Installation and connection of electricity meters
Requirements for the room where the electricity meter is installed
The accuracy of the readings of the measuring device, like any measuring device, is affected by environmental factors (temperature, humidity and chemical composition) air, vibrations, etc.). Therefore, the location of the meter must meet a number of requirements.
The room in which the meter is installed must be dry, heated, the temperature in it must not exceed + 40 ° C, the air must not contain aggressive impurities.
Installation of measuring devices in unheated rooms
It is permitted to place measuring devices in unheated rooms, in railway corridors, as well as in cages and cabinets for external installation. heaters.
It is especially necessary to monitor the air temperature for meters designed to read the generated electricity. The temperature of the air in the room should be within 15 — 25 ° C and controlled by a thermometer. In the absence of such premises, the measuring devices are placed in cabinets where the set temperature is maintained.The insulation requirement does not apply to meters specially designed for low temperature operation.
Requirements for electricity meter installation structures
Counters are installed in cabinets, on panels, in chambers of complete distribution devices, on walls, in niches. The design on which the measuring devices are mounted must be sufficiently rigid, i.e. not subject to vibration, deformation and displacement.
Mounting of measuring devices on wooden, plastic or metal boards is allowed. Installation height 0.8 — 1.7 m (to the terminal box). It is allowed to install the measuring device at a lower height, but not lower than 0.4 m. The plane on which the glucometer is installed must be strictly vertical.
The design and dimensions of cabinets, niches, shields should provide ease of maintenance of measuring devices — unlimited working conditions for their replacement, access to the terminal box from the front.
When placing panels with counters on the wall, the panels are installed with a gap of at least 150 mm.
It is not recommended to place counters on the doors of cabins KSO-266, KSO-272, etc. Practice shows that in these cases the meters are damaged due to shocks during operation of the switches.
Repairing the electricity meter
The counter is mounted in such a way that it can be removed and installed from the front side of the plane. For this purpose, it is recommended to use special rotating mounting brackets or to make threaded sockets for fastening bolts.
In places where there is a risk of mechanical damage to the measuring instruments or their contamination, or in places accessible to unauthorized persons (pathways, stairs, etc.), a lockable cabinet with a window at the level of the dial. Similar cabinets should also be installed for joint placement of meters and current transformers when the measurement is made on the low voltage side (at the user's input).
Current transformers are mounted so that their nameplates are in front. When the current transformers are located under the meter, there is a risk of electric shock to the service personnel due to the fall of the instrument. That is why it is recommended to install a horizontal insulating barrier between the meter and the current transformers.
Connection of measuring instruments with measuring transformers
A number of technical requirements apply to secondary circuits and must be fully complied with. The measuring devices are connected to measuring transformers with wires of brands PV, APV, LPRV, PR, LPR, PRTO, etc.; cables of brands AVVG, AVRG, VRG, SRG, ASRG, PRG, etc.
The minimum cross-section of the conductor is limited by the condition of mechanical strength, the maximum should not exceed 10 mm2. If by condition voltage loss a wire with a larger cross-section is required, then to connect it, ears must be soldered or special transition clamps must be used.
Stripping of rubber-insulated cable must be protected from damage by light and air rubber. A vinyl chloride pipe is used for this purpose.Inadmissible connections that are not accessible for inspection - twists, bolted connections, etc.
Transition brackets
Operational maintenance of meters includes such works as checking the correctness of inclusion, checking with sample instruments, replacing meters. Normally, the current values of the meters are included through the transition clamps. It is necessary that the design of the transitional clamps ensures convenient performance of these works. Transition clamps must be adapted for short-circuiting of current circuits, disconnection of current and voltage circuits in each phase, connection of devices without disconnection of wires.
An independent row of clamps or a separate section in the general row of clamps is set aside for the measuring circuits. If the calcd electricity metering is carried out at the user's substation, then the application of the intermediate terminals of the clamps is not recommended or jacketed and sealed. As for measuring devices in networks with a voltage of up to 0.4 kV, work on their installation and replacement can be carried out here only when the voltage is removed from all phases by turning off the switching device of the device or removing the fuses. A switching device or fuses must be located no more than 10 m from the meter.
