General rule

1.25K passenger car is a railway passenger car with a speed of 160km/h, which is the material basis for completing passenger transport tasks, speeding up passenger trains and enhancing the competitiveness of railways in the domestic passenger transport market. In order to ensure the quality of bus maintenance and unify technical standards and quality requirements, this regulation is formulated according to the current production technology level of maintenance units and the actual situation that new technologies, new processes, new materials and new equipment are widely used on 25K buses. This procedure is applicable to the overhaul of A 1, A2, A3 class 25K buses and other buses with speed 160km.

2. This regulation implements the guiding ideology of the railway passenger car overhaul system reform, draws lessons from the advanced overhaul theory and experience of foreign high-speed passenger cars, takes the passenger car quality reliability as the basis, gives priority to the use efficiency, and establishes a planned preventive overhaul system with running kilometers as the main part and time periods as the supplement, so as to achieve "greatly improving the passenger car overhaul quality, greatly improving the safety factor, greatly reducing the overhaul downtime and improving the use efficiency of passenger cars" and fully meeting the needs of railway transportation.

3.25K bus maintenance should completely change the previous operation mode of on-site inspection, on-site inspection and on-site chaos, and implement a new production mode of bus maintenance according to the principle of "off-site inspection, centralized inspection and replacement and repair". Carry out condition-based maintenance to keep the vehicle in good condition all the time, and adopt replacement parts to make the key parts basically meet the original design performance and requirements to meet the needs of safe operation of passenger cars.

4. In order to ensure the high quality and standard of bus overhaul and meet the requirements of passenger transport, each depot must have a certain equipment foundation when overhauling the 25K bus, and establish overhaul process lines such as bogies, wheelset bearings, coupler buffers, braking devices, air conditioning appliances, diesel generator sets, electric fan batteries, axle temperature alarms and monitoring devices, and the equipment level should be suitable for the overhaul workload and standards; And there should be enough spare parts reserves to computerize the maintenance, operation and spare parts reserve management of passenger cars.

The repair course of 5.25K bus is divided into A 1, A2, A3 and A4 grades. 5. 1 A 1 grade: safety maintenance, with a cycle of 200,000 km (20000km) or less, but the time since the last maintenance of A 1 grade or above has exceeded 1 year. Grade 5.2: 400,000 km segment repair, with a period of 400,000 km (654.38+ million km) operation, or less than 400,000 km operation, but it is more than 2 years since the last repair above A2 level. Grade 5.3 A3: 800,000 k m segment repair, with a period of less than 800,000 km (65438+100,000 km), but it has been more than 2 years since the last A2 repair. Grade 5.4: overhaul, running for more than 2.4 million kilometers (400,000 kilometers) or more than 65,438+00 years since new construction or last A4 repair.

6. The repair and maintenance cycle at all levels is determined by the number of kilometers traveled by the bus: (1 10,000 km) 20 40 60 80100120/40160180 200 220 240.

7.25K passenger car A2, A3, A4 repair must be accepted by the acceptance room; The repair units at all levels above A2 level must be bus repair units that have been examined and approved by the competent department of the Ministry of Railways and have the repair capability.

8. In order to reduce the rest time of passenger cars and improve the efficiency of passenger cars, the temporary repair line of the depot with the ability of section repair and good conditions for temporary repair can be repaired at A2 level; Do not have the ability to repair the section or the temporary repair conditions of the line, still need to be sent to the locomotive depot for maintenance.

9. In order to implement the principle of quality and safety, repair units at all levels should ensure the quality of their repair projects (the repair quality guarantee period at all levels includes the extension period): A 1 Repair ensures the safe operation of the repair project of 200,000 kilometers; A2 Repair ensures that A 1 Repair runs 200,000 km for all maintenance projects and 400,000 km for the rest maintenance projects; A3 repair guarantees that A 1 repair will run 200,000 kilometers for all maintenance projects, A2 repair 400,000 kilometers and other maintenance projects 800,000 kilometers. Any damage caused by collision, derailment, overcrowding, overload and improper operation. It is not within the scope of quality assurance in use.

10. According to the principle of unified leadership and hierarchical management, the locomotive depot is fully responsible for the production tasks and maintenance quality of 25K passenger cars, and must implement the technical responsibility system headed by the chief engineer, give full play to the roles of engineers and inspectors, handle technical problems in maintenance seriously and responsibly, organize the broad masses of employees to learn the requirements of the Regulations, and ensure the implementation of the Regulations.

