Electricity + Control November 2016

DRIVES, MOTORS + SWITCHGEAR

Limiter Power Management System (patent pending)

DOL – Direct Online IEC

A motor power management system which optimises the energy consumption and lifespan of electric induction motors using the technology is available owing to the advances in power electronics and system monitor capabilities.

– International Electrotechnical Commission

MTL

– Motor Terminal Latency

PF

– Power Factor

VFD VSD

– Variable Frequency Drive – Variable Speed Drive

Abbreviations/Acronyms

electricity consumption; industry accounts for 64% of this, the commercial sector for 20% and the residential sector 13% general purpose industrial electric motors of between 0,75 kWand 375 kW consumed 4 700 TWh (68% of the total for all motors); their share of global electricity demand is 30% • The three economies with the highest electricity consumption for motors are China, the USA and the European Union which col- lectively consumed 4 000 TWh (56% of global electricity demand for motors); the addition of four more countries (Japan, Russia, Canada and India) adds another 1 200 TWh (18%), which makes a total of 5 200 TWh (74%) • The net mechanical energy used in motor applications is esti- mated to be roughly 50% of the electrical energy input intomotors (e.g. on average it is thought electric motor systems operate at an efficiency of about 50%). The losses occur in the motors them- selves as well as in throttles and dampers, gears, transmissions, clutches, brakes, VFDs, etc. [2] It is estimated that 67,6% of electricity use by electric motors falls into the medium range between 0,75 and 375 kW, (I believe this is actually between 7,5 kW and 375 kW as although the number of small motors (0,75kw to 7,5 kW) in operation is very large these motors tend to be largely in the domestic market and therefore have very low operating hours in a year [3]. Energy-saving technologies and saving potentials The most obvious is improvement of component efficiency. Ac induction motors Standard ac cage induction motors are probably the cheapest and most effective means of converting electrical energy into rotational mechanical power. Medium sized motors (7,5 to 375 kW) The medium range of motors, the largest user of electric power, are manufactured in standard sizes and traded on the world market as a standard, interchangeable product. These products are manufactured to various international standards which means motors from any particular supplier are exchangeable. Most manufacturers manufacture the motors to meet the require- ments of the International Electrotechnical Commission (IEC) specifi- cations, including efficiency. The efficiency classes that cover motors

from 0,75 kW to 375 kW, 2 pole, 4 pole, and 6 pole, for both 50 Hz and 60 Hz. The losses in an ac induction motor consist of the following:

• Stator losses • Rotor losses • Core (iron) losses • Stray (additional load) losses • Friction and windage (mechanical losses)

If each of these points is studied individually, there is always the pos- sibility to reduce the losses in that component. Care must be taken, as changing materials or components can have other effects on the motor performance and characteristics.

Figure 2: Typical induction motor showing components for potential improvements of efficiency.

All this is relevant but if the motor is operating at 94% or 95% the possible increase in efficiency is going to be small; and 1% increase from 94 to 95% in efficiency of a 55 kW motor running at full load is only going to save 0,616 kW, operating for 300 days a year and eight hours per day. a total of 1 478  kWh − financially not a great amount, but a saving. Lower range of induction motors (0,75 to 7,5 kW) There is a large number of these motors in use but the power con- sumed is relatively small. In this range you findmotors used in domes- tic applications where the usage is low and the efficiencies relatively poor − but the total power consumed is very small. These motors are generally mass produced and have poor efficiency … as low as 60%.

November ‘16 Electricity+Control

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