MWAPE KAMPILIMBA FINAL REPORT

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CONTENTS

1) PRODUCTION AT THE NCHANGA SMELTER………………….2 2) POWER DISTRIBUTION…………………………………………...3 THE 11kV SYSTEM………………………………………………....3 THE 33kV SYSTEM………………………………………………....6 3) PREVENTIVE MAINTENANCE…………………………………....7 MONTHLY PM……………………………………………………....7 QUARTERLY PM……………………………………………………8 4) PREVENTIVE MAINTENANCE ON EARTH PITS………………..8 5) TYPES OF STARTING CONNECTIONS AT THE SMELTER…...10 STAR CONNECTION OF THE MOTOR WINDINGS…………....11 DELTA CONNECTION OF THE MOTOR WINDINGS………….11 6) ELECTRICAL IMPROVEMENTS AT THE SMELTER…………..13 7) TROUBLESHOOTING …………………………………………….15 REFERENCES

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PRODUCTION AT THE NCHANGA SMELTER

This is a very complex process in which copper, acid and cobalt alloy is produced, the concentrate comes from a lot of different places namely the underground and other sources given the current situation where the underground section has been put on care and maintenance meaning no mining is going there. The process starts by sending the concentrate via a very efficient conveyer system to the steam dryer where the concentrate is dried by the use of steam, after the drying process the concentrate is later transferred to the flash smelting furnace (FSF) where the process of smelting starts from by the use of oxygen from the oxygen plant together with other fuels necessary for flash smelting. Three main resultants come from the FSF namely blister, sulphur dioxide and FSF slag. The blister is later sent to the anode furnaces for the production of copper anodes which are later sent to the refinery for the production of copper cathodes generally known as copper. The sulphur dioxide is transferred to the acid plant for the production of sulphuric acid and the slag is later processed for the extraction of colbalt alloy in the cobalt recovery furnaces and the remaining blister is transferred to the anode furnances while the waste is later passed on as granulated slag. The flow sheet below illustrates the full process at the nchanga smelter

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POWER DISTRIBUTION An electric power distribution system is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. In this situation the final stage of transmission is when the electricity reaches the smelter where it is later stepped down and distributed to other substations for use. The smelter has 5 main substations namely substation 1(SS1), (SS2), (SS3),(SS4) and (SS6). The lack of SS5 was due to planning issues when the smelter was being constructed given the smelter is a modern day plant that was completed and commissioned in 2008. All the power comes from ZESCO the biggest energy company in Zambia, later the power is regulated by the Copperbelt Energy Cooperation (CEC) inorder to give a more stable form of electricity to KCM. CEC have 2 substations around KCM namely Avenue and Stadium. The Avenue Substation steps down 66/11kV and distributes it to SS1 where it is later distributed to other substations THE 11kV SYSTEM

11kV incomers from Avenue to SS1 The Avenue substation steps down 66/11kV using two 20MVA and three 15MVA thus feeding SS1 through 4 incomers namely I/C1, I/C2,

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I/C4 and I/C5. I/C3 has been rerouted to TLP, thus leaving SS1 with 4 incomers . SS1 has BUS A,B,C,D,E and F with BUS E and F having been equipped with all the emergency loads incase of a power failure. Each substation has two transformers, a main transformer and a back up transformer that kicks in whenever there is a power failure. The back up transformer gets its power from the Diesel Generators (DG) which becomes operational 3-4 secs when the power from CEC has a fault. Basically when power is limited in I/C4 and I/C5 a signal is sent to the main control system that authorizes the opening of B/C 4 and the closing of bus section B/C5 that’s after 2 or more DGs are operational thus supplying power to the loads that are on bus E and F which mainly are used for cooling and lighting. This is because the DGs can only produce up to 8MW when running at full capacity thus can not sustain the full load of the smelter in turn can only manage to run a few loads, the critical loads Switching on and off of equipment in the 11kV is done by using a vacuum circuit breaker which can be seen in the picture below

