6.1 MEASURING INSTRUMENT
Measuring instrument shall be of panel flush mounting type with square escutcheon plate finished matt black and pressed steel case. They shall be of industrial grade type adequately shielded against stray magnetic fields, conform to the measuring scales and arrangements as shown in the Drawings and calibrated for correct readings. They shall comply with MS 925 and relevant parts of IEC 60051. External zero adjustment shall be provided for ammeters and voltmeters.
Ammeters, unless otherwise specified, shall be of moving iron type having continuous overload capacity of 120% of rated value and full scale value accuracy of ± 2%. They shall be provided with maximum demand indicator, if specified. Voltmeters shall be of moving iron type having overload capacity of 200% of rated value and full scale value accuracy of ± 1.5%. Kilowatt-hour meter shall be of 6 numbers wheel cyclometer aluminium type with both the current and voltage coils on laminated cover fabricated from high quality silicon steel strip. They shall have overload capacity of 200% of rated value and accuracy of ± 0.5% at the supply voltage and frequency characteristic.
Power factor meters shall be of balanced type using ferrodynamic, cross-coiled mechanism with measuring range from 0.5 lagging to 0.5 leading. Full scale value accuracy shall be ± 1.5%. Frequency meters shall be of reed type with frequency range from 45 Hz. to 55 Hz. and accuracy of ± 5%. If specified in the Drawings and/or Bill of Quantities, the microprocessor based power meter shall be rated at 240V/415V and operating voltage shall be in a range from 90V to 265V.
The meters shall be housed in robust panel flush mounting case to IP 54 and shall be fully tropicalised and suitable to be used up to an ambient temperature of 50 0C and relative humidity of 95%. The meters shall give direct numerical digital readout of actual measured values and recorded values. The meters shall include one serial communication port for external connection to facilitate external reading and recording of meter data and parameters.
The measurements and their accuracy of the microprocessor-based meters
shall be: –
Parameters / measurements Accuracy:
Volts (V): line-line / line-neutral————-0.5% of reading ± 2 digit
Currents (A): per phase ———————-0.5% of reading ± 2 digit
Frequency (Hz) ——————————–0.1 Hz ± 1 digit
Power Factor: total —————————-1% of reading ± 2 digit
Active Power (kW): total ——————–1% of reading ± 2 digit
Reactive Power (kVAr): total —————1% of reading ± 2 digit
Apparent Power (kVA): total —————1% of reading ± 2 digit
Active Energy (kWh): total——————1% of reading
Reactive Energy (kVArh): total————-1% of reading
Maximum Demands (A, W, VA): total —-1% of reading ± 2 digit
If harmonics content measurement is specified, individual and total harmonics distortion on the current and voltage up to 30th harmonic shall be measured with the accuracy of 1% of reading. There shall be a custom display screen, which can be programmed to display customised specific parameter requirements.
All data shall be continuously and concurrently logged, recorded and stored in internal non-volatile memory. All time base logged-in data can be retrieved and downloaded to a personal computer (PC) using serial communication port. PC connecting cable and data retrieving PC program shall be provided The meters shall comply with IEC 60359 and IEC 60688. The meters shall also comply with relevant parts of IEC 61000 on electromagnetic compatibility.