Id

Failure

 Possible reason

Inspection and trouble-shooting

1

Run-through 

        （1）Residual flux in AC contactor or polluted oil cause power lost and activate time-delay relay

        （2）Failure in cam switches ?

AC contactor does not switch properly

        （1）Inspect whether AC contactor lost the power supply delayed or blocked

        （2）Whether contacts of cam switches operate properly.

        （3）Clean up polluted oil stain in core of AC contactor, replace contactor when necessary

Adjust sequence of cam switches or re-connect circuit, ensure step-by-step control in good condition.

2

Hand crank operates well, while fail to operate tap changer in “local” condition

No power supply or failure in motor control, for example, spring fails to restore in manual diving mechanism, causing contacts of protective switch S8 not to connect.

Check power supply or control circuitof motor, after trouble shooting and performing test

3

When motor drive unit in running, Q1 circuit breaker trips off.

Assembly of cam switches is in displacement

4

Tap change fails to control direction of operation

Disconnected circuit in capacitor of motor, poor contact or fault in capacitor

Inspect circuit of capacitor of motor, and solve the poor contact area, disconnected circuit or capacitor replacement.

5

Motor drive unit failsto operate in both directions of.1-N N-1

No power supply or lack of one phase, contacts of protective switch S8 for manual shaft fail to restore

Inspect whether power supply of three phases is normal, or contact area of protective switch in good condition.

6

Remote control fails, while locally operates well.

Fault in remote control circuit

Check remote control circuit, and perform test after solving the failure

7

Motor drive unit operates normally in “remote” and “local” modes, and tap position shows correctly, while voltmeter and ammeter have no reflection.

Tap changer fails to operate and disconnect between tap changer and motor drive unit, like connection pin for vertical or horizontal shaft falls off.

Inspect whether position of tap changer is identical as that of motor drive unit, if not, adjust the connection of driving shaft.

8

Diverter switch fails to switch or switching time is prolonged

Spring in Energy-accumulating mechanism turns fragile, broken or blocked

Replace spring or check mechanical gearing mechanism

9

Position of tap changer is not identical as that of motor drive unit

Fault in shaft connection between tap changer and motor drive unit

Check out the reason and re-connect the shaft .

10

The oil level in tap changer conservator rises abnormally or lowers to that in transformer conservator

 If the phenomena is still there after adjusting oil level in tap changer conservator to the right position, it should be defect of oil compartment seal which causes mutual oil leakage between transformer tank and tap changer oil compartment. If the bleeding screw of oil compartment is not fastened, it will also cause oil leakage.

Open the tap changer cover to find out the leakage point. If there is no oil leakage point, observe if there is any leakage on the insulting cylinder inner tank, tap leads screw and seal of driving shaft under the oil pressure of transformer tank. Then change the sealing or process tightness handling. If there are air-bleeding hole or oil-bleeding screw, fasten the screws and change the gasket.

11

excess amount of H2,C2H2 and total hydrocarbon in chromatographic analysis of transformer inner insulation

Stop tap changing and analyze the chromatogram of transformer oil. If the amount of dissolved gas and the factor of created gas are getting down, that  means the oil in the tap changer oil compartment leaks to transformer tank.

 Inspection and exclusive measurement as serial No.

12

Frequent signal alarm during tap changing

There is partial discharge source in oil compartment which causes continuous gas accumulation

Lift out the insert and check if the floating potential discharges and other abnormal partial discharge sources

13

There is deformation on the brackets of fixed contacts of tap selector or changer-over selector which causes the DC resistance of transformer winding to exceed the standard. Tap changer failures to operate or inner partial discharges

 Material of brackets of tap selector and changer-over selector is not good. The force to the tap leads and installation verticality do not meet the requirement.

 Change the brackets of fixed contacts. Adjust the tap leads to avoid force to tap changer. Tap changer should be installed vertically in free situation.

14

 The DC resistance measured together with transformer winding is not stable.

There is oil film or dirt on the fixed contacts which have not operate for a long time or have no current go through. Thus, it will cause poor contact.

maintain the tap changer every year together with transformer

15

After reinstallation of diverter switch, measure the DC resistance together with transformer winding, and find the DC resistance value of two adjacent taps is same or with two-step difference in the condition that there is no change of changer-over selector

Driving arm and turning arm of diverter switch are in dislocation and can‘t operate at one time, Thus, it will cause diverter switch failure to work and tap selector work only.

Lift out the insert, put the driving arm and turning arm in same direction, driving arm in the hollow. Operate it manually and observe whether the diverter switch can operate in both left and right side. Then fill oil and mount OLTC again. Measure the DC resistance of winding wire to ensure correctness of mounting.

16

Failure of energy accumulation mechanism

Operate the tap changer without oil after drying. Foreign body falls into the diverter switch.

It is not allowed to operate the tap changer without oil after drying, and remove the foreign body.

17

Moving contacts of diverter switch

Y shape arm neutral wires of diverter switch consist of several naked flexible wires, which untangle easily and locate among diverter switch taps. It will be break down and discharge easily under step voltage.

Wrap insulation material around Y shape arm neutral wires of diverter switch.

18

Tap changer has partial discharge and creepage trace

Fastener or electrode has point discharge. Looseness of fasteners or floating potential discharges

Remove the points, fasten the fasteners and eliminate the discharge of floating potential

19

 Driving shaft breaks

Connection dislocation of tap changer and motor drive unit or serious deformation on changer-over selector

reason caused deformation on changer-over selector, and find out the countermeasure or replace the driving shaft. Judge the location of setting position and verify the connection.