1 1.25K bus maintenance at all levels must strictly implement the quality inspection and acceptance system. When the provisions are unclear or inconsistent with the actual situation in the implementation process, the locomotive depot and the locomotive depot acceptance room will jointly study and solve them realistically. When the two sides disagree, they can handle and submit according to the opinions of the chief engineer or technical person in charge of the locomotive depot, and make records at the same time, and report to the competent department of the railway bureau and the acceptance room of the Ministry in the bureau.

12. The maintenance of wheelsets, axle boxes, bearings, air brakes, air conditioners and electrical appliances shall be carried out in accordance with the following regulations, procedures and standards promulgated by the Ministry of Railways and relevant product manuals. The above provisions are as follows: Maintenance Rules for Vehicle Air Brakes, Management Regulations for Maintenance and Operation of Air-conditioned Passenger Cars, Technical Conditions for Assembly and Maintenance of Disc Brake Wheelsets of Railway Passenger Cars (Trial), and Notice on Publishing Safety Control Measures for Fast Passenger Cars (Trial) and Quality Standards for Passenger Cars (No.GKY[ 1997]3 1).

13. As the basis for inspection and acceptance of 25K passenger cars and other passenger cars with speed 160km, this regulation must be seriously implemented. These Provisions shall be implemented as of the date of promulgation.

The second A 1 repair course is A 1 repair course for 25K buses: namely, safety maintenance. According to the safety requirements of passenger cars, the key safety components are replaced and other components are repaired to deal with the faulty components, restore their basic performance and requirements, and ensure the safety of passenger cars. A 1 maintenance shall be implemented for the train preparation line, and the replacement and repair standards shall be implemented for the parts replaced in the condition maintenance. See table 1 for the maintenance contents of A 1.

Table 1 A 1 Level Repair ContentNo. Repair scope Check and repair internal capacity 1 Vehicle upper state Repair steel structure, windshield, pedal (door pedal), flap device and ventilator; Wood structure and interior decoration: doors and locks, windows and glass, seats, sleepers, floors, floor cloths, luggage racks, wallboard, coat hooks; Replacement and repair of distribution valve, pressure gauge condition repair (1) brake device and gas supply system of water supply device, toilet system, washbasin and other infrastructure: air duct, air cylinder and hanger, unit brake cylinder, hose assembly, plug door, empty and loaded vehicle adjustment valve, height adjustment valve, differential pressure valve and hand brake; (2) Wheelset axle box device; (3) Bogies: hydraulic shock absorber, air spring, frame, bolster, spring joist, bolster crane, suspension shaft, traction rod, anti-roll torsion bar, cross bar, steel spring, etc. Static test of electronic anti-skid, performance test of electro-pneumatic bicycle, electronic anti-skid of air-conditioning electrical appliances, passenger information system, axle temperature alarm, lighting, socket, switch, emergency power supply, etc. After the overhaul, the new fan, dining car refrigerator, liquid level display device, pager, electric heat tracing device, electric heater, connector and seat, junction box (room), broadcast antenna, warm water tank, storage battery box, DC600V/AC380V vehicle-mounted electrical appliances, and body wiring were tested as required, and the insulation of power supply trunk and DC wiring was tested.

Three A2-level repairs: A2-level repairs for 25K passenger cars, that is, 400,000 km section repairs. Through parts replacement and condition repair by units and parts, the upper and lower parts of the car are basically restored to the technical state, which ensures the safety of the bus and improves the service efficiency of the bus. A2-level maintenance adopts the balanced maintenance mode, which uses the downtime of the garage to carry out maintenance in the maintenance line, temporary maintenance line or garage in stages, and the replaced parts are overhauled centrally according to A3-level maintenance requirements, so as to reduce downtime and ensure maintenance quality; When the parts replaced in condition repair are repaired, the replacement repair standard shall be implemented. See Table 8 for A2-level maintenance.

