Service Manual 06/2011
Contents
1. 25 C Suction Gas Return 3 7 Technical Information D7 9 2 0910 0611 E R134a Discus medium temp R134a Discus low temp D2DL75X D2DB75X D3DA75X D3DC100X D3DS150X D2DL40X D2DB50X D3DA50X D3DC75X D3DS100X D4DF100x D4DA200X D4DH250X D4DJ300X D6DH350X D6DJ400X D4DL150X D4DT200X D6DL270X D6DT320X D8DL370X D8DH500X D8DJ600X D8DT450X SN Se ar nes Dee der GE GS us mn ne 65 PTT TEL 80 60 H 75 70 G i P Soi Len p 65 g 50 245 r S 55 So ool 50 ai o E 45 E 35 m 40 a o z 230 S 30 c 2 25 LES O O O 20 O 15 H 15 i 10 10 5 5 25 20 15 10 5 0 5 10 15 20 25 30 25 20 45 10 5 0 5 10 15 Evaporating Temperature C Evaporating Temperature C 25 C Suction Gas Return __ 25 C Suction Gas Return Figure 3 Inverter operation with standard motor 25 to 60 Hz R134a 4 3 Minimum Speed The minimum allowable frequency of 25 Hz is governed by the lowest speed at which the lubrication system can operate effectively 4 4 Over speed with Special Motors By using a motor designed for a voltage lower than 400V 50 Hz in conjunction with a 400V supply it is possible for the inverter to increase the voltage during over speed Normally the ratio of voltage frequency V f is kept constant and it is only when the required voltage is above the supply voltage that the amps increase For example a 380V 60 Hz motor will only require 320V at 50 Hz according2. S EMERSON MMT Climate Technologies Date of last update 06 11 Ref D7 9 2 0910 0611 E Application Engineering Europe USE OF INVERTERS WITH DWM COPELAND COMPRESSORS 1 Introduction Inverters are used to vary the speed of motors and in this way can be used to control the capacity of a compressor For refrigeration users they can be an effective method of accurately matching compressor capacity to load requirement A way of reducing compressor output is needed in almost every application With the emphasis today on saving energy by reducing head pressures an effective capacity control method can bring enormous benefits Without the means to run efficiently at low capacity compressor cycling by switching on off is most commonly used This method introduces large fluctuations and high power consumption due to heavily loaded heat exchangers Multiple compressor solutions overcome this problem to some extent and stepping by means of cylinder unloading is used with piston compressors The advantages of varying compressor speed are m the load is more closely matched with minimal variation in evaporating pressure and fluctuations in load temperature are minimised better system efficiency at part load extended lifetime of equipment due to continuous operation instead of cycling low starting current obviates the need for assisted start devices with gradual speed increase from standstill there is less risk of sudden liquid or o
3. a compressor operating with an inverter will always be more than for a direct connected compressor running at the same speed It is important to choose a high quality inverter because the inverter absorbs a certain amount of power and also the nature of the electrical waveform at the motor is disjointed resulting in increased motor losses When considering an inverter drive the following points should be taken into account Loss of efficiency unless care is taken with system design and control Conventional capacity control methods may not be used with inverter drive Vibration resonance may occur at certain speeds and these are very difficult to predict Restrictions on operating envelope may be necessary Risk of electrical disturbance to control signals 4 Limits of Use with Copeland Brand Compressors With many inverters it is very easy to alter the maximum and minimum output frequencies and the frequency range so care must be taken to ensure the frequencies are correctly adjusted to prevent serious damage to the compressor NOTE In most variable frequency drives it is possible to program skip frequencies to avoid vibration resonance that may occur at certain speeds 4 1 Approved Frequency Ranges with Standard Motors Model Family Speed Range DK DL D2D D2S D3D D3S D4D D4S D6D 25 60 Hz D6S D8D D amp S 2 7 Technical Information D7 9 2 0910 0611 E 4 2 Operating 50 to 60Hz with Standard Motors The o
