A New Type of Dehumidifier for Enclosed High-voltage Switchgear Cabinet

Transcription

1 TELKOMNIKA, Vol.10, No.7, November 01, pp. 1637~164 e-issn: X aredited by DGHE (DIKTI), Deree No: 51/Dikti/Kep/ A New Type of Dehumidifier for Enlosed High-voltage Swithgear Cabinet Jinbo Zhang* 1,, Tongguang Shao 1,, Yu Wang 1,, Jing Wang 1, 1 College of Computer & Information Engineering, Hohai University, Changzhou, China 130 Jiangsu Provinial Key Lab. of Power Transmission Equipment Tehnology Changzhou, China 130 *orresponding author, stg@gmail.om Abstrat In order to eliminate the internal ondensation of enlosed swithgear abinet, this paper introdued a subminiature and high-performane dehumidifier based on semiondutor refrigeration tehnology. This equipment utilized a Fuzzy self-tuning PID intelligent ontroller to monitor the humidity hange in the abinet ontinuously and judged the dehumidifier start-stop automatially. Besides, real-time ommuniation with a host omputer through RS485 interfae was also onsidered. Experiments showed that this design ould effetively redue the internal humidity, eliminate the ondensation, and provide a pratial and effetive solution to prevent the power devie aidents aused by wet and ondensation. Keywords: high-voltage swithgear, semiondutor refrigeration, ondensation, dehumidifier Copyright 01 Universitas Ahmad Dahlan. All rights reserved. 1. Introdution In the power system, the insulation onditions of power transmission and transformation equipment are essential fators to the seurity of it, espeially in the omplex limate onditions. Due to wet and ondensation, the degraded insulation performane initiates operational aidents easily, whih brings about serious eonomi loss to soiety. Thus how to solve the problem of wet and ondensation is a signifiant issue to ensure the seurity of power equipment. In swithgear abinet, ontrol abinet, terminal box and other power equipment, the traditional methods to prevent the wet and ondensation are heating and exhausting air, whih generally funtions well. Given the high humidity in the enlosed abinet, the traditional ways fae some limitations. Compared with these traditional methods, semiondutor refrigeration has many advantages, suh as no moving parts, high reliability, long life, ompat volume, easy to ontrol, apable to ahieve high temperature differene, green and non-pollution [1]. Therefore, it is neessary and important to develop and researh a new type of dehumidifier for enlosed high-voltage swithgear abinet based on semiondutor refrigeration tehnology. For enlosed abinet, drops will generate on metal surfae when the temperature of this metal surfae dereases blew dew-point, this phenomenon is alled ondensation. Whether ondensation will generate depends on several variable quantityies inluding ambient temperature, abinet internal temperature, relative humidity, dew-point, et. The main situations that make enlosed abinet generate ondensation easily are: 1. High humidity and hangeful daily temperature. Drops may easily generate on metal surfae when hot and old air exhange.. The bottom of abinet boy is wet and even there s some water in able hannel. When water evaporates and the metal surfae temperature is lower than the air temperature, ondensation will generate. 3. Some devies are in the outage statue, abinet internal temperature is often lower than the ambient temperature, so that ondensation will also generate. One these devies are put into use in this ondition, aidents may easily our, suh as reepage and flashover phenomenon. Aording to its formation mehanism, two onditions must be met before vapor ondensation formation: high ambient relative humidity and ambient temperature variation, in whih ambient relative humidity has the greatest influene. In order to prevent ondensation, at Reeived July 3, 01; Revised September 9, 01; Aepted Otober 10, 01

