Major repair of electrical equipment of distribution substations

Electrical equipment substation switchgear must provide reliable power to consumers. The structural elements of the equipment wear out during operation and their characteristics deteriorate.

To equipment of transformer substations works properly and does not break down at the wrong time, it is necessary to carry out periodic repairs. There are several types of repairs — routine repairs, major repairs and emergency repairs.

Regular repairs provide for partial performance of the work that is determined to be performed during the main repair. Repair of emergency equipment is carried out in case of emergency situations of the distribution equipment of the substation.

Most emergency situations that require equipment repair are due to an inability to overhaul the equipment to the extent provided by the current regulatory documents in the electrical installation, in particular, flow diagrams, work projects, instructions for maintenance and operation of the equipment.

That is, we can conclude that overhaul of equipment is carried out in order to ensure reliable, correct and trouble-free operation of the equipment during its operation, both in normal and emergency modes of operation of electrical networks. In this article, we will briefly consider what kind of work involves overhauling various substation switchgear.

Overhaul of high voltage equipment

High voltage equipment is switchgear equipment with a voltage class higher than 1000 V.

Before carrying out major repairs on one or another piece of equipment, an external inspection of the equipment taken out for repair is first carried out in order to identify possible defects. The repair team, in addition to checking the equipment, clarifies with the personnel serving this electrical installation about possible defects, violations of the normal operation of an element of the equipment. Defects and violations of the normal operation of the equipment are recorded by the service personnel in the log of defects and malfunctions of the equipment.

In addition, depending on the name and type of equipment, it is repaired. The sequence of equipment repair operations, as a rule, is indicated in work flow charts (RTC), work projects, equipment operation and maintenance instructions.

Consider the list of works that are carried out during the overhaul of each element of high-voltage equipment:

• electrolaboratory testing of insulation;

• revision, testing of supports, bushing insulators;

• processing places from chips, cracks in porcelain insulation, if their area and depth are higher than the permissible values ​​​​according to the passport, then the insulators are replaced;

• cleaning of metal structures from dirt, rust, painting;

• inspection of grounding devices, revision of grounding locations;

• revision and processing of pressed contact connections;

• revision of bolted contact connections;

• measurement of contact resistance of contact connections;

• lubrication of moving parts;

• color of the busbars in accordance with the color marking of the phases;

• checking the functionality of the electromagnetic blocking;

• checking and revision of block contacts of equipment such as KSA, emergency KSA, KSU;

• testing of devices for relay protection and automation, secondary switching circuits.

Below we will briefly look at the lists of work performed, specific to the various high voltages.

High voltage circuit breakers

If it is a high voltage oil breaker, the first step is to drain the oil from the tank. At this stage, the operation of the oil indicators is checked, the hatches of each of the phases are removed so that the internal elements of the switch can be checked.

Next, the internals of the switch are checked. Based on the inspection, repair or replacement of damaged elements, elements that have worn out their service life are carried out.

During oil circuit breaker overhaul, circuit breaker tanks (valves, tank insulation, gas outlets, oil drain valves), internals (arc extinguishing devices, circuit breaker internal mechanism, movable and fixed contacts) and the circuit breaker actuator is being repaired.

Regardless of the type of circuit breaker (oil, vacuum, SF6), during overhaul the circuit breaker actuator, actuator heater or circuit breaker tank is repaired

When carrying out repair work, the operation of the switch is checked, the compliance of its operating characteristics with the values ​​specified in the passport data of the switch (own time of switching on and off, the speed of movement of moving contacts when switching on and off, characteristics of the drive and etc.)

Overhaul of the modern Circuit breakers SF6 produced, as a rule, by the official representatives of the manufacturer. The company that operates this equipment only performs routine repairs — in fact, they are reworking the switch, without opening the tank.

Major repair of vacuum breakers is not carried out; when their resource is exhausted, such circuit breakers must be replaced. During their operation, only current repairs are carried out, which include electrical laboratory tests of the circuit breaker, revision of contact connections, wiping of insulation, painting of metal elements, inspection and revision of the drive.