4. power input to the compressor will depend on the efficiency of the inverter and the frequency The framework should be designed such that resonance frequencies are above 65 Hz The system should be designed or the variable frequency drive should be configured skip frequencies programmed such that there is no operation at resonant frequencies There are inherent inefficiencies associated with the operation of the inverter Care must be taken when setting up the inverter to ensure it does not operate outside the specified frequency range and that it operates at maximum efficiency m Cable sizing from the mains supply and to the compressor motor must be sized to account for higher currents than for a similar size system without inverter The control circuit should be designed such that the inverter cannot operate with the output from the inverter to the motor open circuit Reduced gas velocities at lower speed may necessitate re design of discharge and suction pipe work 6 7 Technical Information D7 9 2 0910 0611 E Appendix Cross reference list DWM compressor and corresponding inverter from Control Techniques Control Techniques inverter product range Commander SK Inverter Control Inverter Control Inverter Control Compressor Techniques Compressor Techniques Compressor Techniques Commander SK Commander SK Command ander SK SK4402 DKM 5X SKB3400110 D2SC 65X SK2404 D4DT 220X DKJ 7X SKB340
5. 0150 D2SK 65X SK2404 D4SJ 300X SK4403 SK3401 SK3401 SK3401 SK3401 SK3401 SK3402 SK3402 SK3402 SK3403 SK3403 SK3403 SK3403 SK3403 SK3403 D8DL 370X SK4401 SK4401 SK4401 SK4401 SK4401 SK4401 D4SL 150X SK4401 SK4401 SK4402 SK4402 SK4402 D4SH 250X SK4402 SK4402 717
6. il return to the compressor on start up The objective of this bulletin is to provide technical guidelines to developers designers or installers that intend to use inverters in refrigeration equipment with DWM Copeland semi hermetic compressors The operation of an inverter the effect on compressor application range performance and power precautions and some implications on system design are discussed 2 Operation of an Inverter An Inverter works by converting the input mains alternating current to direct current and from this regenerating a simulated A C signal at the required frequency A compressor driven by a squirrel cage motor will run at a speed corresponding to the frequency The speed will be in direct proportion to the frequency 50 or 60 Hz Suppl Hz pply A 2 5 320 Hz Voltage Myr 9 s Current TI TJI Control Circuits Speed Ref Speed Feedback Figure 1 1 7 Technical Information D7 9 2 0910 0611 E 3 Evaluation and Important Considerations Most inverters are capable of generating frequencies from 2 5 Hz to over 300 Hz This is well outside the range of any refrigeration compressor care must be taken to respect the approved frequency range Limits arise due to the capability of the oil pump to maintain lubrication at low speed and motor cooling Excessive losses at high speeds can result in inefficient operation and overheating high discharge temperatures The power absorbed by
7. mains size for 20 more current than standard 7 Start Contactor Positioning The inverter should not be allowed to operate with the output from the inverter to the motor open circuit There should be a contactor each side of the inverter ie between the inverter and the mains and between the inverter and the compressor motor They should be interlocked to break the mains side first When switching on the motor side contactor should be made first When using an inverter bypass care should be taken to ensure there can be no voltage feedback to the inverter Therefore when the bypass contactor is closed and the bypass Is in operation the contactors on either side of the inverter must be open 8 Starting and Ramp Up An inverter is capable of delivering a soft start but at the same time care must be taken to ensure that stalling does not occur The inverter must be able to deliver sufficient power at the lower frequencies to ensure that the compressor accelerates to nominal speed in approximately 3 seconds or less Only general guidance can be given here because the exact torque requirements will depend on system pressures at the time of start up Longer ramp up times could result in inadequate lubrication It may be necessary to set the inverter to deliver a slightly increased voltage compared to the normal V f rule in Section 4 4 at the low frequency applicable during ramp up but this should not result in deviation from the V f rule during no
8. rmal operation 9 Electrical Shielding and Voltage Rise Wiring of the electrical enclosure and the installation must be carefully conducted in accordance with EMC recommendations High quality high reliable pressure sensors must be used and it is necessary to follow EMC measures to ensure that the inverter does not disturb the signals from pressure transducers Suction and high pressure sensors signals must be noise free to the controller input The inverter itself can be fitted with suitable EMC filters eg EN 55011 Class B Since the waveform generated by the inverter is built up from pulses there is a danger that the rate of voltage rise on an individual pulse can be too fast Generally this is measured in kV per microsecond and limits at the motor terminals which should be adhered to during the first microsecond are given in EN 60034 In order to minimize the risk of motor problems it is suggested that the variable frequency drive be operated at its lowest switching frequency and that the distance between the frequency drive and the compressor be as short as possible 10 Vibration A compressor running at fixed speed imposes vibrations on its associated framework at a set group of frequencies The framework can of course be designed so that its natural frequencies differ from the imposed frequencies A compressor driven at variable speed will impose different frequencies at each speed so the framework design to eliminate vibration througho