Table 8 A2 Level Maintenance Contents Repair Scope Repair Contents 1 Repair of steel structure, windshield, pedal (door pedal), flap device and ventilator in the upper state of vehicle; Wood structure and interior decoration; Door and lock, window and glass, seat, sleeper, floor, floor cloth, luggage rack, wallboard, coat hook; Inspection and maintenance of water supply device, toilet system, washbasin and other facilities and paint on exterior wall of car body. 2. Replacement and repair of basic parts (1) coupler buffer devices: coupler tongue, coupler tongue pin and coupler tail flat pin; (2) Bogie part: oil damper (including fastening bolts of 209HS bogie mounting seat); (3) Wheelset axle box device; (4) Braking and air supply system: foundation brake cross bolt, corner plug door, cut-off plug door, dust collector complex, distribution valve, electro-pneumatic valve, pressure gauge, anti-skid exhaust valve condition maintenance (1) coupler buffer device: condition maintenance without changing accessories; (2) Bogie part: frame, bolster and suspension device, anti-rolling torsion bar device, steel spring, suspender, suspension seat, control rod and axle box positioning device; (3) Brake and air supply system: basic brake fittings, friction plates, pin sleeves, air ducts, cylinders and hangers, valves and plugs, emergency brake valves, unit brake cylinders, brake hoses, metal rubber hoses, empty weight valves, height adjustment valves, differential pressure valves, hand brake test completion inspection, coupler three-state test, electro-pneumatic single vehicle test, electronic anti-skid static test and hand brake test. Electro-pneumatic brake connector, shaft report, electronic anti-skid device for restoring the state of electric tea stove, information display system, lighting, socket, switch, emergency power supply, control cabinet, air conditioning system, exhaust fan, waste exhaust fan, new fan, dining car refrigerator, liquid level display device, pager, electric heat tracing device, electric heater in passenger room, each connector seat, junction box (room), broadcast antenna and temperature and humidity controller.

Four A3-level maintenance: A3-level maintenance of 25K bus, that is, 800,000km section maintenance, which ensures the safe operation of the bus through extensive replacement and maintenance of key parts of the bus; Carry out high-standard state maintenance on the upper part of the vehicle, and fully restore the functions of the upper part of the bus facilities. A3-level maintenance, vehicle overhaul in the garage (factory), replacement parts detection in different places, professional maintenance, reducing downtime and improving platform utilization; When the parts replaced in condition repair are repaired, the replacement repair standard shall be implemented. See table 13 for the contents of the three-level repair.

Table 13 A3 Level Repair ContentNo. Repair Scope Repair Internal Capacity 1 Vehicle Upper State Repair Steel Structure, Windshield and Pedal (Plug Pedal); Check and maintain the conditions of doors and locks, windows and glass, seats, sleeping berths, floors, floor cloths, luggage racks, wall panels, ventilators, coat hooks, flap devices, pedals, water supply devices, toilet systems, washbasins and other facilities, repaint and mark them according to the provisions of this regulation, and conduct water pipe leakage tests after maintenance. 2. Replace the basic parts and repair (1) the coupler buffer device; (2) Bogies; (3) Wheelset axle box device; (4) Braking and air supply system: distribution valve, electro-pneumatic valve, differential pressure valve, height adjustment valve, empty and heavy vehicle valve, brake hose, metal rubber hose, valve and plug, dust collector complex, disc brake device, brake pipeline system for unit brake cylinder condition repair, air duct, cylinder and bracket, etc. , electro-pneumatic single car test, coupler three-state test, electronic anti-skid static test, hand brake function test, continued from the table number maintenance scope inspection and maintenance content 3 air-conditioning electrical parts replacement and maintenance air-conditioning system, electronic anti-skid, control cabinet, electric tea stove, emergency power supply, electric power, communication, centralized control, electro-pneumatic brake connector, axle report, dining car refrigerator off-board machine, exhaust fan, waste exhaust fan, new fan condition maintenance passenger information system, lighting, and new fan. Radio antenna, warm water tank, dining car refrigerator, battery box, DC 600V/AC 380V vehicle-mounted electrical appliances, car body wiring test, after maintenance, according to the requirements of maintenance content, car body wiring should be tested for insulation.

Design of Power Supply for 25G Bus Maintenance Ditch

Zhao Jianchuan, Jinzhou Survey and Design Institute of Shenyang Railway Bureau

Overhaul the power transformer in the gutter from the bus! Based on two main problems of lighting voltage level, this paper discusses the maintenance and repair of G-type bus gutter.

