HOT OFF THE PRESS

C4.16.1 General Requirements

(a) Active harmonic filter (hereinafter referred to as “AHF”) shall be used to eliminate harmonic currents circulating across the installation so that the Total Harmonic Distortion (THD) may be limited to a given percentage as specified in the Particular Specification. (Note: For precise definition of this percentage, reference shall be made to sensitive equipment specifications regarding the acceptable THD for trouble-free operation or to the applicable standards at the point of common coupling.)

(b) Active harmonic filter shall be installed in parallel with the distribution system, i.e. shunt connected, wherever attenuation of harmonic current is needed. Preferably, active harmonic filter shall be located close to those loads generating harmonic currents in order to avoid circulation of the harmonic currents along the cables.

(c) AHF shall conform to IEC 61000 or other similar recognised international standards on Electromagnetic Compatibility (EMC) compliance for industrial or commercial applications and shall be manufactured to ISO 9001. Certificate of compliance shall be issued for each standard rating of AHF after being fully tested at the manufacturing facility.

(d) AHF shall be manufactured by a reputable manufacturer which has continuously manufactured AHF for at least 3 years and their manufacturing facility shall have a local agent to provide full technical support which includes adequate spares holding and technical expertise in testing, commissioning and trouble- shooting. Training shall be provided by the manufacturer’s representatives for government staff on operation and maintenance aspects including essential trouble-shooting techniques.

(e) Full technical details of the AHF as submitted by the manufacturer shall be provided for the Architect’s approval and shall cover the following:

(i) technical guide on its applications,

(ii) schematic and wiring drawings down to circuit board level released by the manufacturer,

(iii) shop drawings and as-fitted drawings,

(iv) operation manuals with commissioning guide,

(v) maintenance manuals with trouble-shooting guide, and (vi) parts list and recommended spare parts with price.

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(f) The following technical requirements shall apply:

(i) Input voltage : 380 V a.c. + 6%, 3 phases (ii) Frequency : 50 Hz + 2%

(iii) No. of phases : 3-phase without/with neutral, 3/4 wires as specified in the Particular Specification

(vi) Unit capacity : as specified in the Particular Specification but up to 150kVA for any single AHF (v) Harmonic orders : 2nd order to 25th order or

more compensation (vi) Filtering efficiency : 85% or more (vii) Power factor correction : up to 0.98 lagging (viii) Response time : 40 ms or less (ix) Ventilation : Forced air cooled (x) Noise level : 65 dBA or less

(xi) Heat losses : 8% of rated capacity or less (xii) Service condition : Ambient temperature - 0 to

40oC

Relative humidity - up to 85% Operating altitude - 1000 m or less

C4.16.2 Performance Requirements

(a) The operating principle of AHF shall be based upon the injection of a harmonic current with appropriate phase shift corresponding to the harmonic current drawn by the load which shall be analysed by the AHF continuously. Consequently, the current supplied by the source shall remain sinusoidal under the effective operating range of the AHF.

(b) AHF shall be compatible with any type of load, and shall guarantee efficient compensation, even when changes are made to the installation. The AHF shall also be capable of delivering its rated output harmonic current to the point of connection irrespective of load condition.

(c) If the compensation of neutral harmonic current is required, in the neutral conductor, the AHF shall be capable of compensating the harmonic current three times greater than the phase current, particularly to compensate harmonic current of order 3 and its multiples.

(d) Start-up and shut down of AHF shall be initiated by control push buttons or remote control. After a main power break-down, start-up of AHF shall be automatic.

(e) Should the AHF be overloaded during transient operation of certain loads or permanently, this should not affect the reliability of its operation. Under such circumstance, the AHF shall operate in a current limiting mode and still deliver to the network its rated harmonic current.

(f) For better adaptation to any installation, AHF shall be capable of operating in association with other harmonic reduction systems. It shall also be possible to associate 2 or more AHF’s in parallel to increase the compensation capacity, or to enhance dependability, i.e. redundant operation.

(g) To compensate the harmonics at different levels in the distribution network, it shall be possible to connect the AHF at any point in the distribution network, or to connect several AHF’s at different points in the installation for maximum effectiveness.

C4.16.3 Construction

(a) AHF shall use an isolated gate bipolar transistor (IGBT), bridge or other similar technique to inject the proper harmonic current on the network, and will be controlled by a microprocessor based system.

(b) AHF shall be housed in an industrial grade cabinet constructed from high quality steel sheet of minimum 1.2 mm thick side and back plate and 1.5 mm thick hinged front door with key lock. Protection class of the cabinet shall be not less than IP44 for indoor and IP55 for outdoor application. The entire surface shall be applied with chemical rust inhibitor, rust resisting primer coat and topcoat to give maximum corrosion protection.

(c) The dimension of AHF shall be as small as possible. Particularly, it will be preferable to have the AHF fitted in low voltage cubicle switchboard or in motor control centre.

(d) AHF shall include the following kinds of protection: (i) thermal overload protection,

(ii) internal short circuit protection, and

(iii) invertor bridge abnormal operation protection.

A three or four poles circuit breaker shall be installed close to the point of the connection to the system to protect the connection cables. It shall be selected according to general selection practice for circuit breakers and the manufacturer recommendation.

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(e) As a minimum the AHF shall include the following read-out: (i) an indicator for each phase of the incoming power

supply,

(ii) an indicator for normal operating condition, (iii) an indicator for AHF shut down, and

(iv) an indicator for fault condition.

Also a diagnostics panel shall be accessible from the front of the unit to help the operator to identify the origin of abnormal situation and control push buttons will be provided for ON/OFF operation and alarm reset.

(f) AHF shall be equipped with built-in RS 485/232 serial communication ports for control, programming and monitoring of the AHF by PC or other user interface.