How to improve HV reactive power compensation with low cost and high efficiency?

1. The problems of high voltage reactive power compensation

Traditioanl HV system reactive power compensation usually adopts shunt reactors or LC circuit to do the comepensation job,these strategies not only cost much ,but also leads under or over compensation problem ,and is hard to conduct routine maintenance work.

Hence ,a more effective compensation mode and easy to maintain strategy now is urgently needed.

Low voltage compensation is a stable technology that can also improve power

factor. In order to achieve the high voltage compensation desired effect, we take a better

solution from low voltage side compensation,the final compensation accuracy and compensation effect can achieve an ideal state.

2. CoEpower new reactive power compensation strategy for HV system

CoEpower configure the new reactive power compensation by accessing current sampling CT at HV side ,installing CoEpo static var generator at LV side with inductive and capacitive compensation capability from -1 to 1 ,this will not only reduce user’s budget but also support a more effective compensation performance than traditional HV side compensation.

3,how to conduct HV sampling LV compensation?

When we use high voltage sampling and low voltage compensation , the current transformer CT access point should between high voltage grid side and transformer. Meanwhile, the current transformer installation direction is P1 point to the grid side, P2 point to the load side, the most important thing is that only A and C phase wiring with the current transformer.

4.Centralized controller MCGS operation description

4.1 Monitoring Screen

4.2 HV sampling LV compensation debug screen

The description of each parameter:

K_Q：K_Q is reactive closed-loop output ratio, It is calculated from the reactive power closed-loop and don‘t need to be set.

CT Ration SET：The current transformer ratio of the primary side current to the secondary side current, for example, the ratio of the primary side current to the secondary side current ratio is 300, you need to set 300:5

CT Position：CT at load side ,CT Position need to be set as 0. CT at grid side,CT Position need to be set as 1. Due to HV sampling and LV compensation mode ,Hence,a CT position need to be set 1.

Q/PF target：The value within 100 indicates the target value of the remaining grid reactive power, and the value above 100 indicates the target power factor, and the setting range is -1000~1000. In high sampling and low compensation mode, there is no need to set it.

Phase Offset：Reactive power phase correction value, the setting range is -100~100. Since the transformer is sampled as the high-voltage side current and the equipment is sampled as the low-voltage side current, there will be a phase difference of 30 degrees. For the dyn11 transformer, the low-voltage phase lags the high-voltage phase by 30 degrees, so the value here should be set to -30/360*400 = -33 , where 400 refers to the number of points in a cycle, which is a constant, and can be analogized for other modes of transformers.

Q KP/KI：Reactive power closed-loop control enable coefficient, the setting range is 0~10. In high sampling and low compensation mode, there is no need to set it.

PF Target Set：Reactive power closed-loop control, power factor setting value, setting range -1.00~1.00.

Light Load CurTresh：Current threshold value. The setting range is 0~1000. When it is lower than the threshold, the equipment outputs fixed reactive power. The meaning of this function is that when the line or transformer is empty, the sampling error is not enough to achieve the accuracy of the no-load compensation. At this time, the equipment can be fixed to output a certain amount of reactive power to offset the no-load reactive power.

Transfor.Ratio：Voltage ratio between high voltage side and low voltage side, setting range: 0 ~ 1000. For example, 10kV at high-voltage side and 0.4kV at low-voltage side should be set as 10 / 0.4 = 25.

Output@Light Load：Fixed output value of reactive power under no-load, setting range -1000 ~ 1000. This value needs to be used in coordinate with the no-load current threshold.

KP: Reactive power closed-loop control, proportional coefficient, setting range 0~1, default 0.1, if oscillation occurs, this value can be reduced.

KI：Reactive power closed-loop control, integral coefficient, setting range 0~1, default 0.1 If oscillation occurs, this value can be reduced.

Limit：Reactive closed-loop control, limit coefficient, setting range 0 ~ 1, can limit the maximum output of the whole machine. 1 is the rated 100% output, and 0.5 is the maximum 50% rated output.

Grid P Average：The average value of active power of the grid.

Grid Q Average：The average value of reactive power of the grid.

Expected PF：Reactive power closed-loop control，the power factor target value.

Reactive Closed Loop：Reactive power closed-loop control coefficient. A variable obtained by calculation from the target power factor, use this variable to do closed-loop calculations.

Remain Q Target：Reactive power closed-loop control，the current reactive output value.

