Types of devices of reception and electric power distribution
The electrical energy developed by stations arrives to the place of consumption through the system of the interconnected transferring, distributing and reformative electric units. Electric power transmission is carried out on overhead power transmission lines with tension from several honeycombs to hundreds of thousands of volts. Electrical energy on system air networks is transferred with tension 35, 110, 150, 220 kV and above on the scale of rated voltage.
The installations serving for reception and electric power distribution are called the distributing devices (DD). They contain switching devices, combined and connecting tires, auxiliary devices (compressor, accumulator and others) and also devices of protection, automatic equipment and measuring apparatuses. The centers of the power supply (CPS), the distribution points (DP), the distribution lines (DL) treat RU.
The center of the power supply are called RU of generating tension of power plant or RU of secondary voltage of step-down substation of the power supply system with the regulating system which distribution networks of the specific area join.
The distribution point is called the substation of the industrial enterprise or the city network circuit intended for reception and electric power distribution with one tension without its transformation.
The line feeding the number of transformer substations from the CPU or IS and also large electric units is called distribution.
Distributing devices can be opened (to the SHOUTING — all or capital equipment is located in the open air) and closed (ZRU — the equipment is located in the building). Especially it is necessary to allocate the most widespread complete distributing devices (CDD) consisting from in whole or in part the closed cabinets or blocks with built in them devices, devices of protection and automatic equipment delivered in collected or the look which is completely prepared for assembly and released both for internal, and for outside installation.
Substation call the electric unit serving for transformation and electric power distribution and consisting of transformers or other energy converters, distributing devices, control units and auxiliary constructions.
The substation on which alternating current voltage will be transformed by means of the transformer is called transformer (TP). If alternating current voltage on TP is transformed to lower, it is called lowering and if in higher — raising.
On transformer substations install the transformers serving for voltage variation. Along with transformation of tension also the number of lines usually changes. For example, approach TP one or two of the line of high tension, and several lines of low tension depart from it.
Distinguish two types of transformer substations: open in which the capital equipment is located on the open areas, and closed which equipment is placed in rooms.
If on substation transformation of tension is not made, and only the number of lines changes, then it is called distribution.
Converter substations serve for alternating-current straightening or transformation of the direct current in variable. On all substations install devices for switching of network circuits and different instrumentations.
Network circuits are subdivided on tension into networks of low — up to 1 kV - and high — more than 1 kV of tension.
Most the industrial enterprises receive the electric power from substations. On substations two and more transformers through which energy from the power supply system on lines of high tension (35, 110 or 220 kV) is transmitted on sectioned workers (or reserve) tires with tension of 6-10 kV are installed.
The substation eating directly from the power generating system (or factory power plant), is called the main step-down substation (MSDS) of the enterprise, and substation on which tension goes down directly for the power supply of electroreceivers of one or several workshops — the shop transformer substation (TS).
Transformer and converter substations, as well as distributing devices, are delivered complete (KTP, the check point) in the collected or completely prepared for assembly look.
Measurement of current and tension on tires of distributing devices and in electric circuits is made by means of the current transformers or voltage transformers serving for lowering of current or tension of primary circuits of alternating-current electric units and also for the power supply of coils of the measuring apparatuses, devices of relay protection and automatic equipment attached to their secondary winding.
Application of measuring transformers allows:
- to measure any tension and currents by normal measuring apparatuses with the standard windings expected voltage of 100 V and current 5 A;
- to separate measuring apparatuses and the relay from voltage over 380 V, ensuring safety of their service.
Primary winding of the measuring transformer is under the influence of the measurand, and secondary — is closed on measuring apparatuses and devices of protection.
The touch to the measuring apparatuses which are directly included in the chain of high tension is dangerous to the person therefore in this case measuring apparatuses and the equipment of automatic protection (relay) join in the secondary circuit of measuring transformers connected with the chain of high tension only through the magnetic flux in the core. Besides, measuring transformers serve for expansion of limits of measurement of alternating-current devices, like additional resistors and shunts. Application of measuring transformers with different transformation ratioes allows to use devices with standard limits of measurements (100 V and 5 A) when determining the most different tension and currents.
Distinguish two types of measuring transformers: voltage transformers and current transformers.
Voltage transformers feed potential winding of measuring apparatuses and the relay (voltmeters, frequency meters, counters, wattmeters, the relay of tension, power, etc.) in installations with tension of 380 V and above.
Current transformers feed current winding of measuring apparatuses and the relay (ampermeters, counters, wattmeters, the relay of current, power, etc.).
Sources of power supply of most the industrial enterprises are power generating systems, but some enterprises receive energy from own factory power plants. Development and energy distribution within the enterprise from own power plants is made generally in the generating mode with tension of 6 and 10 kV.
Electric circuits of distributing devices and substations can be primary and secondary.
The shinoustroystvo and current carrying parts of devices connected in the certain sequence belong to primary circuits.
Chains by means of which in primary circuits of RU of substations electric measurements are carried out, relay protection, the alarm system, distance control and automation belong to secondary, i.e. secondary circuits provide control, protection, convenient and safe service of primary circuits.
On key diagrams of primary circuits show all basic elements of the electric unit: shinoustroystvo, disconnectors, switches, safety locks, transformers, reactors, etc. and also connections between them. Better to imagine work of installation and its certain sites, usually show in primary schemes without electrical connections the main devices and devices of secondary circuits, measuring apparatuses, devices of relay protection and automatic equipment. Modern RU can have different schemes of connections.
It is necessary to remember that shutdown of the line, free from loading, is connected with the rupture of its charge current which the is more, than the line is longer.
The switch of loading installed instead of the disconnector allows to disconnect and include the line at loading within rated.
In this case on accession measuring current transformers are installed, and linear and tire disconnectors serve for the dump from the switch and current transformers at survey, repair, check and other works. As actions with disconnectors are possible only at the switched-off switch which breaks off the current circuit, the order of shutdown of the line following: at first switch-off the switch, then the linear disconnector and, at last, the tire disconnector. Order of inclusion of the line the return. Such option of accession to RU is applied to lines with heavy loads and the big short-circuit current.
Usually such scheme is applied to accession of air-lines. The grounding knives in this case serve for grounding and short circuit of the line after shutdown as in the disconnected line emergence of the electric charges induced by atmospheric electricity or the row the laid lines is possible. Dischargers are intended for branch to the earth of the electric charges of atmospheric electricity creating in the included line considerable the overstrain, dangerous to all installation.
In open RU dischargers join directly the main tires.
For disconnection of this transformer from network the tire disconnector serves (shutdown has to be made only at no-load operation of the transformer); protection against high and low tension is carried out by safety fuses.
This scheme includes the switch intended for operational switchings and the relay protection (RP) which devices receive the power supply from measuring current transformers.
Use of complete distributing devices and transformer substations allows to reduce terms of installation works, to reduce their cost and to improve quality.