POWER TRANSFORMER PARTS

POWER TRANSFORMER PARTS

1.       Primary and secondary terminal boxes.

2.       Transformer tank

3.       Primary winding

4.       Secondary winding

5.       Radiator tubes

6.       Conservator

7.       Explosion vent

8.       Buchholzs relay

9.       Oil temperature gauge

10.   Breather

11.   Oil drain valve

12.   Cooling fans

SAMPLE OIL COLLECTION, OIL TESTING BDV –  

Transformer winding are placed in oil for cooling as well as for insulation, Oil samples to be collected and tested for breakdown voltage as per the recommendation of the manufacturer. Generally the transformer oil will be tested once in three years for the BDV. One oil sample collected will be placed in a test kit and tested. It should withstand 30KV for one minute. The sphere gap will be kept at 2.5 mm

ON AND OFF LOAD TAP CHANGER:  

To adjust the operating voltage occasionally off load and on load tap changers are used. Off load tap changer can be operated only when the transformer is isolated from service. The on load tap changer can be operated even in short times or at peak load obtain the desired output voltage without switching off the transformer from service.

VECTOR GROUP DYN 11: 

The primary is connected in Delta and secondary in star. The star point is connected to neutral. There is phase displacement of +30 between the primary and secondary. There is a phase shift of 30 forward. Hence the number 11 refers to hour 11’O clock.

ONAN:  

Oil natural, Air Natural Cooling. The oil converts the heat from core winding to the tank and equalizes temperature on natural ventilation. Dissipation of heat is assisted by construction of tank with corrugated surface or by fitting cooling tube to it, this type of transformer is most common and can be used in output 3000 K. V. A.

ONAF: 

Oil Natural, Air Forced Cooling : In this type of cooling the winding is cooling by air with alternative additional forced air cooling by running the fan fixed at the radiator tubes.

PERCENTAGE IMPEDENCE: 

6.5% which means the percentage of normal voltage required on primary to cause full load current flow through secondary being shorted. It refers to the short circuit, a short circuit on the full load current. Hence for an example the percentage impedance of a Desalter transformer will be 100% so that even at shorted H.T. terminals (because of water high level) the primary current will not go beyond the full load current and continue to work.

OIL AND WINDING ALARAM AND TRIP: 

The Power Transformer is provided with dial thermometer for oil temperature range 0 – 100c. Alarm contact set at 84.5c on actuation, flag relay falls and initiate ‘Minor trouble’. Winding temperature indicator facilities monitoring and indicating transformer hot spot temperature which initiates alarm and trip circuits.

PROTECTION OF TRANSFORMER:

        Buchholz relay (1^st stage):  

This relay detects the gas evaluation due to internal trouble and gives and alarm, and suited to the detection of minor or slowly developing faults.

Buchholz relay (2^nd stage): 

When a major fault takes place suddenly inside the Transformer. Oil flows suddenly from the transformer proper to the conservator. The second stage of Buchholz relay is actuated by this oil current.

Pressure relief device: 

When the internal pressure of the Transformer rises above the set value, the pressure relief device function.

Differential relay: 

This relay detects the internal defects by comparing the input current and the output current of the Transformer. If it functions combinedly with other protection devices, it is indicative, in almost all cases of an internal fault. Note that this relay sometimes functions by the exciting current when the Transformer is made line, and this is of course not attributed to an internal defects.

Over current relay Ground fault relay: 

These are intended for detecting faults in the electric system connected with the Transformer. A fault in the Transformer results in the function of these relays, which is always accompanied by the actuation of protective devices of the Transformer.