Author: ABBdriveX

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AQ: What is a soft starter?

Motor starter (also known as motor soft starter) is a electronic device integrates soft start, soft stop, light-load energy saving and various protection functions for motor controls. Its main components are the three phase reverse parallel thyristors between power supply and being controlled motor and related control circuits. Control the conduction angle of the three phase reverse parallel thyristors by different methods, to achieve different functions by the changeable of the input voltage on the controlled motors.

The difference between soft starter and frequency inverter

Soft starters and AC motor speed control, it can change output voltage and frequency at the same time; actually, soft starter is a regulator for motor starting, only changes output voltage but not the frequency. The frequency inverter has all the features of soft starter, but its price is much more expensive than the soft starter, and the structure is much more complex.

Frequency inverter allows the AC motor smooth start up, control startup current growing from zero to motor rated current, reduce impact to the power grid and avoid the motor being burned out, also provide protection in motor running process. Besides these functions, the main function of frequency inverter is adjusting the motor running speed according to actual operation conditions, to achieve energy saving effect.

AQ: Change 230V to 460V for operating an Electric Motor

I have a generator of 3 hp, and it outputs 230 V, and I have a submersible Electric Pump, the motor of which is rated to operate at 460 V, Can I use a step up transformer to increase the voltage output from my generator and power the pump? What more parameters do I need to know of in this case?

Check to see if the generator has 3 phase power output. A typical home generator will provide 230 volt single phase output. You will not be able to step up to 460 volt and start a 3 phase motor with single phase. The only way at that point to generate 3 phase would be to use a VFD with single phase input capability and use the drive to generate 3 phase. You will still need to use a transformer. Variable frequency drives won’t normally behave well on generator power but may for an intermittent load like a submersible pump.

AQ: Soft starter energy saving principle

Induction motor is inductive load, the current lags the voltage, most electrical appliances are the same. In order to improve the power factor we need to use capacitive load for compensation, parallel capacitors or with synchronous motor for compensation. Reduce motor excitation current also can improve the power factor (HPS2 saving function, reduce excitation current by reducing voltage at light loads, to increase COS∮). Energy-saving operation mode: decrease voltage in light loads to reduce excitation current, the motor current divides into the active component and reactive component (excitation component), to increased COS∮.

Energy saving operation mode: when the motor load is light, the soft starter working at energy-saving conditions, PF switch to Y position, under the current feedback action, the soft starter reduces the motor voltage automatically, to reduce excitation component of the motor current. Thereby improving the power factor of the motor (COS∮). If the contactor in bypass state, this feature cannot works. TPF switch provides energy saving features with two reaction times: normal speed and slow speed. The soft starter operation in energy saving state automatic (In normal and slow speed), saving 40% energy in no-load and 5% with load.

AQ: What is the soft stop of an electric motor?

In electric motor stop, the traditional control ways are accomplished by momentary power cutting off. But in lots of applications, it’s not allowed the motor instant shutdown. For example: high-rise buildings, building’s water pump system, it will appear huge water hammer during instant shutdown, to damage the pipe, even the pumps. To reduce and avoid “water hammer” phenomenon, the pumps motor need be shut down gradually, that is soft stop. The soft starter can meet such requirements. In pumping station, soft stop technology can avoid the pump door damaged of the pumping station, to reduce maintenance costs and maintenance works. The soft stop function in soft starter is, when the thyristor gets stop instruction, decrease conduction angle gradually from full conduction, and achieve full closed after a certain time. Stopping time can be adjusted according to actual requirements within 0 – 120s.

AQ: Soft starter protection features

1) Overload protection: the soft starter has current control loop to track and detect of the changes of the electric motor current. Achieve overload protection by increasing overload current settings and inverse time control mode, to cut down the thyristor and send alarm signals when motor is overload.
2) Phase loss protection: soft starter detects changes in the three-phase line current all the time, to make phase loss protection response once the current off.
3) Overheating protection: the soft starter detects the thyristors internal radiator’s temperature by its thermal relay, automatic cut down and send alarm signal once the radiator’s temperature exceeds the allowable value.
4) Other features: achieve lots of mixed protection functions by combination of the electronic circuits.

AQ: Soft starter MCC control cabinet

MCC is shorted for Motor Control Center. Soft starter MCC control cabinet consists of the following components: (1) input circuit breaker, (2) Soft starter (including electronic control circuit and three phase thyristor), (3) soft starter bypass contactor, (4) secondary-side control circuit (for manual start, remote start, soft start and direct start functions selection and operation), and voltage, current display, fault, running and working status indicators.

We can achieve various complex functions with combinations of soft starter MCC control cabinet. For example: add logic controller to two control cabinets to form a “alternative solution” for building’s fire protection system, sprinkler pumps etc. Couple with PLC (programmable logic controller), we can achieve automatic detection (eg half a month) and shutdown of the fire pump system; couple with corresponding logic controller to make the pump running at low speed and low pressure in setting time when we maintenance the whole system working status. Combine logic controller with several motors for residential pump system and other dedicated systems, active each motor according to actual requirements and also can reduce motor gradually to achieve optimum operation efficiency. Also can achieve multiple motors running by turns according to customer requirements, to make all motors operating life in the same.

