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Electric Megger (Insulation Tester)

From the Collection of Kiewa Valley Historical Society Mount Beauty Information Centre 31 Bogong High Plains Rd Mt Beauty Victoria

Description
A rectangular box in dark brown bakerlite casing. It has an agent's plaque fixed to the left of the face and on the right is the marker's recessed stamp. In the middle in a transparent window so the level of ohms can be read. The front also has two recessed fixing knobs in black. On one side is a crank handle with a knob that lifts up and is turned vigorously to create the voltage. The back has four recessed screws and four small leather pads. There is a hole on each side to insert wires. There are two copper insulated wires.
Size
Case: 135mm x 100mm x 60mm/ Handle: 90mm with 23mm knob/ SECV plaque: 48mm x 25mm/ Agent's plaque: 44mm x 35mm/ wires: 126m
Object Registration
KVHS 1185
Keywords
electrical meters, electrical equipment, fuses, safety, state electricity commission of victoria, mt beauty, bogong village
Historical information
Megger as the device was called, is in fact its brand name. It is a device that supplies a DC (direct current as per car batteries) voltage to enable testing of electrical apparatus. This particular device produces 250volts DC when the handle is turned vigorously. If an electrical device, such as a kettle or toaster, blew a fuse or tripped a circuit breaker, when switched on, then it must be checked electrically before any more use. Following the repair of the faulty item a megger would be used to check if either of the AC 240volt plugs leads were touching the metal case (earth). The output leads of the megger would be connected with one to the earth (metal case) and the other to each of the power connections in turn. A good megger reading of 50,000 ohms (resistance) would enable the device to be returned to service. A reading of zero ohms resistance would mean that it would again blow a fuse, and was therefore unsafe to use. In the electrical industry e.g. the former State Electricity Commission, a megger would be used to test lots of similar item in sequence. Because of the vigorous job of winding the handle, two persons were often used to save time. One would crank madly whilst the other shifted the leads. This particular megger is of a small voltage, but other meggers are bigger and have a few ranges of DC voltages able to be selected. The optimal megger for large Generating machines was motor driven megger. This was applied to the device being tested for a duration of approximately 30 minutes with reading of the resistance taken at regular intervals.
Significance
All equipment belonging to the State Electricity Commission of Victoria was labelled with a metal plaque attached to it. The SECV constructed the Kiewa Hydro Electric Scheme in the Upper Kiewa Valley and on the Bogong High Plains. The scheme began in 1938 and finished in 1961 when this megger was used and also possibly later as the SECV remained to maintain and operate the Scheme. This megger is of significance in relation to the advancement of technology.
Inscriptions & Markings
The SECV Plaque states: State/Electricity Commission/of/Victoria/ Electrical Engineer's Section/ No.1747
The Agent's Plaque states: H. Rowe & Co. Pty Ltd/Melbourne & Sydney/Sole Agents/in Australia for/Evershed & Vignoles Ltd
Maker's states: 500 volts/Megger/Regd Trade Mark/Made in England/Patent No/400728
Last updated
8 Mar 2020 at 10:28PM