The problems existing in electrical design are discussed and compared from the aspects of technology, economy and safety, and the methods to solve the problems are put forward.

Keywords: 25G passenger car maintenance ditch power supply design ditch lighting

25G new air-conditioned buses have been put into operation one after another, and the subsequent air-conditioning power is not less than 8..kw, and the total installed power of gOOkW is equipped with three diesel engines for power generation.

There is a high demand for power supply to the car body during in-section maintenance. Our bureau manages the units, and the rated output power of each unit is 3ookw.

The basic configuration of electrical equipment in existing car depot (bus depot) is a problem that should be paid attention to in the design before speeding up.

According to the power supply capacity, it is impossible to guarantee the increased power load level of the newly added bus body ① after the speed increase.

Ground power supply _ How to reasonably determine the additional power demand according to the number of newly overhauled buses? According to the regulations, the power supply of air-conditioned passenger cars overhauled in the trench is designed according to the secondary load.

The capacity of the source is a problem that should be considered. Standard Code for Design of Power Supply and Distribution System (GBS ... Energy -9, Article 2o. , level 2.

In the technical arrangement of vehicles for trench maintenance, the maintenance workload in the trench is increased, and the power supply should be provided by two ways ... When using cable wires, two wires should be used.

In addition, higher requirements are put forward for the working environment and lighting conditions of the trench. Not only does it need a line composed of cables to supply power, but each cable should be able to withstand 00% of the first-class load. "

Organize drainage, and set working lighting within the width of 1. Zm, depth 1. Zm long and narrow "electrical design rules" article 3.o.8 a 2' secondary load should be supplied by reliable power supply. That's right.

There are also many problems worth studying in trench lighting. When there is a second power supply nearby and the connection is convenient, you can consider providing the second power supply. "

1 power supply design Because all bus sections have two power supply conditions, in order to ensure normal maintenance work,

(1) The design specification requires that the second power supply should be provided as much as possible.

New Code for Railway Electric Power Design (TB 10o08-99) (hereinafter referred to as "Determination of Power Load Factor")

Rules ") does not specify how to supply power during the overhaul of air-conditioned bus bodies; The power consumption of the new air-conditioned bus is electrothermal. The power factor is close to or equal to 1.

Code for Design of Railway Locomotive and Rolling Stock Equipment (TB 10o05-98) (hereinafter referred to as "vehicle inspection or maintenance demand coefficient K") shall conform to the design technology of railway electric power engineering.

Regulations) 3. 1. 17 stipulates that the maintenance of air-conditioned buses "should be equipped with various pipe wiring manuals (electric power)" (hereinafter referred to as "manuals"). Table 2- 1. Take .. one .. 8 The whole column is empty.

At the same time as the test of passenger car dispatching platform of Zhou Railway Passenger Car, which is an independent three-phase power supply suitable for air-conditioned passenger cars, the power consumption synchronization coefficient k should be taken as ... 8.

Equipment design specification (1September 1999) (hereinafter referred to as "passenger car design rules") ... 9 If multiple air-conditioned bus units are tested at the same time, the coefficients are at the same time.

In article 3.3. 17, it is required that "the external electric quantity KE of the air-conditioned bus vehicle maintenance line shall be ... 1.9".

The power supply capacity should meet the requirements of simultaneous testing of the whole air conditioning unit, and the power supply box is located in the selection of power transformer.

The end of the maintenance station "... When the existing bus section or bus maintenance station is rebuilt, due to the need of transformation,

(2) The bus power supply device has a large capacity, so a transformer specially designed for air-conditioning bus maintenance should be set separately as far as possible.

It is understood that the length of the whole air-conditioned bus varies according to the number of trains, and the maximum number of trains of air-conditioned bus starts from the equipment. According to the demand coefficient and simultaneous coefficient of ②, an air-conditioned bus is 18.

The 25G air-conditioned car body composed of auxiliary car body is an instantaneous car body with power supply voltage rating unit. Each car is calculated as 48A, and the whole train needs 8 Hua ... 8769 pull power.

It must be AC three-phase 38, that is, 220v, 50Hz. The rated current of each vehicle is 48 A, and the normal test of air conditioning units can only be guaranteed by forced power supply: therefore, 1 500 is needed.

There are two distribution trunk lines on each car body, and the three-phase lines of each trunk line are powered by three kvA transformers respectively.

