Showing posts with label motor. Show all posts
Showing posts with label motor. Show all posts

Sunday, May 26, 2013

Motor Starting

The worked example here is a very simple power system with two voltage levels and supplied by a single generator. While unrealistic, it does manage to demonstrate the key concepts pertaining to motor starting calculations.

Step 1: Construct System Model and Collect Equipment Parameters

Simplified system model for motor starting example

The power system has two voltage levels, 11kV and 415V, and is fed via a single 4MVA generator (G1). The 11kV bus has a standing load of 950kVA (S1) and we want to model the effects of starting a 250kW motor (M1). There is a standing load of 600kVA at 415V (S2), supplied by a 1.6MVA transformer (TX1). The equipment and cable parameters are as follows:
Equipment Parameters
Generator G1
  •  S_{g1} , = 4,000 kVA
  •  V_{g1} , = 11,000 V
  •  chi_{d}^{} , = 0.33 pu
  •  cos phi , = 0.85 pu
Generator Cable C1
  • Length = 50m
  • Size = 500 mm2
(R = 0.0522 Ωkm, X = 0.0826 Ωkm)
11kV Standing Load S1
  •  S_{s1} , = 950 kVA
  •  V_{s1} , = 11,000 V
  •  cos phi , = 0.84 pu
Motor M1
  •  P_{m1} , = 250 kW
  •  V_{m1} , = 11,000 V
  •  I_{LRC} , = 106.7 A
  •  I_{LRC}/I_{FLC} , = 6.5 pu
  •  cos phi_{m} , = 0.85 pu
  •  cos phi_{s} , = 0.30 pu
Motor Cable C2
  • Length = 150m
  • Size = 35 mm2
(R = 0.668 Ωkm, X = 0.115 Ωkm)
Transformer TX1
  •  S_{tx1} , = 1,600 kVA
  •  V_{t1} , = 11,000 V
  •  V_{t2} , = 415 V
  •  u_{k} , = 0.06 pu
  •  P_{kt} , = 12,700 W
  •  t_{p} , = 0%
Transformer Cable C3
  • Length = 60m
  • Size = 120 mm2
(R = 0.196 Ωkm, X = 0.096 Ωkm)
415V Standing Load S2
  •  S_{s2} , = 600 kVA
  •  V_{s2} , = 415 V
  •  cos phi , = 0.80 pu

Step 2: Calculate Equipment Impedances

Using the patameters above and the equations outlined earlier in the methodology, the following impedances were calculated:
Equipment Resistance (Ω) Reactance (Ω)
Generator G1 0.65462 9.35457
Generator Cable C1 0.00261 0.00413
11kV Standing Load S1 106.98947 69.10837
Motor M1 16.77752 61.02812
Motor Cable C2 0.1002 0.01725
Transformer TX1 (Primary Side) 0.60027 4.49762
Transformer Cable C3 0.01176 0.00576
415V Standing Load S2 0.22963 0.17223

Step 3: Referring Impedances

11kV will be used as the reference voltage. The only impedance that needs to be referred to this reference voltage is the 415V Standing Load (S2). Knowing that the transformer is set at principal tap, we can calculate the winding ratio and apply it to refer the 415V Standing Load impedance to the 11kV side:
 n = frac{415 left( 1 + 0% 
<br />ight)}{11,000} = 0.03773 ,
The resistance and reactance of the standing load referred to the 11kV side is now, R = 161.33333 Ω and X = 121.00 Ω.

Step 4: Construct the Equivalent Circuit

Equivalent circuit for motor starting example
The equivalent circuit for the system is shown in the figure to the right. The "Near" Thevenin equivalent circuit is also shown, and we now calculate the equivalent load impedance  Z_{eq} , in the steady-state condition (i.e. without the motor and motor cable impedances included):
 Z_{eq} = Z_{C1} + left[ Z_{S1} || left( Z_{C3} + Z_{TX1} + Z_{S2} 
<br />ight) 
<br />ight] ,
 = 64.59747 + j 44.80458 ,
Similarly the equivalent load impedance during motor starting (with the motor impedances included) can be calculated as as follows:
 Z_{eq,s} = Z_{C1} + left[ Z_{S1} || left( Z_{C3} + Z_{TX1} + Z_{S2} 
<br />ight) || Z_{C2} + Z_{M1} 
<br />ight] ,
 = 20.371997 + j 31.22116 ,

