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Maintenance Jobs in DAVR Panel (A to D) Prior to Functional Testing: A. Cleaning & checking of Electronic Circuits: Rack out one by one all cards from swing frame. While racking out the cards ensure card location identification is marked (AB13, AB25 etc) on the card front plate or on the connector side of the card. This will ensure that the same card is inserted at the exact slot in the rack from where it is removed. Remove dust deposits of complete DAVR panel by blowing with the help of clean & dry air. Clean each card using restricted compressed dry air. Clean the connectors with proper electronic cleaner. Look for dry solder on all cards. Switch/jumper settings of every modules to be checked which should be as per latest commissioning report of that particular machine. Power, CT/PT Sensing, field current sensing and pulse connection tightness to be checked. Look for pitting of breaker pole contacts by removing the arc chutes. Field breaker contact adjustment to be done if required. Manual operation (Close/Trip) of the Field breaker to be done and jamming of tripping circuit if any to be checked. Check the values of Discharge resistor R2 (5.5ohm, 30A, 10kW) & Bleeder resistance R13 (150ohm, 500W). Resistance between Gate – Cathode of each thyristor is to be checked, which should be in the range of 17ohms to 30ohms. Restore the Cards back to their respective locations. •
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B. Checking of LPTs: Check the contacts of draw out type PTs. Proper earthing of PT neutral is to be ensured. Tightness of HT fuse Clips to be checked. PT secondary should not have limit switches in its circuit. Discard such limit switches if present. PT secondary circuit should have Fuses not MCBs in its circuit for protection. Replace MCBs by Proper size fuses 2A/4A in case MCB is present, since MCBs have higher contact drop. Tightness of all terminal links is to be checked at TB’s in PT junction box. • • • •
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Prepared by: A K MALIK , IOCL HALDIA REFINERY; REFINERY; Check ed by: P K DAS, BHEL-EDN, BHEL-EDN, BANGALORE BANGALORE
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C. Checking of Power Supply MCBs: Switch ON Station 110V DC supply (F56). Switch ON MCB F51 – power supply for Channel-1. Check the various levels of voltages (i.e. +24Vdc, +/-15Vdc, +5Vdc) with respect to 0V on the power supply module at AA37 rack. Switch ON MCB F52 – power supply for Channel-2. Check the various levels of voltages (i.e. +24Vdc, +/-15Vdc, +5Vdc) with respect to 0V on the power supply module at AA01 rack. Switch ON MCB F53 – power supply for Control & Signal. Check the various levels of voltages (i.e. +24Vdc, +/-15Vdc, +5Vdc) with respect to 0V on the power supply module at AB01 rack. Switch ON MCB F79 – power supply of DC-DC converter. Keep the MCB F80 in OFF condition. Check the availability of 48Vdc with respect to 0V on the power supply module at AG06 rack. Switch ON MCB F80 – power supply of DC-DC converter. Keep the MCB F79 in OFF condition. Check the availability of 48Vdc with respect to 0V on the power supply module at AG16. Also availability of 48V power supply to TB’s of Digital I/O modules A01, A02, A03, A51, A52, A53 etc. • •
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D. Checking of parameter Settings: Auto channel CPU parameters / K-Flags are to be re-checked. The settings should be as per latest commissioning report. PLC parameters are to be re-checked. The settings should be as per latest commissioning report. Monitoring parameters / K-Flags are to be re-checked. The settings should be as per latest commissioning report. •
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E. Functional Testing of DAVR at generator standstill (E to I): Before proceeding with any functional testing of DAVR during Standstill condition of the Generator. a) Isolate cable connection from AVR output TBR1&2 to Exciter field. b) Isolate AVR P.T Sensing connection (TBR 17,18&19) by opening links/external P.T.connections to prevent back charging of P.T. c) Remove pulse cable connectors X3 & X4 from Auto/Manual thyristor pulse boards. d) Logic Forcing: Force the logic “Turbine speed >90%” by shorting terminals TBA01/25 & 26, required for excitation control. This is required only if turbine is not running at its rated speed. Force the logic “Generator Breaker Open” by shorting terminals TBA01/23 & 24, required for excitation control. This is required only if Generator breaker is completely racked out and plug kept removed. •
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Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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If Unit Lockout Relay is not Reset or taken out for maintenance during DAVR test, force the logic “ULR Reset” by shorting terminals TBA02/1 & 2, required for Field breaker control.