VACUUM CIRUIT BREAKER

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11kV BUS E

The above figure illustrates emergency bus E with bus section B/C4 and B/C5. It also shows incomer 4 (IC4) and the loads on bus E The figure below shows emergency bus F where a capacitor bank, loads on bus F and all the emergency transformers namely 12,14,17,19,21 and 23 are located. All these emergency transformers get their power from the diesel generators (DGs) when there is a power failure. Power failures are categorized in numbers, the worst of them is known has category 3 (cat 3). A category 3 power failure is when there is a nation wide blackout. That’s when the DGs kick in automatically like explained earlier. When there is insufficient power in I/C4 and I/C5 a signal is relayed to the main control panel which authorizes the DGs to start running inorder to provide power to the loads that need power at all times. The main control panel is always on thanks to an effective UPS system

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11kV BUS F

THE 33kV SYSTEM

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The 33kV system gets its power from the CEC Substation called stadium where power is stepped down 66/33kV with a current rating of 1250A and fed to substation 2 SS2 at the smelter via I/C1 and I/C2 which is equipped with sulfur hexafluoride circuit breakers. There onwards power is fed to the electric furnaces transformers namely Slag cleaning furnaces (SCF) and Cobalt recovery furnace (CRF) transformers. The CRF furnaces are on the 33kV bus A system and the SCF on bus B. The electric furnaces use transformers that step down the voltage from 33kV/0.32kV using two 15 MVA transformers for the Cobalt recovery furnace and one 20MVA transformer for the slag cleaning furnace. The transformers step down 33kV/0.32kV producing up to 46kAmps. The current increases substantially in-turn using the current heating effect for slag cleaning and cobalt recovering. The 33kV system is also used to supply power to some auxiliary equipment, mainly pumps, cooling fans etc around the electric furnaces. Their motor control centre (mcc) and (pmcc) power motor control centre for bigger equipment are located in respectable substation

PREVENTIVE MAINTENANCE Preventive maintenance in KCM is a procedure carried regularly to ensure equipment around the plant stays in tiptop condition. Maintenance at the smelter electrical department can be broken down in 2 parts, namely quarterly pm and monthly pm. Monthly pm is carried out once a month and quarterly pm is carried out every after a 3 month period hence the name quarterly.

MONTHLY PM Mainly there is checklist with procedures that need to be followed for example, the characteristics of a monthly pm on a motor rated 185kWatts, RPM 1475 on the motor side there is need check motor and local pushbutton station cleanliness, check for slip ring cleanliness, check for carbon brush worn out, check for power & control cables cerawool covering, check for motor TB & JB sealing properly, check for bed bolt tightness and earthing cable tightness, observe for smooth run/no noise. On the panel side not much work is done, mainly check for the feeder/module cleanliness, check for spare gland holes sealed properly, observe for any burnt out/Terminal colour change, check for SFU handle operation and check for indication lamps (ON, OFF, TRIP, etc)

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QUARTERLY PM The quarterly checklist has everything that can be found on the monthly pm checklist and more tasking procedures that cant be done everytime you carry out preventive maintenance. Example of a quarterly pm checklist on a motor air compressor (MAC) B filter fan motor in the oxygen plant is as follows, the first thing that can be done on the motor side is checking for power cable tightness, earthing cable tightness, check for power cable tightness at jbs , check for motor space heater cable tightness. So basically what needs to be done is to check for tightness on all cables on the compressor. Also check motor and local pushbutton station cleanliness, check for slip ring cleanliness, check for carbon brush worn out, check for power & control cables cerawool covering, check for motor TB & JB sealing properly, check for bed bolt tightness On the panel side check for power cable tightness, control cable tightness, check for main contactor fixed contactor tightness, check for moving contact spring tension, check for main & moving contacts cleanliness. There is also need to check for feeder/module cleanliness and observe for any burnt / terminal colour change, check for SFU handle operation and also check for indication lamps (ON,OFF TRIP etc) These are the tests that need to be carried out during the quarterly pm schedule. The most vital of all the procedures is checking for Insulation Resistance Test that is carried out using an insulation resistance tester commonly known as the megger. The first step is to carry out an IR test with the power cable and motor together Red phase-Earth, Yellow phase-Earth and Blue phase-Earth. If the insulation is ok the megger will show give an infinite reading. The same procedure is repeated with the control cable and the motor without the control cable. These are examples of the procedures set up by KCM to ensure all the equipment is tip top condition at all time PREVENTIVE MAINTENANCE ON EARTH PITS The main reason for doing earthing in electrical networks is for safety. When all metallic parts in electrical equipment are grounded then if the insulation inside the equipment fails there are no dangerous voltages present in the equipment case. What makes earthing work are earth pits below shows an illustration of an earth pit

