Transformer non-power protection details
First, gas protection
1, gas protection is the main protection of the oil transformer, this is because the transformer power protection (differential protection, current flow protection, zero sequence protection, etc.) is not sensitive to the internal fault of the transformer. This is mainly the internal fault generally starts from the short circuit between turns, although the fault current inside the short circuit turns is very large, but the line current is not reflected, only when the fault develops to multi-turn short circuit or short circuit to the ground when the protection device can cut the power supply, then the severity of the fault has expanded. Therefore, the power protection can not be used as the main protection of the transformer internal fault. 2. The round oil storage box installed above the transformer is the transformer oil pillow. The oil pillow is a kind of oil storage device for the transformer. When the volume of the transformer oil expands or shrinks with the change of oil temperature, the oil pillow plays the role of oil storage and oil supplement, which can ensure that the mailbox is full of oil. The equipment of the oil pillow greatly reduces the contact surface between the transformer and the air, and the moisture, dust and oxidized oil dirt absorbed from the air are deposited in the depositor at the bottom of the oil pillow, thus greatly slowing down the deterioration rate of the transformer oil. The body gas relay is installed in the pipeline between the oil tank and the oil pillow of the transformer, the use of the transformer internal fault to decompose the oil to produce gas or cause oil flow surge, so that the gas relay contact action, connect the specified control loop, and timely signal alarm (light gas) or start the operating mechanism automatically cut the transformer (heavy gas). Simply put, it is an air collecting box and a baffle.
Gas protection can not only reflect the transformer tank and internal faults, but also reflect the non-serious inter-turn short circuit that can not be reflected by the travel protection, and any relay can not detect the core fault and its internal air entry. Therefore, the gas relay can accurately and sensitively act on the internal fault of the transformer, and is the main protection of the main transformer.
3, gas protection is generally divided into light gas and heavy gas two categories.
(1) Light gas: overheating inside the transformer. Or partial discharge, so that the transformer oil temperature rises, produce a certain gas, collected in the relay, so that the gas relay a group of contact points on, produce light gas signal.
Simply put, gas is generated inside the tank, and the gas density rises and accumulates to the top of the gas relay, and then the liquid level of the top cavity drops, and then the float on the top drops with the liquid level, and the contact on the top closes, and the alarm is raised.
(2) Heavy gas: When there is a serious short circuit in the transformer, a large amount of gas will have an impact on the transformer oil, making a certain oil rush to the baffle plate of the relay, making the heavy gas action of the gas relay trip.
4, the following gas relay national standard: according to the "GB/T6451-2008 - Oil immersed transformer technical parameters and requirements", 800kVA and above transformers should be equipped with gas relays. When the gas collecting capacity of the gas relay reaches 250mL~300mL or the oil speed is within the setting range, the corresponding contacts should be connected respectively.
The setting of gas relays is mainly carried out in accordance with the current industry standard JB/T9647-1999 - Gas Relays. When the gas collection volume of type 25 gas relay is below 250mL, the signal node should be switched on, and when the gas collection volume of type 50/80 gas relay reaches 250mL~300mL, the signal node should be switched on. The heavy gas working mode of the gas relay mainly depends on the adjustment of different flow rates. The velocity setting is mainly based on different gas relay calibers. Generally, the speed of the oil flow to the oil pillow is 1.0-1.2m/s. The trip node should be connected.
5, the gas relay also has a function that can monitor the liquid level, show the liquid level drop light gas alarm, and then drop too much, heavy gas trip.
6, the load regulator transformer has two oil storage tanks, a load regulator device, a main transformer body, they are separated from each other. Therefore, it is necessary to set gas protection for them, so the essence of on-load gas protection and body gas protection are the same, but the object of protection is different.
Second, temperature protection
For commonly used oil-immersed transformers, their actual service life is mainly determined by the life of solid insulation. The aging speed of insulation is mainly determined by temperature, water and oxygen. The insulation life of the transformer in operation is mainly determined by the thermal effect. The appropriate operating temperature is very important to extend the service life of the transformer. Therefore, it is necessary to monitor and control the transformer temperature to ensure the safe and stable operation of the transformer.
Temperature protection is a relay protection method used to detect the temperature of a device or system. It is usually composed of temperature sensor, logic unit, actuator and corresponding temperature blocking loop. It mainly monitors the temperature of the transformer in real time through the temperature sensor, and protects the transformer according to the monitoring results, and sends an alarm signal to remind the operator to deal with the problem in time. First understand the components of transformer temperature monitoring - transformer oil temperature meter and winding temperature meter.
1, transformer temperature relay
The oil temperature of the oil-immersed transformer is too high, which will lead to the rapid deterioration of the transformer oil, the aging speed of the insulating paper, and eventually the internal insulation damage of the transformer, and the occurrence of serious faults such as short circuit. Therefore, it is necessary to monitor the oil top temperature of the transformer, when the oil temperature is too high, timely alarm or trip signal is issued to remind the maintenance personnel to deal with it in time.
The thermometer has two hands, a black hand for real-time temperature measurement, and a red hand indicating the highest temperature. The red hand is connected to the adjusting knob on the instrument lens; The red pointer is the highest temperature ever recorded by the black pointer. When the temperature rises, the black pointer will push the red pointer, and push it to the highest temperature indicator, when the black pointer returns when the red pointer does not return; In this way, we can know the record high temperature of the black pointer through the reading of the red pointer (it is important to show the highest temperature reached by the thermometer).
Transformer winding thermometer (hereinafter referred to as winding thermometer) is a kind of instrument that uses thermal simulation measurement technology. In short, the winding thermometer can not directly measure the temperature of the winding, it is by measuring the top layer of the transformer oil temperature T, and then apply a transformer load current change additional temperature rise △T, the sum of the two T=T₁+△T can simulate the winding of the most hot spot temperature.
Transformer winding thermometer measurement principle:
1, when the transformer is not loaded, the top oil temperature is the same, the temperature packet of the thermometer has a temperature sensing medium, when the oil temperature changes, the volume of the temperature sensing medium also changes, through the transmission of the capillary, so that the measuring element in the table has the corresponding offset, to achieve the temperature measurement.
2. When the transformer is loaded, the winding temperature is higher than the oil temperature. In addition to measuring the oil temperature through the temperature packet, the winding temperature meter also needs to be connected to the transformer bushing CT. By obtaining the current proportional to the load, and then adjusting it through the current matcher, the heat is generated on the electric heating element to offset the indicating pointer, and the temperature rise of the winding to the oil is approximately obtained. The temperature obtained is the hottest temperature of the winding.
3, why should the transformer install more than two thermometers?
In recent years, the oil level thermometer of the transformer is generally installed two, mainly for the transformer with a large capacity, the space in the tank is large, the heat and heat dissipation of the transformer is also uneven, in different areas of the transformer, the temperature difference may be larger, for safety reasons, it is necessary to measure the oil temperature of the transformer more accurately. Therefore, sometimes a signal thermometer is set at each end of the long axis of the transformer to detect its oil temperature to ensure safer operation of the transformer. In this way, when one of the thermometers fails, the oil level temperature of the transformer cannot be monitored due to the inability to arrange power outage treatment.