The zero line of the parallel line in the sentence M is 1 70mm "line, and the economy of power supply transformation is discussed with the protection line (PE). A set of numbers in the table 1 can be used to give

The metal car body is connected by total equipotential bonding. The two trunk lines are placed on both sides of the car body. It was explained that the data in the table were adjusted when designing ditches for the preparation of express trains at passenger technical stations.

There are four special three-phase four-wire sockets at both ends of the car body (KC20 power supply connection to check the actual situation

Device) is 25 (; Power generation capacity of KD25G air-conditioned bus.

Table 1 False Investment Table

Preface}} Project} Civil Engineering 1} Piezoelectric Cable Arrays for Power Equipment, 1 _ Remarks 1 Talents/Li Wu

1

Renovation of existing substation/ten thousand yuan}1.1}}121one for the whole section.

Add 3 low-voltage cabinets to regular chess or t}som, 1} and replace them with 1...kvA transformer }0.skm}4km}300kVA and 1...TLKVA.

,

There are 893 new substations nearby, each with a total price of RMB10,000.00 yuan, for the use of art SG.

The scale or quantity is 12.m, including one} three high-voltage cabinets, five low-voltage cabinets and two: one for 00kvA transformer Zkm05km} _

There is a box-type substation nearby; 35 per 10,000 yuan; 25G each.

A foundation pit: ... KVA and 2 km -0.5 in m-1.

Note: This table is compiled according to the simultaneous power supply of two air-conditioned bus units. The estimated figures all consider the capacity increase of 500kVA, and the capacity increase fee is not listed.

The transformation of existing substations is often limited by geography and topography, and there are not many new substations nearby, which saves civil engineering costs and is welcomed.

Box-type substation may not have a suitable location, because of its small size, reactive power compensation is usually needed.

Wanfang Data

Power supply design of 25G passenger car maintenance ditch

According to the previous analysis, the electricity consumption of 25G air-conditioned buses is electrothermal, and the power

The factor is close to 1, so reactive power compensation is not needed.

Selection of low voltage side switch of transformer

Because the air-conditioning car body does not decompose and unhook when it is overhauled on the ground, the pressure is changed.

The low-voltage side switch of the device is per train 1 loop, and the rated current is relatively large. Therefore, in the selection.

When the low-voltage side switches, it is recommended to choose an intelligent low-voltage circuit breaker with a microprocessor, which

Class A circuit breaker with 4-stage protection has long delay, short delay, instantaneous and grounding faults.

Protection, setting current and action time can be adjusted in a wide range, especially

Detecting zero-sequence current and setting protection are similar to traditional low-voltage circuit breakers.

In contrast, adding ground fault protection is a great progress, which is very important for the safety of distribution system.

Integrity is very beneficial.

As the safeguard means of railway transportation system, the maintenance ditch of air-conditioned passenger cars is powered by power supply.

Therefore, ensuring power supply will be the guarantee of the future.

Prerequisites for licensed transportation

Grounding and single-phase grounding protection

Direct connection of 380/220 V neutral point in the design of maintenance ditch power distribution project

Ground distribution system. The 1 1 system should be selected, because diesel oil will be produced when the train runs normally.

Motor power supply, the "ground" in the system is essentially the body. Car parking maintenance, divided into

Do not protect the grounding zero line of the distribution box on the ground of the maintenance ditch on the transformer side and the power supply side.

(\) and protective ground wire (PE) are not used together to form TT system.

In the design, attention must be paid to the ground fault protection of TT system distribution lines.

Meet the following requirements:

R.ai, the town is 50 volts.

Where r is the grounding resistance of the exposed conductive part of the electrical device, J2;

Several-the current that makes the protective appliances operate reliably within the specified time, a,

2 Maintenance ditch lighting design

Because the maintenance work under the air-conditioned bus body needs lighting, combined with the maintenance work

In fact, the lighting should be placed on the side wall of the maintenance ditch. How to choose?

Users often have different opinions on voltage grade, specification and design.

The lighting voltage level of vehicle maintenance ditch is not specified, only in

-.4.3, which stipulates that "for the fixed type which is easy to touch and has no electric shock prevention measures".