F. Checking the Logic Sequence of Operation: DAVR Logic as priority are: 1 st priority – Trip, Automatic channel changeover; 2 nd Priority – Commands (Raise / Lower etc. in multiples of 20mSec); 3 rd Priority – Indications (position of channel – Auto / Manual limiters in operations etc.) Keep the DAVR control in LOCAL. Perform all types of operation like Field breaker ON/OFF, Excitation ON/OFF, Ch1-Ch2 changeover, Reference Raise/Lower etc as per relevant scheme logic from the Operating & Signaling board (UNS 2661). Change the DAVR control to REMOTE. Perform all types of operation like Field breaker ON/OFF, Excitation ON/OFF, Ch1-Ch2 changeover, Reference Raise/Lower etc as per relevant scheme logic from the Control Desk as well as GRP panel relay actuation.(P.T. fuse failure etc.) •
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G. Functional Testing of PID by Injection of Signals: PMG supply signal (open Link L-1, L-2 & L-3), CT signal ((open Link 21-R, 23-R, 25-R) etc prior to injection of signals. Also open the link S452 on UNC4660 cards (for both U01 & U02) prior to connecting variable 3Vdc with the use of battery or DC source having variable potentiometer. Inject 3phase 110Vac signal (Ug) with the help of external injection kit at Terminals 17-R, 18-R, 19-R & 20-R (This signal should not go towards LPTs). Put the links L-4, L-5 & L-6 in place and switch on Test supply MCB F74. Inject 3phase Secondary Current signal (Ign) corresponding to rated generator CT secondary current with the help of external injection kit at Terminals 21-R, 23-R, 25-R & 22-R (This signal should not go towards CTs). Connect 3Vdc variable source between terminals X-261 (+ve) and X-265 (-ve) of U01 & U02 in each unit. Don’t inject more than 10V DC as it may result in failure of A/D converter modules UN0610, UN0611. Measure the signals developed by various points as per the signal flow diagram Fig.-C on following modules: 1. On UNC4660 modules (U1):- Measure AC voltage between sockets X-250 & X251, X-250 & X252, X-251 & X252. The value should be 22Vac (Ug).(with 110V AC signal between U01 TB1,2,3) •
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Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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2. On UNC4660 modules (both U1 & U2): - Measure AC voltage between terminals X-253 & X254, X-253 & X255, X-254 & X255. The value should be 22Vac (Usync). 3. On UNC4660 modules (U1):- Measure AC voltage between terminals X-257 & X258, X-257 & X259, X258 & X259. The value should be 3Vac (Ig). 4. On UNC4660 modules (both U1 & U2):- Measure DC voltage between terminals X-261 & X265. The value should be set to less than 3Vdc as per injected voltage (If). 5. On UN0663 modules: - Measure AC voltage between terminals R & S, R & T, S & T. The value should be 22Vac (Usync).(AA29 & AA65) 6. On UN0663 modules: - Measure DC voltage between terminals If & 0V. The value should be as per injected If signal (less than 3VDC). 7. On UN0661 module: - Measure AC voltage between terminals UR, US, UT w.r.t. 0V. The value should be 4.37Vac (Ug). Also measure Ug w.r.t 0V which should read 7Vdc. The DAVR KV meter should also read 11KV. If not then adjust U R, US & UT pots to keep Ug at 7Vdc.Micro Terminal reads U G = 100%. 8. On UN0661 module: - Measure AC voltage between terminals IR & I S, IR & I T, IS & I T. The value should be 5Vac (Ig). Also measure Ig w.r.t 0V, which should read 7Vdc. Micro Terminal reads I G = 100%. 9. On UN0661 module: - Measure If w.r.t 0V, which should read 3Vdc.(as per injected DC signal) Micro Terminal reads 100%. 10. On Micro Terminal: - For measured values of Ug=7Vdc, Ig=7Vdc & If=3Vdc on UN0661 module, the UG act, Ig, If1& If2 should read 100%. If not then the UN0610 (A/D conversion module) if faulty. 11. On Micro Terminal: - By varying phase angle between Ug & Ig injected with the help of injection kit, corresponding Cos(phi), MVAR (Q), MW (P), Icos(phi), Isin(phi), load angle (delta) etc are to be read. These values should be as per calculated values corresponding injected signals. 12. Check for variation of U C for both channels by increase/decrease of Ch1/Ch2 reference value. Also for fixed reference value alter U g/ If signal for Ch1/Ch2 respectively and ensure variation in U C of Ch1/Ch2 is happening.
Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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13. Check for proper functioning of Automatic follow up circuit. 14. Check one by one all limiters by reducing the set limit values & observe variation of control voltage U C in Auto channel before & after the limiter comes into operation. •
Remove the external signals injected (Ug, Ign & If). Put back the link S-452 in place.
H. Checking of Firing Pulses: Switch on the Field Breaker & Excitation ON with AVR in Channel-1 (AUTO). With the help of CRO, view the waveform of input/output pulses for every phase of thyristor by connecting the probe one by one or two at a time to its corresponding signal available on UN0809 module of Channel-AG01. The waveforms should be as shown in Fig. –C. Also check the non availability of output pulses in UN0809 module AG03 of Channel-II, which is not in operation, and availability of input pulses for channel in AG03.(input pulses at r+,t-,s+ r-,t+,s- outpulses R+,T-,S+,R- T+,S-) Repeat the above procedure after switching over the operation to Channel-II.(Manual input/output pulses will be available but input pulses will be available for Auto channel but Auto channel output pulses will be blocked). •
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I. Light load Test of DAVR: a) Set switch S865 to Pos1 in UN0663 modules (AA29 & AA65) (Raise/Lower of Excitation is possible from modules front plate only) b) Set Switch S850 to Pos’0’ (10degrees Rectifier Limit)& Switch S851 to Pos.F (170 degrees, Inverter limit) in UN0663 modules (AA29 & AA65). c) Connect back pulse cable connectors X3 & X4 at Auto/Manual pulse boards. Connect the External variable resistance (R FLD) of rating 100ohms, 10Amps across the DAVR output at the terminal 1-R & 2R along with a DC ammeter after disconnecting the outgoing cable to main exciter field. Prepare the test setup as per fig.-A. Set RFLD at its maximum value(100 ohms). Switch ON exciter Fld Breaker & Excitation ON. Use RAISE Push button on front plate of module (AA29/AA65) to increase the excitation till MAX.LED lights up in module front •
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Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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plate. Measure control voltage Uc at module from plate. It will be around +9.8 to +10VDC Gradually decrease the R FLD so that there is flow of around say 4.18Amps (value of no load field current at GTG-1 of Haldia Refinery). In CRO observe all six pairs of devices are conducting equally. Refer Fig.E Note down the values of Vdc, Uc (control voltage on UN0663 card) .The max output DC voltage V DC will be around 1.35 x V AC when Uc is at max.positive DC voltage (ie +9.8 to +10VDC) Then reduce the reference using LOWER push button on modules front plate to say 95%. Again adjust the R FLD so that the same current 4.18Amps flows through it. Note down the values of Vdc, Uc (control voltage on UN0663 card). Repeat the above procedure of lowering Uc. Uc reaches nearly –10VDC.Each time adjust RFLD to maintain 4.18ADC before noting the readings. Set RFLD to Max.(ie 100ohms)before repeating the procedure for 2nd channel, OR else thyristors will be damaged. Switch off the exciter and normalize the DAVR. Plot the graph using the values as measured above – a plot for Vdc vs Uc.The curve obtained should be linear one similar to as shown in Fig. – B .
J. Simmulated Loop testing using 50Hz supply instead of PMG Switch off MCB F74,& remove the links L4,L5,L6 Connect back the Links to L1,L2&L3. Remove the cables for PMG supply (TBR4,5,6) Inject through a 3 phase variac AC supply equal to PMG voltage but of 50Hz at TB 4,5,6.(Ensure proper phase sequence as per Scheme) Normalise switch settings of S865, S850&S851 as per commissioning report for UN0663 module (Pos.AA29 & AA65) Remove the If signal injecting setup (between X261 & X265) of U01 & U02. Connect back switch S452 in U01 & U02 Replace RFLD with a resistor equivalent to exciter field winding resistance, of high current capacity (equivalent to say 20ADC, ceiling current) Decrease PT/Ct injected voltage/current to Zero Select AVR channel-2 Manual. Close Exct.Fld breaker & make Excitation ON. Gradually increase PT voltage to its rated value (110VAC) Raise Channel-2 reference so that no load current or nearly 40% of rated field current is flowing through R FLD. • • •
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Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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Ensure Automatic follow up of Auto-Channel. Use Raise/Lower command in UNS2661 (Command input module) of Channel-1 to delibrately create a difference (+ve) And then (–ve) DC value in AUTO-Manual balance indicating meter. Ensure automatic follow up of Auto channel for both + & deviation of balance indication.
