Introduction
The consumption mode of photovoltaic users includes “all self-use”, “full access to the Internet” and “spontaneous self-use surplus electricity online”, and the grid-connected charging mode is different according to different consumption modes.
“Self-generated surplus electricity online” users set two meters, one metering meter, the downward electricity as the basis for consumption electricity settlement, the upward electricity as the basis for sales electricity settlement, an evaluation form statistical generation as the basis for generation subsidy billing; “All self-use” users set two meters, one meter meter, only count the downward electricity as the basis for electricity settlement, upstream electricity is not counted, and an evaluation table statistics power generation as the basis for power generation subsidies. “Full access” users set up a meter, only counting the electricity generation as the basis for electricity bill settlement and power generation subsidy charging.
1. The influence of three absorption modes of photovoltaic power stations on low and medium voltage line loss
1.1 Influence of all self-used photovoltaic power stations on low and medium voltage line loss.
The number of “all self-use” photovoltaic users is small, according to the low-voltage line loss calculation caliber, for the consumption method of “all self-use” users, regardless of the nature of the user’s electricity consumption, do not participate in the line loss calculation.
“All self-use” photovoltaic users, the power generation can be absorbed by themselves, and the low and medium voltage line loss has no effect; The remaining power generation is returned to the medium-voltage line for other users to use, but the returned power is not calculated, resulting in the power supply of the participating line loss calculation is smaller than the actual consumption, and the line loss rate is low or negative.
1.2 The impact of fully connected photovoltaic power stations on low and medium voltage line losses
The users of “full Internet access” are divided into three ways: special line, special transformer and low voltage.
1.2.1 Connecting dedicated lines to the network
The special line is connected to the grid directly into the 10kV bus of the substation, and the metering point is at the substation side, which reduces the remote transmission power and variable loss, and is conducive to reducing the middle voltage line loss.
1.2.2 Ad-hoc grid connection
The customized grid-connection is directly incorporated into the 10kV line, and the metering methods include high supply high meter and high supply low meter. The difference of measurement methods determines whether the variable loss is included in the medium-voltage line or the user. For high supply and high meter, the corresponding transformer loss is accounted for by the user side, which will not affect the line loss. For the high supply and low meter, when the power is returned, the transformer loss is included in the line loss, resulting in a larger line loss rate.
The current network transformer configuration is mostly step-down, reverse power will be used as a boost transformer, but the transformer design needs to consider the power loss, the primary coil in addition to transfer to the secondary power, but also provide copper loss, iron loss, eddy current and other losses, secondary to increase the coil to offset the voltage loss, and the first and second coil voltage, current level, coil specifications have different standards. Inverted use will increase transformer losses and reduce reliability.
1.2.3 Low-voltage grid connection
Low-voltage grid-connected directly into the public distribution substation area 400V line, the metering point is near the grid-connected line. The power generation can be fully absorbed in the station area, reducing the remote transmission power and variable loss, which is conducive to reducing the line loss in the station area; When the power generation can not be fully absorbed in the station area, part of the power is sent back to the medium-voltage line through the distribution transformer, reducing the remote transmission of power and variable loss, which is conducive to reducing the line loss in the station area, but the reverse loss of the transformer is included in the line loss, resulting in a larger line loss rate.
380V and 220V “full access” photovoltaic power station system single-direction data collection, that is, power generation, but the photovoltaic power station does not generate power when the inverter to use the system power, the power is not collected and charged, included in the line loss, each inverter power consumption is small, the line loss rate is less, but the inverter volume is larger, the power consumption time is longer, resulting in the loss of power rising year by year. It leads to other power consumption phenomena in photovoltaic power plants.
1.3 Influence of photovoltaic power stations with self-generated surplus electricity on low and medium voltage line loss
“Spontaneous self-use surplus electricity online” more users, divided into specialized and low-voltage two ways to connect to the grid, the impact on low-voltage line loss is basically the same as the “full Internet” users, only the inverter power consumption has been included in the user’s power consumption, no inverter power loss.
