| Material Group | Comparative Tracking Index (CTI) – in Volts |
|---|---|
| Insulating Material group – I | 600V and above |
| Insulating Material group – II | 400V to 599V |
| Insulating Material group – IIIa | 175V to 399V |
| Insulating Material group – IIIb | 100V to 174V |
In Practice there wiill always difference in phase displacement between primary and secondary currents, Allowed limits are defined in IEC 61869-2.
Severity Test for Assembly is Degree of impact a defect has on its operation, under conditions of high humidity combined with cyclic changes in temperature.
Rated Impulse Voltage (Uimp) for Overvoltage category — I, II, III, IV at various nominal Voltage (Ue) is suggested in IEC 60664.
Utilization Categories indicate the type of Load and Duty Cycle of the load basis which selection of Switchgear should be done for the intended application.
Current transformer Accuracy class is highest permissible percentage error at rated current for that accuracy class, as per IEC 61869-2 and IS 2705.
Lightning is electrostatic discharge, causing the instantaneous release of energy. SPD diverts surge to ground without impacting utility supply.
Heat is a flow of energy from higher temperature object to lower temperature object. Heat transfer continues until two objects reaches thermal equilibrium.
Typical safe ability of Transformer, Generator and Cable to withstand Isc – short circuit fault current in multiple of its In – rated current, without damage to the equipment.