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Main transformer introduction

Mar 15, 2017

Power transformer is a stationary electrical equipment used in the power system which converts AC power of certain voltage and current into power of another voltage and current with the same frequency through electromagnetic induction.


Main transformer

Ash   handling transformer

HV auxiliary   transformer

Lighting   transformer

Startup/standby   transformer

Water   intake transformer

LV auxiliary   transformer

Water   intake LV lighting transformer

LV common   transformer

Water   intake LV lighting transformer

LV Startup/standby   transformer

Excitation   transformer


Main transformer

main transformer  


Main components of main transformer


1. Oil tank

2. Iron core

3. Winding

4. Transformer bushing (HV,Neutral point, LV)

5. CT of bushing type (HV side, Neutral point)

6. No-excitation tap changer (rated voltage regulating range: -2×2.5%~+2×2.5% )

Performance requirement: for the contact of tap changer with current for a long time, when the current is 1.2 times of the rated current, the temperature of contact will not influence the temperature rise of transformer oil.

The mechanical service life of tap changer should be more than 300000times, it’s copper contact.

Tap changer brand:MR

7. Cooler and control box

Cooler: the power supply and circuit of motor are equipped with overvoltage, short-circuit and phase-loss protection, the frequency of motor power of cooling system is 60HZ, and the motor power is three-phase three lines and voltage is 460V, for control power, it’s DC with 110V.

The cooler is installed next to oil tank and its bottom is connected by butterfly valve.

Oil flow indicator is installed under every group of cooler.

Cooler control equipment: the control panel is intelligent module control system with PLC mode. It has two circuits power which are standby for each other and can be transferred automatically. Namely, when one circuit power has fault, another circuit power will be put into service automatically and send out power transfer signal. Stop or start coolers automatically according to the temperature and load current.

Install oil filter valve on the oil tank and emergency drain valve which is big enough under it.

Gas relay

Oil conservator: there is oil-fill, oil discharge, air discharge and drain device and moisture absorber with oil seal.

The insulation oil of transformer is #25 transformer oil. Oil level meter, thermometer to measure the temperature of upper layer oil an winding.

For OFAF transformers at environment temperature of 40℃ and below, the upper layer oil temperature should preferably not exceed 75℃ frequently, 85℃ in maximum and the temperature rise should not exceed 45℃ at most.

The preset value of transformer oil temperature indicator and winding temperature indicator: (for reference)

a)  Transformer oil temperature indicator

Fan starting temperature:  65℃

Fan stop temperature:   50℃

Alarming temperature:  85℃

Tripping temperature:95 ℃

b)  Transformer winding temperature indicator

Fan starting temperature:  80℃

Fan stop temperature:   70℃

Alarming temperature:  105℃

Tripping temperature:  120℃