AQ: How to learn PLC technology languages

The PLC languages themselves are fairly similar between different manufacturers. You basically have ladder logic (which looks like a relay contact map), function blocks (which are more akin to an electronic circuit overview) and structured language (of which there are several variants. Most look a lot like high-level programming languages). You might encounter some functions having different names or in-/outputs between manufacturers but most of them look much the same. They have the same functionality although complex programming is easier in structured code. If you have worked with high-level programming, you might want to take a look at structured languages first as these will likely feel familiar.

As for ease-of-use, I usually recommend the larger manufacturers; not because these have the best, cheapest or easiest software but because they have very substantial and comprehensive online support which, for a beginner, is more helpful than a cheap program. The big companies such as Siemens, Schneider, ABB and Rockwell all have very comprehensive online help, programming examples and guides as well as manuals available. Most also have “starter-kits” of their software and hardware available although these of course require some form of budget.

AQ: Energy Efficient Motor VS Standard motor

This is a very simplified comparison for a very complex issue. Every motor manufacturer is somewhat different in their approach, and there are literally thousands of design details in each machine that can be accommodated as the designer balances efficiency VS performance VS cost VS reliability VS safety VS manufacturability.

To generalize a bit, take a look at the following list. Not everything is there (not by a long shot!) but there should be enough to give you a reasonable overview. Note that some items are “design” related, while others are “operation” related.

1. Use a lower loss material for both stator and rotor laminations.
2. Use a larger copper cross-section for the same power rating.
3. Skew rotor winding with respect to stator winding.
4. Use more magnetic material (diameter, length, or both) to reduce flux densities.
5. Effectively size the machine for a somewhat higher rating than nameplate (because the typical peak of the efficiency curve occurs somewhere between 70 and 85 percent “rated” load).
6. Operate the machine at reduced temperatures and/or increase coolant flow.
7. Limit input frequency and/or voltage variation to tighter tolerance (note that this is a specification approach, not a manufacturing approach).
8. Better bearings / lubrication to reduce friction loss.
9. More care taken with internal geometry – i.e. closed slots, large air gaps, generous tooth dimensions, smooth surfaces, etc – to reduce windage.

AQ: Electric motor rotor and stator

When building a traditional electric machine (motor or generator), the idea is to distribute the flux very evenly over both the rotor and stator surfaces where they contact the air gap. This means using either grain-oriented steels and rotating each lamination slightly from the previous one to provide a relatively even flux path, or using a non-grain-oriented steel and having the flux distribute on its own.

Grain-oriented steels are good for lowering magnetizing flux – provided the grain in each lamination is aligned in the same direction. This can also help with reducing stray loss and eddy loss (flux that travels parallel to the shaft and does no useful “work”).

Most electrical steels used in stator and rotor construction also have an insulating coating applied; some of these are organic materials and some are inorganic (solvent-based) materials. The choice is typically made based on a combination of temperature gradient and local environmental laws. The inorganic (solvent) materials can generally withstand higher temperatures but are far less eco-friendly in the manufacture of the coating material or in the curing of the coating after it is applied.

Since most coatings are applied after the rolling-to-thickness process, these are usually cold-rolled steels. The use of cold- vs hot-rolled material can also be based on tooth / slot geometry: for very narrow teeth that require “post processing” for a coating, hot rolled is often used because the material will retain its geometry better through the temperatures used to cure the coating.

Skewing is the relationship between a rotor “turn” and a stator “turn”. Each manufacturer is different; and different machines (synchronous, induction, Permanent magnet, direct current) approach it differently. For example – it is usually easier to skew the stator laminations of an AC machine, because the insertion of the coils is easier. For a DC machine, skewing of the rotor is preferred for the same reason. The amount of skew is typically one slot pitch … which means that one end of the machine has the slot centerline aligned with the opposite end’s tooth centerline.

Grain orientation only applies to the lamination steels … not the conductor materials.

Energy efficient bearing is really a misnomer. However, they can be thought of as those that are sized to have relatively low friction coefficients and therefore low thermal losses (so that you don’t have to use extra energy to cool the lubricant). In the bigger picture, they would also use a lubricant that is less energy-intensive to produce and / or require less replacement.

AQ: Die-cast rotor design

The method of creating a die-cast rotor is as follows:

1. An assembly of steel laminations (which may or may not be grain-oriented) containing the openings for both rotor bars and ventilation (as required) is made and clamped together to form a cylindrical iron core.
2. The assembly is inserted into a mold, which has space both above and below the core for the end (shorting) ring assembly.
3. The molten conductor material (aluminum or copper, usually) is injected into the mold and allowed to flow through the bar openings. It also fills the end ring spaces.
4. The entire assembly is allowed to cool so that the conductor solidifies.
5. The “cast” core is then shrunk onto a steel shaft.

Now we have a “cast” rotor assembly, ready for bearings and mounting into machine.