1. Overview
With the continuous expansion and development of the power system, and the continuous commissioning of large-capacity, high-parameter units in the power grid, the stability of the power system and the safe operation of power generation equipment have increasingly higher requirements for relay protection and automatic devices. It not only requires relay protection devices to have good reliability, but also requires them to have good stability. However, the impact of hidden faults in relay protection and secondary circuit systems on the power grid and power equipment cannot be ignored. When a fault occurs in the power grid system or power generation equipment, hidden faults can easily cause major system accidents or expand the accident, exacerbating damage to equipment and undermining the stable operation of the power grid system. The existence of hidden faults in electrical equipment is inevitable. Relay protection plays a very important role in power plants and power systems. Some disturbances start as independent and occasional events. When hidden faults in relay protection and secondary circuits cause protection devices to malfunction or refuse to operate, it is highly likely to expand the accident and seriously damage the stability of the system.
The occurrence of electrical equipment accidents generally goes through a certain development process. Some unpredictable events put equipment in abnormal operating states, such as local heating of electrical equipment, slight inter-turn short circuits in windings, etc. Due to the lack of real-time monitoring equipment or the misjudgment of system operating conditions by operators and insufficient understanding of operating states, when a fault or abnormality occurs somewhere in the equipment, it may cause a series of chain reactions. Theoretically, whether it is a system fault or a local electrical equipment fault, it is removed by the relay protection device (automatic device) of the section where the faulty equipment is located, or through backup protection with time delay. Due to hidden faults in protection devices and secondary circuits, protection devices may mis-trip, refuse to operate, or trip beyond the level during faults. In this way, the system becomes more unstable, further weakening the stability and safety of the power system. The power grid may be divided into several independent small systems, leading to the collapse and disintegration of the power grid, causing large-scale power outages and equipment damage.
A hidden fault refers to a fault that has no impact on the system during normal operation. When certain parts of the system and equipment change, this fault is triggered, leading to large-scale system failures. Hidden faults cannot be detected during normal operation of equipment. Once a fault occurs in the power system or electrical equipment, after the relay protection correctly operates to clear the fault, the power flow distribution changes. Under the new operating state, protection devices and secondary circuit systems with hidden faults may misoperate. The danger of hidden faults is that their impact on the system is only exposed when the system is under stress, such as when system or electrical equipment faults occur, and after faults, transient low voltage, overvoltage, system oscillation, and other related abnormal conditions occur.
2. Analysis of Causes of Hidden Faults
Hidden faults may exist in relay protection devices and secondary circuit components, such as PT, CT bodies, protection outlet pressure plates, protection device plug-in connections, terminals of secondary circuit wiring, fiber optic channels, etc. There are many causes of hidden faults, usually including the following situations:
Incorrect setting calculation values and unreasonable coordination of settings.
Some hidden faults of devices, such as component aging and failure, component damage, poor contact of various plug-ins, etc.
Errors in secondary wiring.
Loose secondary wiring terminals and poor contact.
Maintenance and operation personnel accidentally touching or misoperating protection equipment.
Protection devices not strictly calibrated according to calibration procedures.
Parasitic circuits in secondary circuits.
Poor operating environment of protection equipment, and inadequate maintenance by maintenance and operation personnel.
3. Preventive Measures for Hidden Faults
Through the analysis of the above 8 situations, hidden faults in relay protection and secondary circuits can be completely prevented. The main protection devices used by Xuanwei Company are currently relatively advanced protection equipment in China. The main protection devices have self-diagnostic functions and can monitor some abnormal conditions of the devices online. The key issue is to strengthen equipment management, strictly implement rules and regulations, and establish and improve the basic technical ledger of equipment. Ensure that equipment maintenance and overhaul are in place, personnel work is in place, record some subtle changes of equipment in files, compare and analyze the changes of operating equipment, find out existing problems, and deal with them in a targeted manner. Try to reduce the harm of hidden faults in equipment and avoid large-scale accidents in the system and electrical equipment.
The large-scale power outages in the United States, Australia and other countries in 2004 and the power outage in Russia in 2005, from data analysis, were all caused by local faults in the power grid system, where misoperation and refusal of relay protection and automatic devices expanded the accident, leading to the collapse of the power grid system and large-scale power outages, which had a significant impact on people's production, life, and social stability. Taking this as a lesson, in field work, we must strictly implement rules and regulations, with a good work style and serious work attitude, and not let go of any clue. Only in this way can we eliminate abnormal conditions of equipment in the bud and ensure the healthy and stable operation of equipment.
