IEC 60255-5:2000 pdf free download

IEC 60255-5:2000 pdf free download
IEC 60255-5:2000 pdf free download.Electrical relays
Category II applies where:
a) the auxiliary circuits (power supply circuits) of the relay are connected to a voltage supply used only for the power supply of static relays. If the leads are short and in the absence of switching of other circuits connected to the supply, the levels of transient voltage on the supply leads will be lower than specified in overvoltage category III;
b) the input energising circuits of the relays are not connected directly to voltage or current transformers and good screening and earthing are employed on the connection leads;
c) the output circuits are connected to a load by short lead lengths.
Category III applies to most practical cases of the application of measuring relays and protection equipment and shall, in particular, be used where:
a) the auxiliary energising circuits (power supply circuits) of the relay are connected to a common battery and/or, due to long lead lengths, common mode transient overvoltages of a relatively high value may appear on the supply leads and differential mode voltages may arise from switching in other circuits connected to the same battery or supply source;
b) the input energising circuits of the relay are connected to current and voltage transformers;
c) the output circuits are connected to a load by long leads, with the result that common mode transient voltages of a relatively high value may appear at the output terminals.
4.2.2.3 Impulse voltage insulation coordination within the measuring relays
For parts or circuits within the relay which are significantly influenced by external transient overvoltages, the rated impulse voltage of the relay applies. Transient overvoltages which can be generated by the operation of the measuring relay shall not influence external circuit conditions beyond what is specified in 4.2.2.4.
For other parts or circuits within the relay which are specifically protected against transient overvoltages so that they are not significantly influenced by external transient overvoltages, the impulse withstand voltage required for insulation is not related to the rated impulse voltage of the relay but to the actual conditions for that part or circuit.