P12x/EN T/Eb6 - Schneider - error

P12x/EN AP/Eb6Page 22/78Application GuideMiCOM P120/P121/P122/P123Their operating characteristics is according to the formula:V = C.I 0.25Where−V: Instantaneous voltage applied to the non-linear resistor (Metrosil)C: Constant of the non-linear resistor (Metrosil)I: Instantaneous current through the non-linear resistor (Metrosil)With the sinusoidal voltage applied across the Metrosil, the RMS current would beapproximately 0.25 times the peak current. This current value can be calculated as follows:⎧Vs(rms).Irms = 0.52⎨⎩ C42 ⎫⎬⎭Where−Vs(rms): RMS value of the sinusoidal voltage applied across the Metrosil.This is due to the fact that the current waveform through the Metrosil is not sinusoidal butappreciably distorted.For satisfactory application of the non-linear resistor (Metrosil), its characteristics shouldcomply with the following requirements:−−At the relay voltage setting, the non-linear resistor (Metrosil) current should be aslow as possible, but no greater than approximately 30mA rms for 1A currenttransformers and approximately 100mA rms for 5A current transformer.At the maximum secondary current, the non-linear resistor (Metrosil) should limitthe voltage to 1500V rms or 2120V peak for 0.25 second. At higher relay voltagesettings, it is not always possible to limit the fault voltage to 1500V rms, so higherfault voltage may have to be tolerated.The following tables show the typical types of Metrosil that will be required, depending onrelay current rating, REF voltage setting etc.6.4.1 Metrosil units for relays with 1A CTThe Metrosil units with 1A CTs have been designed to comply with the following restrictions:−−At the relay voltage setting, the Metrosil current should be less than 30mA rms.At the maximum secondary internal fault current, the Metrosil unit should limit thevoltage to 1500V rms if possible.The Metrosil units normally recommended to be used with 1Amp CTs are shown in thefollowing table:Relay Voltage Nominal Characteristics Recommended Metrosil Typesetting C β Single pole Relay Triple pole relayUp to 125V rms125 to 300V rms4509000.250.25600A/S1/S256600A/S1/S1088600A/S3/1/S802600A/S3/1/S1195NOTE:Single pole Relay Metrosil Units are normally supplied withoutmounting brackets unless otherwise specified by the customer.