitors fail frequently and are replaced on a regular basis. We have measured each bank's deliverable in terms of KVAR. And depending upon its age of replacement, bank wise capacitor effectiveness found is between 30 to 60%. It may be noted that capacitors do not necessarily fail at once with a blast; rather most common capacitors failure happen silently gradually reducing its KVAR delivery.
Building harmonic filter- Onsite Harmonic Study
Onsite power & harmonic measurements carried out during May 2012 using a high quality 3phase power quality and harmonic analyzer, type PowerPro. It has a sampling rate of 256samples/cycle. It calculates RMS values of all recorder parameters at every cycle. It measures and records 3phase and neutral power and harmonics namely THDi, THDv, individual harmonics up to 64th order with their respective voltage and current waveforms. On power quality signature analysis, it captures Inrush current and voltage spikes with 65uS precisions for both 3ph voltage & current and stores 6-7cycles of continuous waveforms per occurrence. Further details of the measuring instrument could be obtained from Candura instruments. Before installation of harmonic filter, the harmonics are measured and details are shown in Annexure-III under its various exhibits.
The current waveform at the LT PCC Bus Section-1of the grid incomer is highly distorted. The THDi is 20%, measured with 1450A-peak load current and I5 and I7 as major current harmonics as shown in Fig.1.
The voltage waveform at the LT PCC Bus Section-1 of the grid incomer is also distorted. The THDv is 7%, measured with 338V-peak load voltage (RMS value of rated phase voltage is 240V) and V5 and V7 as major voltage harmonics as shown in Fig.2.