9. to the constant V f rule and can therefore be safely operated at all conditions up to 60 Hz with a suitable inverter By moving to 230V 50 Hz motor the scope for increased voltage speed is even greater 25 50 6065 25 50 65 Frequency Hz Frequency Hz Figure 4 lt is important to note that when using special motors in this way there is no option of running direct on line in the event of inverter failure 4 7 S EM ERSON Technical information D7 9 2 0910 0611 E limate Technologi 5 Control of Inverter Frequency The signal necessary to control the inverter depends on the type of inverter used They are normally controlled by a 4 to 20 mA or a voltage signal This can be driven from the parameter which is used to control the refrigeration system for example suction pressure or room temperature 6 Power Measurement and Cable Sizing The inverter can cause distortion of the sinusoidal current waveform and between the inverter and the motor there is a stepped current approximating to a sine wave High quality inverters will introduce less distortion and power losses Power can be measured using the two wattmeter method on the input to the inverter Currents can exceed the amounts calculated from this power Cables fuses and contactors will need to be sized for the true RMS current flowing through them General rules for this are m cable from motor to inverter size for 10 more current than standard m cable from inverter to
10. ut the speed range is more complex The framework structure should be stiff enough so that its resonant frequencies are above the maximum frequency ie 60 or 65 Hz Designing with natural frequencies below the minimum speed of 20 or 25 Hz could lead to vibration problems during start up Spring mounts should not be used as they have a natural frequency below 65 Hz 5 7 Technical Information D7 9 2 0910 0611 E NOTE The system should be designed or the variable frequency drive control should be configured skip frequencies programmed so that there is no operation at resonant frequencies between 20 and 70 Hz 11 Internally Compounded Compressors The operation of internally compounded compressors at variable speed may require the selection of a different liquid injection interstage cooling expansion valve Please consult Emerson Climate Technologies for further details 12 Recommended Inverter Range Emerson Climate Technologies recommends the use of Control Techniques brand inverter with DWM Standard and Discus compressors Please see the corresponding cross reference list in the Appendix 13 Summary The following is a summary of the main considerations when using inverter drive as capacity control The compressor must not operate outside the range 25 to 60 Hz The compressor application range might be reduced for motor loading if over speed is used The capacity of the compressor will be in direct proportion to the speed The
11. utput voltage from the drive can not exceed the input voltage to the drive Most Copeland brand compressors are designed to operate at 60 Hz speeds as they are marketed in areas where this is the mains supply frequency Therefore they can safely and reliably operate at this frequency However it must be noted that when connected to a 400V 50 Hz supply the inverter can only deliver a maximum voltage of 400V The standard motor requires a higher voltage at 60 Hz In the range between 50 and 60 Hz the amps could increase and therefore reduce the envelope such as shown in the following envelopes for the D4D D6D and D8D Discus compressor models for R404A and R134a R404A Discus medium temp R404A Discus low temp D2DC50X D2DD50X D2DL75X D2DB75X D3DA75X D3DC100X D2DL40X D2DB50X D3DA50X D3DC75X D3DS100X D4DF100X D3DS150X D4DA200X D4DH250X D4DJ300X D6DH350X D4DL150X D4DT220X D6DL270X D6DT320X D8DL370X D6DJ400X D8DH500X D8DJ600X D8DT450X So e a De ar a 60 l l l l l l l l l l l 55 sn 55 l 50 H G Qs i L a D 45 r L 2 40 a D 205 z Q 30 Nr LI a D 20 L 45 c c O O O 15 a O 10 l 10 r 5 l 5 0 45 40 35 30 25 20 15 10 5 0 5 10 55 50 45 40 35 30 25 20 15 10 5 0 Evaporating Temperature C Evaporating Temperature C _ 0 C Suction Gas Return C A 25 C Suction Gas Return Figure 2 Inverter operation with standard motor 25 to 60 Hz R404A
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