OPERATING MANUAL FOR AUTOMATIC C. P. RECTIFIER

Index sheet

PAGE NO.

1.0 GENERAL DESCRIPTION 3

2.0 BRIEF TECHNICAL SPECIFICATIONS 4

3.0 OPERATION OF THE UNIT 6

4.0 CIRCUIT DESCRIPTION 7

5.0 INSTALLATION 9

6.0 TESTING AND COMMISSIONING OF THE UNIT 10

7.0 FINAL SETTINGS 11

8.0 MAINTENANCE AND FAULT FINDING 12

9.0 BILL OF MATERIALS 13

- DRAWINGS

a) General Assembly Drawing for Rectifier b) Circuit diagram for Rectifier c) Wiring diagram for Rectifier

1.0 GENERAL DESCRIPTION

1.1 CorrosionUnderground and underwater corrosion of all metallic surfaces is basically an electrochemical phenomenon, in which different parts of the structure undergoing corrosion act as electrodes, while the surrounding soil or water act as electrolytes. A difference of potential is set up between two parts of the submerged underground metallic structure due to varying conditions of electrolyte like difference in temperature, salt content, oxygen availability, moisture, etc. This difference of potential acting between different parts of the structure sets up a flow of galvanic current between these parts. The current set up this way causes corrosion. At the points at which these galvanic currents emanate, the metallic ions react and get dissolved into the electrolyte, leaving pits and causing leaks on the surface of the metal.

1.2 Prevention of corrosion by cathodic protectionThe corrosion of submerged metallic structures which takes place due to electrolytic action as explained above can be prevented by counter-acting the galvanic corrosion currents by means of superimposed DC currents using an external DC source. Thus, when direct current is applied to a submerged/underground structure with a polarity which opposes the natural galvanic current and is of sufficient magnitude so as to polarize all the anodic area, corrosion is prevented. This forms the basis of impressed current cathodic protection system. However, the current required to provide complete protection depends on various conditions in which the structure operates. For example, a ship may ply with different drafts in water of varying salinity and temperatures and with varying speeds in different sea water velocity. Thus the current value to protect such ships has to be varied continuously. The amount of current so impressed has a bearing on the degree of protection to the structure. If the current impressed is higher than the required value, there is a risk of damage to the protective coating, while if the current is lesser than the required value, the structure would be partially protected.

Thus to obtain the optimum level of protection under varying conditions, it is necessary to vary the impressed current continuously so as to maintain a constant level of protective potential at the structure. This continuous monitoring and control can be achieved by providing an automatic control for the cathodic protection system.

The ACTechno Automatic Cathodic Protection rectifier accomplishes this by monitoring the structure to electrolyte potential with respect to a reference electrode continuously adjusting the impressed current to maintain the structure to soil potential at a preset optimum value. This potential is kept constant under varying conditions of soil/water, temperature, stray currents, etc., thus providing the desired protection to the structure.

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2.0 BRIEF TECHNICAL SPECIFICATIONS

A. Electrical Characteristics1.1 AC Input Voltage 230V 10%, 1 Ph., 60Hz, AC

1.2 AC Input Current 6.0 A Max. 1.31.3 DC Output Voltage 0 to 10 V

1.4 DC Output Current 60 A.

1.5 DC Power Output 600 Watt.

1.6 KVA Rating of the Transformer 1000 VA

1.7 Full load efficiency of the unit About 70 %

1.8 Ripple Less than 5% at rated load

B. PROTECTION2.1 Factor of safety for Diodes/Thyristor Voltage - 300% factor of safety

PIV - 1200V min. Current - 300% factor of safety

2.2 Insulation Level 2000 Volt for 1 minute.

2.3 Wound Components - Insulation Class - Overload Capacity

Class ‘F’25 %Over loaded with rated load for 1 Hour

2.4 Surge Diverters for diodes/Thyristors MOV / capacitors / R-C Networks

2.5 Protection 2 pole MCB in AC input. HRC fuses in input & output.Glass cartridge fuses in the live line of all lamps, Auxiliary power lines to control circuit. Fast acting electronic overcurrent limit circuit & short ckt. protection for output. All reference fail indication and automatic setting of DC O/P voltage to preset value under this condition.