Remain Q Feedback：Reactive power closed-loop control,reactive power required output value, that is, the current system sampling value.

Remain Q ERROR：Reactive power closed-loop control,the current reactive power deviation value.

PI OUT Q：Reactive power closed-loop control，reactive power closed-loop output value.

5.Data check and equipment debugging

After the wiring is completed and confirmed there is no error, then power on SVG, and set the necessary parameters, observe the monitoring screen data.

5.1 Set the necessary parameters according to the real system requirement, save and quit.

CT Ratio SET：The current transformer ratio of the primary side current to the secondary side current. For example, the ratio of the primary side current to the secondary side current ratio is 300, you need to set 300:5

CT Position：CT at load side ,CT Position need to be set as 0. CT at grid side,CT Position need to be set as 1. Due to take HV sampling and LV compensation mode ,so CT position need to be set 1.

Transfor.Ratio：The ratio of the voltage on the high voltage side and low voltage side,the setting range is 0~1000. For example, 10KV on the high voltage side and 0.4KV on the low voltage side, here should be set to 10/0.4=25.

Phase Offset：Reactive power phase correction value, the setting range is -100~100.Since the current transformer sampling high-voltage side current and the equipment sampling low-voltage side voltage, there has a phase difference of 30 degrees. The value here should be set to about -30/360*400=-33.

5.2 Observe the monitoring screen data.

The centralized controller displays the grid voltage, grid current, grid reactive power, grid active power, power factor, etc. Check if those data are consistent with the meter data. If they are consistent, proceed to next step. If they are inconsistent, check if the transformer wiring and phase sequence are correct after power off.

5.3 Equipment Debug

After the data is confimred, start debugging.

(1) First, Modify the certain output reactive power value to see if the equipment is operating normally. Set the no-load current threshold to 50A, and the output value at no-load is 50. When the equipment grid active current is less than the no-load current threshold 50, the equipment outputs a fixed reactive current of 50/sqrt(2)=35A.

After confirming that there is no fault alarm, click the running button to observe the data display. After the equipment is started, the “compensation current” and “load rate” will increase correspondingly, and the “Grid PF” will change..

After confirming that there is no abnormal alarm information, if compensation is not required , you can shut down the device on the monitoring screen, stop outputing compensation, and enter the standby state

6.Cases show

This site is a mining industry application, and there are problems with low power factor and high grid reactive power. After the application with 4 sets SVG , the power factor has been significantly improved.

6.1 Set the necessary parameters according to the actual requirement.

Transfor.Ratio: The voltage of High voltage side is 10.28KV,The Low

voltage side is 400V，Transformer Ratio should be set 10.28/0.4≈25.

CT Ration SET：This site uses two sets of transformers, which are connected to equipment 1 and equipment 2, according to the actual transformer ratio , to set 500 and 400 respectively

CT Position：As we connected CT at the grid side, CT Position need to be set 1.

Phase Offset:According to the transformer nameplate, we can get the transformer type that is DYN11, so Phase Offset need to be set -33.

6.2 Observing the meter data and monitoring screen data before starting SVG

Observing the meter data before starting SVG, we can see that the power factor is 0.9112, the grid reactive power is 530Kvar, the grid current is 72.32A, and the grid active power is 1172Kw.

Observing the Monitoring screen data before starting SVG, we can see that the power factor is 0.907, the grid reactive power is 541Kvar, the grid current is about 77A, and the grid active power is 1172.4Kw.

It can be concluded that the Monitoring screen data is close to the meter data, which indicates that there is no problem with the wiring, as shown in the figure below.

Figure1. Meter data before starting SVG

Figure2. Monitoring screen data before starting SVG

6.3 HV Sampling and LV Compensation closed-loop parameter setting

PF Target Set：set 0.96

KP/KI: Reactive power closed-loop control, KP/KI coefficient, The coefficient is adjusted according to the actual situation. When it is set to 0.10, no oscillation will occur.

Figure3. HV Sampling and LV Compensation parameter setting

When all 4 equipment are running, it can be seen that the grid reactive power has dropped from 541Kvar to 254Kvar, and the power factor has been increased from 0.907 to 0.959.

Figure4. Monitoring screen data after compensation

When the power factor value is setting to 1, the meter shows that the grid reactive power has dropped to 38Kvar, and the power factor has reached a nice effect of 0.99, as shown in the following figure. It can be concluded that the site has achieved the ideal compensation effect.