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Trouble Shooting

Protective

and

supervisory

instruments

various

components

fault Possible cause Remedial measure

Buchhoz

relay

Alarm at buchholz

relay

1. Oil loss2. Gas generation due to

inside failure

3. Accumulation of air4. Violent vibration5. Fault tripping

Transformer operation must only be continued

when a check shows that there is no internal

fault.

The following tests and examinations for

analysis of the warning should be made

1. Check oil level, pipes, position of valves2. Check tripping mechanism of the buchholz

relay

3. Check if gas in buchhoz relay isinflammable. Inflammability indicates an

internal transformer fault.

4. Analyze and evaluate buchholz relay gas5. Analyze and evaluate the oil taken from top

oil sampling valve

6. Undo all bushing connections and make thefollowing measurements.

6.1 measure the insulation resistance betweenthe systems and against earth

6.2 measure ratio between the systems in allpositions of the OLTC

6.3 Measure the winding resistance in allpositions of the OLTC

6.4 Measure the no-load current by applyinglow voltage and compare the results with

data given in the transformer test

certificate or in the O&M manual

7. Check all electrical connections8. Vent transformer tank and piping and put it

back into operation.

9. if faults cannot be found or faults havebeen eliminated. If one fault occurs

frequently, contact CTSS.

Buchholz relay

tripping

1. Oil loss2. Violent oil surge due to

inside flashover

3. Violent gas generation dueto inside failure

4. Violent vibration5. Fault tripping

1. Maintain the shutdown status!2. Carry out tests and measurements as

described under point 1 to 7

3. Vent transformer tank and piping and put itback into operation if faults cannot be

found or faults have been eliminated.

4. If one fault occurs frequently, contact CTSS.Pressure

relay/

Tripping due to strong

oil surge

Surge produced through a fault

in the diverter switch

1. Maintain the shutdown status.2. Check the tripping mechanism.

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protective

relay for

OLTC

3. Remove and check the diverter switch.4. Reset the tripping mechanism and put the

transformer into operation.

Resistance

thermometer

Thermostat

Dial-type

thermometer

for oil or

winding

Oil temperature too

high

Winding or oil temp.

too high

1. Transformer overloaded orinadequate cooling

2. Incorrect temperatureadjustment

1. Reduce load of the transformer2. Put fans or cooling equipment in service3. Clean the cooling equipment4. Check the position of butterfly valves5. Adjust incorrect temperature setting.6. Check the thermometer by comparative

measurements.

7. Check the electrical connections and thetripping mechanism

8. Check control devices for coolingequipment

9. Check current transformers andthermometers

Oil levelindicator

Oil level too low Not enough oil (low temp. oroil loss)

Check for tightnessTop-up oil

Oil flow

monitor

No oil flow 1. Gate valve closed2. Pipe clogged3. Pipe leaky4. Oil circulation pump

faulted(no voltage or

voltage too low defective

winding incorrect direction

of rotation, bearing

damage)

1. Open gate valve2. Clean pipe3. Seal pipe leaks4. Repair oil circulating pump(check fuses,

and direction of rotation)

5. Check the over current tripping feature6. Check the electrical connections and the

tripping mechanism.

Water flow

monitor

No water-flow or

reduced water flow

1. Leaks in the water coolingsystem

2. Reduction of cooling waterquantity

1. Top-up cooling water to the required level2. Check the electrical connections

Pressure

relief device

Internal tank pressure

too high

1. Conservator pipe shut-offor clogged

2. Electric flashover insidethe tank

1. Check the pipes and shut-off devices2. Check the transformer as described in

buchholz relay(1-7)

Motor drivefor OLTC

Drive cannot beoperated electrically

1. No voltage supply atmotor protective switch

2. Motor protective switchnot in operating position

3. Motor contactor does notpick up

4. Motor contactor stuck5. Brake contactor does not

pick up

6. Open circuit an one ormore motor phases

1. Check supply feeders2. Close motor protective switch3. Check supply feeders and contactors, and

replace if necessary

4. Clean or replace5. Check contactor, clean or replace if

necessary

Drive keeps on

running

Brake contactor stuck Clean or replace

Motor protective 1. Emergency stop button is 1. Repair or replace emergency stop button

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switch trips during

operation of motor

drive

on or stuck

2. Motor current excessivedue to overload or phase

failure

2. Check drive for stillness with crack handle3. Request a factory engineer. If a mechanical

fault in the tap-changer is suspected.

Off-circuit

tap changer

1. Operation notpossible

2. Gas in buchholzrelay

1. Adjusting device detective2. Carbon formation on

contacts

1. Repair adjusting device, operate multiplethe tap changer once a year over all

positions (extraction points)

2. Check the transformer as described for thebuchholz relay(1-7)

Dehydrating

breather

1. The colour of thedrying crystals

changes from

below

2. Changes from top3. In general

1. High atmospherichumidity.

Glass cylinder leaky

2. Moisture in conservatorPipe leaky

Glass cylinder leaky

3. Glass cylinder burst,maintenance intervals toolong

1. Replace dehydrating agentReplacing glass cylinder or seal properly

2. Seal pipe leaks, check the oil for moisturecontent

3. Flush the conservator with dry air

Electrical

breakdown

voltage of

the oil

1. Breakdownvoltage too low

2. Water content toohigh

1. Breather inoperable oftransformer in service very

long time

2. Leaks in water coolingsystem

3. Water pressure reducerinoperable

1. Put breather into operation2. Seal or repair coolers3. Contact manufacturer4. Dry the oil if necessary

Terminal lugs

on bushing

control

Discoloration of

connecting parts

Poor contact making Clear the contact faces

Tighten the screws

Control

cabinet

1. Electricalapparatus does

not operate

properly

2. Contactscommanded or

contaminated

3. Apparatushousing bend

1. Excision humidity incontrol cabinet

2. Water or dust inside thecabinet

3. Excessive hightemperature in the cabinet

1. Set the cabinet heater to a highertemperature

2. Seal the cabinet door. Fit a dust cleaner ifnecessary

3. Protect the cabinet against solar irradiation,provide for better ventilation

Earthing

connection

Earthing line

interrupted

1. Excessive current due toexternal flash overs

2. Impermissible currentloops through multiple

earthing

1. Clean the contacts tighten the screws andcheck the electrical distances.

2. Open up current loops3. Only one earthing with a sufficient cross

section.

Pressure

gauge for

HV-bushing

Oil pressure in

HV-bushing too high

1. Incorrect contactadjustment

2. Bushing over-loaded, oiltemperature too high due

to solar irradiation

1. Correct the contact adjustment2. Check the reading3. Check the bushing, reduce the transformer

load, increase the cooling effect

Pressure

monitor for

Oil pressure in

HV-bushing too high

1. Incorrect contactadjustment

4. Correct the contact adjustment5. Check the pressure monitor and reset the

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HV-bushing 2. Bushing over-loaded, oiltemperature too high due

to solar irradiation

3. Violent vibration ontransformer

auxiliary switch

6. Check the bushings, reduce the transformerload, increase the cooling

Air flow

monitor

No air flow or reduced

air flow

1. Protective screen iced upor clogged.

2. Cooler clogged or verydirty

3. Fan motor faulty (windingdefective or over-heated.

Bearing damage)

4. Incorrect direction ofrotation

1. Clean the screen, open the front flaps2. Clean coolers3. Check the supply leads4. Repair fans5. Correct direction of rotation6. Check over-current tripping features7. Check electrical connection, signaling and

tripping

Oil sight roof Traces of oil on the

water surface

Leakages in the oil circuit or

the water cooling system

Seal and repair coolers