Step 5: Calculate the Initial Source EMF

"Near" Thevenin equivalent circuit for motor starting example
 
 
Assuming that there is nominal voltage at the 11kV bus in the steady-state condition, the initial generator emf can be calculated by voltage divider:
 E_{0} = V_{n} left( 1 + frac{Z_{G1}}{Z_{eq}} 
<br />ight) ,
 = 11,821.25 + j 1,023.33 = 11,865 , Vac

Step 6: Calculate System Voltages During Motor Start

Now we can calculate the transient effects of motor starting on the system voltages. Firstly, the current supplied by the generator during motor start is calculated:
 I_{G1} = frac{E_{0}}{Z_{eq,s} + Z_{G1}} ,
 = 138.8949 - j 219.36166 = 259.64A ,
Next, the voltage at the 11kV bus can be found:
 V_{11kV} = E_{0} - I_{G1} ( Z_{G1} + Z_{C1} ) ,
 = 9,677.024 - j 132.375 = 9,677.9 , Vac (or 87.98% of nominal voltage)
The voltage at the motor terminals can then be found by voltage divider:
 V_{M1} = V_{11kV} frac{Z_{M1}}{Z_{C2} + Z_{M1}} ,
 = 9,670.597 - j 118.231 = 9,671.3 , Vac (or 87.92% of nominal voltage)
The voltage at the low voltage bus is:
 V_{415V} = V_{11kV} frac{Z_{S2}}{Z_{C3} + + Z_{TX1} + Z_{S2}} ,
 = 9,521.825 - j 280.698 = 9,525.6 , Vac, then referred to the LV side = 359.39Vac (or 86.60% of nominal voltage)
Any other voltages of interest on the system can be determined using the same methods as above.
Suppose that our maximum voltage drop at the motor terminals is 15%. From above, we have found that the voltage drop is 12.08% at the motor terminals. This is a slightly marginal result and it may be prudent to simulate the system in a software package to confirm the results.
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Friday, April 12, 2013

PWM Dimmer Motor Speed Controller

This is yet some other mission born of necessity. Its a simple circuit, but does precisely what its designed to do - dim LED gentles or management the rate of 12V DC motors. The circuit makes use of PWM to regulate the effective or moderate current in the course of the LED array, 12V incandescent lamp (such as a automobile headlight bulb) or DC motor. The best distinction between the two modes of operation is the addition of an influence diode for motor speed control, even supposing a small diode will have to be used for dimmers too, in case long leads are used on the means to create an inductive back EMF when the MOSFET switches off.

  
hoto of Completed PWM Dimmer/Speed Control

The photograph presentations what a achieved board seems like. Dimensions are 53 x 37mm, so its imaginable to set up it into kind of small areas. The parts used are without difficulty to be had, and lots of subsitiutions are available for both the MOSFET and energy diode (the latter is only needed for motor speed management). The opamps will have to not be substituted, because the ones used have been chosen for low power and their capability to swing the output to the terrible supply rail. Note that if used as a motor velocity managementler, there is no remarks, so motor pace will change with load. For many softwares the place DC motors are used, steady speed in spite of load isn't needed or fascinating, but it's up to you to make a decision if this could risingly suit your wants.

Description
First, an outline of PWM is warranted. As the pot is circled clockwise, the input voltage modifications linearly with rotation. At first, the voltage is such that the comparator output is simply slim spikes, which turn the MOSFET on for an awfully quick period. Average current is low, so related LEDs will most probably be reasonably dim, or a motor will run (relatively) slowly. As the enter voltage coming from the pot increases, the MOSFET is on for lengthyer and lengthyer, so increasing energy to the burden.

figure 1 - PWM Waveform Generation

Figure 1 displays how the PWM idea works. The red trace is the triangle wave reference voltage, and the green trace is the voltage from the pot. When the input voltage is bigger than the reference voltage, the MOSFET activates, and current drifts within the load. Because the frequency is comparatively high (about 600Hz), we dont see any flicker from the LEDs, however the tone is audible from a motor thats PWM controlled. The PWM signal is proven in blue. The moderate present in the direction of the load will depend on the ratio of on-time to off-time, and when each are equal, the moderate present is exactly half of of that which would be drawn with DC.

Figure 2 - Dimmer/Speed Controller Schematic

The circuit is shown in Figure 2. U1 is the oscillator, and generates a triangular waveform. R4 and R5 simply set a half voltage reference, so the opamps can perform around a 6V centre voltage. U2A is an amplifier, and its output is a 10V top to peak triangle wave that's used by the comparator in line with U2B. This circuit evaluates the voltage from the pot with the triangle wave. If the input voltage is at zero, the comparators output remains low, and the MOSFET is off. This is the zero atmosphere. In truth, the reference triangle waveform is from at least about 1.5V to a maximum of 9.5V, so there's a small part at each and every end of the pots rotation the place nothing occurs. 