2. Effect of photovoltaic power station on 10kV line loss
2.1 10kV line model and line loss formula
Line loss rate = (line power supply – line power consumption)/line power supply x 100%. Among them:
Line power supply =P0 +P1 inverse +P2 inverse +P3 inverse
Line power consumption =P0 inverse +P1 positive +P2 positive
2.2 Analysis of the impact of photovoltaic power stations on 10kV line losses
Line power supply =P0 +P1 inverse +P2 inverse +P3 inverse -P0 inverse
Line power consumption =+P1 +P2 +P3
The analysis shows that the line power supply reduces P0 inversely, resulting in the line loss rate decreasing. The larger the inverse P0 is, the lower the line loss ratio is. The line power consumption is less P3 positive (P3 is a specialized photovoltaic power consumption, basically a constant value), resulting in increased line loss, line loss rate, and the smaller the P0 inverse, the greater the line loss rate. That is, the 10kV line loss is reduced when the line reverse power is large; The 10kV line loss increases when the amount of power is very small or no.
2.3 Analysis of 10kV line negative loss causes
The negative loss is caused by the error of line metering meter, and the CT ratio of 10kV public line is generally 400/5, 500/5, 600/5. The meter counts 8000, 10000, 12000; The metering meter is accurate to 0.01 bit, the maximum error power is 80, 100, 120 degrees, and the reverse feed power is lower than the maximum error power, which can not be accurately calculated on the day, resulting in an increase in line loss rate, especially for light load lines, the lower the power on the day, the greater the line loss rate; When the power data accumulates to a certain extent, the data is reported on the same day, and the power consumption is greater than the power supply, and the line loss becomes a negative loss.
3. Effect of photovoltaic power station on loss of public distribution transformer area
3.1 Common distribution transformer area model and line loss formula
Station line loss ratio = (station power supply – Station power consumption)/Station power supply ×100%. Among them:
Station power supply =P0 +P2 inverse +P3 inverse
Station power consumption =P0 inverse +P1 positive +P2 positive
3.2. Analysis of the impact of photovoltaic power stations on 10kV line losses
Station power supply =P0 positive +P2 inverse +P3 inverse -P0 inverse
Station power consumption =P1 +P2 +P3
The analysis shows that the station area line loss rate decreases when the power supply in the station area is reduced by P0 inverse. The larger the inverse P0 is, the lower the line loss ratio is. The power consumption of the station area is less P3 positive (P3 positive is the total on-grid photovoltaic power consumption, basically a constant value), resulting in the increase of the line loss of the station area, the increase of the line loss rate, and the smaller the P0 inverse, the greater the line loss rate.
The photovoltaic power station can reduce the loss of the distribution substation. The greater the amount of power sent back, the smaller the loss rate. When the power supply in the distribution transformer area is very small or not, the loss in the distribution transformer area increases, but the increase part is very small, not greater than the loss caused by the remote transmission of photovoltaic power generation, so the loss rate in the distribution transformer area is reduced.
4. Conclusions
According to the grid-connection mode and the grid structure of the photovoltaic power station, different countermeasures are formulated to reduce the impact of photovoltaic grid-connection on the grid. The conclusions are as follows:
1) The reverse power of all self-used optical power stations can lead to low loss rate or negative loss, so it should be counted and included in the calculation to restore the real data of line loss;
2) The variable loss of the upper return power of the transformer with high supply and low meter can lead to the increase of the line loss, and the theoretical variable loss should be increased in the calculation;
3) Full on-grid photovoltaic power station only power generation data collection, no power consumption data lead to increased line loss, should improve the system, increase electricity consumption collection and electricity bill settlement;
4) If the line loss calculation formula is inconsistent with the actual situation and the line loss calculation is abnormal, the system calculation formula should be modified to restore the authenticity of the data.
