ANEXO 2 ( http://www.andritzautomation.com/documents/evenharmonicresonance.pdf )
ANEXO 3 ( http://sureshks.netfirms.com/article/rp/rp.htm#1 )
POOR POWER FACTOR AND HARMONIC CURRENTS
AT A PLASTIC FILM PROCESSING INDUSTRY - A CASE STUDY
|Articles in Electrical Engineering from Suresh Kumar K.S |
Suresh Kumar. K.S.
Department of Electrical Engineering
National Institute of Technology Calicut
Calicut-673601, Kerala State , India
The Industry covered in this article manufactures blown plastic film material in the form of covers, bags etc. from Linear Low Density Polyethylene or Polypropylene plastic granules. It also does pattern printingon plastic covers produced thereby. There are three machine systems for production of plastic sheets - the biggest one - HM-1 - with a DC Drive rating of 45kW and HM-2 with a DC Drive rating of 25HP are used to produce H.M quality (High Molecule Polyethylene) and the smallest one with 10HP DC Drive is used to produce P.P variety (Polypropylene). Each machine system consists of an extruder and a diehead by which the plastic material is melted and kneaded and then processed into the inflated tubular film with the help of triple action aluminum air ring and blower. And then it is passed through set of nip roller and is taken out as per required size. Finally the film is wound on two station or four-station winder. In addition to these machine systems there is another machine system to carryout design printing on pre-prepared plastic film.
The film production units involve main DC Motors fitted with Thyristor controls, small DC and AC motors for auxiliary drives and various heaters for barrel zone heating, die heating etc.
The firm receives Grid supply at 11kV level and steps it down using a 250 kVA , 11kV/433V , 13.12A/333.3A , 4.41 % Impedance Transformer. The connected load asper the approved diagram is 76 kW + 72 HP + 5 kW lighting load. The Contract Demand is 110kVA and the minimum chargeable Maximum Demand is 83 kVA.
The production schedule is as per the customer order position and there is considerable fluctuation in the monthly production level - especially in the case of P.P material. The PP machine is used rarely since the PP production level is usually low.Production tends to peak in June-July-August period of the year.
The Firm could keep their Recorded Maximum Demand below 83 kVA till about 6 months back. They reported that the RMD started reaching the level of 100 kVA or so for the last few months. This resulted in extra/penalty payments to the Grid Authority. They approached NIT Calicut in this connection and wanted a harmonic study to be carriedout before deciding on the size of capacitor to be installed at the factory to control the MD level. Experts from Energy Audit Cell, Department of Electrical Engineering, NIT Calicut visited the factory on 2-9-2002 and carried detailed harmonic measurements at the two machine systems and at the power transformer LT side bus. This document reports the findings and recommendations.
The Problem - Reportedly high Maximum Demand Level at the Factory
Cause Identified - The Half-Controlled AC-DC Converters used inside the Thyristorised Drives for 60HP HM Machine and 25HP HM Machine work at low displacement power factor and draw large harmonic currents thereby contributing heavily to Maximum Demand on both counts.
Proposed Solutions - One of the following two proposed...