This is commonplace and practical, due to the fact we would like a well defined off and most environment. Because of this vary, for lighting fixtures applications, an business standard zero-10V DC management sign can be used to set the mild stage. C-BUS (as smartly as many other home automation machines) can present 0-10V modules that may management the dimmer. While a 1N4004 diode is proven for D2, that is handiest appropriate if the unit is used as a dimmer. For motor pace management, a excessive-current quick recovery diode is required, this sort ofs a HFA15TB60PBF ultra-fast HEXFRED diode. There are many prospects for the diode, so you want to use whatever is without difficulty available that has appropriate scores. The diode should be rated for at least 1 of 2 the entire load present of the motor, and the HFA15TB60PBF urged is good for 15A continuous, so is adequateay with motors drawing as a lot as 30A.

Construction
While its unquestionably conceivable to build the dimmer on veroboard or identical, its somewhat fiddly to make and mistakes are easily made. Also, take no lengthyere that on account of the current the circuit can deal with, it may be very necessary use thick wires to give a boost to one of the crucial skinny tracks. This is even important for the PCB model. Naturally, I suggest the PCB, and this is to be had from ESP. The board is small - fifty three x 37mm, and it automobileries the entire skinnyg, together with the screw terminals. The PCB is double-sided with plated-through holes, and has solder maskss on both sides. The MOSFET will desire a heatsink except you are using the dimmer for light hundreds only. It is vital to insulate the MOSFET from the heatsink generally, for the explanation that case of the transistor is the drain (PWM output).

For use at excessive current and that which you can imagine excessive temperatures, the warmthsink may need to be higher than expected. Although the MOSFET must on the whole only dissipate about 2W or so at 10A, it's going to dissipate much more if its allowed to get scorching. Switching MOSFETs will cheerfully go into thermal runaway and self destruct if they have got inadequate heatsinking. You may also use an IGBT (insulated gate bipolar transistor) - most should have the identical pinouts, and they do no longer endure from the same thermal runaway drawback as MOSFETs. As noted above, there are rather a lot of different MOSFETs (or IGBTs) and fast diodes which are usable. The IRF540 MOSFET is a good choice, and being rated 27A it has a generous security margin. There are many differents that are equally suitable - in truth any switching MOSFET rated at 10A or more, and with a most voltage of more than 20V is quite adequate.

Testing

Connect to an appropriate 12V power supply. When powering up for the first time, use a one hundred ohm \"safety\" resisor in collection with the optimistic provide to limit the present if when you have made a mistake within the wiring. The complete present drain is about 2.5mA with the pot totally off, rising to 12.5mA when totally on. Most of this current is in the LED, which can also be fed from the PWM provide so you will see that the entire lot is working with no need to attach a load. Make sure that the pot is fully anti-clockwise (minimum), and apply power. You will have to measure not greater than 0.25V throughout the security resistor, rising to 1.25V with the pot at most. If adequate, do away with the safety resistor and install a load. High depth LED strip lights can draw up to ~1.5A each, and this dimmer should be capable of drive as so much as 10 of them, depending on the capabilities of the potential supply and the size of the warmthsink for the MOSFET.

source: http://sound.westhost.com/project126.htm
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12 V Bidirectional Motor Control Circuit

This simple circuit drives DC motors with a maximum current of 1 A and can be built with readily available components.The output voltage is adjustable between 0 and 14 V and the polarity can be changed so that not only motor speed but also rotation direction can be adjusted by turning a knob. 

The circuit is also ideal as a controller for a DC model railway or small low voltage hobby tool. Power for the circuit is supplied by a 18 V mains transformer rated at 1.5 A. Diodes D1to D4 rectify the supply and capacitor C1 provides smoothing to give a DC output voltage of around 24 V. A classic ‘H’ bridge configuration is made up with transistors T1/T3 and T2/T4. Transistors T5 and T6 together with resistors R7 and R8 provide the current sense and limiting mechanism. The maximum output current limit can be changed from 1 A by using different value resistors for R7 and R8: IOUT = 0.6 V / R where R gives the value for R7 and R8. For increased current limit the mains transformer and diodes will need to be changed to cope with the extra current as well as the four transistors used in the bridge configuration. 