2 1638 e-issn: X least one of these two formation onditions must be broken. Both reduing the relative humidity and reduing the temperature differene ould be taken as anti-ondensation measures. Currently, heating with heater and ventilating with fan are mainly taken to ahieve antiondensation inside the abinet. But these two methods on abinet anti-ondensation are less effetive in high humidity regions or seasons, numbers of aidents have ourred as a result of ondensation. Heating method an only alleviate the abinet internal ondensation, it an t redue the relative humidity in enlosed abinet, and lots of water vapor in the abinet is not disharged. Furthermore, prolonged heating not only onsumes large amounts of energy but also leads to equipment aging and shortens the life of equipment. Consequently, relative humidity inside the abinet must be redued, so as to truly ahieve the purpose of dehumidify and anti-ondensation. When a glass of water is taken out from refrigerator in summer, large amounts of drops will generate on its surfae. This ondensation phenomenon will go on forever as long as the temperature differene exists between the surfae of this glass and the ambient air, and the moisture in ambient air will be absorbed ontinuously if the ondensate is removed, this is the dehumidifier phenomenon or dehumidifier priniple. In general, ommerially available dehumidifiers are made up of ompressor, fan, ondenser, refrigerant materials (F1 or other materials), et. However, this kind of dehumidifier an only be used in a large spae but not enlosed abinet as a result of its volume and power onsumption. Subminiature and high-performane dehumidifier developed with semiondutor refrigeration tehnology an make up for all the defiienies of above methods.. Semiondutor Refrigeration Semiondutor refrigeration (thermoeletri ooling) is a ross subjet developed between refrigeration tehnology and semiondutor tehnology in 1950s, it uses the speial semiondutor material to make up a P-N juntion, whih forms a thermoouple and refrigerates with diret urrent..1. Priniple of Semiondutor Refrigeration Thermoeletri Cooler (TEC) is a kind of heat pump, it has no mehanial moving parts and an be used in ertain situation where the spae is limited, reliability requirements is strit and refrigerant pollution is not tolerated. Figure 1. Shemati diagram of semiondutor Refrigeration As shown in Fig.1, a single of refrigeration piee onsists of two erami piees made from N-type and P-type semiondutor material (Bi Te 3 ), this semiondutor omponent is onneted with series form in the iruit. TELKOMNIKA Vol. 10, No. 7, November 01 :

3 TELKOMNIKA e-issn: X 1639 When an N-type and a P-type semiondutor material onnet into a galvani ouple pair, after being onneted with diret urrent, energy transfer ours. Current flows from N-type omponent to P-type omponent joint to absorb heat and beome a old end, urrent flows from P-type omponent to N-type omponent joint to release heat and beome a hot end. The sale of endothermi and exothermi is determined by the value of urrent and the number of N, P omponents, hundreds ouples of galvani are onneted into a thermopile in refrigeration piee in order to enhane the effet of ooling(heating). Semiondutor refrigeration is developed on the foundation of thermoeletri effet, whih onsists of 5 different effets; they are Seebek effet, Peltier effet, Thomson effet, Joule effet and Fourier effet. The Seebek, Peltier and Thomson effet are reversible, while Joule and Fourier effet are irreversible. Although the semiondutor refrigeration is the interation of these five effets, Peltier effet plays a major role in them. Figure. Shemati diagram of Peltier effet In 1834, Frenh physiist Peltier disovered that when diret urrent flows through the losed iruit omposed by two different metals, the heat Q was absorbed on one joint, while the same amount of heat was released on the other joint. This kind of heat was named Peltier Heat, and the shemati diagram of it is shown in Figure. The heat of the old end is transferred to the hot end after onneting the power supply, and the temperature of old end dereases while it inreases in the hot end, this is the famous Peltier effet... Fundamental Refrigeration Calulation When a ooling devie (a PN juntion ouple or single-stage thermoeletri hip) gets into thermal equilibrium under the ation of urrent I, old end temperaturet, hot end temperature T h and hot-old ends temperature differene τ, the orresponding driving voltage U, ooling apaity Q (sometimes an also be interpreted as old load), eletrial power N 0, ooling effiieny E an be represented as follows []: 0 0 Q = αt I I R K τ (1) 0 N = I R + α τ I () U = R0I + N0 (3) E = Q N (4) 0 Among them, α, R0 and K are the ooling devie s equivalent Seebek oeffiient, total equivalent resistane and equivalent thermal ondutivity, respetively. Defined Z as the thermoeletri material s figure of merit, the maximum ooling apaity urrent I Qmax and the maximum effiieny urrent I E max an be omputed as follows: A New Type of Dehumidifier for Enlosed High-voltage Swithgear Cabinet (Jinbo Zhang)

4 1640 e-issn: X α Q max, α = = R0 0 I T Z I E max τ = max R K α τ = R Z T 1 1 ( + ( + τ ) ) ZT (5) (6) (7) I best has two meanings: When T and T h are fixed, it represents the maximum ooling apaity urrent I Q,max ; when T h and Q are fixed, it represents the maximum thermoeletri urrent I τ,max. max I τ,max urrent is τ is the thermoeletri urrent between the hot and old ends while the working in the ondition that Q = 0 [3]. Figure 3. Shemati diagram of a dehumidifier Figure 4. Dehumidifier struture design TELKOMNIKA Vol. 10, No. 7, November 01 :

