Pneumatic economy

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 4. Switchgears and substations

Switchgears and substations with voltages above 1 kV. Pneumatic economy

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Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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4.2.172. To supply compressed air to switching devices (air switches, pneumatic drives to switches, disconnectors) switchgear of power stations and substations, a compressed air installation must be provided, consisting of a stationary compressor unit and an air distribution network.

Removal for repair or failure of any element of a compressed air installation should not lead to disruption of the air supply to switching devices.

4.2.173. Dry air is produced in a compressor unit using a thermodynamic air drying method, for which two pressure levels are provided:

compressor (increased) - for compressors and air collectors-accumulators of compressed air, selected from the condition of ensuring the required relative humidity in the switching devices;
working (nominal) - for the air distribution network, in accordance with the nominal air pressure of the switching devices.

The compressor and operating pressure systems must be interconnected by bypass valves.

To supply compressed air with the required dew point temperature to the switches, it is allowed to additionally use a physico-chemical (adsorption) method of air drying. In this case, the number of air purification units must be at least two.

4.2.174. The performance of working compressors must be selected to ensure:

1) in units with compressors up to 10 MPa:

0,5 h of continuous operation with a 2-hour pause;
restoration of pressure in the air collectors, reduced for ventilation of air switches and for leaks of the entire system, in 2 hours, while the compressors are not operating - within 0,5 hours;

2) in units with compressors with a pressure of 23 MPa:

1,5 h of continuous operation with a 2-hour pause;
restoration of pressure in the air collectors (conditions are similar to those stated in paragraph 1) - within 1,5 hours.

For any number of working compressors, based on the conditions for the reliability of air supply to the switching devices, one or two reserve ones should be provided, depending on local conditions.

This does not apply to a substation with one switching device having a pneumatic drive, where two compressors must be installed, one of which is a backup one.

To supply compressed air to the switching devices of substations and switchgear of industrial enterprises, the use of a factory pneumatic installation is allowed, provided that it meets the requirements of this chapter.

4.2.175. Air replenishment in the reservoirs of switching devices in operating and emergency modes should be carried out using the air supply in the compressor pressure air collectors.

The capacity of the air collectors must ensure coverage of the total air flow (with compressors not operating):

in operating mode - for ventilation of air switches and for leaks of the entire system for 2 hours, while the compressors are not operating. In this case, the residual pressure in the air collectors must be such that the permissible moisture content of the air in the switching devices is ensured;
in emergency mode - to restore pressure in the reservoirs of air circuit breakers (to the lowest permissible value according to the operating conditions of the circuit breakers) while simultaneously disconnecting the largest number of circuit breakers possible according to the operating mode of electrical installations, taking into account the operation of relay protection and automation. In this case, the lowest compressed air pressure in the air collectors must be higher than the nominal compressed air pressure in the devices:
by 30% - in units with compressors up to 10 MPa;
by 80% - in installations with compressors with a pressure of 23 MPa.

4.2.176. In calculations, it should be assumed that the beginning of the emergency mode with mass shutdown of switches coincides with the moment of periodic activation of the compressor unit (i.e., when the pressure in the air collectors has decreased to the starting pressure of the compressor).

4.2.177. For each value of the nominal pressure of the switchgear switching devices, there must be its own air distribution network, fed by at least two bypass valves from the compressor unit.

4.2.178. Bypass valves must maintain pressure in the air distribution network and in the air circuit breaker tanks within specified limits.

The capacity of the bypass valves and air ducts of the distribution network must ensure the restoration of air pressure (to the lowest permissible value under the operating conditions of the circuit breakers) in the circuit breaker reservoir, which can be switched off during an unsuccessful automatic reclosure cycle (including in the presence of a double automatic reclosure).

A bypass valve, in normal operation, should generally be able to continuously bypass a small amount of air to cover leakage and venting in the system downstream of the valve.