2.6 Lightning Arrestor (Input & Output)

RMS Voltage :- 500 VRMS Current :- 5.0 KAImpulse Discharge Current :- 10 KA

C. CONTROL ELEMENT3.2 Control Element The DC O/P will be controlled using latest solid

state Thyristor. These Thyristors will be controlled by the commands from the electronic circuits. All the electronic circuits will be assembled on plug-in type, glass epoxy control cards.

3.3 Mode Of Operationa) CVCC mode: In this mode the unit can be operated in either

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constant voltage (CV) mode or constant current (CC) mode. The DC voltage will be adjustable from 0 to rated value by means of a stepless voltage setter potentiometer.The DC current will be adjustable from 0 to rated value by means of a stepless current setter potentiometer.

3.4 Voltage Setting RangeAccuracy

0 to 10 V DC 0.25V

3.5 Current Limit setting RangeAccuracy

0 to 60 A 0.5 A DC

D INDICATION & METER4.1 Indications :

(LED’S are 5mm)1) ‘AC Input ON’ (22.5ø)2) Current Limit

4.2. Meter : Analog 96 x 96 (Accuracy 1.5%)

DC O/P Voltage : 0 to 20 VDC O/P Current : 0 to 100 A (75mV)

E. CLASSIFICATION & SERVICE5.1 General

TypeArea

AC Operated Auto Rectifier UnitNon Hazardous

5.2. Cooling Natural Air Cooled – IP55

5.3 ServiceLocationMinimum AmbientMaximum Ambient

Outdoor+5 ⁰C+ 55 ⁰C

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3.0 OPERATION OF THE UNIT

As indicated earlier, the unit can be operated in a single mode :

a) Auto Mode (CVCC Mode)

3.1 Auto ModeIn this mode the unit can automatically control the set voltage and current. In this mode DC output voltage feedback is provided through potential divider chain of resistances on the MB01. The output voltage of the unit can be set anywhere from 0V to the rated value by means of the potentiometer marked DC VOLTAGE SET. The unit then maintains this voltage within +0.25V of the set value for full change in output load and full change in Mains input voltage within the specified limits.The current limit can also be set anywhere from 0 to rated current by means of the potentiometer marked OVERCURRENT SET. Whenever the load current tries to exceed the set limit, the unit automatically goes from constant voltage mode to constant current mode and maintains the current within ±0.5 Amp of the set value under all conditions. The indication for current limit operation is provided by means of the LED marked CURRENT LIMIT.

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4.0 CIRCUIT DESCRIPTIONReference has to be made to the circuit diagram and wiring diagram to follow the description and working of the circuit. Basically, the entire circuit can be divided into two parts:a) Main Power Circuitb) Control and Alarm Circuit

4.1 Main Power CircuitThe input to the unit is brought by 1 phase AC wires through the Gland plate. The input cable is terminated at terminals marked A.C. Input. Through the HRC fuses F1, the input lines go to ON-OFF circuit breaker MCB1. The 230V LED lamp LP1 indicates the presence of AC power. The lightning arrestor LA1 is put in the lines to protect main SCRs from transients. The supply lines then go to the Main Transformer TRM.

In the Auto Mode, the secondary output from Transformer TRM is rectified and controlled by a rectifier consisting of SCR1/2 & Diode D1/2. These SCRs/Diodes have been provided with surge suppressors consisting of RC across them for protection against transients.

