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Zhejiang ERG Technology Joint Stock Co.,Ltd

Mobile: 86-18257346462

Tel: 86-576-83200088


Contacts: Wu Nick/Bella Zheng/Blanca Chen

Add: 135 Haisha Road, Shaliu Economic DevelopmentZone, Sanmen County, Zhejiang, P.R.China

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Transformer Operating Temperature Monitoring And Regulation-Zhejiang ERG Technology Joint Stock Co.,Ltd.
- May 08, 2018 -

Transformer operating temperature monitoring and regulation

-Zhejiang ERG Technology Joint Stock Co.,Ltd.

3.1 Ambient temperature

The national standard GB 1094.1-1996 "General provisions of the first part of power transformers" provides as follows:

The highest temperature +40 °C;

The highest annual average temperature +20 °C;

Minimum temperature -25°C (outdoor type) -5°C (indoor type);

Water cooler inlet temperature +25°C.

3.2 2 temperature monitoring during transformer operation

Including the top oil temperature and the winding temperature (if the winding thermometer is set) two temperatures.

3.3 top oil temperature limit

For self-cooled and air-cooled transformers, 95°C, in order to prevent over-speed aging of the transformer oil, it is usually controlled by a decrease of 10 degrees, ie not exceeding 85°C, and an alarm of 80°C is set for each operating unit. For the strong oil circulating transformer is 85 °C, usually by reducing 10 degrees that does not exceed 75 °C control, each operating unit set 70 °C alarm.

3.4 Winding Temperature Limits:

If the transformer is equipped with a winding thermometer and the temperature indicated by the winding thermometer is the hottest part of the transformer winding, the maximum temperature specified by the winding temperature is 95~100°C (general winding temperature is 10~15°C higher than the oil top layer temperature, if the oil is top layer The temperature is controlled according to the 85°C limit, and the winding temperature is controlled according to the 95~100°C limit). Usually the alarm is set at 90~95°C.

3.5 Regulations for temperature rise limits of various parts of transformers

According to the national standard GB1094.2-1996 "The temperature rise of the second part of the power transformer" provides:

Temperature rise limit = maximum temperature - ambient temperature

3.5.1 The temperature rise limit of each part of the transformer is as follows:

- The temperature rise limit of the top oil is 55K (full seal is 60K)

- The transformer for strong oil circulation is specified as 40K

- Coil temperature rise limit is 65K

- The internal metal surface of the core and the transformer is 80K

- The junction of the bushing terminal block, the temperature rise in the air is not more than 55K, the temperature rise in the oil is not more than 15K

3.5.2 The temperature rise limit of transformer top oil and winding is as follows:

According to the transformer designed by national standard GB1094, the normal life withstand temperature value of Class A insulation is 98°C, the average life temperature of the normal life is 20°C, and the average temperature difference between the coil and the coil is 13K, so the coil temperature rise limit is 98. -20-13=65K. The maximum oil temperature for normal oil operation is 95°C, and the maximum temperature is 40°C, so the top oil temperature rise limit is 95-40=55K.

3.5.3 Temperature rise regulations for areas with high altitude or ambient temperature exceeding the specified requirements:

When operating at altitudes above 1000m, the average temperature rise of the windings is reduced by 1K for each 400m increase in the self-cooled transformer (AN), and the air-cooled transformer (AF) is lowered by 1K for every 250m raised.

When the ambient temperature exceeds the monthly average temperature of 30°C or the average annual temperature of 20°C, the temperature rise limit of the transformer's top layer oil, winding, and core should be reduced by the value exceeding the part. 3.6 Control Settings for Thermostats

a. Top oil temperature control settings (users can self-regulate), if the user does not require, can be set as follows:

80 °C, temperature alarm (strong oil circulation 70 °C alarm)

When 45°C (GB/T6451 stipulates 50°C), the air-cooled radiator fan stops (Note: The strong oil air cooling transformer cannot stop completely).

At 55°C (GB/T6451, 65°C), the air-cooled radiator fan is started and the auxiliary cooler of the strong oil air cooler is activated.

At 105°C, the transformer trips.

b. The control settings of the winding thermometer (the user can self-regulate), if the user does not require, can be set as follows:

90 ~ 95 °C, the temperature alarm.

At 70°C, the fan of the air-cooled radiator is started, and the auxiliary cooler of the strong oil air-cooler is started.

At 115°C, the transformer trips.

3.7 Relative Heat Aging Rate of Transformers

According to the transformer designed in GB1094, the aging rate is related to the hot spot temperature of the winding. Under the rated load and normal ambient temperature, the commonly used reference value of the hot spot temperature is 98°C. The transformer load guideline specifies the relative aging rate at this temperature (98°C). Equal to 1. The relative heat aging rate at a certain temperature is equal to the ratio of the heat aging rate at the temperature and the heat aging rate at 98°C, and the relative heat aging rate at 98°C, ie: γ=heat aging at θ temperature Rate/heat aging rate at 98°C

Where θ - temperature at runtime °C

γ - relative heat aging rate

According to the formula, for every 6 degrees increase in temperature at 98°C, the aging rate doubles (the aging rate at 98°C is 1) and the life is reduced by half. This is the famous 6-degree rule. The change rule is shown in the following table (by 6 Degree of regular change):

Thank you for your kindly attention. Hope everything goes well with you.


This is Blanca Chen, from Zhejiang ERG Technology Joint Stock Co.,Ltd. We manufacturer and design transformers accessories. 

Products: (Sorry that for the e-mail not to be sent back,our catalogue and web are not attached for our first contact.)

1. All kinds of transformer cooler
2. Oil pump
3. Butterfly valve
4. Oil flow relay 
5. Control cabinet

6. Terminal box etc.
ERG join the draft of the standard for chinese government in transformers accessories, with certifications:CE, CRCC,IRIS,EUP,TS,CNAS,BV etc. 


Whatsapp/Wechat/Tel: 86 13626615457



Best Regards,

Blanca Chen