4.2.179. Bypass valves must be solenoid operated.

The automatic control of turning on and off the bypass valves must be carried out regardless of the operating mode of the compressors. The electromagnetic drives of the bypass valves should be controlled using electric contact pressure gauges installed in the compressor unit room.

4.2.180. The compressor installation, with the exception of the air purification unit, must be automated and operate without permanent personnel on duty.

The control circuit of the compressor installation must provide for: automatic start and stop of working and standby compressors, maintaining pressure in the air collectors and in the tanks of the switches within the established limits; automatic purging (removal of moisture and oil) of water-oil separators; automatic control of bypass valves; protection of compressor units in case of disturbances in normal operation.

The compressed air installation must be equipped with an alarm system that operates in case of violations of its normal operation.

4.2.181. The construction of automated compressor installations with machines with a capacity of up to 5 m3/min in the reactor plant is regulated by the current rules for the design and safe operation of stationary compressor installations, air and gas pipelines of the State Mining and Technical Supervision of Russia.

4.2.182. Air collectors must comply with the Rules for the Design and Safe Operation of Pressure Vessels of the Gosgortekhnadzor of Russia.

4.2.183. Air collectors must be installed outdoors at a distance of at least 1 m from the compressor room wall, preferably on the shady side. A special canopy over them (to protect from solar radiation) is not required. It must be possible to install and dismantle any air collector without disturbing the normal operation of the others. It is allowed to install air collectors in a separate room of the building in which the indoor switchgear with air circuit breakers is located.

4.2.184. Drain valves of the compressor water-oil separators and purge valves of 23 MPa cylinders are connected to the drainage system, which is discharged outside into a well specially provided for this purpose.

4.2.185. For normal operation of compressors, the temperature in the compressor unit room must be maintained not lower than +10 ºС and not higher than +40 ºС, for which heating and supply and exhaust mechanical ventilation must be provided.

4.2.186. The air distribution network should, as a rule, be made circular, divided into sections using shut-off valves.

The air supply network must be supplied by two lines from the compressor unit.

4.2.187. To protect the air distribution network with a pressure of 2,0 MPa of a compressor unit up to 10 MPa, safety valves must be installed in it, which are triggered when the pressure in both lines of the supply line of the air distribution network is exceeded.

4.2.188. Linear water separators are installed in both lines of the supply line of the air distribution network with a pressure of 2,0 MPa of a compressor unit up to 10 MPa. The linear water separator must have a drain valve and fittings with flanges for connecting the inlet and outlet air ducts.

4.2.189. The distribution network air ducts can be laid openly along structures and equipment racks, in cable tunnels, channels and trays together with cables, and in enclosed spaces - also along walls and ceilings.

4.2.190. Air ducts should be laid with a slope of at least 0,3% with drain valves installed at the lowest points for purging the network. Branches to the devices should be laid with a slope of at least 0,3% in the direction of the main line.

4.2.191. To compensate for temperature deformations, compensators made from pipes of the same diameter must be provided in the air distribution network. The design of compensators is determined by the design organization.

4.2.192. The air ducts of the compressor unit, distribution network and branches to control cabinets must be made of seamless steel pipes, and stainless steel for a pressure of 23 MPa; air ducts from control cabinets to tanks of air switches are made of copper pipes; the use of seamless pipes made of corrosion-resistant steel is allowed. Air ducts between cabinets and pneumatic drives of steel pipe disconnectors.

Compressor pressure air ducts located outside the compressor unit to the air collectors and within the wall through which they pass must be covered with thermal insulation.

4.2.193. Steel air ducts must be butt welded; connections to fittings are flanged.

For pipes with an internal diameter of 6-8 mm, flange connections or connections using nipples are allowed.

4.2.194. The internal surfaces of air collectors and linear water separators must have an anti-corrosion coating.

4.2.195. The outer surfaces of air collectors and linear water separators installed outdoors should be painted with a durable, light-colored paint.

4.2.196. All elements of the compressed air installation must be accessible for disassembly and cleaning.

See other articles Section Rules for the installation of electrical installations (PUE).

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