The output of rectifier is filtered through a single section L-C filter which consists of inductor L1 and filter capacitor bank C1. This filter reduces the RMS ripple content in the DC output voltage to less than 5% at rated load. Resistance RB1 is a bleeder resistance which is used to discharge the filter capacitors. The meters V1 & A1 read output voltage, current & Reference Potential respectively. The filtered output is then connected to anode through HRC fuse F2 and cathode leads. A 2 Pole, DC output ON/OFF MCB, MCB2 has been provided in DC output to isolate the DC output from anode bed if required. This MCB also protects the unit from overloads on the output side. The current feedback for overcurrent control is taken from shunt SH1. The lightning arrestor LA2 connected in DC output protect the unit from transients appearing on DC side.

4.2 Control and Alarm CircuitsThe entire control circuit of the unit has been assembled on printed circuit card which is plugged into sockets for ease of maintenance. The control circuit consists of the following:1) Pulse Driver Card : Control Card Type PDC 2) Firing Card : Control Card Type CVC

A brief description of the functioning of this card is given including the working of the various alarms in the system.

4.2.1 Functioning of Control Card

1. PULSE DRIVER CARD - Control Card type PDC

This card is mounted inside the unit on the L.H.S. side base plate in the top section of the unit. This card amplifies the pulses produced by the firing card to a level required for reliable and steady firing of the power SCRs SCR1/2. This card also provides isolation between the pulses produced by the firing card and the gates of the main SCRs.

Two separate LEDs have been provided on this card to indicate pulse output from this card to individual SCRs.

2. FIRING CARD - Control Card Type CVC

This card generates the line synchronized pulses required to trigger main SCRs SCR1/2 connected in the rectifier configuration in the secondary side of the main transformer TRM. The firing card receives its control signal from the potentiometer P1.The pulses produced by the firing card are synchronized to main AC cycle by using synchronizing circuits. The position of the synchronized pulses with respect to the start of each line half cycle is governed by the control voltage. Thus, by changing this control voltage, the firing angle of the main SCRs SCR1/2 can be changed, which in turn gives rise to control of the rectified output

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voltage, thereby controlling the DC output voltage of the unit. Thus it can be seen that the DC output voltage of the rectifier can be directly controlled by the control voltage fed to the firing card. Two LEDs have been provided on this card to indicate normal functioning of the card. The green LED indicates that the card is energised while the red LED (normally dimly lit) indicates the presence of pulses generated by the card.

4.3 ALARMS & INDICATIONSThe following alarms and indications have been provided.

1. MAINS ONThe 230V LED lamp LP1 mounted on the front panel labeled MAINS ON provides MAINS ON indication. A glass fuse AF2 has been provided in the lamp circuit for protection against short circuiting of the lamp.

2. CURRENT LIMITThe 'CURRENT LIMIT' indicator LED LD1 mounted on the front panel is energised whenever the DC output current reaches the current limit set. The unit then goes in constant current mode and maintains the current at the limit value irrespective of changes in MAINS voltage and load resistance. Whenever the current falls below limit value, the unit automatically comes out of the constant current mode and the CURRENT Limit indicator LED is turned OFF. It may be noted that, the CURRENT Limit indication is not a very precise indication and a difference of about 3A to 5A may exist between actual point of current limit and the current level at which the CURRENT Limit LED turns ON.

4.4 METERING AND CONTROLSA brief description of various indicating instruments and controls provided in the panel is as under:

1. D.C. OUTPUT VOLTMETERThe voltmeter V1 labeled 'D.C. VOLTAGE' reads D.C. output voltage. This voltmeter has been provided with ON/OFF toggle switch TSW1 and glass fuse AF3.

2. D.C. OUTPUT AMMETERThe ammeter A1 labeled 'D.C. CURRENT' reads DC output current. This ammeter has been provided with ON/OFF toggle switch TSW2.

4. OUTPUT VOLTAGE SETTER POTENTIOMETER

The potentiometer P1 marked 'O/P VOLTAGE SET' can be used to set the DC output voltage to desired value in the Auto mode of operation. The setting range provided is from 0V to rated DC O/P Voltage.