Step test of DAVR at generator FSNL condition (J): K. Step Test of DAVR: Ensure normalization of DAVR for its readiness of operation with the Generator. Switch on the excitation in Ch-1, with a present level of say 100% of Uref. Through the micro terminal enter the value of U ref as 95% and press Enter. Note the variation in the generator terminal voltage. Adjust PID if necessary to obtain one over shoot, one undershoot and then Gen. Voltages stabilizes to the voltage corresponding to Uref=95%. Repeat the above procedure from U G=100% for sudden change to Uref=105% (+5% step). Similarly from UG =100%, decrease the Uref with a step of 90% (-10% step). Now perform the above procedure with U G from 100% to 110% (+10% step) by suddenly increasing the reference & note the oscillation in generator terminal voltage. In all the above cases one overshoot followed by one under shoot and then stabilzation in Gen. Terminal voltage to be obtained, without actuation of over voltage stage 1 relay. If the DAVR stabilization takes place with over damped or under damped behavior, then the PID filer parameter optimization is required for which BHEL expert is to be consulted. •
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Dynamic test of DAVR at generator (K): L. Dynamic Test of DAVR: Note: For performing this test, proper permission from concerned management is to be obtained. If permitted, the test may be carried out in the following procedure. Synchronize the generator with other running generators & gradually load it up to 50% of its rated capacity. •
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Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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Ensure there is enough spinning reserve in generation system so that if the machine under test trips, further load shedding shall not be required on account of this. Suddenly in one step decrease load on the generator by 25%. Repeat this procedure of sudden de-loading at 50%, up to 100% load. Observe the response of DAVR & system parameters Turbine frequency etc) during this condition. Now increase the loads in steps permitted by Turbine control system within max quantium and observe the DAVR response. Repeat the above procedure load step size of (permitted from Turbine system) & each step change in load. Observe the response of DAVR and system parameters.
Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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3ph PT i/p 110Vac (Ug)
ATTENUATOR
+
PROBE
-
CRO
1 : 0 1
DC out ut 3ph CT i/p 1Aac (Ig)
Stn Suply 3ph 415Vac
D A
RFLD, 100ohm, 10A Vdc
V Stn DC supply 110Vdc
R A
Fig. A : Setup for carrying out Light Load Test on each channel thyristor at generator standstill
Vdc
-10Vdc
Uc
+10Vdc
Fig. – B: Vdc Vs Uc plot as results of light load test
Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
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110Vac (Ug)
UNC4660
UN0663 X250,251,252 = 22Vac (Ug)
110Vac (Usync)
X253,254,255 = 22Vac (Usync)
Ign (rated sec.)
X257,258,259 = 3Vac (Ig)
3Vdc (If)
S452
R S T
= 22Vac
If = 3Vdc
X261-U265 = 3Vdc (If)
UN0661
4.37Vac = MICRO TERMINAL (UNS 2660) UN0610 5.0Vac =
Ugact=100% Igact =100% If =100% ---
UR US UT IR IS IT
D 7Vdc = Ug 7Vdc = Ig 3Vdc = If
A 0V
Fig.C: PID Signal Flow diagram
Prepared by: A K MALIK, IOCL HALDIA REFINERY; Checked by: P K DAS, BHEL-EDN, BANGALORE
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Full Firing Uc=+10VDC
VDC
0
60
120
0
0
180
240
0
300
0
0
360
3600
Fig-E In case if there is any missing waveform in the entire zone of +u c control voltage then
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Full Firing Uc=+10VDC
VDC
0
60
120
0
0
180
240
0
300
0
0
360
3600
Fig-E In case if there is any missing waveform in the entire zone of +u c control voltage then Either- pulse is missing Or- faulty UN0663 Or faulty Pulse final stage UN0809 Or- Thyristor device failure Or- Pulse transformer in Pulse Transformer board faulty Or- Thyristor Arm fuse failure Or- Loose contact in pulse cables Or-AC Supply not reaching at input to Thyristor bridge Or-Improper Synchronization of Thy. Bridge AC input voltage with U syn at UN0663
Prepared by: A K MALIK , IOCL HALDIA REFINERY; Check ed by: P K DAS, BHEL-EDN, BANGALORE
