1.hvdc operation & maintenance

7/30/2019 1.HVDC Operation & Maintenance

1/19

MAINTENANCE

OF

HVDC

EQUIPMENT


2/19

Valve HallValve Hall

The status of the Thyristor levels in the valve hall is available

online in the VBE printer.

VBE monitors continuously, the healthiness of the thyristors

and associated valve hall components while in service

Failure of thyristor is reported in the VBE printer and also in the

work station for the operator

Alarm is generated up to 3 thyristor failures in a valve and on

4th failure, trip is generated


3/19

Failure may be in

Thyristor

Snubber capacitor

Snubber resistor TE card

To test the thyristor level Thyristor Level Test Unit is used

which tests thyristor and associated components

Type of failure in the thyristor can be detected Open circuit,

short circuit, gate open circuit FO cables from VBE to the TE card are tested using the FO

Attenuation test kit

Inspection of Grading electrodes Yearly / 2yearly

Valve Hall Thyristor level testing


4/19

Thyristor level test unit


5/19

Inspection of grading electrodes


6/19

Converter Transformer

Following tests are done during yearly shutdown

Capacitance and tan of the bushings

Used to determine the healthiness of the bushing insulation

Checking the operation of the buchholz relays and Pressure Relief

Devices (PRD)

Checking of the WTI & OTI alarms and trips

Checking whether all the alarms are reported to HMI system

Checking the operation of fire fighting deluge valve system


7/19


Replacement of the oil filters of OLTC (On-Load tap Changer) can be

replaced online when the alarm is generated

Periodic testing of the oil DGA to determine the incipient internal

faults of the transformer

Testing of all the associated protection relays


8/19

Converter Transformer OLTC Inspection of the OLTC

Maintenance of OLTC after every 1 lakh operations

Wear and tear of all mechanical & electrical parts of the

OLTC to be inspected.

Replacement of mechanical parts with high wear & Tear.

Cleaning of Fixed and moving contacts.

Cleaning of OLTC chambers

Filling with fresh oil



9/19

Overhauling of OLTC


10/19

Overhauling of OLTC


11/19

AC Filter

Maintenance of filter bay equipment includes

Associated breaker testing -Operation timings, alarm,

lockout checks etc.

Testing of CT C & Tan

Capacitance stack measurement and balancing if required

Inspection of capacitor stack for oil leakage

Measurement of resistors and reactors for deviation Testing of associated protection systems


12/19

Apart from the yearly maintenance, failure of capacitor cans calls

for

Measurement of individual capacitor stacks /cans

Calculation of unbalance in the Capacitor H-bridge

Replacement of capacitor if required for balancing of the bridge

AC Filter


13/19

Valve cooling

Maintenance of Valve Cooling

Replacement of resin in the resin chamber yearly or if the conductivity reaches

the alarm level 0.25S/cm which ever is early

Provision is there to replace the resin without the shutdown of the valve cooling

system

Cleaning of 50m main filter cartridges yearly this requires shutdown of the

system

Cleaning of 50m filters in the path of resin chambers and make up water line

path can be done without shutdown

Top up of hardness removal salt in the water treatment plant if the level falls

below 20%

Apart from this, daily monitoring of the parameters / motors / pumps is done

to detect the alarm levels in advance to take corrective action before it develops

into a major problem


14/19

Valve Cooling- Maintenance of Main filter


15/19

DC Yard disconnectors

Maintenance of DC disconnectors

Cleaning of the Male & Female contacts

Applying contact grease

Measurement of contact resistance

Replacement / Adjustments of mechanical linkages if

resistance found high

Tightening of the clamps & connectors


16/19

DC Yard Maintenance


17/19

Auxiliary System

Yearly servicing of DG sets and protection relays testing rating

1400KVA 2sets

Fire Fighting system checking the hydrant points

AC switchyard Maintenance of Circuit Breaker, CT, CVT and

Isolators as per standard procedures of AC stations

Maintenance of station batteries, chargers and UPS systems

LT system Relay testing & LT breaker maintenance


18/19

Maintenance of LT breakers & Relay testing


19/19

1.hvdc operation & maintenance

Documents