High-voltage distribution cabinets: Transformer relay protection

Transformer relay protection is to use when the transformer inside and outside the fault, due to the current, voltage, oil temperature and other consequential changes, through these sudden changes to find, judge the transformer fault nature and scope, and then make the appropriate response and treatment.

Checking and processing after action

After the relay protection action, such as confirming the quick-break protection action, can temporarily lift the signal sound. If there is gas protection, first check whether the gas protection action, such as no action, indicating that the fault is outside the transformer, focus on checking the transformer and high-voltage circuit breaker to the transformer power supply line, see whether the cable, busbar phase short-circuit fault. In addition, should also focus on checking the transformer high-voltage leads with or without obvious failure points and other obvious anomalies, such as transformer oil spray, fire, temperature rise is too high.

If found to be gas action, can basically determine the fault within the transformer. First, when the transformer winding turns and layers of local short circuit, core insulation, and transformer serious oil leakage, oil level drop, light gas will be action; when the transformer internal serious failure, such as a winding failure caused by phase-to-phase short-circuit, the fault current makes the transformer to produce a strong airflow and oil flow, the impact of the heavy gas baffle plate, so that the heavy gas action, the circuit breaker falls off and send a signal. Secondly, if the transformer at that time no obvious abnormality, can collect transformer gas, further analyze, determine the nature of the fault. Collected gas if colorless, tasteless, and non-flammable, the cause of the gas relay action is caused by the air discharged from the oil; if the collected gas is yellow, not easy to burn, indicating that the transformer is a wooden part of the failure; such as the gas is yellowish with a strong odor and combustible, it is the failure of the insulating paper or cardboard; when the gas is gray or black flammable, it is the failure of the insulating oil. For outdoor transformers, you can open the gas valve of the gas relay and ignite the gas discharged from the bleeder valve, if the gas is flammable, it will burn and emit a bright flame. It should be noted that when the oil begins to overflow from outside the bleeder valve, the bleeder valve should be closed quickly; for indoor transformers, it should be prohibited to carry out the ignition test indoors; judge the color of the gas should be rapid, otherwise the color of the gas will disappear very quickly; take the transformer gas gas should be carried out after the power failure. Thirdly, if the gas protection action is still not identified, in order to further confirm whether the transformer is in good condition, you can take out the transformer oil samples for simplified test, to see whether there is a reduction in voltage resistance and oil flash point drop phenomenon. If there is still no problem, should further check the secondary circuit of gas protection, to see whether the gas protection error, to confirm the reliability of relay protection. Transformer heavy gas action, circuit breaker off, such as failure to carry out troubleshooting and indeed prove that the transformer is not faulty, can not be reclosed to send power.

If it is found that the differential protection action, need to judge the cause of action. To accurately determine whether it is caused by the transformer casing, or the cause of internal transformer failure.

Precautions

Relay protection device should be selected with good quality relays and protection components, components of the contact as little as possible; installation quality should be qualified, protection disk, control panel should be firm and reliable, to avoid installing in the vibration of the place, the quality of the terminals should be qualified, wiring should be good. Before the relay is put into operation, the duty personnel and operation personnel should clearly interpret the working principle of the protection device and so on.

During the operation of relay protection device, abnormal phenomenon should be found to strengthen the monitoring and immediately report to the person in charge; the running relay protection device, except with the consent of the dispatching department or the person in charge, shall not be arbitrarily thrown out of the protection operation, nor change the setting value and the secondary line at will; the input or withdrawal of the running relay protection device by the operating personnel must be approved by the dispatcher or the person in charge, and be recorded in the record book of the duty. If it is necessary to change the setting value of relay protection or the wiring of secondary circuit, it must be agreed by the relay protection personnel.

All work on the secondary circuit shall comply with the relevant provisions of the Electrical Safety Regulations.

When the operation duty personnel reversing operation involves relay protection circuit, they should carry out necessary treatment on relay protection according to the performance of relay protection device and operation regulations, but remember that the duty personnel’s operation on relay protection device is only allowed to connect or disconnect the protection pressure plate; switching changeover switch; and loading and unloading the fuse of the fuse.

Relay protection action circuit breaker tripped, not immediately after the signals will fall off the restoration, but should check the protection action, and find out the reasons, in the elimination of faults to restore power supply before the signals will fall off the restoration of all the signals.