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EARTH PIT

Preventive maintenance is carried out on earth pits by the help of an instrument known as an earth tester that checks the resistance of the soil. The earth resistance test is done by using a 3 point system test In this method earth tester terminal P1 and P2 are shorted to each other and connected to the earth electrode (pipe) under test. Terminals E1 and E2 are connected to the two separate spikes driven in earth. These two spikes are kept in same line at the distance of about 25 meters due to which there will not be mutual interference in the field of individual spikes. After the tests are carried out the resistivity should be at its minimum so that the soil should be able to conduct any over current for safety purposes, it is the resistance of soil to the passage of electric current. The earth resistance value (ohmic value) of an earth pit depends on soil resistivity. It is the resistance of the soil to the passage of electric current. To reduce the resistivity, it is necessary to dissolve in the moisture particle in the Soil. Some substance like Salt/Charcoal is highly conductive in water solution but the additive substance would reduce the resistivity of the soil, only when it is dissolved in the moisture in the soil

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after that additional quantity does not serve the Purpose. And make sure all Oxidation is removed from joints and joints should be tightened

EARTH RESISTANCE TESTER

TYPES OF STARTING CONNECTIONS AT THE SMELTER The objective of star-delta connection is this starting method is used with three-phase induction motors, is to reduce the starting current. In starting position, current supply to the stator windings is connected in star (Y) for starting. In the running position, current supply is reconnected to the windings in delta (∆) once the motor has gained speed. As the name suggests, direct-on-line starting means that the motor is started by connecting it directly to the supply at rated voltage. Direct-on-line starting, (DOL), is suitable for stable supplies and mechanically stiff and well dimensioned shaft systems – and pumps qualify as examples of such systems. Direct-on-line (DOL) starting motors only require adequate

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motor protection, whereas star-delta starting implies a more complex circuitry composed of several relays and contactors. The following two images demonstrate the different possibilities for electrical connection:

The following images show the electrical circuitry of the three motor windings and their phase voltages

STARCONNECTIONOFTHEMOTORWINDINGS

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DELTA CONNECTION OF THE MOTOR WINDINGS

As shown in the above illustrations, the difference in connections is not just limited to the different circuitries, but also in the resulting voltages of the windings. Where as in the DOL connection the windings are supplied by the voltage they are designed for permanently, the STAR connection is operated at a voltage reduced by the factor √3. Following principles result from this, which have to be respected by all means for a continuous operation of a STAR-DELTA motor

The motor-current (Amps) of a STAR-DELTA motor during start (IҮ) is reduced roughly by factor 0,58; a motor with a nominal starting current of 550A will consume only 317 A in STAR – connection. This fulfills the requirement of a current reduced start. The available mechanicalperformanceontheshafttodrivethepumporwhateverequipmentisbeingrun, isalsoreducedto1/3of thenominalperformance.Toavoid an overloading of the motor, it is necessary to observe thepowerdemandoftheequipmentduringstartupincomparisonwiththestartcurrentofthemotor.

The available shaft torque (MҮ) also reduces while start to 1/3 of the nominal torque. This also raises the necessity, to compare the demanded starting torque of the equipment to the available torque of the motor, and to do the right selection.

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THE ADVANTAGES OF STAR DELTA CONNECTION Normally, low-voltage motors over 3 kW will be dimensioned to run at either 400 V in delta (∆) connection or at 690 V in star (Y) connection. The flexibility provided by this design can also be used to start the motor with a lower voltage. Star-delta connections give a low starting current of only about one third of that found with direct-on-line starting. Star-delta starters are particularly suited for high inertias, where the load are initiated after full load speed.

ADVANTAGES OF DOL

DOL starting is the simplest, cheapest and most common starting method. Furthermore it actually gives the lowest temperature rise within the motor during start up of all the starting methods.