5. OVERCURRENT SETTER POTENTIOMETERThe potentiometer P2 marked 'OVERCURRENT SET' can be used to set the DC current limit to desired value. The current limit set by this potentiometer comes into effect in Auto mode. The setting range provided is from 0 Amp to the rated value.

6. MAINS ON/OFF CIRCUIT BREAKERThe 2 pole miniature circuit breaker MCB1 mounted on the front panel, labeled MAINS ON/OFF can be used to switch the AC supply to the unit ON and OFF. This MCB also protects the unit from overloads.

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5.0 INSTALLATION

5.1 The unit may be installed indoors on a suitable foundation. For foundation details, please refer GA Drg.

5.2 The cable entry into the unit is to be taken through the gland plate through suitably sized cable glands.

5.3 After taking the unit to the site, carefully inspect the outside of the unit and check for transit damages. Open the front and back doors of the unit and visually inspect the inside of the unit carefully. Check all the components inside to ensure that there is no damage in transit. Tighten all connections.

5.4 Install the unit on the foundation. Care should be taken to ensure that the horizontal level of the foundation is correct. Incorrect foundation level will affect the alignment of the panel doors which may cause difficulty in closing the doors.

5.5 Check the insulation between the AC input terminal and panel body by means of a DC Megger. The initial Megger reading should be at least 1-2 M.

5.6 The unit should be earthed by a bare copper conductor to be connected between the station earth and the earthing bolt provided on the base channel of the unit.

5.7 The various Input/Output terminals are provided on the Main Bakelite Terminal strip provided at the bottom of the unit. The various cables to be connected are as under.

a) AC Input Cables : These are to be connected to stud type terminals marked "A.C. INPUT" - 'L' & 'N'. Care should be taken to ensure that the live and neutral wires are connected to the respective terminals only.

b) DC Output Cables : These are to be connected to stud type marked "DC OUTPUT". The anode cable should be connected to the positive terminal while the structure is to be connected to the negative terminal.

5.4 Inspect the printed circuit card which is housed inside the control circuit box mounted on the front inner door. Clean the gold plated fingers of these cards with a clean piece of cheesecloth if required. Insert the card firmly in its position as marked on the control box.

This completes installation of the unit. The unit is now ready for testing and commissioning.

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6.0 TESTING AND COMMISSIONING OF THE UNITAfter completing the installation and cable connections as indicated in chapter 5, the unit may now be energized. To energize the unit, follow the steps given below very carefully.

6.1 General CheckingCheck the insulation between the AC input and the earth terminal by means of a DC Megger. The Megger reading should be more than 2 to 3 M initially. (To check Megger insulation, the external AC cables connected to the unit should be removed).After ensuring that the Megger reading is OK the unit can now be energised.

6.2 Energizing and checking the unit in Auto ModeTo energize the unit, perform the following steps:

i) Keep the AC INPUT MCB in OFF position.

ii) Switch OFF the DC OUTPUT ON/OFF MCB mounted on Fuse plate inside.

iii) Turn the knob of potentiometer marked O/P VOLTAGE SET fully counterclockwise.

iv) Energize the 230V, 1 Ph AC power to the unit from the power distribution board.

v) Check the AC Mains voltage. Verify that the voltage is within the specified limits.

vi) Switch on the AC INPUT ON/OFF MCB. The 'MAINS ON' indicator lamp should light up indicating presence of AC Power. Switch ON the DC voltmeter and DC ammeter and observe that the readings shown by the two meters are zero.

vii)Switch ON the DC OUTPUT ON/OFF MCB mounted on the fuse plate inside the unit. The DC voltmeter may show a reading of 1V - 2V though the output of the unit is zero. This voltage is the back EMF generated by the anodes and is one of the signs of a healthy anode bed.

