The needle or pointer deflection (The movement of pointer on the scale is known as deflection) is a function of ratio of the current in the coils and provides a direct reading of insulation resistance. The hand-driven generator has a permanent magnet and provides the test voltage. The open circuit voltage (when the. R is infinity) is generally about 5% the rated voltage and with zero ‘R’ the voltage will be practically zero.
There are two scales are present on the megger, ohm meter-an ohms scale, normally 0-100Ω or 0-200Ω), for continuity testing; and a mega ohms scale, normally 0-500MΩ) or 0-100MΩ for insulation testing. It is also important in all cases to turn the handle at a steady constant speed of about 160 r.p.m. Because of its extreme simplicity in use, it can .be operated with one-hand. But, the battery operated megger instrument is now much in favour.
In normal condition the pointer of the megger indicate the infinity value Or in normal condition the pointer is stand-still at infinity scale. Megger has two terminals, one is for earth ‘E’ and other for live ‘L’. The testing circuit loads are connected to these two terminals. All the wiring test such as, insulation test polarity test, continuity test, short-circuit test are commonly performed by using a megger. We also check the winding insulation of transformers generatOt5 and motors by using a megger. It is available in various voltage range such as 500V, 1000V; 2500V. But, now a days electronic insulator meter are also available which works with 6 cells of 1.5 volt each and hence don’t required hand operation It can also measure resistance between 0-2Ω high resistance 0.05MΩ to 100MΩ and AC voltage up-to 500 volt:
what is the usable age of a meggar please?
ReplyDelete