RRB JOBS QUESTION BANK : JUNIOR ENGINEER (AC) ESSAY ANSWER TYPE QUESTIONS
QUESTION BANK FOR SELECTION TO THE POST OF JUNIOR ENGINEER (AC)
ESSAY TYPE QUESTIONS:
1) What action has to be taken when a compressor is not working?
Ans: (a) Compressor-1/ 2 over load red indication LED glowing
(i) Ensure both the condenser motors are working. If not follow the instructions for rectification of condensor motors problem.
(ii) Check the working condition of RSW5. If it is not working, bypass it. If supply not available, check the continuity of wire No. 48 at outgoing terminal of RSW5 from C2, C3 contactors.
(iii) Check over load relays (OL-4, OL-5). If
(a) They are in tripped condition, check the over load setting (10-14 A) and reset it.
(b) OL-4 and OL-5 are found defective; bypass them by shorting 52 with 54 and 63 with 65.
Note: Before bypassing OL-4 and OL-5, ensure 3-ph supply is available at T10, T11, T12 for CP1 and T13, T14, T15 for CP2 terminals of compressors to avoid single phasing and measure the load taken by the compressors in each phase.
(iv) Check MCB-4 & MCB-5 and ensure supply voltage of 415V AC, 3- ph at outgoing terminals of MCB-4 (352, 353 and 354) of CP-1 and MCB-5 (355, 356, 357) of CP-2. If found defective, bypass it.
(v) Check the incoming terminals of contactor (C4) (331, 332, 333) of CP-1, contactor (C5) (334, 335, 336) of CP -2 and outgoing terminals of contactor (C4) (310,311,312) of CP-1, contactor (C5) (313, 314, 315) of CP2 respectively. If found defective, bypass the contactors.
(b) HP1 or HP2 red LED glowing
(i) Check the working condition of the condenser motors as per the procedure.
(ii) Check the condition of HP1/HP2 cutout switch. If tripped, reset it manually. (Setting 415 PSI)
(c) LP1 or LP2 red LED glowing
(i) Check the load of respective compressors with clip on meter. If current drawn is
less than 6.5 Amps, replenish gas where ever possible. (ii) Ensure that return air filters are clean.
(iii) Check and ensure that all the grills are in open condition.
(iv) Check the direction of rotation of blower as per the procedure.
(v) Check LP1 or LP2. If defective, bypass by shorting 29, 31 for LP1 and 35, 37 for LP2.
2) (a) How do you provide through feeding DC – DC for an AC coach?
Ans: POWER PANEL TO/FROM AC CONTROL PANEL (U/S TYPE)
(i) Switch OFF AC plants before extending TC from DC Power Panel to DC Power Panel.
(ii) Remove 250A Inverter +VE, -VE fuses in the power panel for one of the inverter supply.
(iii) Extend the DC supply from (2514 or 2513) terminals of power panel of healthy/defective coach to terminals of (B +VE, B -VE) control panel of defective/healthy coach with 2 core 35 sq. mm copper cable as shown in the figures.
(iv) After ensuring through feeding connections, re-insert the 250A fuses of the inverters in both the healthy and defective coaches.
(v) Remove the battery fuse of the defective coach.
(vi) Switch on AC plant by balancing the load on both coaches to avoid over loading of healthy coach Alternators and batteries.
(b) How do you provide through feeding AC – AC for an AC coach?
Ans: THREE PHASE AC FEED EXTENSION PROCEDURE - PANEL TO PANEL
(i) When Inverter is not working due to low battery voltage, extend the TC from the adjacent coach AC control panel
(ii) Switch off the AC plants and inverters in healthy and failed coaches before extending TC.
(iii) Disconnect the existing incoming supply cables in AC control panel of the defective coach at terminal block before RSW1 (TB,TY, TR).
(iv) Extend 3-ph AC supply with 3 core 16 sq.mm copper cable from the AC control panel of healthy coach (TB, TY, TR) to AC control panel of failed coach (TB, TY,TR)
(v) Check the control supply. If it is taken from sine wave output of inverter, remove the same and extend supply from 2-phase of the bus bar (358, 359) to incoming terminal of MCB-8.
(vi) After ensuring the connections, switch on the inverter in the healthy coach and check the availability of 3-ph supply as well as control supply in the control panel of failed coach.
(vii) Switch on blower in the defective coach and check the direction of rotation of blower.
(viii) If shows air loss indication, interchange any two phase wire in the terminal block (TY, TB and TR).
(ix) To avoid over loading of inverter, switch on AC plants of both coaches either with one compressor in each AC plant of defective and healthy coach or two compressors in any one AC plant of defective/ healthy coach.
3) How do you provide E.F.T to a TL coach?
Ans: The detailed procedure of emergency feed extension is given as under
(a) Action to be taken in healthy coach
(i) The availability of power supply in the emergency feed terminal should be ensured. (ii) Only one dark coach should be extended feed supply from one healthy coach.
(iii) Before connecting, the polarity of healthy coach as well as dark coach shall be checked.
(iv) L-II circuit of the healthy coach shall be switched off before connecting supply to dark coach.
(v) The rotary switch of (socket paralleling main) SPM-I and II shall be kept in ON position.
(b) Action to be taken in defective coach and feed extension
(i) L-II and fan circuit of the dark coach shall be switched off before connecting supply from healthy coach.
(ii) The rotary switch of (socket paralleling main) SPM-I and II shall be kept in ON position.
(iii) The L-I circuit is having essential/emergency lighting circuit.This includes all lavatory lights 50% of compartment lights, and night lights in all types of IInd class coaches.
(iv) Remove (+ve) fuse from battery box and (-ve) main fuse from junction box to disconnect the power supply to/from battery.
(v) The earth fault shall be checked up with the help of testing lamp. If earth fault is there then feed extension should not be done.
(vi) The feeding shall be given to L-I circuit only of the dark coach from healthy coach.
(vii) The defective coach shall be attended and cable should be removed at the first available opportunity by TL staff.
(viii) The size of the cables for the feed extension shall be of 16 sq.mm PVC Aluminum / 2.5 sq.mm elastomeric /2.5 sq.mm e-beam copper cables.
(ix) The length of the wire for feed extension shall be 2x1.5 meter (for both terminals). The length of the cable shall not be more than 1.5 meter.
(x) Both ends of the cable shall be provided with suitable size of lug.
(xi) The cable shall be secured tightly by the screws or bolts, nuts and plain washer. The proper tightness of the connections should be ensured.
Study Kit for Railway Recruitment Board (RRB) Exams
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Courtesy: Indian Railway