viii) Now turn the O/P VOLTAGE SET potentiometer slowly in clockwise direction. DC output voltage and current will slowly increase. Increase the DC voltage to about 3V. Observe the DC current and ensure that there is no abnormal overloading or short-circuit in the DC output. Increase the DC voltage to about 10V and leave the unit ON for about 3 - 4 minutes. This initial slow build-up of DC output voltage is necessary to provide gradual forming of electrolytic filter capacitors and this should always be observed whenever the unit is energised after long periods of the order of few months.

ix) After allowing for capacitor forming at 10V for 3 - 4 minutes, increase the output voltage gradually (very slowly) till the DC voltage reaches the rated value or the DC current reaches the rated value. (If the DC current reaches the rated value before the DC voltage reaches the rated value, the overcurrent indicator LED may come ON as the overcurrent limit is factory set at the rated value.) Leave the unit ON in this condition for at least 5 minutes to ensure full formation of electrolytic filter capacitors.

x) Reduce the output voltage to zero by turning the O/P VOLTAGE SET potentiometer fully counterclockwise. (It should be noted that the DC voltmeter may show a reading of 1 - 2V due to anode back EMF as explained earlier.) Switch off the mains ON/OFF MCB. This completes the initial energising and capacitor formation. The unit can now be put in service.

xi) Switch ON the unit. Increase the DC output gradually by means of O/P VOLTAGE SET potentiometer.

Note the DC voltage and current as well as AC voltage and AC current.

This completes the testing of the unit in Auto Mode.

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7.0 FINAL SETTINGS

After finishing the testing of the unit as described in Chapter 6, the unit can now be taken into service after making the final settings as described in this chapter.

7.1 Current Limit SettingTo set the desired current limit, follow the steps given below.

(Important Note: The current limit has been Factory set at rated value. It is recommended that, this should not be disturbed as far as possible. Follow the procedure given below only if the current limit setting is to be changed, otherwise skip all the steps mentioned below. )

i)Keep the AC INPUT ON/OFF MCB in OFF position

ii) Put the unit in AUTO mode, ensuring that O/P VOLTAGE SET potentiometer is in fully counter clockwise or 'Zero' position.

iii)Rotate the CURRENT Limit SET potentiometer fully clockwise (maximum position).

iv) Switch ON the unit and increase the output current gradually by means of O/P VOLTAGE SET potentiometer. Adjust the current to a value about 5-7 Amps higher than the required 'limit' value.

v)Now slowly turn the CURRENT Limit SET potentiometer in counter clockwise direction till the current falls to the desired ‘limit’ value. Observe that the OVERCURRENT indicator LED lights up. Tighten the lock-nut on the potentiometer lightly. The unit shall now always work within this current limit.

7.2 Voltage setting

Set the output DC voltage to a desired value by means of O/P VOLTAGE SET potentiometer. The unit will always maintain the output DC voltage at this value while working in AUTO mode. (However, if DC current tends to exceed the current limit value, then the overcurrent limit circuit will override voltage control circuit and output voltage will fall from the set value and the unit will automatically go into constant current mode.)

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8.0 MAINTENANCE AND FAULT FINDING

Although the complete control circuitry has been designed around solid state components to increase the reliability and to reduce maintenance to minimum, certain periodic maintenance always helps in obtaining trouble free service. Should the faults occur during the operation of the unit, then these can be analyzed and corrected with the help of circuit description and principle of operation. However if a major problem arises, the manufacturer may be consulted immediately. A few useful points regarding some likely faults and steps to be taken for their correction are listed below.

Readings of all the meters provided in the unit should be taken periodically. These should be recorded in the Log Chart given at the end of the manual in the chapter 10.

1. FaultOutput is zero irrespective of setting of voltage in Auto mode. Mains ON indicator lamp is OFF. AC showing zero reading.

a) Check for the blown fuses F1. If found fused, replace.