Or move the lamp, the installation height is 2. Zm≤ off the ground, and has the following

Under the condition of one train, its working voltage should not exceed 24v；; 1 Particularly wet place 2

The high temperature place 3 is a place with conductive dust; There is conductive grounding at 4 places. "

There is no specific regulation on lighting in "one car, one regulation". Article 3. "Passenger Vehicle Regulations" 3. 12 stipulates "inspection"

Check that the trench should have good drainage and low-voltage lighting facilities. " There is no sign of low voltage.

Specific level. Comply with Chapter 7 "Low Voltage Distribution and Electrical Equipment" of "Electrical Code"

Let's take a look at low voltage, which generally refers to 500 volts AC and below. In the electrical design of civil buildings

Low-voltage power distribution refers to "power frequency" in chapter 8 of JJ/T16 92 "Electric meter specification.

Distribution design below AC 1 000 V "(8. 1. 1).

According to the above specifications, two lighting modes can be selected to maintain the trench.

One is to configure a safety transformer to reduce the voltage below 24 V, and the other is to use it normally.

For 220 V lighting equipment, take measures to prevent electric shock, such as using enclosed lamps.

Install leakage protector at the power supply end. In the actual design, according to the user's intention

Look, there are two groups of lights in the inspection ditch wall under each car body, each group.

Lamp spacing13-o 25 (; The length of air-conditioned bus body is 26.7 1 m, which is required for 18 cars.

480 meters long maintenance ditch. Technical and economic measures should be taken to set up 24 V lighting in a long distance.

Economic aspects are determined after comparison.

According to the design of 24 V circuit, the voltage drop of incandescent lamp is cos0 = I e conductor.

According to manual calculation, the results are shown in Table 2.

Table 2 Selection Table of Copper Conductor Section in 5% Voltage Drop of 24V Line (C = 0. 144)

Number/group of lamps-1-23-1'{5-1; An 8},

Distance /m- 1 13.526. : 1 139.: 52.565.578.59 1.5 105- 1 18.

Power//kW one by one ..., ...1} 0.1o1t].1} "1}1},

Load torque-1.35-114-17.9513.219.8-127.6-36./kloc-. 259.

The calculated value s 211.115.6}118332-4-1. , 65.5438+0.9. 1000000000 1

Y, fi value 2, 1 12.5 1 15 1 } 16 1 125 13: 1} 5. 1 17095

Verify nL'/Y,113.814.1} 3-51137 391} 3- , 43

According to Table 2, using 16 mm' conductor, each safety transformer can be equipped with two faces.

Load of 5 sets of lamps. Maintenance of Safety Transformer with Length of 500 VA. 980 m

The ditch * * * needs 8 safety transformers. 25 mm wires are used, and each wire is completely modified.

The device is equipped with a lamp group and needs four 1 000 VA safety transformers. Both schemes are necessary.

It is necessary to add nearly 400 m of low-voltage cables. Moreover, in the 24 V lighting system, you can only choose

Using incandescent lamp as light source can not achieve the effect of green lighting. Although the voltage of 24 V

The grade is safe voltage, but in terms of technology and investment, this situation uses 24.

V lighting is not ideal.

When using 220 V lighting, enclosed lamps should be used for safety protection.

The grade should reach IP55, so that vehicle maintenance personnel will not touch it unconsciously at work.

To the live part of lamps and lanterns and cause an electric shock accident; At the same time, install rated leakage on the power supply side.

Operate the leakage circuit breaker with a current of 30a to ensure that the leakage exceeds 30a.

When current flows, the circuit can be reliably disconnected, and personal safety will not be harmed.

When using the leakage circuit breaker, we must pay attention to the selection of products certified by the national electrician.

(CCEE) products. Economically speaking, a lamp with a voltage of 220 V is relatively easy to choose.

16 mm conductor is used for the conductor within the length of 480 m, and the voltage drop can be controlled in May.

Compared with the 24 V distribution mode, the safety transformer is omitted, and the low-voltage cable lighting source also

You can choose green light sources with high luminous efficiency and long life, such as high voltage.

Sodium lamp, etc. To protect the environment and save energy.

3 Conclusion

When dealing with special power supply problems such as maintenance ditch of air-conditioned passenger cars, we should first

Determine its load level, analyze its load nature, correctly select various coefficients, and provide

Comprehensive comparison of electrical schemes is the only way to make a better design and overhaul the trench.

The design of lighting is the same, and the decision should be made after technical and economic comparison.