CN205910263U - Earth -free distribution network capacitance current measurement system of neutral point - Google Patents

Abstract

The utility model relates to an electrical technology measures the field, concretely relates to earth -free distribution network capacitance current measurement system of neutral point, including the generating line, still including connecting respectively reactive power compensator and voltage transformer on the generating line. Reactive power compensator includes a plurality of adoption star connection's power capacitor bank. The reactive power compensator that this measurement system will connect on the generating line reads phase voltage numerical value as the electric capacity of setovering, the direct busbar potential transformer that follows, does not need other additional instrument and equipments, has avoided adding the potential safety hazard of having brought when setovering electric capacity on the generating line, operates safely, convenient. Have higher precision, it is less influenced by distribution network imbalance degree.

Description

A kind of isolated neutral capacitance current of distribution network measuring system

Technical field

This utility model belongs to electrical technology fields of measurement, particularly to a kind of isolated neutral capacitance current of distribution network Measuring system.

Background technology

In order to improve reliability and the seriality of power supply, the low and medium voltage distribution network of China's early stage, adopting isolated neutral more Mode, occur singlephase earth fault when, in the case that electric network capacitance and current is little, ground arc can self-extinguishment, power distribution network can Tape jam continues power supply 1～2 hour.With the continuous development of China's power distribution network, the ratio of cable run particularly in urban distribution network Example more and more higher, direct-to-ground capacitance is on the increase, and leading to circuit when there is singlephase earth fault, flowing through the capacitance current of trouble point Greatly increase.Various ground arcs in order to ensure occurring in electrical network can reliably extinguish, and wants when system capacitive current is more than code During the limit value asked, arc suppression coil must be installed with compensation of ground capacitance current.Accurately measurement is that decision is to the capacitance current of power distribution network The no premise installed arc suppression coil and determine arc suppression coil reasonable compensation capacity.

The measurement of isolated neutral system line capacitance electric current mainly has the direct method of measurement, artificial neutral point's method, injection Signalling and Biased capacitor method.

The measurement result of the direct method of measurement is more accurate, but operation and wiring are complicated, and is likely to result in ungrounded phase Insulation weakness damages thus causing line to line fault, threatens the safety of operator and distribution system.Artificial neutral point's method needs To enter the capacitor of one group of simulation neutral point in 10kv side joint, the method not only operates and is related to primary side, hidden with safety Suffer from, and have larger error in the larger electrical network of measurement direct-to-ground capacitance, or even imponderable situation occurs.Injection Signalling often using the resonance method or vector method although not needing to be operated in primary side, but affected by unbalanced power supply degree Larger, it is required for designing power frequency notch filter to filter the interference of power frequency component, need the measuring instrument of specialty.Biased capacitor method is subject to The impact of unbalanced power supply degree is less, measuring principle and simple to operate, but remains a need for connecing a partially installing capacitor on primary side circuit, There is potential safety hazard.

Utility model content

The purpose of this utility model is voltage transformer on reactive power compensator and the bus providing on a kind of utilization electrical network Can complete to measure work it is not necessary to prepare other electrical equipments and survey tool, safety simple to operate, and there is higher essence The measuring system of exactness.

For achieving the above object, the technical solution adopted in the utility model is: a kind of isolated neutral power distribution network electric capacity Current measurement system, including bus, also includes reactive power compensator and the voltage transformer being connected on described bus；Institute State the power capacitor group that reactive power compensator includes multiple employing Y-connections.

Above-mentioned isolated neutral capacitance current of distribution network measuring system, using the reactive power compensator on bus and electricity Pressure transformer can obtain power distribution network ground capacity and capacitance current.

Operation principle of the present utility model: to measure the capacitance current of power distribution network using Biased capacitor method, mother will be connected to Reactive power compensator on line, as partially installing capacitor, directly reads phase voltage numerical value from bus-bar potential transformer, is existed by measurement In a certain phase plus partially installing capacitor before and after this phase voltage size, draw the zero sequence electric capacity of electrical network, thus obtaining power distribution network over the ground Capacitance current.

The beneficial effects of the utility model are: above-mentioned isolated neutral capacitance current of distribution network measuring system is by parallel connection Reactive power compensator on bus as partially installing capacitor, directly read phase voltage numerical value from bus-bar potential transformer it is not necessary to Other additional instrument and equipments, it is to avoid the potential safety hazard brought on bus plus during partially installing capacitor, safe operation, convenient.Should Measuring system has higher precision, less by power distribution network position influence.

Brief description

Fig. 1 is the measuring system schematic diagram of a specific embodiment of the present utility model；

Fig. 2 is the measuring principle figure of a specific embodiment of the present utility model.