5 TELKOMNIKA e-issn: X Enlosed High-voltage Swithgear Cabinet Dehumidifier A new type of dehumidifier applied to enlosed high-voltage swithgear abinet is designed based on the theory above Dehumidifier s Hardware The subminiature and high-performane enlosed high-voltage swithgear abinet dehumidifier mainly onsists of abinet internal temperature sensor, abinet wall temperature sensor, ondensation plate temperature sensor, abinet internal humidity sensor, miroproessor, RS485 interfae, LCD, relay drive iruit, refrigeration devie, drainage devie, power supply, et. The eletrial blok diagram of it is shown in Figure 3 and the integral struture of it is shown in Figure 4. Cabinet internal temperature sensor, abinet wall temperature sensor and ondensation plate temperature sensor are respetively used for the measurement of the abinet internal temperature, abinet surfae temperature and the ondensation plate surfae temperature. Cabinet internal humidity sensor, whih uses a linear temperature sensor, is used for the measurement of the relative humidity inside the enlosed abinet. 3.. Dehumidifier s Software Software design is an important part of the enlosed high-voltage swithgear abinet dehumidifier. Its major task is to initialize the dehumidifier, reeive ommands from keys, obtain and proess the data from different sensors, display parameters and states on LCD, ommuniate with the host omputer and ahieve the Fuzzy self-tuning PID ontrol Control Flow The main program of enlosed high-voltage swithgear abinet dehumidifier onsists of initialization module, key-press module, display module, et. The olletion of the temperature data, sale transformation and ontrol algorithm are realized by its subprogram. Figure 5 shows the program flow hart. e( t ) (t) e Figure 5. Algorithm flow hart After obtaining the humidity information olleted by the sensors, MPU alls the sale transformation module to alulate the feedbak data, and the input is alulated based on the A New Type of Dehumidifier for Enlosed High-voltage Swithgear Cabinet (Jinbo Zhang)

6 164 e-issn: X deviation e( t ) and the deviation variation rate e (t), then output is produed by the Fuzzy selftuning PID intelligent ontrol algorithm. Then, the output will be onverted to a PWM signal used to drive relays, and at last the ontroller ahieves the ontrol of refrigeration devie Fuzzy self-tuning PID Intelligent Control Algorithm PID ontrol law is a fairly ideal, whih introdues integration on the basis of proportion to eliminate the residual error, and differentiation an improve the system s stability [4]. It is suitable for the oasions with a large ontrol hannel time onstant, apaity lag or high ontrol requirement. The PID ontroller is alulated as follows: 1 d( e( t)) u( t) = K p e( t) + e( τ ) dτ + TD (8) TI dt In whih, e( t ) is the system feedbak deviation, K p is the proportional oeffiient, T I is the integral time and T D is the differential time. Introduing fuzzy ontrol algorithm to the traditional PID ontrol system makes up a new Fuzzy self-tuning PID intelligent ontroller. The purpose of using this intelligent ontroller is to make the ontroller adjust PID parameters with fuzzy ontrol algorithm on-line and adaptively aording to the atual situation, so as to ahieve the real-time optimal adjustment and make up the defiienies of fuzzy ontroller and PID ontroller when they at alone and improve the overall ontrol effet on system. The Fuzzy self-tuning PID intelligent ontroller s blok diagram of enlosed high-voltage swithgear abinet dehumidifier is shown in Figure 6. e(t) K p Ki K d e ( t) Figure 6. Fuzzy self-tuning PID intelligent ontroller In the view of the dehumidifier s appliation effet, the Fuzzy self-tuning PID intelligent ontroller has the flowing features: 1. The system has good dynami harateristis.. The system has an ideal steady quality, the steady proess has no osillation, and the humidity ontrol preision is within ±1 o C. 3. System s jamming-rejetion apability is improved and has a good inhibition on the field interferene 4. The ontrol system an still maintain a good adaptability and robustness when the ontrol proess parameters hanged. 4. Results and Analysis For the purpose of proving the effet of this way on anti-ondensation, following experiment was done. Experimental environment: ambient temperature 10-0 o C, humidity 40-70%. Semiondutor hilling plate selets TEC1-171, working voltage 1V, working urrent 1A, theoretial power 144W. Use CPU radiator as the old surfae of hilling plate, and dissipate heat with 00W heater fan on the hot surfae. TELKOMNIKA Vol. 10, No. 7, November 01 :

