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Station: NTPC- Simhadri BHEL Ref No.PS-DC-186-500-0042

NTPC Ref no SIM/1/TS/1/42Sheet 1 of 10

Plant area: BOILER

PROCEDURE FOR COMMISSIONING OF DRUM WATER LEVEL INDICATOR

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LIST OF CONTENTS

PLANT DETAILS

OBJECTIVE

PROPOSAL

SERVICES REQUIRED

SAFETY PERECAUTIONS

EMERGENCY PROCEDURE

STATE OF THE PLANT

METHOD

COMPLETION CRITERIA

APPENDICES

A. TECHNICAL SPECIFICATIONS

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PLANT DETAILS

BHELVision 20 System consists of a pressure vessel, withelectrodes mounted on it, Ascertor cabinet, local and remotedisplay units. An array of electrodes mounted on the pressurevessel measures the resistance of water and steam. Theelectrode outputs are processed in a compact electronics cabinetviz., Ascertor. Water/Steam levels are indicated by a high brightLED based local display mounted on the Ascertor cabinet.Information is transmitted to the control room for driving the UCBmounted remote display unit and optional display unit at firemansdoor. Hence, the system consists of the following items.

Necessary mechanical hardware including a pressure vessel ofappropriate size with isolation and drain valves

Sufficient number of rugged flange type electrodes (typically 12Nos.)

Ascertor cabinet mounted at drum floor with integral local display

PTFE cable between electrodes and the Ascertor cabinet

(Standard) 15 Metre length

Remote display unit for UCB

Remote display unit for firemans floor (optional)

Necessary cable from the Ascertor cabinet to remote display unitat UCB and at firemans floor.

2 Nos. of pressure vessels fitted with electrodes. 2 Nos. ofBHELVISION 20 Ascertor cabinets and 2 sets of remote level

indicators are supplied, to cover both sides of the drum

STATUS

Signatures

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Employing the principle of measuring the different conductivitiesof water and steam, BHELVISION 20 offers a degree ofaccuracy unmatched by conventional level indicators.

The Ascertor continuously monitors the system. The electrodesare exicted by the AC source and the output signals are precisionrectified and compared with necessary threshold values. If thesignal is less than the lower threshold value, the output indicatesthe presence of water. On the other hand, if the signal is higher,than the upper threshold value, the output indicates the presenceof steam

BHELVISION 20 incorporates several safety features. Notableamong these are:

Separate electrical processing for each electrode to ensure

only single level loss on any component failure

Firmware based validation circuitry to confirm the information

conveyed by the Ascertor is always true. Invalid sensing byany electrodes (i.e. water above steam or steam below water)is indicated by a fault lamp on the display. Only the validsignals initiate the trip relays for high or low trip.

Dual power supplies (one supplying odd channels and the

other even channels). Even if one power supply fails, theother power supply automatically feeds the entire system,thus ensuring availability of power supply all the time.

4 to 20 mA current output expounds the applicability of

BHELVISION 20 both on indication and data acquisition fortrending and diagnostics.

STATUS

Signatures

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OBJECTIVE

The objective of this procedure is to commission theBHELVISION 20 Drum Level Indicator and make it available forUnit Operation.

PROPOSAL

It is proposed to commission this Drum Level Indicator andcompare its performance with respect to i) Direct water levelgauge and ii) Other remote water level Indicator of Drum

SERVICES REQUIRED

Communication and lighting facility at Drum Level and at Controlroom.

Availability of boiler with drum filled and preferably, boiler insteaming condition

Availability of a good working crew to attend to any electrodeleakages during commissioning

Availability of LT supply (AC & DC) (Refer TechnicalSpecification).

STATUS

Signatures

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STATE OF THE PLANT

Pressure vessel erected as per recommended drawing to thecorrect limbs in the drum (Both RHS & LHS)

Electrode erection completed

Control Cabinet (Ascertor Unit) and the connected cablingcompleted from drum level to control room

PTFE Cabling from electrodes to Ascertor Panel completed

Remote indicator in control room erected and ready forcommissioning

Operating floor indicator erected (This is optional)

Input power supply is made availablea. 1110 V AC, 220 V AC/DCb. 24 V DC

(Single or Dual feeder)

Electrical checks completed and system ready for commissioning

STATUS

Signatures

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METHOD

When the unit is under steaming condition, charge the pressurevessel very slowly by opening the isolating valve in the water limbfirst and then steam limb. Warm up the vessel sufficiently.

Observe for any leakage and attend

Slowly close the drain valve (kept open for warm up) andpressurise the vessel to the unit working pressure

Observe for any leakage and attend

Charge the electrical system and switch on the circuits foroperation

Observe the level indicated by the level indicator and compare itwith direct level indicators / other drum level indicator

(Generally, this type of drum level indicators are more accurateas it performs on conductivity and does not require any densitycorrection)

Both BHELVISION 20 Drum Level Indicators are commissionedas above and released for operation of the Unit.

STATUS

Signatures

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COMPLETION CRITERIA

With completion of activities as proposed in Section 3.0,Commissioning of Drum Level Indicator is concluded.

APPENDICES

a. Technical Specification

1) Basic Equipment

Electrodes - Typically 12

PTFE Cables from - 15m standard lengthElectrodes to ascertor

Ascertor Unit - IP55 enclosure, wall mountable with raincanopy.

Remote Indicator - Hi-bright LED type indicator with greencolour for water, red colour for steamand yellow for fault.

Local Indicator - Same as above, mounted on AscertorUnit.

Operator Floor Indicator - Optional.

STATUS

Signatures

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2) Pressure Vessel

Capable of withstanding upto - 207 bar

Steam / Water tapping distance - 635 mm for 12 probes(other sizes on request)

Probe sight range - 550 mm (for 12 probes)

Steam/ water connections - 25 mm bore butt weld.

Made up of forged carbon steel, thick wall design.

No. of probes variable based on boiler drum size. (Standard is 12probes)

3) Electrodes

Type of construction - Rugged Flange type with SS body,

fitanium tip and ceramic insulator.

Manufacturer - BHEL/EPD, Bangalore.

4) Electrical Specifications

Freely selectable alarm/trip - 25 to 275 mm (in steps of 50 mmfor high and low).

STATUS

Signatures

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Change over - 0.25A @ 220V AC.Contact rating - 0.5A @ 125V AC.

- 1.00A @ 60V AC- 2.00A @ 30V DC.

Current output - smooth 4 to 20 mACorresponding to water level.

Self checking

Firmware based validation

100% resolution even with one power supply fail condition.

Input power supply - 110V AC, 220V AC/DC 24V DC(Single or Dual feeder). Any

combination can be ordered.

STATUS

Signatures

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PROCEDURE FOR COMMISSIONING OF

DRUM WATER LEVEL INDICATOR

Documents

BHEL VIS