Power wiring has become, along with the water supply, sewerage and ventilation, one of the essential components of modern infrastructure of the property. Consumption electric current on it is subject to registration and payment of the applicable tariffs. The main measuring device, readings which are used in the determination of fees for spent electricity is the electric meter.
This apparatus is turned on so-called the interface between the operator of the electrical networks and the consumer according to the rules described in detail Chapter 1.5 PUEAnd begins to function when the at least one user.
The need to use transformers connecting the electric meter and its design features
Due to the high capacity industrial power consumers have to pass through the sense counter entire consumption of current. It is most expedient to reduce by a current transformer.
Scheme activation of the counter only through a current transformer characteristic for enterprises, rated voltage of which an input feeder 380 V. In case a higher voltage before supplying it to the counter is reduced by including additional voltage transformers without loss of flow control accuracy.
When using only current transformers indicate polukosvennoy wiring diagram, respectively, using two kinds of transformer gives indirect scheme.
In view of the three-phase circuit to provide power meter must have 10 or 11 contacts: three for each phase: two for a current (input and output) and one for voltage and one or two common for all phases of the neutral conductor contacts.
To connect the current contacts is necessary to use wire of 2.5 mm2, she switched on the basis of clause 1.5.23 of the SAE must be done via a dedicated test terminal block.
10-wire connection diagram of 3-phase electricity meter to the mains is shown in Figure 1.
In its implementation contact pairs 1 and 3, 4 and 6, 7 and 9 perform the functions of the current and are included through the secondary winding of the current transformers. Potential contacts 2, 5 and 8 are connected directly to the feeder.
Strengths of this scheme:
- easy to operate the network (mainly due to the lack of need for load shedding at the counter replacement);
- operational safety because of the grounding current circuits;
- accurate readings, as determined by an independent data collection for each phase.
The main drawback - the increased consumption of materials during construction. It is eliminated in the schemes with two current transformers, one embodiment of which is shown in Figure 2. The price of this operation to save less accuracy.
The main characteristic distinguishing feature 7-wire circuit is grounded one of the terminals of each current transformer, i.e. combining all of the windings to each other.
One embodiment of such a scheme with the association pin I2 of the current transformer shown in Figure 3.
Regarding the advantages and disadvantages of this scheme is basically repeats the-wire embodiment 10, being more economical, but less reliable: the failure counter ceases to function correctly circuit portion common to all three phases.
Driving with the combined chain is shown in Figure 4. Characterized a direct connection of one of the counter current contact with a potential with a phase conductor. It is considered obsolete and is not applicable to the newly created networks.