Cable Insulation Resistance (IR) Test
The insulation resistance (IR) is the resistance in ohms of wires, cables and electrical equipment. It is important to guard against electric shocks and avoid equipment damage from accidental discharges. The method of measuring the insulation resistance is to test and assess the state of the isolation. The IR test used to judge the cable, system or equipment condition of any electrical installation and is generally done before a new electrical installation is energized. Also, the IR test is performed for energizing a system, which has been shut down for a long period. The IEC 60364-6 or BS7671:2008 is the reference as the standard.
Earth Fault Loop Impedance Test
Earth fault loop impedance also referred to as the loop test is the total impedance in ohms of the circuit path formed during a fault between the earthed metal work and live parts. It includes the external impedance circuit (e.g. Resistance of the metal work, resistance of the earthing rods, etc..) and the resistance of the phase and earthing conductors. The earth fault loop impedance is tested at the furthest point of each circuit. The main reason for earth loop impedance testing is to ensure that if a fault occurs in an electrical installation, sufficient current will flow to operate the fuse or circuit breaker protecting the faulty circuit within a predetermined time. Earth fault loop impedance also ensures the circuit continuity, level of earthing system and electrical shock protection. Reference standards are IEC 60364.6.61 and BS7671:2008.
Earth Resistance Test
An earthing of an electrical installation plays a pivotal role in safer operation of circuit breakers under a faulty condition. Also, it prevents differences in voltage potential from a possible flashover from lightning strikes. The earthing system is a mandatory requirement of an electrical installation. The purpose of an earth is to provide a safe path for the dissipation of fault currents, lightning strike, static discharges, EMI and RFI signals and interference. The measuring of resistance of the earthing pit is referred as the earth resistance test or ground resistance test. Generally 3 point method also called as“fall of potential” method is used to measure the earth resistance. The amount of earth resistance test is very important to verify the reliability and consistency of safety of the installation and also can early attend if any improvements required. It is noteworthy if these tests can be performed twice a year. IEC 60364.6.61, BS7671:2008 are being used as the reference standard of this test.
Residual Current Devices (RCDs) Test
An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors. In the case of a single-phase circuit, the device monitors the difference in currents between the line and neutral conductors. Residual current circuit breakers, Residual current breakers with over-current, Earth leakage relay and Earth fault relay are less popular RCDs in any electrical installation. RCD test is carried out according to the procedures subscribed in the IEC 61008-1 and BS7671:2008 standard. RCD Test at the commissioning stage of an installation is mandatory and periodic tests are very important to ensure reliable and consistent operation of RCDs. The testing frequency of RCDs should be decided by a qualified person depending on the application and operating environment of the RCD.
Power System Analysis and Harmonics Surveys
Harmonics are AC Voltages and Currents with frequencies with integral multiples of the fundamental frequency. The rapid advancement of power electronics in the industrial applications makes industrial load non-linear which generates harmonics. Since the load is non – linear, the current will be distorted and become non – sinusoidal. Harmonics arise from inverters, VFDs, rectifiers, voltage controllers, frequency controllers and other semiconductor switching devices generators, transformers, welders and arc furnaces. Main objective of the analysis is to identify and prevent the current and voltage harmonics which lead to depreciation of power quality.