7 TELKOMNIKA e-issn: X 1643 Experiment found that there is no ondensation on hilling plate when the ambient humidity was below 40%, and when it was about 40%, ondensation phenomenon appeared. As a result of the refrigeration equipment s low ooling rate but high heating rate, the original heater part an be onsidered using the heat released from hot-side; the old-side ahieves ondensation in abinet and disharges water. If the ooling effet is too better to produe frost, stop the equipment five minutes every 3 hours to make it defrost in order to ensure the ooling effet. For relatively enlosed abinet, internal temperature will be raised and at the same time the humidity will be redued. In addition, the power supply of refrigeration equipment should be ut off when the temperature is over the pre-set upper limit. 5. Conlusion Enlosed high-voltage swithgear abinet dehumidifier is designed aording to priniple above. The humidity value ould be preset by the keyboard of this equipment within the range of 30-90%. The refrigeration equipment is fored to turn on when the humidity is over the preset value, or the abinet internal temperature is over 3 o C than the wall temperature while the internal humidity is over 40%. At present, most of the power grid appliation is working in natural environment, of whih the limate is very ompliated and variable. The eletri power operation aidents and eonomi loss have reahed a very amazing point as a result of insulation performane reduing aused by vapor ondensation. Therefore, how to deal with moisture-proof and anti-ondensation problem of eletrial equipment is an important issue diretly related to whether the power equipment an run safely. This paper provides a sientifi and effiient method for improving the reliability and seurity of the power grid and ompletely avoid major aidents aused by vapor ondensation. Aknowledgement: Tehnology Support Program of Jiangsu Provine (SBE ) Referenes [1] K. Matsuzawa, N. Sekiguhi and K. Takagi, Development of Metal-Enlosed Swithgear Equipped with Automati Dehumidifier, IEEE Power Engineering Review. 1984, 4(10): [] U. Ghoshal. Strutured Cold Point Thermoeletri Coolers Devie Researh Conferene, 60th DRC. Conferene Digest, 00, [3] REN Depeng and Jia Yang. Numerial simulation for operating harateristis of thermogenerator, Spaeraft Engineering, 008, 17: [4] X.-T. Peng, S.-M. Liu, T. Yamakawa, P. Wang, and X. Liu, Selfregulating PID ontrollers and their appliations to a temperature ontrolling proess, in Fuzzy Computing; Theory, Hardware, and Appliations, M. M. Gupta and T. Yamakawa, Eds. Amsterdam, The Netherlands: Elsevier, 1988: [5] Zimparov, Energy onservation through heat transfer enhanement tehniques, Int. J. Energy. Res : [6] Qian-lin Zhou. The Priniple of Thermoeletri Tehnology and Appliation in Engineering Physis Experiment, Physial Experiment of Collage. 010, 3: [7] M. Braae and D. A. Rutherford, Seletion of parameters for a fuzzy logi ontroller, Fuzzy Sets Syst.1979, : [8] B. Kosko, Fuzzy Engineering. Englewood Cliffs, NJ: Prentie-Hall, [9] C. W. de Silva, Fuzzy Logi Appliations, Intelligent Control. New York: CRC, [10] M.A. Kedzierski, J.M. Gonlaves, Horizontal onvetive ondensation of alternative refrigerants within a miro-fin tube, J. Enhan. Heat Transf. 1999, 6: [11] H.S. Wang, H. Honda, omparison of predition methods for heat transfer, Condensation of refrigerants in horizontal mirofin tubes. Int. J. Refrig. 003, 6: [1] George K. I. Mann, Bao-Gang Hu, and Raymond G. Gosine, Analysis of Diret Ation Fuzzy PID Controller Strutures, IEEE Transations On Systems Man, and Cybernetis-part B: ybernetis No 3, [13] Nasution, Henry, Jamaluddin, Hishamuddin; Syeriff, Jamaluddin Mohd. Energy analysis for air onditioning system using fuzzy logi ontroller. Telkomnika, 011, 9(1): [14] PithaiVijaya, Karuppanan; Mahapatra, KamalaKanta. Adaptive-fuzzy ontroller based shunt ative filter for power line onditioners. Telkomnika, 011, 9(): A New Type of Dehumidifier for Enlosed High-voltage Swithgear Cabinet (Jinbo Zhang)