ELECTRICAL IMPROVEMENTS AT THE SMELTER At the smelter the electrical department is slowly moving over to a more complex and efficient way of starting equipment by the introduction of a soft start device. This device ensures smooth starting by torque control for gradual acceleration of the drive system thus preventing jerks and extending the life of mechanical components. It also helps in the reduction of the starting current to achieve break-away, and to hold back the current during acceleration, to prevent mechanical, electrical, thermal weakening of the electrical equipment such as motors, cables, transformers & switch gear. A motor soft starter is a device used with AC electrical motors to temporarily reduce the load and torque in the power train and electric current surge of the motor during start-up. This reduces the mechanical stress on the motor and shaft, as well as the electro dynamic stresses on the attached power cables and electrical distribution network, extending the lifespan of the system. It can consist of mechanical or electrical devices, or a combination of both. Mechanical soft starters include clutches and several types of couplings using a fluid, magnetic forces, or steel shot to transmit torque, similar to other forms of torque limiter. Electrical soft starters can be any control system that reduces the torque by temporarily reducing the voltage or current input, or a device that temporarily alters how the motor is connected in the electric circuit. Soft starters can be set up to the requirements of the individual application. In pump applications, a soft start can avoid pressure surges. Conveyor belt systems can be smoothly started, avoiding jerk and stress on drive components. Fans or other systems with belt drives can be started slowly to avoid belt slipping.. In all systems, a soft start limits the

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inrush current and so improves stability of the power supply and reduces transient voltage drops that may affect other loads. Like seen at the smelter acid plant, a blower of rating 1850kW using a soft starter system to enable the blower starts smoothly avoiding any pressure surges. The pictures below show examples of a soft starter for the 4650kW blower found at the acid plant. The soft starter is located inside of Substation 6 (SS6)

SOFT STARTER FOR 4650KW BLOWER

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4650 kW BLOWER AT THE ACID PLANT

TROUBLESHOOTING Troubleshooting in electrical engineering means tracing, finding and rectifying a fault in an electrical system. In a complex electrical system at the smelter it is inevitable not to have problems. We face enough challenges but we have enough competent people to tackle any problem that can come alone the way. One of the most common troubleshooting techniques taught to technicians is the so-called “divide and conquer” method, whereby the system or signal path is divided into halves with each measurement, until the location of the fault is pinpointed. However, there are some situations where it might actually save time to perform measurements in a linear progression (from one end to the other, until the power or signal is lost). Efficient troubleshooters never limit themselves to a rigid method if other methods are more efficient. Here is an example of troubleshooting encountered at the smelter by the lighting crew. An electrician is troubleshooting a faulty light circuit, where the power source and light bulb are far removed from one another

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As you can see in the diagram, there are several terminal blocks (“TB”) through which electrical power is routed to the light bulb. These terminal blocks provide convenient connection points to join wires together, enabling sections of wire to be removed and replaced if necessary, without removing and replacing all the wiring. The electrician is using a voltmeter to check for the presence of voltage between pairs of terminals in the circuit. The terminal blocks are located too far apart to allow for voltage checks between blocks (say, between one connection in TB2 and another connection in TB3). The voltmeter’s test leads are only long enough to check for voltage between pairs of connections at each terminal block. In the next diagram, you can see the electrician’s voltage checks, in the sequence that they were taken

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Based on the voltage indications shown, you can determine the location of the circuit fault. The fault is located somewhere between TB3 and TB4. Whether or not the electrician’s sequence was the most efficient depends on two factors not given in the problem. The distance between terminal blocks and the time required to gain access for a voltage check, upon reaching the terminal block location. Another of problem encountered at the smelter that needed troubleshooting was with SCF bottom cooling fans. The problem was that the earth leakage relay kept showing signals of an earth leakage in turn resulting in the bottom cooling fan going off. So we had to troubleshoot by carrying out a continuity test. A continuity test is a test carried out to determine weather they are any cables touching thus a complete pathway for electric current. So we had to start from the power source to the VFD valuable frequency drive. The circuit showed continuity, we later tried to carry out continuity from the VFD to the motor, the circuit showed continuity. The diagnosis was that the earth leakage relay malfunctioned and that it had to be replaced. The image below shows an example of valuable frequency drive that can be found at the smelter

VALUABLE FREQUENCY DRIVE

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REFERENCES

1) http://en-us.fluke.com/training/training-library/test-tools/digital-multimeters/digital-multimeter-fundamentals.html

2) Substation 1 SCADA system 3) http://www.allaboutcircuits.com/worksheets/basic-troubleshooting-

strategies/ 4)http://www.controleng.com/troubleshooting/62b50ab77c8fcb3.html