Concept Behind ELV Machines
This is “literally” achieved in practice by:
1. Using an “Extra-Low-Voltage supply:
This in terms of classroom OH&S: Minimises the possibility of electric shock due to inadvertent physical contact with live conductors
The voltage selected was derived from the then standard (1970) NSW(Australia) 3 phase + Neutral, 4 wire, MEN, distribution system of 415/240 Vac. 50 Hz supply
In order to make the apprentice/student experimental meter readings and their associated calculations appear more realistic/representative of actual industrial practice, the supply voltage of 41.5/24.0 Vac, 50Hz was selected (i.e. 1/10th of the actual distribution voltage, or in mathematical terms the decimal point has simply been moved one place)
2. Reduction of Output Power at the shaft:
the machines have been designed to have a nominal full load torque of 0.31Nm, and
Dependent on motor type, and full load speed, having a nominal output power of 50 Watt
The reduction of energy levels in terms of classroom OH&S: minimises arcing flash, skin burns, material burning &/or fire due to inadvertent incorrect &/or short-circuit connections.
The output shafts are fitted with relatively large smooth surface steel couplings which enable the apprentice/student, with relative safety, to physically grasp the output shaft in the palm of their hand. This feature enables the apprentice/student to physically load, or stall, the machines by hand and physically feel the differences in starting torque, whist observing ammeter current changes, to physically confirm the “abstract” predictions of their theoretical calculations
These are outcomes which cannot be reproduced using full voltage(LV) high power machines.
I have noted that some teachers are worried the student may become complacent, after training with ELV, and not treat normal Low-Voltage (LV) motors in the field with the respect they deserve.
Their concern is valid to a point. However, their argument must be balanced against the fact that students may, or at sometime in the future, be required to work with High-Voltage (HV) motors (11kV, 22kV etc,)
It must be remembered, the function and responsibility of TAFE is to provide the “supplementary” theoretical education to “complement” the intensive full-time on-the-job training.
TAFE needs to be able to operate without the extra restrictive OH&S practices and teacher responsibility that Low Voltage (LV) would introduce into the hands-on practical(laboratory) sessions. An unnecessary distraction which would detract the emphasis away from the theory component
The responsibility, of providing the full-time training, and enforcement, of the safe working practices, and protocols, required for working with Low & High Voltages (or currents) is the duty of the employer.
Notwithstanding, motors can be supplied to operate on Low voltages(LV) supplies (415V, 240V, 120V etc) and/or other frequencies if required.
However, output power (torque) will also increase making them unsuitable for students to stall the motors with their hand.