In the power circuit, the current transformers of these meters are installed after the switching devices in the direction of power flow. With a positive power direction, they are installed between the switching device and the line, and with a negative direction - between the switching device and the busbars.This arrangement makes it possible, if necessary, to simply remove the voltage from the meter and all its circuits.
The use of a special adapter box, the design of which was developed by Mosenergo, is very effective. The box mounted directly under the meter has clamps for short-circuiting the windings of the current transformer and disconnecting the voltage circuits when disconnecting the meters for replacement and testing. This allows all meter work to be done without interrupting power to users.
Storage of electricity meters
Measuring devices should be stored in a heated room with a relative humidity of no more than 80%. Counters are stored individually packed on racks or shelves no more than ten rows high.
Electricity meter installation procedure
Before installing the glucometer, it is necessary to draw up a circuit diagram or make the necessary changes in the secondary circuits of this connection. The measuring device, prepared for installation, is subjected to an external inspection. The counter is cleaned of dirt and dust; the suitability of the measuring device is checked by its type and technical characteristics; the presence of gaskets is checked to check the condition of the screws securing the housing.
The seal shows the year and quarter of the state inspection, as well as the stamp of the state inspection. Installed three-phase meters must have state seals for inspection no more than 12 months old; the integrity of the housing and glass is checked, the presence of all screws in the terminal box, the presence of fastening screws with sealing holes in the cover of the terminal box, the presence of a diagram on its inside.
The meter, like any measuring device, must be protected from shock and impact. They can cause damage to the supports, bending of the axis and, as a result, an increase in errors and even friction of moving parts. Therefore, measuring devices should only be transported in special packaging. The transport box must have padded sockets and be firmly secured in the passenger compartment.
After transporting the meter, it is recommended to make sure that the moving part has not been rubbed. For this, the counter, holding it in the hands, rotates around the axis and simultaneously observes the movement of the disk. The measuring device must be fixed with three screws, having pre-marked the holes for them according to the installation dimensions. After installation, you need to make sure that the meter is strictly vertical.
When connecting the wires to the terminals of the meter, it is recommended to leave a margin of 60 - 70 mm. This will allow measurements to be taken with an electrical clamp and reconnected if the circuit is assembled incorrectly. A marking label is placed on the end of the wire.
Each wire is clamped into the terminal box with two screws. Tighten the top screw first. Give the wire a slight tug to make sure it is tight.Then tighten the bottom screw. If the installation is carried out with a multi-core wire, its ends are tinned.
Installation of electricity meters for direct connection
When installing direct connection meters, certain rules must be followed. If the rated current of the meter is 20 A and above, then the connected wires are provided with lugs to ensure the reliability of the contact. The wire is soldered to the tip with a sufficiently powerful soldering iron.
When installing electrical wiring to connect direct meters, it is necessary to leave the ends of the wires at least 120 mm near the meters.
The insulation or sheath of the neutral wire 100 mm long in front of the meter must have a distinctive color. When connecting aluminum wires to the meter, the following rules must be observed: the contact surface of the wire is cleaned with a steel brush or file and covered with a layer of neutral technical petroleum jelly.
Before connecting, the contaminated vaseline is removed from the wire and now a thin layer of vaseline is applied again in its place; the screws are tightened in two steps. First, without numbness, tighten with the maximum allowable effort, then the tightening is significantly weakened (not completely), then a secondary, final tightening is performed with normal effort; measuring circuits are maintained only by personnel designated for them.
In order to close access to them for other persons, the accounting chains are sealed. The meter terminal box and terminal block, adapter box or test block shall be sealed.If the power supply organization installs a meter in the user's substation, then the voltage transformer chamber, disconnector handle and bracket are also sealed.