Disconnectors, insulators, short circuits

The list of works on overhaul of disconnectors, separators and short circuits includes:

• repair of working knives, rotating columns (cleaning of contact surfaces, revision of bearings, flexible connections, repair or replacement of structural elements with defects);

• repair of fixed earthing blades of disconnectors (revision of flexible connections, contact surfaces);

• inspection and revision of equipment attachments to the foundation;

• drive repair (repair or replacement of rods, shafts, bearings, clamps; for separators and short circuit — springs, holders, release mechanisms);

• setup, operation check, removal and performance comparison with passport data.

Current transformers, voltage transformers

When carrying out major repairs current transformers or voltage, the following work is done:

• for oil-filled transformers — oil samples are taken for analysis, oil is topped up or oil is changed if necessary;

• for SF6-insulated transformers, if necessary, the SF6 pressure is equalized (pumped or vented) to a value that is normal for the average daily ambient temperature;

• for transformers with dry insulation, its integrity is checked;

• for current transformers with fuses — revision of fuse holders, cleaning and processing of contact surfaces, checking the integrity of fuses, replacement if necessary;

• repair or replacement of bushings for low and high voltage, revision of contact connections.

Power transformers

During work power transformers major repairs are carried out without removing the windings, which include:

• draining oil, opening the transformer;

• based on previously taken samples of transformer oil, it is dried, regenerated or replaced;

• cleaning and removing defects on the magnetic circuit, the transformer tank;

• cleaning and repair of winding insulation, external inputs, tap windings;

• inspection, cleaning, repair of cooling devices;

• revision, check of operability of load switches, load switches;

• revision of the thermosiphon filter, air dryer, replacement of silica gel in them;

• checking and repairing oil indicators, temperature sensors, checking the operation of automatic devices for cooling systems.

Complete switchgear (switchgear, switchgear, switchgear)

Overhaul of the equipment of complete switchgear is carried out for each part of the equipment separately. For example, in the cell feeding the outgoing line, the circuit breaker, current transformers, stationary grounding blades, plug sockets (the degree of their rigidity, alignment) and other equipment and structural elements of the cells are repaired. Each of the elements of the cell equipment is repaired in accordance with the list of works determined for each of the elements located in the distribution cell (KRUN, GIS).

Limiters and overvoltages

Major repair of arresters and surge arresters is usually combined with the repair of other items of equipment of the same connection. When carrying out a major repair, the following work is carried out:

• disassembly and repair of defenders;

• checking the tightness of the restraints, the integrity of the insulation;

• revision of ground busbars of limiters (SPN);

• revision and testing of surge arrester (SPD) recorders;

• taking the operational characteristics of arresters (SPD), comparing with the passport ones.

Major repair of low-voltage equipment

Low-voltage equipment includes equipment with a voltage class of up to 1000 V. At substations, this is equipment for switchboards of 0.23 / 0.4 kV, equipment for switchboards 110/220 V DC.

Let's list what works are carried out in low and voltage distribution cabinets:

• inspection and, if necessary, repair of the cabinet door, locking devices, fasteners, mounting panels, rails;

• inspection, wiping of busbars, insulators, tightening of contact connections, checking the integrity of the insulation of wires and cables;

• checking the operation, the reliability of the contact connections of low-voltage equipment - circuit breakers, circuit breakers, fuses, measuring instruments, current transformers, signal lamps, control switches, buttons, magnetic starters, pack switches, gear motors, contactors, voltage relays, relay for time and equipment with other elements with which the cabinets are completed, depending on their purpose;

• checking the operation of protection and automation devices — ground fault protection, automatic transfer switch, equipment control circuits, light and sound alarms, indication of equipment operating modes.

Checking the functionality of the circuit breakers is to carry out a recall.To do this, the circuit breaker is connected to a special test installation, with the help of which a certain load current is supplied to the electrical device under test and the response time is measured in accordance with the characteristics of thermal and electromagnetic releases specified in its passport.