2. FaultThe DC output voltage and current are zero in Auto mode.

a) Check for blown fuse AF1 on Auxiliary Transformer TRC. Replace if found fused.

b) Replace the Pulse Driver Card

3. FaultOutput voltage is high but the output current is zero or less than normal. The structure is underprotected.

a) Check for blown fuse . If found fused, replace.

b) If all fuses are OK, then check for open anodes.

4. FaultCurrent Limit not working. Output current high.

a) Turn the overcurrent setter potentiometer counterclockwise and try to adjust the current.

5. FaultThe Main Transformer is making an abnormal humming noise. The transformer temperature has risen above normal level.

a) Check if both LEDs are glowing on the Pulse Driver Card. If on of the LEDs are not glowing, then replace the pulse driver

b) Replace the pulse driver card PDC.

c) Check for a opened or faulty Main SCR.

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9.0 BILL OF MATERIAL

CLIENT : ADANI, MUNDHRA..

PROJECT : PLANT PIPELINE

CODE DESCRIPTION MAKE

F1, F2 HRC Fuses in Input AC Input, NSD 10Amp, Type BS88 in fuse holder Type 32NNSF

Bussmann

F3, F4 HRC Fuses in individual DC output, 80Amp, Type TSD80 in fuse holder Type SM125H

Bussmann

F5 HRC Fuses in Filter Capacitor bank, NSD 10Amp, Type BS88 in fuse holder Type 32NNSF

Bussmann

AF1-2 Auxiliary fuses in the live leads of various, meters, & auxiliary supply lines. 1A, Glass Cartridge type.

Reliance

LP1 ‘AC Supply ON’ indicator lamp, Housed in 22.5 mmholder. LED type, 240V, AC

Esbee

LP2 Panel Illumination lamp 240V, 25W Philips

MCB1 Miniature Circuit Breaker in AC input2 Pole, 10A. Type C.Breaking Capacity : 10KA

Schneider or Eqv.

TRM Main transformer with shield, double wound, varnish impregnated type. Primary : 240V 10%Secondary : 0 - 15V Capacity : 1000 VAInsulation : Class F

Amruta

V1 Voltmeter to read DC Output voltage. Analog type, 96 X 96mm.Range : 0 to 20 V DCType : M96

Meco

A1 Ammeter to read DC Output Current Analog type, 96 X 96mmRange : 0 to 100A with ext. Shunt of 75mVType : M72

Meco

SH1 Shunt for DC Output Ammeter. 75mV at 100A

Sumo

L1 Filter choke in DC output. 7.5 mH at 75A.

Amruta

C1 Filter capacitor bank in DC output. 4700 uF, 50V X 6 electrolytic capacitors.

Rescon

SCRM Silicon Controlled Rectifiers in Bridge CircuitIav : 105 AmpPIV : 1200VType : IRKT105/14

RIR

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DM Diode in the Bridge CircuitIav : 105 AmpPIV : 1400 VType : IRKD105/14

RIR

TSW1-2 ON/OFF Toggle switches in various Meters and Timer circuits. 1 pole, ON/OFF, 6A, 240VToggle Type

Switchon/Kaycee

LA1, LA2 Lightning arrestor at AC input and DC output. RMS Voltage : 500VRMS Current : 5 KVImpulse Discharge current : 10 KA

LAMCO

SS1-4 Surge Suppressor MOV across SCRs and diode.RDN 275/20

ELPRO

RB1 Bleeder resistance across DC output.50, 100W, WW

Yesdee or Eqv.

P1 Reference voltage setter potentiometer.1K, 3W, WW

Pankaj

P2 Output voltage setter potentiometer.2.5K, 3W, WW

Pankaj

LD1 Status/Alram indicator LEDs.10mA, red colour. 5mm Ø

H. P./ National

Firing Card Control Card. Type CVC VE

Pulse Driver Card Control Card. Type PDC VE

Fuse Socket Box 3 Pin, 5 Amp utility Mains Supply Outlet. Anchor

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