3、 Protection and maintenance contents of transformer
If the above eight skills and conditions are met, the operators of the transformer can carefully complete the following protection and inspection items during operation, analyze the abnormal phenomena in the inspection results, adopt countermeasures in
time, or state to the equipment department in time, organize analysis and demonstration, and adopt methods to avoid accidents.
（1） Supervision of transformer coil insulation
Before the transformer is put into operation after equipment or maintenance (usually after drying) and after long-term shutdown, the insulation resistance of the coil shall be measured, and the measured value and the measured oil temperature shall be
recorded in the transformer experience card.
A 1000 ~ 2500 volt megger shall be used to measure the insulation resistance of the coil.
The allowable value of coil insulation resistance is irregular.
The ratio of the insulation resistance measured during the operation of the transformer to the value measured before the transformer is put into operation after the equipment or overhaul is dry is the main basis for judging the insulation condition of the
transformer in operation. The insulation resistance shall be measured with a megger with the same voltage at the same temperature as possible.
If the insulation resistance of the transformer drops sharply to 50% or lower of the initial value, the Tg of the transformer shall be measured separately δ、 Capacitance ratio and oil sampling test (including measuring oil volume resistance and TG) δ)。
The final conclusion of transformer insulation condition should be obtained by synthesizing all the experimental data and comparing with the data in operation.
（2） Switch on, switch off and change tap of transformer
Before closing the switch of the transformer, the personnel on duty must carefully check the transformer to be sure that the transformer is in good condition, check whether all temporary grounding wires, signboards and barriers have been removed, and
check whether the operation ticket has been handed over when closing the switch after maintenance. Then measure the insulation resistance (the transformer often pulled in or often used does not need to be measured every time. If the cable is
separated without a barrier switch, the insulation resistance of the transformer coil can be measured together with the cable), and it is necessary to disconnect the voltage transformer.
If the insulation resistance of the transformer is less than the regular value, it shall be reported to the superior leader immediately to decide whether it can be put into operation.
All standby transformers shall be able to be put into operation at any time, and the standby transformers that have been out of service for a long time shall be charged regularly.
For forced oil circulation water-cooled transformer, start the oil pump first and then the water pump before putting it into operation.
The operating procedures of transformer closing and switching off shall be regulated in the site procedures, and the following items must be strictly observed:
1. The charging of the transformer shall be measured by the power supply equipped with protection equipment. Once there is a short circuit fault in the transformer, it can be blocked by the protection equipment;
2. If there is a circuit breaker, it is necessary to use the circuit breaker for input and blocking:
3. If there is no circuit breaker, the transformer with no-load current not exceeding 2 amps can be pulled and closed with a barrier switch.
If the transformer after overhaul of new equipment or replacement coil is connected with the generator as a unit, when it is put into operation, it shall be charged from zero, and other transformers can be charged by impulse closing.
After overhaul, trouble repair and oil change, the transformer can be charged and loaded without waiting for the elimination of bubbles in the oil (but the withstand voltage test is outside).
Before switching on the transformer equipped with oil conservator, the remaining air in the external charge and the upper part of the radiator shall be discharged.
If it is impossible for the tap changer of the transformer to adjust the voltage under load, the transformer shall be disconnected from the power grid with a blocking device and a blocking switch before the AC tap. When changing tap, pay attention to the
correctness of tap orientation.
Change the tap. In the future, it is necessary to check the integrity of the circuit and the uniformity of three-phase resistance with an ohmmeter or measuring bridge.
If the transformer has equipment for voltage adjustment with load, special procedures shall be prepared according to the data of the manufacturer, so that the personnel on duty can operate according to the special procedures.
The change of transformer tap shall be included in the on duty operation record book.
The orientation of transformer tap shall be specially recorded so that it can be checked at any time.
（3） Operation of gas relay protection equipment
When the transformer is changed from operation to standby, the gas protection equipment shall be connected with the signal as usual. The purpose is to find the oil level of the non operating transformer falling in time, so as to add oil in time.
When filtering or refueling the transformer in operation, the gas relay protection equipment shall be connected to the signal. At this time, other relay protection equipment of the transformer (such as differential protection, current blocking equipment, etc.)
shall still be connected to the trip coil.
After the transformer is refuelled or filtered, the gas relay protection equipment can be fully put into operation again when the air bubble discharge of the transformer is completely stopped.
When the oil level indicated on the oil level needle rises abnormally, in order to find out the reason for the rise of the oil level, before removing the connecting piece of the tripping circuit of the gas relay, it is prohibited to open all kinds of plugs for venting or
oil drainage, sort out the holes of the respirator or or carry out other operations, so as to avoid misoperation and tripping of the vas relay.
（4） Operating temperature of transformer
The service life of transformer is closely related to the concave convex of operating temperature. The temperature of transformer is based on the temperature of the upper layer of transformer oil, which has a great impact on the service life of transformer.
The service life of transformer is generally the service life of its insulation (cotton yarn, paper, silk and other materials soaked in insulating paint or insulating oil). When the operating temperature of the transformer increases by 8 ~ 9 ℃, the insulation life
will be reduced by half. The transformer operates at the normal operating temperature of 95 ℃, and its service life is 20 years; If the temperature rises to 105 ℃ for operation, the service life will be shortened to 7 years; If the temperature rises to 120 ℃
for operation, the service life will be shortened to 2 years. If the transformer continues to operate at 170 ℃, it will be scrapped in 10 to 12 days.
The temperature bump of transformer has four elements:
1. Ambient temperature. The temperature of transformer in summer is higher than that in winter, and the temperature of indoor transformer is higher than that of outdoor transformer.
2. The manufacturing quality of the transformer itself. The transformer with good production quality has small copper loss and iron loss, and the temperature is low.
3. Load of transformer. The heating capacity of the transformer coil is directly proportional to the square of the load current. The transformer often operates according to the additional capacity, and its service life shall not be less than 18 to 20 years. If it
operates under overload, its service life will be greatly shortened.
4. Operation voltage of transformer. The working voltage of the transformer should be kept at the additional voltage. If it often exceeds the additional voltage, the service life of the transformer will be shortened; When the operating voltage is 10% higher
than the additional voltage, the iron loss of the transformer should be increased by 30 ~ 50%, and the temperature should also be increased.
The temperature of the transformer refers to the temperature of the upper layer of the transformer oil, which shall not exceed 95 ℃ according to the rules. In practice, in order to avoid the rapid deterioration of the transformer oil, the upper layer oil
temperature should not often exceed 85 ℃. If the mercury thermometer is pasted on the transformer shell for measurement, the temperature is allowed to drop by 5 ~ 10 ℃ (i.e. 75 ~ 80 ℃). If the allowable value is exceeded, it is necessary to find out
what the reason is and adopt countermeasures. For example, if the ambient temperature is high, it can be reduced by adding electric fan, water cooling and other methods. If the load, voltage and ambient temperature are the same as in the past, but the
temperature is more than 10 ℃ higher than in the past and keeps rising, there may be something wrong inside the transformer, so it is
necessary to stop the operation immediately.