Circuit diagram:
12 V Bidirectional Motor Control Circuit Diagram  12 V Bidirectional Motor Control Circuit Diagram
 
Motor speed control and direction is controlled by a twin-ganged linear pot (P1). The two tracks of P1 together with R1/R2 and R3/R4 form two adjustable potential divider networks. Wiring to the track ends are reversed so that as the pot is turned the output voltage of one potential divider increases while the other decreases and vice versa. 

In the midway position both dividers are at the same voltage so there is no potential difference and the motor is stationary. As the pot is rotated the potential difference across the motor increases and it runs faster. The voltage drop across D5 and D6 is equal to the forward voltage drop VBE of the bridge transistors and ensures that the motor does not oscillate in the off position with the pot at its mid point.


http://www.ecircuitslab.com/2011/07/12-v-bidirectional-motor-control.html
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Tuesday, April 2, 2013

Electric Motor Repair

Electrical engines are a significant aspect of most large functions. They are used to make current that can be linked with a strength or to immediately petrol other systems. These engines are complicated items of professional systems and consequently it is not recommended for a individual who is not a certified fix individual to attempt to fix them. This transforms digital strength into technical strength.

They come in a wide range of types and the type that you use will depend on what you need it for. The primary parts are the blades and the stator. The blades is the going aspect and the stator is the invitations aspect of it. These two items make the time frame for it.

Most engines are attractive in characteristics. Both the blades and the stator generate a attractive area which makes a twisting, or demand on the powerplant base and makes the revolving of the powerplant. This is how it functions.

Finding a reliable serviceman for your powerplant can be a complicated procedure. The crucial aspect is making sure that the serviceman you seek the services of is certified in mending. An search can help you discover certified serviceman in your community that can fulfill your immediate and continuing needs.

Once youve found the serviceman or fix company youd like to use, you should have them come and visit the site as soon as possible to analyze it. Once the serviceman has analyzed the position of your powerplant unit, he can give you an calculate regarding the money of the fix.

The fix is the first step in a long procedure of its servicing. Once it has been fixed, youre going to want to set up a frequent servicing routine in order to reduce the cost and agony of upcoming fixes. Maintenance is the single greatest factor you can do to reduce the need for fixes.

The best factor you can do with regards to fix is to put the extra persistence in to make sure that frequent servicing is being done. Effectively managed engines need less fix and cause less problems for you. If you can keep your engines properly managed youre less likely to need comprehensive and expensive fixes.

Electric powerplant fix can take many types, based on what type of powerplant unit you have and the characteristics of its use in your business. The best factor you can do with your damaged powerplant unit is to discover and seek the services of a reliable serviceman to do the fixes. Electrical powerplant fix can be reduced by exercising servicing on your powerplant unit.
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Wednesday, March 20, 2013

Two Basic Motor Speed Controllers

Here are two simple 12V DC motor speed controllers that can be built for just a few dollars. They exploit the fact that the rotational speed of a DC motor is directly proportional to the mean value of its supply voltage. The first circuit shows how variable voltage speed control can be obtained via a potentiometer (VR1) and compound emitter follower (Q1 & Q2). With this arrangement, the motor’s DC voltage can be varied from 0V to about 12V. This type of circuit gives good speed control and self-regulation at medium to high speeds but very poor low-speed control and slow starts. The second circuit uses a switchmode technique to vary motor speed.

Circuit diagram:
basic-motor-speed-controller-circuit-diagram1
Fig.1: a very simple motor speed controller based on a compound emitter follower (Q1 & Q2).

Here a quad NOR gate (IC1) acts as a 50Hz astable multivibrator that generates a rectangular output. The mark-space ratio of the rectangular waveform is fully variable from 20:1 to 1:20 via potentiometer VR1. The output from the multivibrator drives the base of Q1, which in turn drives Q2 and the motor. The motor’s mean supply voltage (integrated over a 50Hz period) is thus fully variable with VR1 but is applied in the form of high-energy "pulses" with peak values of about 12V.

Circuit diagram:
basic-motor-speed-controllers-circuit-diagram2
Fig.2: this slightly more complicated circuit gives better low speed control and higher torque.

This type of circuit gives excellent full-range speed control and gives high motor torque, even at very low speeds. Its degree of speed self-regulation is proportional to the mean value of the applied voltage. Note that for most applications, the power transistor (Q2) in both circuits will need to be mounted on an appropriate heatsink.
 
 
 
Source by : Streampowers
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