Specific embodiment

Below in conjunction with the accompanying drawings embodiment of the present utility model is described in detail.

The technical scheme below adopting for specific embodiment, as shown in figure 1, a kind of isolated neutral power distribution network electric capacity Current measurement system, including bus, also includes reactive power compensator and the voltage transformer being connected on described bus；Institute State the power capacitor group that reactive power compensator includes multiple employing Y-connections.

Above-mentioned isolated neutral capacitance current of distribution network measuring system, mainly uses reactive power compensator on bus Split-phase switching, and the reading of voltage transformer to be calculating the direct-to-ground capacitance of power distribution network, thus calculating capacitance current.

As shown in figure 1, circuit 1 and circuit 2 and circuit 1, circuit 2 direct-to-ground capacitance are had on 10kv bus, 10kv bus connects Connect voltage transformer and reactive power compensator.

In order that with present embodiment isolated neutral capacitance current of distribution network measuring system with reference to for the sake of, provide following The step being embodied as measurement:

1) by the neutral ground of reactive power compensator, according to compensation capacity calculate reactive power compensator has accessed electrical network Compensating electric capacity c, reads a phase voltage u from bus-bar potential transformer_a；

2) compensating electric capacity that reactive power compensator is accessed a phase increases δ c_a, after voltage stabilization, read from voltage transformer Go out a phase voltage u_a’；

3) power distribution network ground capacity c can be calculated according to following formula_suma:

$c_{suma}=\frac{u_a^{\′}}{u_a-u_a^{\′}}\×{\mathrm{\δc}}_a-c$

4) by step 1), 2), 3) described in operation be repeated once b, c are biphase, calculate c_sumbAnd c_sumc, average c_sum=(c_suma+c_sumb+c_sumc)/3；

5) according to formula i_c=ω c_sumu_φ, power distribution network ground capacity electric current i can be calculated_c.

In above formula, ω is power distribution network industrial frequency angular frequency,For electrical network specified phase voltage.

Above-mentioned steps 1) in, reactive power compensator is made up of multigroup power capacitor group using Y-connection, every group of electricity Container can realize split-phase switching, can calculate and access electricity according to the switching situation of the size of compensation capacity or capacitor bank The capacitance of net.

Above-mentioned steps 2) in, increase the compensating electric capacity of a phase by individually putting into a capacitor to a phase, and should use up Amount selects the less electric capacity of capacitance (electric capacity minima takes 1 μ f).

Above-mentioned steps 3) principle as follows:

Measuring principle figure is as shown in Fig. 2 it is partially installing capacitor δ c_aThe Thevenin equivalent circuit at two ends.Partially installing capacitor accesses The open-circuit voltage at front two ends is busbar voltage u of this phase_a, equivalent internal resistance is the zero sequence direct-to-ground capacitance c of electrical network₀(power distribution network is over the ground Electric capacity c_sumaWith the direct-to-ground capacitance c sum increasing after reactive power compensator ground connection), after accessing partially installing capacitor, partially installing capacitor two The voltage at end is changed into u_a', had according to voltage divider principle:

$u_a^{\′}=\frac{{\mathrm{\δc}}_a}{c_{suma}+c+{\mathrm{\δc}}_a}\×u_a$

Thus can be in the hope of:

$c_{suma}=\frac{u_a^{\′}}{u_a-u_a^{\′}}\×{\mathrm{\δc}}_a-c$

As seen from the above analysis, the model being adopted is accurate in principle, and result of calculation has higher precision.

Above-mentioned steps 4) in, miss to reduce the impact to measurement result for the power distribution network degree of unbalancedness and other measurement Difference, carries out identical measurement operation in a, b, c three-phase, the power distribution network ground capacity tried to achieve is averaged.

This specific embodiment to measure the capacitance current of power distribution network in principle using Biased capacitor method, directly using female Reactive power compensator on line and voltage transformer to be realizing measurement of correlation, it is to avoid brings on bus plus during partially installing capacitor Potential safety hazard, safe operation, convenient, and there is higher precision.

It should be appreciated that the part that this specification does not elaborate belongs to prior art.

Although the specific embodiment of the present utility model above in association with Description of Drawings, those of ordinary skill in the art It should be appreciated that these are merely illustrative of, various deformation or modification can be made to these embodiments, without departing from this practicality New principle and essence.Scope of the present utility model is only limited by the claims that follow.

Claims (1)

1. a kind of isolated neutral capacitance current of distribution network measuring system, including bus it is characterised in that also including connecting respectively It is connected on the reactive power compensator on described bus and voltage transformer；Described reactive power compensator includes multiple employing Y-connections Power capacitor group.